贝叶斯频谱估计算法在测量人工传输线长度中的应用

首先通过公式的推导给出贝叶斯频谱估计的基本思想,然后结合一个人工传输线长度测量的具体实例介绍了如何在实际中运用此估计方法,并与传统方法进行了简单的比较。结果表明,此算法的精确度优于传统算法。     

The effects of experimental reservoir creation on the bioaccumulation of methylmercury and reproductive success of tree swallows (Tachycineta bicolor)

Reservoir creation results in decomposition of flooded organic matter and increased rates of mercury methylation. Methylmercury (MeHg), the most toxic form of mercury, bioaccumulates through aquatic food webs. Our objective was to quantify the transfer of MeHg from aquatic food webs into terrestrial organisms. We examined rates of MeHg bioaccumulation in an insectivorous songbird, the tree swallow, breeding near an experimentally created reservoir. We also determined the impact of flooding and MeHg bioaccumulation on the reproductive success of these birds. Mean MeHg burdens in nestling swallows from near the experimental reservoir increased from 1,210 +/- 150 ng before flooding to 2,200 +/- 102 ng after flooding. Postflood MeHg concentrations in both the body and feathers of the birds were significantly greater than preflood MeHg concentrations. Although MeHg burdens in swallows were elevated in postflood years, we found no overt toxicological affects. An increase in dipteran productivity (the primary food source of tree swallows) after reservoir creation resulted in earlier nest initiation, larger eggs, and faster growth rates of wing and bill length in nestlings raised during postflood years.     

Analytical g-function for inclined boreholes in ground-source heat pump systems

In the design of ground-source heat pump systems, the calculation of the total length of the bore field is very important because it is responsible for the major part of the initial cost. Some technologies, like direct expansion systems and pile systems, often use inclined boreholes. Most design methods do not consider this effect and may overestimate the total length needed for a typical application. This paper gives a method for the calculation of time response factors in a form called g-function for inclined boreholes. The analytical model can be used in a parameterized optimization algorithm to design an optimum bore field. The method is a generalization of a method previously proposed for vertical boreholes. Comparison of the new g-function with tabulated values found in the literature is given, and an application for a typical design is presented as an example.     

A measure of regional diversification and efficiency

This paper develops a model to measure regional industrial diversification in a Markowitz portfolio context, using the notion of a regional efficiency frontier. It argues that a region can be considered to be optimally diversified when it is on this efficiency frontier. The extent to which a region's portfolio deviates from the efficiency frontier suggests a useful measure of diversification with normative aspects that are conspicuously absent from the more commonly used indices. In this context, regional diversification is then compared to various other measures using Canadian provincial employment data.     

Reactivity and mobility of new and old mercury deposition in a boreal forest ecosystem during the first year of the METAALICUS study. Mercury Experiment To Assess Atmospheric Loading In Canada and the US

The METAALICUS (Mercury Experiment To Assess Atmospheric Loading In Canada and the US) project is a whole ecosystem experiment designed to study the activity, mobility, and availability of atmospherically deposited mercury. To investigate the dynamics of mercury newly deposited onto a terrestrial ecosystem, an enriched stable isotope of mercury (202Hg) was sprayed onto a Boreal forest subcatchment in an experiment that allowed us, for the first time, to monitor the fate of 'new' mercury in deposition and to distinguish it from native mercury historically stored in the ecosystem. Newly deposited mercury was more reactive than the native mercury with respect to volatilization and methylation pathways. Mobility through runoff was very low and strongly decreased with time because of a rapid equilibration with the large native pool of "bound" mercury. Over one season, only approximately 8% of the added 212Hg volatilized to the atmosphere and less than 1% appeared in runoff. Within a few months, approximately 66% of the applied 202Hg remained associated with above ground vegetation, with the rest being incorporated into soils. The fraction of 202Hg bound to vegetation was much higher than seen for native Hg (<5% vegetation), suggesting that atmospherically derived mercury enters the soil pool with a time delay, after plants senesce and decompose. The initial mobility of mercury received through small rain events or dry deposition decreased markedly in a relatively short time period, suggesting that mercury levels in terrestrial runoff may respond slowly to changes in mercury deposition rates.     

