Computation in networks of passively mobile finite-state sensors

The computational power of networks of small resource-limited mobile agents is explored. Two new models of computation based on pairwise interactions of finite-state agents in populations of finite but unbounded size are defined. With a fairness condition on interactions, the concept of stable computation of a function or predicate is defined. Protocols are given that stably compute any predicate in the class definable by formulas of Presburger arithmetic, which includes Boolean combinations of threshold-k, majority, and equivalence modulo m. All stably computable predicates are shown to be in NL. Assuming uniform random sampling of interacting pairs yields the model of conjugating automata. Any counter machine with O(1) counters of capacity O(n) can be simulated with high probability by a conjugating automaton in a population of size n. All predicates computable with high probability in this model are shown to be in P; they can also be computed by a randomized logspace machine in exponential time. Several open problems and promising future directions are discussed. Supported in part by NSF grants CCR-9820888, CCR-0098078, and CNS-0305258 (Aspnes), by ONR grant N00014-01-1-0795 (Diamadi), and by NSF grant CSE-0081823 (Fischer and Peralta). A preliminary version of this paper appeared in the proceedings of the 23rd ACM SIGACT-SIGOPS Symposium on Principles of Distributed Computing, St. John’s, Newfoundland, Canada, July 2004.     

红外光谱技术的进展及其应用

对漫反射、衰减全反射傅里叶变换红外光谱和差谱等技术及其应用进行了简单介绍     

Evaluation of 12 models to estimate hourly diffuse irradiation on inclined surfaces

This study evaluates the performance of 12 models to estimate hourly diffuse solar irradiation on inclined surfaces from those measured on horizontal surfaces. Total solar irradiation incident on a tilted surface consists of three components including: beam, diffuse and reflected from the ground. On a semi-hourly basis, the beam component can be calculated by the ratio of the incidence angle to the solar zenith angle. The reflected component has a small effect on calculations and may be calculated with an isotropic model. In contrast, models for estimating the diffuse component show major differences, which justify the validation study that this paper discusses. Twelve models were tested against recorded south- and west-facing slope irradiances at Karaj (35°55^′N; 50°56^′E), Iran. The following models were included: Badescu [Ba], Tian et al. [Ti], Perez et al. [P9], Reindl et al. [Re], Koronakis [Kr], Perez et al. [P8], Skartveit and Olseth [SO], Steven and Unsworth [SU], Hay [Ha], Klucher [Kl], Temps and Coulson [TC], and Liu and Jordan [LJ].The relative root mean square error (RMSE), for the south-facing surface ranges from 10.16% to 54.89% for the SO and TC models, respectively. For the west-facing surface, RMSE ranges from 30.71% for the P9 model to 63.53% for the TC model. Statistical indices show that all models produce large errors for the west-facing surface. Statistical indices for the south-facing surface show reasonably good agreement with measured data.     

Advanced nickel metal catalyst for water-gas shift reaction

A comparative study has been performed to investigate the effectiveness of a Ni metal catalyst before and after impregnation with potassium for the water-gas shift (WGS) reaction. The potassium-modified Ni metal is both more active and more selective for the WGS reaction than the unmodified Ni catalyst. Furthermore, there is no carbon deposition on the modified Ni catalyst. The amount of H₂ produced and the CO conversion via WGS over the potassium-modified Ni catalyst are higher than those for the commercial high-temperature shift (HTS) catalyst under severe experimental conditions (gas-hourly space velocity = 80 000 h⁻¹, CO 60% and H₂ 40%). The suppression of methanation over the modified Ni metal is attributed to the action of the incorporated potassium in increasing the density of the active hydroxyl group that takes part in the WGS reaction to form the intermediate.     

An investigation of the performance of 14 models for estimating hourly diffuse irradiation on inclined surfaces at tropical sites

The performance of 14 models for estimating hourly diffuse irradiation on inclined surfaces was investigated. In order to obtain solar radiation data for this investigation, equipment for measuring solar radiation on inclined surfaces facing to the north, south, east and the west at different tilted angles to the horizontal surface (30°, 60° and 90°) were constructed and installed at two tropical sites in Thailand, namely Nakhon Pathom (13.82 °N, 100.04 °E) and Ubon Ratchathani (15.25 °N, 104.87 °E). Radiation data encompassing different periods of 1–4 years were used in this work. Diffuse irradiance measurements at different tilted angles were compared with various model algorithms. Results show that the Muneer and Gueymard models have comparable performance in terms of root mean square difference (RMSD) and these models give the lowest RMSD, as compared to that of the other models.     

