25 research outputs found
Fast Adaptive S-ALOHA Scheme for Event-driven Machine-to-Machine Communications
Machine-to-Machine (M2M) communication is now playing a market-changing role
in a wide range of business world. However, in event-driven M2M communications,
a large number of devices activate within a short period of time, which in turn
causes high radio congestions and severe access delay. To address this issue,
we propose a Fast Adaptive S-ALOHA (FASA) scheme for M2M communication systems
with bursty traffic. The statistics of consecutive idle and collision slots,
rather than the observation in a single slot, are used in FASA to accelerate
the tracking process of network status. Furthermore, the fast convergence
property of FASA is guaranteed by using drift analysis. Simulation results
demonstrate that the proposed FASA scheme achieves near-optimal performance in
reducing access delay, which outperforms that of traditional additive schemes
such as PB-ALOHA. Moreover, compared to multiplicative schemes, FASA shows its
robustness even under heavy traffic load in addition to better delay
performance.Comment: 5 pages, 3 figures, accepted to IEEE VTC2012-Fal
Waiting but not Aging: Optimizing Information Freshness Under the Pull Model
The Age-of-Information is an important metric for investigating the
timeliness performance in information-update systems. In this paper, we study
the AoI minimization problem under a new Pull model with replication schemes,
where a user proactively sends a replicated request to multiple servers to
"pull" the information of interest. Interestingly, we find that under this new
Pull model, replication schemes capture a novel tradeoff between different
values of the AoI across the servers (due to the random updating processes) and
different response times across the servers, which can be exploited to minimize
the expected AoI at the user's side. Specifically, assuming Poisson updating
process for the servers and exponentially distributed response time, we derive
a closed-form formula for computing the expected AoI and obtain the optimal
number of responses to wait for to minimize the expected AoI. Then, we extend
our analysis to the setting where the user aims to maximize the AoI-based
utility, which represents the user's satisfaction level with respect to
freshness of the received information. Furthermore, we consider a more
realistic scenario where the user has no prior knowledge of the system. In this
case, we reformulate the utility maximization problem as a stochastic
Multi-Armed Bandit problem with side observations and leverage a special linear
structure of side observations to design learning algorithms with improved
performance guarantees. Finally, we conduct extensive simulations to elucidate
our theoretical results and compare the performance of different algorithms.
Our findings reveal that under the Pull model, waiting does not necessarily
lead to aging; waiting for more than one response can often significantly
reduce the AoI and improve the AoI-based utility in most scenarios.Comment: 15 pages. arXiv admin note: substantial text overlap with
arXiv:1704.0484
Divergence in function and expression of the NOD26-like intrinsic proteins in plants
<p>Abstract</p> <p>Background</p> <p>NOD26-like intrinsic proteins (NIPs) that belong to the aquaporin superfamily are plant-specific and exhibit a similar three-dimensional structure. Experimental evidences however revealed that functional divergence should have extensively occurred among NIP genes. It is therefore intriguing to further investigate the evolutionary mechanisms being responsible for the functional diversification of the NIP genes. To better understand this process, a comprehensive analysis including the phylogenetic, positive selection, functional divergence, and transcriptional analysis was carried out.</p> <p>Results</p> <p>The origination of NIPs could be dated back to the primitive land plants, and their diversification would be no younger than the emergence time of the moss <it>P. patens</it>. The rapid proliferation of NIPs in plants may be primarily attributed to the segmental chromosome duplication produced by polyploidy and tandem duplications. The maximum likelihood analysis revealed that <it>NIPs </it>should have experienced strong selective pressure for adaptive evolution after gene duplication and/or speciation, prompting the formation of distinct <it>NIP </it>groups. Functional divergence analysis at the amino acid level has provided strong statistical evidence for shifted evolutionary rate and/or radical change of the physiochemical properties of amino acids after gene duplication, and DIVERGE2 has identified the critical amino acid sites that are thought to be responsible for the divergence for further investigation. The expression of plant NIPs displays a distinct tissue-, cell-type-, and developmental specific pattern, and their responses to various stress treatments are quite different also. The differences in organization of <it>cis</it>-acting regulatory elements in the promoter regions may partially explain their distinction in expression.</p> <p>Conclusion</p> <p>A number of analyses both at the DNA and amino acid sequence levels have provided strong evidences that plant NIPs have suffered a high divergence in function and expression during evolution, which is primarily attributed to the strong positive selection or a rapid change of evolutionary rate and/or physiochemical properties of some critical amino acid sites.</p
Learning Adaptive Display Exposure for Real-Time Advertising
In E-commerce advertising, where product recommendations and product ads are
presented to users simultaneously, the traditional setting is to display ads at
fixed positions. However, under such a setting, the advertising system loses
the flexibility to control the number and positions of ads, resulting in
sub-optimal platform revenue and user experience. Consequently, major
e-commerce platforms (e.g., Taobao.com) have begun to consider more flexible
ways to display ads. In this paper, we investigate the problem of advertising
with adaptive exposure: can we dynamically determine the number and positions
of ads for each user visit under certain business constraints so that the
platform revenue can be increased? More specifically, we consider two types of
constraints: request-level constraint ensures user experience for each user
visit, and platform-level constraint controls the overall platform monetization
rate. We model this problem as a Constrained Markov Decision Process with
per-state constraint (psCMDP) and propose a constrained two-level reinforcement
learning approach to decompose the original problem into two relatively
independent sub-problems. To accelerate policy learning, we also devise a
constrained hindsight experience replay mechanism. Experimental evaluations on
industry-scale real-world datasets demonstrate the merits of our approach in
both obtaining higher revenue under the constraints and the effectiveness of
the constrained hindsight experience replay mechanism.Comment: accepted by CIKM201
Elevated atmospheric CO2 delays the key timing for split N applications to improve wheat (Triticum aestivum L.) protein composition
Late stage nitrogen (N) applications following basic fertilization are commonly used to ensure grain yield and increase grain protein content in wheat. Split N applications at the late growth stage of wheat are an effective measure to improve N absorption and transport and thus increase grain protein content. However, whether split N applications can alleviate the decrease in grain protein content induced by elevated atmospheric CO2 concentrations (e[CO2]) remains unclear. In the present study, a free-air CO2 enrichment system was used to investigate the effects of split N applications (at booting or anthesis) on grain yield, N utilization, protein content, and the composition of wheat under atmospheric (ACO2; 400 ± 15 ppm) and elevated CO2 concentrations (ECO2; 600 ± 15 ppm). The results showed that wheat grain yield and grain N uptake increased by 5.0% (being grains per ear by 3.0%, 1000-grain weight by 2.0%, and harvest index by 1.6%) and 4.3%, respectively, whereas grain protein content decreased by 2.3% under ECO2 conditions. Although the negative effect of e[CO2] on grain protein content was not alleviated by split N applications, gluten protein content was enhanced due to the alteration of N distribution in different protein fractions (albumins, globulins, gliadins, and glutenins). Compared to that without split N applications, the gluten content of wheat grains increased by 4.2% and 4.5% when late stage N was applied at the booting stage under ACO2 and anthesis under ECO2 conditions, respectively. The results indicate that rational handling of N fertilizers may be a promising approach to coordinating grain yield and quality under the effects of future climate change. However, compared to ACO2 conditions, the key timing for improving grain quality by split N applications should be postponed from the booting stage to anthesis under e[CO2] conditions