Carbide-based fuel system for undersea vehicles

In underwater applications such as unmanned undersea vehicle (UUV) propulsion, mass and volume constraints often dictate system energy density and specific energy, which are targeted to exceed 300 Wh L⁻¹ and 300 Wh kg⁻¹, respectively, in order to compete with state-of-the-art battery technologies. To address this need, a novel carbide-based fuel system (CFS) intended for use with a solid oxide fuel cell (SOFC) is under development that is capable of achieving these energy metrics as well as sequestering carbon dioxide. The proposed CFS uses calcium carbide and calcium hydride that react with water to generate acetylene and hydrogen as the fuel and calcium hydroxide as a carbon dioxide scrubber. The acetylene is hydrogenated to ethane and then reformed to syngas (carbon monoxide and hydrogen) before being utilized by the SOFC. Carbon dioxide effluent from the SOFC is reacted with the calcium hydroxide to produce a storable solid, calcium carbonate, thus eliminating gas evolution from the UUV. A system configuration is proposed and discussion follows concerning energy storage metrics, operational parameters and preliminary safety analysis.     

Gini系数在镜质体反射率量测分析上之应用

该研究主要利用Gini系数来探讨镜质体反射率量测上不均性的结果,由单一煤样之水洗样(Y₂)及富集壳质组之样品(Y₃),与原始样(Y₁)作Gini系数的比较。分析显示水洗样Y₂之镜质体反射率有向平均值集中的情形,而富集样Y₃之Gini系数则有向平均值两端分布的趋势;向高值端的部分系受水洗的影响,而向低值端的发展,系受壳质组富集的影响。由Gini系数特性的研究可推广至已知再沉积材料之镜质体反射率的量测上,以取得一个可靠之Gini系数分布范围,作为将来分析样品时的参考。      

Understanding Bulk Defects in Topological Insulators from Nuclear‐Spin Interactions

Non‐invasive local probes are needed to characterize bulk defects in binary and ternary chalcogenides. These defects contribute to the non‐ideal behavior of topological insulators. The bulk electronic properties are studied via ¹²⁵Te NMR in Bi₂Te₃, Sb₂Te₃, Bi_0.5Sb_1.5Te₃, Bi₂Te₂Se, and Bi₂Te₂S. A distribution of defects gives rise to asymmetry in the powder lineshapes. The Knight shift, line shape, and spin‐lattice relaxation are investigated in terms of how they affect carrier density, spin‐orbit coupling, and phase separation in the bulk. The present study confirms that the ordered ternary compound Bi₂Te₂Se is the best topological insulator candidate material at the present time. These results, which are in good agreement with transport and angle‐resolved photoemission spectroscopy studies, help establish the NMR probe as a valuable method to characterize the bulk properties of these materials.     

Irregular growth of AlSb in solid aluminum-solid antimony diffusion couples

An investigation was made of the growth of the intermediate phase aluminum antimonide (AlSb) in solid aluminum-solid antimony diffusion couples, AlSb being the only intermediate phase present in the equilibrum phase diagram. Most diffusion couples were assembled from polycrystalline aluminum and antimony, but a few were made from single crystals; the diffusion couple surfaces were prepared in a variety of ways and the couples were isothermally annealed at temperatures between 450° and 615°C. It was found in all cases that AlSb nucleates at the original interface and after sufficient time coalesces into a highly irregular layer, irrespective of the details of the surface treatment. In several cases in which limited nucleation of AlSb took place, the morphology of the crystals was such as to suggest that the observed anisotropic growth was related to the zinc-blende crystal structure of the AlSb. Formerly Graduate Student, Department of Physical and Engineering Metallurgy, Polytechnic Institute of Brooklyn, Brooklyn, N. Y. Formerly Graduate Student, Department of Physical and Engineering Metallurgy, Polytechnic Institute of Brooklyn.