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We propose a new class of error correction codes for low-delay streaming communication. We consider an online setup where a source packet arrives at the encoder every M channel uses, and needs to be decoded with a maximum delay of T packets. We consider a sliding-window erasure channel -C(N, B, W ) -which introduces either up to N erasures in arbitrary positions, or B erasures in a single burst, in any window of length W . When M = 1, the case where source-arrival and channel-transmission rates are equal, we propose a class of codes -MiDAS codes -that achieve a near optimal rate. Our construction is based on a layered approach. We first construct an optimal code for the C(N = 1, B, W ) channel, and then concatenate an additional layer of parity-check symbols to deal with N > 1. When M > 1, the case where source-arrival and channel-transmission rates are unequal, we characterize the capacity when N = 1 and W ≥ M (T + 1), and for N > 1, we propose a construction based on a layered approach. Numerical simulations over Gilbert-Elliott and Fritchman channel models indicate significant gains in the residual loss probability over baseline schemes. We also discuss the connection between the error correction properties of the MiDAS codes and their underlying column distance and column span.

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Winter wheat (Triticum aestivum L.) cultivars Yangmai 9 (water-logging tolerant) and Yumai 34 (water-logging sensitive) were subjected to water-logging (WL) from 7 d after anthesis to determine the responses of photosynthesis and anti-oxidative enzyme activities in flag leaf. At 15 d after treatment (DAT), net photosynthetic rate under WL was only 3.7 and 8.9 μmol(CO 2 ) m -2 s -1 in Yumai 34 and Yangmai 9, respectively, which was much lower than in the control. Ratios of variable to maximum and variable to initial fluorescence, actual photosynthetic efficiency, and photochemical quenching were much lower, while initial fluorescence and non-photochemical quenching were much higher under WL than in control, indicating damage to photosystem 2. WL decreased activities of superoxide dismutase and catalase in both cultivars, and activity of peroxidase (POD) in Yumai 34, while POD activity in Yangmai 9 was mostly increased. The obvious decrease in the amount of post-anthesis accumulated dry matter, which was redistributed to grains, also contributed to the grain yield loss under WL.

We study low-delay error correction codes for streaming recovery over a class of packet-erasure channels that introduce both burst-erasures and isolated erasures. We propose a simple, yet effective class of codes whose parameters can be tuned to obtain a tradeoff between the capability to correct burst and isolated erasures. Our construction generalizes previously proposed low-delay codes which are effective only against burst erasures.We establish an information theoretic upper bound on the capability of any code to simultaneously correct burst and isolated erasures and show that our proposed constructions meet the upper bound in some special cases. We discuss the operational significance of column-distance and column-span metrics and establish that the rate 1/2 codes discovered by Martinian and Sundberg [IT Trans. 2004] through a computer search indeed attain the optimal column-distance and column-span tradeoff.Numerical simulations over a Gilbert-Elliott channel model and a Fritchman model show significant performance gains over previously proposed low-delay codes and random linear codes for certain range of channel parameters.

No abstract

Drought and flooding during grain filling have become major constraints to wheat quality and yield. The impacts of water deficits and waterlogging during the grain filling on contents of high‐molecular‐weight glutenin subunits (HMW‐GS) and of glutenin macropolymers (GMP) in grains of the winter wheat cultivar Yumai 34 with high grain protein content (GPC) and Yangmai 9 with low GPC were studied. At maturity, GPC was higher under drought and lower under waterlogging compared to the control, while contents of GMP and HMW‐GS were reduced by the two water‐stress treatments. The contents of both HMW‐GS and GMP were higher in Yumai 34 than in Yangmai 9. A drought event after anthesis increased the accumulation of HMW‐GS during the early grain filling stage. By contrast, waterlogging reduced the accumulation of HMW‐GS during the whole grain filling phase. At maturity, the HMW‐GS and GMP to protein ratios were also depressed under the two water‐stress events, while the HMW‐GS to GMP ratio was very close between the three treatments in Yumai 34 and much higher under the control than the drought and waterlogging treaments in Yangmai 9. It is concluded that the variation in GMP content with various water‐stress treatments is attributed to the changing in accumulation of HMW‐GS in the grain.

The use of multiple description (MD) video coding and path diver sity has been proposed to provide improved perfonnance over lossy packet networks [1]. The goal of'this work waS to develop mod els to accurately and quickly predict and compare the distortion of MO video coding and ·path diversity against conventional single de scription (SO) video delivered over a single path. In the process, we d�eloped (1) a model for the loss process of a two-path path diver . sity system, and (2) a distortion model that maps the losS model to MO distortion values. Given these models we present a number of comparisons between MO video coding and path diversity and con ventional SO vid� over a single path. The proposed model for path diversity may also be useful in other applications not related to MO coding. Furthermore, other fonns of MO coding may be analyzed using similar models for MO distortion.