Delay Reduction in Multi-Hop Device-to-Device Communication using Network Coding

This paper considers the problem of reducing the broadcast decoding delay of wireless networks using instantly decodable network coding (IDNC) based device-to-device (D2D) communications. In a D2D configuration, devices in the network can help hasten the recovery of the lost packets of other devices in their transmission range by sending network coded packets. Unlike previous works that assumed fully connected network, this paper proposes a partially connected configuration in which the decision should be made not only on the packet combinations but also on the set of transmitting devices. First, the different events occurring at each device are identified so as to derive an expression for the probability distribution of the decoding delay. The joint optimization problem over the set of transmitting devices and the packet combinations of each is, then, formulated. The optimal solution of the joint optimization problem is derived using a graph theory approach by introducing the cooperation graph and reformulating the problem as a maximum weight clique problem in which the weight of each vertex is the contribution of the device identified by the vertex. Through extensive simulations, the decoding delay experienced by all devices in the Point to Multi-Point (PMP) configuration, the fully connected D2D (FC-D2D) configuration and the more practical partially connected D2D (PC-D2D) configuration are compared. Numerical results suggest that the PC-D2D outperforms the FC-D2D and provides appreciable gain especially for poorly connected networks

Carbon dioxide dynamics from sediment, sediment-water interface and overlying water in the aquaculture shrimp ponds in subtropical estuaries, southeast China

Aquaculture ponds can emit a large amount carbon dioxide (CO2), with the consequence of exacerbating global climate change. Many studies about CO2 dynamics across the water-air interface, but CO2 in sediment and overlying water received relative less attention. In this study, CO2 concentration in sediment porewater, the diffusive CO2 fluxes across the sediment-water interface (SWI), and the CO2 production rates in the overlying water (CO2_WP) were determined in the shrimp ponds in the Min River Estuary (MRE) and Jiulong River Estuary (JRE), southeast China, to analyze the dynamics of CO2 among different growth stages of shrimps. Our results showed large variations in porewater CO2 concentrations, CO2 diffusive fluxes and CO2_WP rates among different growth stages, with markedly larger values in the middle stage of shrimp growth. The temporal variation of CO2 in both estuarine ponds followed closely the seasonal change of temperature. The internal CO2 production (CO2_IP) in these ponds was dominated by sediments. A significantly larger mean porewater CO2 concentrations, diffusive fluxes and production rate were observed in the MRE ponds than those in the JRE ponds, which could be attributed to the lower water salinity and a larger source of carbon substrates in the former estuary. Considering a total surface area of 6.63 × 103 km2 across the mariculture ponds in subtropical estuaries, it is estimated conservatively that approximately 100 Gigagram (Gg) of dissolved organic carbon and 190 Gg of dissolved inorganic carbon were transported annually from the mariculture ponds into China's coastal areas. Because of the substantial supply of dissolved carbon, the adjacent coastal waters receiving effluent discharge from the mariculture ponds could become “hotspots” of CO2 emissions. Our results highlight the role of aquaculture pond as a major CO2 source in China's coastal areas, and effective actions are needed to alleviate the greenhouse gas (GHG) emissions from these ponds

Production and uptake of dissolved carbon, nitrogen, and phosphorus in overlying water of aquaculture shrimp ponds in subtropical estuaries, China

Water quality deterioration can adversely affect the long-term sustainability of aquaculture industry. Understanding the processes of nutrient regeneration and uptake is important for improving water quality and the overall ecosystem health of aquaculture system. In spite of the importance of dissolved nutrients (DOC, DIC, N-NO , N-NH , and P-PO ) in governing water quality and ecosystem functioning, the spatiotemporal variations in the production and uptake of dissolved nutrients in aquaculture ponds is still poorly understood. In this study, the nutrient production and uptake rates in the overlying water were quantified among different shrimp growth stages in the aquaculture ponds in the Min River Estuary (MRE) and Jiulong River Estuary (JRE), southeast China. Significant differences in the nutrient production and uptake rates in the overlying water were observed among the three growth stages and two estuaries. The temporal variations of DOC and DIC production rates in both estuarine ponds closely followed the seasonal cycle of temperature, while the difference in DOC and DIC production rates between the two estuaries was likely caused by differences in water salinity. The changes in the production and uptake rates of dissolved inorganic nitrogen (N-NO and N-NH ) and P-PO in the water column over time were partly related to the interactions between thermal conditions and phytoplankton biomass (e.g., chlorophyll a concentrations) in the ponds. Our results demonstrate the complex dynamics and environmental risk of dissolved nutrients in subtropical shrimp ponds, and call for a more effective management of nutrient-laden wastewater in safeguarding the long-term sustainability of aquaculture production