Piezoelectric and thermophysical performances of La3+ and Ir4+ co-doped Ba0.95Ca0.05Ti0.94Zr0.06O3 ceramics

Rare earth element-doped piezoelectric ceramics exhibit excellent electrical properties. Platinum group elements can render them catalytically active and conductive. In this study, lead-free Ba_0.95Ca_0.05Ti_0.94Zr_0.06O₃ piezoelectric ceramics doped with 0.12% lanthanum and iridium (varying contents, x) were sintered at 1260 °C. The thermal expansion coefficients and fracture strengths of these ceramics were affected by their strains and structural defects. With an increase in x, the diffuse phase transition weakened first and then accelerated (with further increase in x (> 0.75%)). The best ferroelectric properties were obtained at 400 ms and 25 kV/cm. The effects of the phase, structural defects, and internal stress on the electrical properties of the ceramics were systematically investigated. Relations of electrical properties, mechanical strength, and thermophysical performances were originally researched. In addition, the electrical properties (piezoelectric constants, ∼270 pC/N; mechanical quality factors, ∼70) and thermophysical performances (thermal expansion coefficient, ∼1.2 × 10⁻⁵ K⁻¹) of the ceramics were found to be suitable for practical applications.     

Prognostic significance of interim ~(18)F-FDG PET/CT SUV reduction associated with Ki67 in patients with diffuse large B-cell lymphoma

To detect the prognostic significance of interim F-FDG PET/CT SUV(standard uptake value) reduction(△SUV_(max)) associated with Ki67 in patients with diffuse large B cell lymphoma(DLBCL).47 DLBCL patients underwent PET/CT before initiation and after 2-4 cycles of chemotherapy were included.The SUV_(max)of the dominant lesions were calculated.Ki67 positive indices were provided by enzyme-labeled immunohistochemistry.SPSS17.0 was used for statistical analysis.ASUV_(max) of different groups were compared by t test.Receiver-operator characteristic analysis was performed to determine the optimal cutoff values.KaplanMeier analyses of PFS(Progression-free survival) were compared using log-rank test.The average of △SUV_(max)and △SUV_(max)%were 11.53 and 69.10%,respectively.The optimal cutoff values of △SUV_(max)x and △SUV_(max)%were 11.45 and 82.92%,respectively.Higher △SUV_(max) and △SUV_(max)%indicated longer PFS(p 0.001).The optimal cutoff value of Ki67 was 55%.Ki6755%was revealed to be an indicator of shorter PFS(p = 0.019).Either △SUV_(max)≤11.45 or Ki6755%was defined as an indicator to poor outcome and scored 1 point.The PFS rate was 100%in patients scored 0 point,yet 0%in patients scored 2 points.PFS tended to be shorter along with the score getting higher(p = 0.006).△SUV_(max) and Ki67 positive index were both of significance in DLBCL prognosis.The prognostic value may be confirmed when △SUV_(max) was accordant with Ki67.     

How well can we model stream phosphorus concentrations in agricultural catchments?

Mechanistic catchment-scale phosphorus models appear to perform poorly where diffuse sources dominate. We investigate the reasons for this for one model, INCA-P, testing model output against 18 months of daily data in a small Scottish catchment. We examine key model processes and provide recommendations for model improvement and simplification. Improvements to the particulate phosphorus simulation are especially needed. The model evaluation procedure is then generalised to provide a checklist for identifying why model performance may be poor or unreliable, incorporating calibration, data, structural and conceptual challenges. There needs to be greater recognition that current models struggle to produce positive Nash–Sutcliffe statistics in agricultural catchments when evaluated against daily data. Phosphorus modelling is difficult, but models are not as useless as this might suggest. We found a combination of correlation coefficients, bias, a comparison of distributions and a visual assessment of time series a better means of identifying realistic simulations.     

A simple clear skies model for the luminous efficacy of diffuse solar radiation on inclined surfaces

In the present work we study the luminous efficacy of diffuse solar radiation incident on vertical surfaces for a clear sky and mean hourly values of diffuse irradiance and diffuse illuminance. We develop a model easy to use, similar to a model previously obtained for horizontal surfaces. To develop the present model for vertical surfaces we assume that the slope of the surface influences diffuse illuminance and diffuse irradiance in the same way. As a consequence of this hypothesis, the luminous efficacy of diffuse solar radiation is assumed to be the same for both horizontal and inclined surfaces.     

Thermal performances comparisons of the glass evacuated tube solar collectors with shapes of absorber tube

The thermal performance of a glass evacuated tube solar collector is numerically and experimentally investigated. The solar collector considered in this paper consists of a two-layered glass tube and an absorber tube. Air is used as the working fluid. The length and diameter of this glass tube are 1200 and 37 mm, respectively. Four different shapes of absorber tubes are considered, and the performances of the solar collectors are studied to find the best shape of the absorber tube for the solar collector. Beam irradiation, diffuse irradiation, and shade due to adjacent tubes are taken into account for a collector model to obtain a realistic estimation. In addition, a single collector tube with only beam irradiation is studied as a simplified model, and the results of the simplified model are compared to those of the collector model to identify the difference between these two models. The performance of a solar collector is affected by the shape of the absorber, incidence angle of solar irradiation, and arrangement of collector tubes. The results obtained from the simplified model are very different from those from the collector model, which considered not only beam and diffuse irradiation but also shade due to adjacent tubes.