Modeling gross primary production of two steppes in Northern China using MODIS time series and climate data

AbstractTerrestrial carbon cycle plays an important role in global climate change. As a key component of terrestrial carbon cycle, gross primary production (GPP) is a major determinant of the exchange of carbon between the atmosphere and terrestrial ecosystems. With rapid advancement of remote-sensing technology, it has become a common practice to utilize parameters derived from remote-sensing data to estimate GPP at a regional or global scale. In this study, a satellite-driven model, Vegetation Photosynthesis Model (VPM) was introduced to estimate GPP of two steppes, Xilinhot (XH, 43.5544°N, 116.6714°E) and Duolun (DL, 42.0467°N, 116.2836°E), at Inner Mongolia in Northern China, by integrating moderate resolution imaging spectral radiometer (MODIS) and meteorological measurements at the two flux towers. As defined by the input variables of VPM, two improved vegetation indices (enhanced vegetation index (EVI) and land surface water index (LSWI)) derived from the standard data product MOD09A1 of MODIS, air temperature and photosynthetic active radiation at the flux towers, were included for the model calculating. Canopy-level maximum light use efficiency, a key parameter for VPM, was estimated by using the observed CO2 flux data and photosynthetic active radiation (PAR). Observed GPP derived from flux data were then used to critically evaluate the performance of the model. The results indicate that the seasonal dynamics of GPP predicted by the VPM model agreed well with measured GPP by the flux towers. The determination coefficient (R2) of predicted GPP with measured GPP was 0.86 and 0.79 in 2006, 0.66 and 0.76 in 2007 for DL and XH, respectively. Further, time-series data for the EVI have a stronger linear relationship with the GPP than those for the Normalized Difference Vegetation Index. Results of this study demonstrate that the satellite-driven VPM has been potential for estimating site-level or regional grassland GPP, and might be an effective tool for scaling-up carbon fluxes

Efficient Multiscale Prediction of Cantilever Distortion by Selective Laser Melting

Large tensile residual stress is one major issue for metal components made by selective laser melting (SLM). Residual stress is induced by non-uniform heat input, which leads to part distortion and detrimentally affects product performance. The conventional single track simulation method is not feasible to predict the distortion of a macro part since it demands an exceedingly long computational time. The coupling multiphysics phenomenon during the SLM process further complicates this issue. In this study, a temperature-thread multiscale modeling approach has been developed to predict part distortion of a twin cantilever. An equivalent body heat flux calculated from the micro scan model was imported as the “temperature-thread” to the subsequent layer hatch model. Then the hatched layer with temperature field can be used as a basic unit to build up the macro part. The temperature history and residual stress fields during the SLM process were predicted. And the distortion of twin cantilever was calculated with a reasonable accuracy compared to the experimental data.Mechanical Engineerin

Some comments on the bi(tri)-Hamiltonian structure of Generalized AKNS and DNLS hierarchies

We give the correct prescriptions for the terms involving the inverse of the derivative of the delta function, in the Hamiltonian structures of the AKNS and DNLS systems, in order for the Jacobi identities to hold. We also establish that the sl(2) AKNS and DNLS systems are tri-Hamiltonians and construct two compatible Hamiltonian structures for the sl(3) AKNS system. We also give a derivation of the recursion operator for the sl(n+1) DNLS system.Comment: 10 pages, LaTe

Habitat fragmentation causes rapid genetic differentiation and homogenization in natural plant populations – A case study in Leymus chinensis