Anomalous gtt couplings in the Littlest Higgs Model with T-parity

In this work we calculate the leading electroweak (EW) corrections to the anomalous $gt\bar{t}$ coupling in the Littlest Higgs model with T-parity (LHT), by applying the Goldstone boson equivalence theorem. In the LHT model, such electroweak corrections arise from the loop diagrams of heavy fermions and the ``would-be'' Goldstone bosons. We further examine the EW corrections in the top quark pair production via the quark annihilation process at the LHC. The negative EW corrections in the Standard Model are partially canceled by the positive EW corrections from the loops of the new heavy particles, and the latter dominates in the large invariant mass of the top quark pair.Comment: version appeared in PR

Precise Measurement of Gravity Variations During a Total Solar Eclipse

The variations of gravity were measured with a high precision LaCoste-Romberg D gravimeter during a total solar eclipse to investigate the effect of solar eclipse on the gravitational field. The observed anomaly $(7.0 \pm 2.7) \times 10^{-8}$ m/s$^2$ during the eclipse implies that there may be a shielding property of gravitation

Large fine‐scale spatiotemporal variations of CH4 diffusive fluxes from shrimp aquaculture ponds affected by organic matter supply and aeration in Southeast China

Mariculture shrimp ponds are important CH4 sources to the atmosphere. However, the spatiotemporal variations of CH4 concentration and flux at fine spatial scales in mariculture ponds are poorly known, particularly in China, worlds largest aquaculture producer. In this study, the plot‐scale spatiotemporal variations of water CH4 concentration and flux, both within and among ponds, were researched in shrimp ponds in Shanyutan wetland, Min River Estuary, Southeast China. The average water CH4 concentration and diffusion flux across the water‐air interface in the shrimp ponds over the shrimp aquaculture period varied from 2.29 ± 0.29 to 50.48 ± 20.91 μM and from 0.09 ± 0.01 to 2.32 ± 0.95 mmol·m−2·hr−1, respectively. The CH4 emissions from the estuarine ponds varied greatly between seasons, with peaks in August and September, which was similar to the trend of water temperature and dissolved oxygen concentrations. There was no remarkable difference in CH4 concentration and flux between shrimp ponds but significantly spatiotemporal differences in CH4 concentration and flux within the ponds. Significantly higher emissions occurred in the feeding zone, accounting for approximately 60% of total CH4 emission flux, while much lower CH4 emissions appeared in aeration zone, contributing 14% to total flux. This study suggests the importance of considering spatiotemporal variation in the whole‐pond estimates of CH4 concentration and flux. In light of such high spatial variation within ponds, improving aeration and feed utilization efficiency would help to mitigate CH4 emissions from mariculture ponds

Entanglement and quantum phase transition in alternating XY spin chain with next-nearest neighbour interactions

By using the method of density-matrix renormalization-group to solve the different spin-spin correlation functions, the nearest-neighbouring entanglement(NNE) and next-nearest-neighbouring entanglement(NNNE) of one-dimensional alternating Heisenberg XY spin chain is investigated in the presence of alternating nearest neighbour interactions of exchange couplings, external magnetic fields and next-nearest neighbouring interactions. For dimerized ferromagnetic spin chain, NNNE appears only above the critical dimerized interaction, meanwhile, the dimerized interaction effects quantum phase transition point and improves NNNE to a large value. We also study the effect of ferromagnetic or antiferromagnetic next-nearest neighboring (NNN) interactions on the dynamics of NNE and NNNE. The ferromagnetic NNN interaction increases and shrinks NNE below and above critical frustrated interaction respectively, while the antiferromagnetic NNN interaction always decreases NNE. The antiferromagnetic NNN interaction results to a larger value of NNNE in comparison to the case when the NNN interaction is ferromagnetic.Comment: 13 pages, 4 figures,. accepted by Chinese Physics B 2008 11 (in press

The entanglement in one-dimensional random XY spin chain with Dzyaloshinskii-Moriya interaction

The impurities of exchange couplings, external magnetic fields and Dzyaloshinskii--Moriya (DM) interaction considered as Gaussian distribution, the entanglement in one-dimensional random $XY$ spin systems is investigated by the method of solving the different spin-spin correlation functions and the average magnetization per spin. The entanglement dynamics at central locations of ferromagnetic and antiferromagnetic chains have been studied by varying the three impurities and the strength of DM interaction. (i) For ferromagnetic spin chain, the weak DM interaction can improve the amount of entanglement to a large value, and the impurities have the opposite effect on the entanglement below and above critical DM interaction. (ii) For antiferromagnetic spin chain, DM interaction can enhance the entanglement to a steady value. Our results imply that DM interaction strength, the impurity and exchange couplings (or magnetic field) play competing roles in enhancing quantum entanglement.Comment: 12 pages, 3 figure