The Architecture of Transaction Networks: A Comparative Analysis of Hierarchy in Two Sectors

Many products are manufactured in networks of firms linked by transactions, but comparatively little is known about how or why such transaction networks differ. This article investigates the transaction networks of two large sectors in Japan at a single point in time. In characterizing these networks, our primary measure is “hierarchy,” defined as the degree to which transactions flow in one direction, from “upstream” to “downstream.” Our empirical results show that the electronics sector exhibits a much lower degree of hierarchy than the automotive sector because of the presence of numerous inter-firm transaction cycles. These cycles, in turn, reveal that a significant group of firms have two-way “vertically permeable boundaries”: (i) they participate in multiple stages of an industry’s value chain, hence are vertically integrated, but also (ii) they allow both downstream units to purchase intermediate inputs from and upstream units to sell intermediate goods to other sector firms. We demonstrate that the 10 largest electronics firms had two-way vertically permeable boundaries while almost no firms in the automotive sector had adopted that practice

The Economics of Reprocessing vs. Direct Disposal of Spent Nuclear Fuel

This report assesses the economics of reprocessing versus direct disposal of spent nuclear fuel. The breakeven uranium price at which reprocessing spent nuclear fuel from existing light-water reactors (LWRs) and recycling the resulting plutonium and uranium in LWRs would become economic is assessed, using central estimates of the costs of different elements of the nuclear fuel cycle (and other fuel cycle input parameters), for a wide range of range of potential reprocessing prices. Sensitivity analysis is performed, showing that the conclusions reached are robust across a wide range of input parameters. The contribution of direct disposal or reprocessing and recycling to electricity cost is also assessed. The choice of particular central estimates and ranges for the input parameters of the fuel cycle model is justified through a review of the relevant literature. The impact of different fuel cycle approaches on the volume needed for geologic repositories is briefly discussed, as are the issues surrounding the possibility of performing separations and transmutation on spent nuclear fuel to reduce the need for additional repositories. A similar analysis is then performed of the breakeven uranium price at which deploying fast neutron breeder reactors would become competitive compared with a once-through fuel cycle in LWRs, for a range of possible differences in capital cost between LWRs and fast neutron reactors. Sensitivity analysis is again provided, as are an analysis of the contribution to electricity cost, and a justification of the choices of central estimates and ranges for the input parameters. The equations used in the economic model are derived and explained in an appendix. Another appendix assesses the quantities of uranium likely to be recoverable worldwide in the future at a range of different possible future prices

Bimetallic Palladium Catalysis: Direct Observation of Pd(III)–Pd(III) Intermediates

$PhI(OAc)_2$ is a common oxidant for Pd-catalyzed C−H bond functionalizations. Mechanistic hypotheses since the 1960s have suggested a Pd(II)/Pd(IV) mechanism. Here we present evidence for the relevance of bimetallic Pd(III) complexes to catalysis. A bimetallic Pd(III) acetate was isolated and can afford product by bimetallic reductive elimination.Chemistry and Chemical Biolog

Muir String Quartet, December 1, 2003

This is the concert program of the Muir String Quartet performance on Monday, December 1, 2003 at 8:00 p.m., at the Tsai Performance Center, 685 Commonwealth Avenue, Boston, Massachusetts. Works performed were Quartet in A Major, Op. 18, No. 5 and Quartet in B-flat Major, Op. 130 by Ludwig van Beethoven. Digitization for Boston University Concert Programs was supported by the Boston University Center for the Humanities Library Endowed Fund

Endogenous Entry, Product Variety, and Business Cycles

This paper builds a framework for the analysis of macroeconomic fluctuations that incorporates the endogenous determination of the number of producers and products over the business cycle. Economic expansions induce higher entry rates by prospective entrants subject to sunk investment costs. The sluggish response of the number of producers generates a new and potentially important endogenous propagation mechanism for business cycle models. The return to investment determines household saving decisions, producer entry, and the allocation of labor across sectors. Our framework replicates several features of business cycles and predicts procyclical profits even for preference specifications that imply countercyclical markups.Economic

Validation of Urban NO2NO_2 Concentrations and Their Diurnal and Seasonal Variations Observed from the SCIAMACHY and OMI Sensors Using In Situ Surface Measurements in Israeli Cities

We compare a full-year (2006) record of surface air $NO_2$ concentrations measured in Israeli cities to coinciding retrievals of tropospheric $NO_2$ columns from satellite sensors (SCIAMACHY aboard ENVISAT and OMI aboard Aura). This provides a large statistical data set for validation of $NO_2$ satellite measurements in urban air, where validation is difficult yet crucial for using these measurements to infer $NO_x$ emissions by inverse modeling. Assuming that $NO_2$ is well-mixed throughout the boundary layer (BL), and using observed average seasonal boundary layer heights, near-surface $NO_2$ concentrations are converted into BL $NO_2$ columns. The agreement between OMI and (13:45) BL $NO_2$ columns (slope=0.93, n=542), and the comparable results at 10:00 h for SCIAMACHY, allow a validation of the seasonal, weekly, and diurnal cycles in satellite-derived $NO_2$. OMI and BL $NO_2$ columns show consistent seasonal cycles (winter $NO_2$ 1.6–2.7× higher than summer). BL and coinciding OMI columns both show a strong weekly cycle with 45–50% smaller $NO_2$ columns on Saturday relative to the weekday mean, reflecting the reduced weekend activity, and validating the weekly cycle observed from space. The diurnal difference between SCIAMACHY (10:00) and OMI (13:45) $NO_2$ is maximum in summer when SCIAMACHY is up to 40% higher than OMI, and minimum in winter when OMI slightly exceeds SCIAMACHY. A similar seasonal variation in the diurnal difference is found in the source region of Cairo. The surface measurements in Israel cities confirm this seasonal variation in the diurnal cycle. Using simulations from a global 3-D chemical transport model (GEOS-Chem), we show that this seasonal cycle can be explained by a much stronger photochemical loss of $NO_2$ in summer than in winter.Engineering and Applied Science

Shtukas and the Taylor expansion of LL-functions (II)

For arithmetic applications, we extend and refine our results in \cite{YZ} to allow ramifications in a minimal way. Starting with a possibly ramified quadratic extension $F'/F$ of function fields over a finite field in odd characteristic, and a finite set of places $\Sigma$ of $F$ that are unramified in $F'$, we define a collection of Heegner--Drinfeld cycles on the moduli stack of $\mathrm{PGL}_{2}$-Shtukas with $r$-modifications and Iwahori level structures at places of $\Sigma$. For a cuspidal automorphic representation $\pi$ of $\mathrm{PGL}_{2}(\mathbb{A}_{F})$ with square-free level $\Sigma$, and $r\in\mathbb{Z}_{\ge0}$ whose parity matches the root number of $\pi_{F'}$, we prove a series of identities between: (1) The product of the central derivatives of the normalized $L$-functions $\mathcal{L}^{(a)}(\pi, 1/2)\mathcal{L}^{(r-a)}(\pi\otimes\eta, 1/2)$, where $\eta$ is the quadratic id\`ele class character attached to $F'/F$, and $0\le a\le r$; (2) The self intersection number of a linear combination of Heegner--Drinfeld cycles. In particular, we can now obtain global $L$-functions with odd vanishing orders. These identities are function-field analogues of the formulas of Waldspurger and Gross--Zagier for higher derivatives of $L$-functions.Comment: 90 page