The effects of habitat fragmentations on the forage grass Leymus thinness (Trin.) Tzvel, which has high genetic diversity in northeast China were investigated. Four natural populations of the same ecotype (Grey-green leaf, GGL), namely, BT, ZL, CL and CC (named after location) were collected from different abiotic growing conditions. The CC population has become isolated in a park inside a city by tall buildings though geologically close to CL. Amplified fragment length polymorphism (AFLP) selected primer combinations were highly efficient in revealing the inter-clonal and inter-populational genetic variation in this species. The genetic diversity indices were higher in BT (H = 0.2305) and ZL (0.2467) populations and the lowest in CC (0.1674) population. Cluster analysis showed that the CC population was becoming isolated from the rest with the least gene flow from BT (1.51) as compared from BT to ZL (2.24). Lowest polymorphism was observed in CC (52.31%) as compared to CL (57.69%), BT (70.00%) and ZL (70.38%); this showed a tendency towards homogenization probably due to increased selfing, and due to reduced gene flow apparently caused by city buildings. These results were supported by multiple statistical analyses including Mantel’s test, PCOORDA and AMOVA. Genetic enrichment and epigenetic variation studies can be included in habitat fragmentation analysis and its implications in inducing homogenization and susceptibility in natural plant populations

Effective Dynamic Range in Measurements with Flash Analog-to-Digital Convertor

Flash Analog to Digital Convertor (FADC) is frequently used in nuclear and particle physics experiments, often as the major component in big multi-channel systems. The large data volume makes the optimization of operating parameters necessary. This article reports a study of a method to extend the dynamic range of an 8-bit FADC from the nominal $\rm{2^8}$ value. By comparing the integrated pulse area with that of a reference profile, good energy reconstruction and event identification can be achieved on saturated events from CsI(Tl) crystal scintillators. The effective dynamic range can be extended by at least 4 more bits. The algorithm is generic and is expected to be applicable to other detector systems with FADC readout.Comment: 19 pages, 1 table, 10 figure

A Temperature-Thread Multiscale Modeling Approach for Efficient Prediction of Part Distortion by Selective Laser Melting

Selective laser melting (SLM) is a powder bed based additive manufacturing process to manufacture functional parts. The high-temperature process will produce large tensile residual stress which leads to part distortion and negatively affect product performance. Due to the complex process mechanism and coupling multi-physics phenomena, the micro-scale single laser scan modeling approach is not practical to predict macro part distortion since it demands an exceedingly long computational time. In this study, a temperature-based multiscale modeling approach has been developed to simulate material phase transition of powder-liquid-solid for fast prediction of part distortion. An equivalent body heat flux obtained from the micro-scale laser scan can be imported as “temperature-thread” to the subsequent layer hatching process. Then the hatched layer with temperature filed can be used as a basic unit to build up the macro-scale part with different scanning strategies. The temperature history and residual stress fields during the SLM process were obtained. In addition, the part distortion can be predicted with a reasonable accuracy by comparing with the experimental data.Mechanical Engineerin

Photons, neutrinos and optical activity

We compute the one-loop helicity amplitudes for low-energy $\nu\gamma\to\nu\gamma$ scattering and its crossed channels in the standard model with massless neutrinos. In the center of mass, with $\sqrt{s} = 2\omega\ll 2m_e$, the cross sections for these $2\to 2$ channels grow roughly as $\omega^6$. The scattered photons in the elastic channel are circularly polarized and the net value of the polarization is non-zero. We also present a discussion of the optical activity of a sea of neutrinos and estimate the values of its index of refraction and rotary power.Comment: 9 pages, ReVTeX4, 6 figures include

Robustness analysis of signaling transduction networks based on Monte-Carlo method

The dynamic behaviors of cell system were deep ly affected by structural complexity of cell signal transduction networks and uncertainty of kinetics parameters. How to quantitatively determinate the relation between system behaviors and parameters variations was an important p roblem of systems biology. In order to study robustness of NF - κB signal transduction networks, the parameters of system model were assigned to subject to stochastic distributions. Then, robustness of system output signal NF - κBn with respect to 64 parameters variations and amp litude variation of step input signal IKK was studied by means of Monte - Carlo method. The simulation results demonstrate that the oscillation behavior of system output signal NF - κBn is closely relative to 6 key rate constantswhose robustness isweak, and the amp litude variation of step input signal IKKmakes a great impact on the oscillation behavior of system output