On cost-effective communication network designing

How to efficiently design a communication network is a paramount task for network designing and engineering. It is, however, not a single objective optimization process as perceived by most previous researches, i.e., to maximize its transmission capacity, but a multi-objective optimization process, with lowering its cost to be another important objective. These two objectives are often contradictive in that optimizing one objective may deteriorate the other. After a deep investigation of the impact that network topology, node capability scheme and routing algorithm as well as their interplays have on the two objectives, this letter presents a systematic approach to achieve a cost-effective design by carefully choosing the three designing aspects. Only when routing algorithm and node capability scheme are elegantly chosen can BA-like scale-free networks have the potential of achieving good tradeoff between the two objectives. Random networks, on the other hand, have the built-in character for a cost-effective design, especially when other aspects cannot be determined beforehand.Comment: 6 pages, 4 figure

Precise Algorithm to Generate Random Sequential Addition of Hard Hyperspheres at Saturation

Random sequential addition (RSA) time-dependent packing process, in which congruent hard hyperspheres are randomly and sequentially placed into a system without interparticle overlap, is a useful packing model to study disorder in high dimensions. Of particular interest is the infinite-time {\it saturation} limit in which the available space for another sphere tends to zero. However, the associated saturation density has been determined in all previous investigations by extrapolating the density results for near-saturation configurations to the saturation limit, which necessarily introduces numerical uncertainties. We have refined an algorithm devised by us [S. Torquato, O. Uche, and F.~H. Stillinger, Phys. Rev. E {\bf 74}, 061308 (2006)] to generate RSA packings of identical hyperspheres. The improved algorithm produce such packings that are guaranteed to contain no available space using finite computational time with heretofore unattained precision and across the widest range of dimensions ($2 \le d \le 8$). We have also calculated the packing and covering densities, pair correlation function $g_2(r)$ and structure factor $S(k)$ of the saturated RSA configurations. As the space dimension increases, we find that pair correlations markedly diminish, consistent with a recently proposed "decorrelation" principle, and the degree of "hyperuniformity" (suppression of infinite-wavelength density fluctuations) increases. We have also calculated the void exclusion probability in order to compute the so-called quantizer error of the RSA packings, which is related to the second moment of inertia of the average Voronoi cell. Our algorithm is easily generalizable to generate saturated RSA packings of nonspherical particles

Understanding the performance of the electric power industry in China

© 2012 The Earth Institute at Columbia University and the Massachusetts Institute of Technology.Despite three decades of reform, China's electricity sector is still organized by a “new reformed plan” where capacity investment has been liberalized but prices and production remain controlled. This paper examines the impact of the current plan prices on end-users with reference to the OECD and how the plan price of electricity supply is formed. We argue that the plan price is set in an attempt to balance the interests of the public and the power industry. We find that China's industries do not pay a cheaper price for electricity than the West, and the plan price is formed through bargain between the firm and the state, which allows the firm to have a soft price constraint on its costs

Perturbative QCD Results on Pion Production in pp, pA and AA Collisions

We summarize new pQCD results on pion production in proton-proton (pp), proton-nucleus (pA) and nucleus-nucleus (AA) collisions. Our calculation introduces intrinsic parton transverse momentum (k_T) and is performed effectively at next-to-leading order (NLO), applying a K factor extracted for jet events. Two different factorization scales, Q=p_{T,jet}/2 and p_{T,jet} are used. Experimental data in pA collisions imply a preference for the latter choice at NLO level. We display our results at CERN SPS for AA collisions.Comment: Talk given at Budapest Workshop on Quark and Hadron Dynamics in Relativistic Heavy Ion Collisions (BP 2002) Budapest, Hungary, 3-7 Mar 2002. 11 pages in Latex, 7 PS figure. Submitted to Heavy Ion Physic

Comment on "Potential Energy Landscape for Hot Electrons in Periodically Nanostructured Graphene"

In a recent letter [Phys. Rev. Lett. 105 (2010) 036804] the unoccupied electronic states of single layers of graphene on ruthenium are investigated. Here we comment on the interpretation, which deviates in four points from [J. Phys.: Condens. Matter 22 (2010) 302001] and outline the corresponding consequences

The Changing Nature of Faculty Employment

[Excerpt] The last two decades of the twentieth century saw a significant growth in the shares of faculty members in American colleges and universities that are part-time or are full-time without tenure-track status. Growing student enrollments faced by academic institutions during tight financial times and growing differentials between the salaries of part-time and full-time non-tenure track faculty on the one hand, and tenured and tenure-track faculty on the other hand are among the explanations given for these trends. However, there have been few econometric studies that seek to test these hypotheses. Our paper begins by presenting information, broken down by form of control (public/private) and 1994 Carnegie Category, on how the proportions of full-time faculty at 4-year American colleges and universities that are tenured and on tenure tracks and that are not on tenure tracks have changed since 1989, using information for a consistent sample of institutions from the annual IPEDS Faculty Salary Surveysand the biennial IPEDS Fall Staff Surveys. The latter source also permits us to present similar estimates of the proportions of faculty that are employed part-time and the share of new full-time faculty appointments that are not on tenure tracks. To analyze the role that economic variables play in causing changes in faculty employment across categories, we conduct two types of econometric analyses. First, in section III, we use panel data to estimate demand functions for tenure and tenure-track faculty on the one hand and full-time non tenure-track faculty on the other hand to learn how changes in revenues per student and the average salaries of different types of full-time faculty influence the distribution of faculty across categories of full-time faculty. We do this using both equilibrium models that assume instantaneous adjustments to changes in revenues and faculty salaries and lagged adjustment models that permit partial adjustments to equilibrium each year. Second, in section IV, we estimate models that seek to explain the flow of new hires of each type of faculty member (rather than the levels of faculty employment) using data on new hires that are available from the IPEDS Fall Staff Surveys. To explain new hires, in addition to information on changes in revenues per student, changes in enrollment, and the levels of faculty salaries, we require information on the number of vacant positions that are available to be potentially filled. We construct information on the latter using data on the number of continuing full-time faculty members at an institution each year that the American Association of University Professors (AAUP) collects (but does not publish) as part of its annual salary survey. Continuing faculty members in a rank are defined as the number of faculty members in a rank one year, who also are on the payroll of the institution in the next year, regardless of their rank in the second year. Summing up an institution’s continuing faculty members across ranks in a year and subtracting that number from the institution’s total faculty employment in the previous year provides us with an estimate of the number of full-time faculty vacancies that an institution could have filled in a year if it had replaced each of its departing full-time faculty members. A brief concluding section summarizes our findings and discusses their implications for American colleges and universities and their students