Logistic Changes to Production and some Impacts on Transportation and Materials Handling

There is presently a trend to "internalize" external transport links within the framework of large production system networks. This is made possible by the rapidly increasing capability to swiftly exchange huge masses of data within such networks and the availability of a deregulated transport sector, where the highly competitive trucking industry sets the rules. The result is new forms of logistics systems, designed to meet a set of service requirements which go beyond low cost. The impact of such systems on the evolution of material handling technologies is discussed. Details of one operational Just in Time system and one hypothetical JIT transport system connecting two production plants with particularly unmanned operations are included for the purpose of illustration

An International Analysis of Differences in Logistics Performance

The ratio Value Added to Inventory Value is used as a proxy for logistic performance. Large differences -- up to 8 times -- have been observed among the 14 nations in the study. The rank among the nations has been rather stable for the last 20 years but the ratio has improved considerably in most countries since 1980. Several hypotheses concerning the factors which explain the differences in inventory levels are formulated based on theories and case studies in the areas of production, trade, transport, communication, geography and social-economy. Proxies for some of these factors available in international statistics are used as independent variables in multiple regression analyses. The preliminary result indicates that as much as 80% of the differences could be explained by differences in import share, rail share, wholesale structure and telephone intensity. Hence, the hypothesis that differences in national inventory levels are only due to managerial factors or level of economic development could be rejected. Even if the logistic performance of individual companies can be improved considerably by adopting new management principles -- as many case studies show -- the total logistic performance of a nation seems to have significantly benefited from investments in transportation, production and communication infrastructures. However, it has still to be shown that these historical correlations are also causal relations that hold true for the future

Evidence for Supermassive Black Holes in Active Galactic Nuclei from Emission-Line Reverberation

Emission-line variability data for Seyfert 1 galaxies provide strong evidence for the existence of supermassive black holes in the nuclei of these galaxies, and that the line-emitting gas is moving in the gravitational potential of that black hole. The time-delayed response of the emission lines to continuum variations is used to infer the size of the line-emitting region, which is then combined with measurements of the Doppler widths of the variable line components to estimate a virial mass. In the case of the best-studied galaxy, NGC 5548, various emission lines spanning an order of magnitude in distance from the central source show the expected velocity proportional to inverse square root of the distance correlation between distance and line width, and are thus consistent with a single value for the mass. Two other Seyfert galaxies, NGC 7469 and 3C 390.3, show a similar relationship. We compute the ratio of luminosity to mass for these three objects and the narrow-line Seyfert 1 galaxy NGC 4051 and find that that the gravitational force on the line-emitting gas is much stronger than radiation pressure. These results strongly support the paradigm of gravitationally bound broad emission-line region clouds.Comment: 10 pages, 2 figures, Accepted for publication in Astrophysical Journal Letter

Verification of Markov hypothesis for conserved scalar process: validation of conditional moment closure for turbulent combustion

The Conditional Moment Closure (cmc) is a model for turbulent combustion that describes the physics of the process across the flow for a wide range of situations. The theoretical basis used in closing the model is that conserved scalars develop in turbulent fields similarly to Markov processes. We describe the formulation of cmc in both its deterministic and stochastic forms and show some preliminary results justifying the assumption of similarity with the Markov hypothesis

Transport Consequences of New Logistics Technologies

The Technology-Economy-Society Program at IIASA focuses the evolution, competition, and management of technologies; on identifying economic and social prerequisites; and on assessing the socioeconomic impacts of technological developments. This reprint summarizes the results of a study performed within the New Logistics Technologies Project in order to explore the interplay between the introduction of some 18 different types of new logistic technologies and the development of freight transport systems. One in-depth explorative case study from the automotive industry was performed to generate hypotheses and a conceptual framework, which were then tested on some 20 cases from early users of new logistics technologies

The UV spectra of NLS1s - Implications for their broad line regions

We study the UV spectra of NLS1 galaxies and compare them with typical Seyfert 1 galaxies and quasars. The NLS1 spectra show narrower UV lines as well as weaker CIV lambda 1549 and CIII] lambda 1909 emission. We show that these line properties are due to a lower ionization parameter and somewhat higher BLR cloud densities. These modified conditions can be explained by the hotter big blue bumps observed in NLS1s, which are in turn due to higher L/L_Edd ratios, as shown by our accretion disk and corona modeling of the NLS1 continua. We also present evidence that the Boroson & Green eigenvector 1, which is correlated with the optical and UV emission-line properties, is not driven by orientation and hence NLS1s, which have extreme eigenvector 1 values, are not viewed from an extreme viewing angle.Comment: Contributed talk presented at the Joint MPE,AIP,ESO workshop on NLS1s, Bad Honnef, Dec. 1999, to appear in New Astronomy Reviews; also available at http://wave.xray.mpe.mpg.de/conferences/nls1-worksho

The high frequency power spectrum of Markarian 766

An analysis is presented of the power spectrum of X-ray variability of the bright Seyfert 1 galaxy Mrk 766 as observed by XMM-Newton. Over the 0.2-10 keV energy range the power spectral density (PSD) is well-represented by a power-law with a slope of alpha_low ~ 1 at low frequencies, breaking to a slope of alpha_hi = 2.8 (-0.4/+0.2) at a frequency f_br ~ 5 x 10^-4 Hz. As has been noted before this broken power-law PSD shape is similar to that observed in the Galactic black hole candidate Cygnus X-1. If it is assumed that Mrk 766 shows a power spectrum similar in form to that of Cyg X-1, and that the break timescale scales linearly with black hole mass, then the mass of the black hole in Mrk 766 is inferred to be < 5 x 10^5 M_sun. This rather low mass would mean Mrk 766 radiates above the Eddington limit. The coherence between different energy bands is significantly below unity implying that variations in the different energy bands are rather poorly correlated. The low coherence can be explained in the framework of standard Comptonisation models if the properties of the Comptonising medium are rapidly variable or if there are several distinct emission sites.Comment: 6 pages, 5 figures, accepted for publication in MNRAS Letter

Cosmic ray production in supernova remnants including reacceleration: the secondary to primary ratio

We study the production of cosmic rays (CRs) in supernova remnants (SNRs), including the reacceleration of background galactic cosmic rays (GCRs) - thus refining the early considerations by Blandford & Ostriker (1980) and Wandel et al. (1987) - and the effects of the nuclear spallation inside the sources (the SNRs). This combines for the first time nuclear spallation inside CR sources and in the diffuse interstellar medium, as well as reacceleration, with the injection and subsequent acceleration of suprathermal particles from the postshock thermal pool. Selfconsistent CR spectra are calculated on the basis of the nonlinear kinetic model. It is shown that GCR reacceleration and CR spallation produce a measurable effect at high energies, especially in the secondary to primary (s/p) ratio, making its energy-dependence substantially flatter than predicted by the standard model. Quantitatively, the effect depends strongly upon the density of the surrounding circumstellar matter. GCR reacceleration dominates secondary CR production for a low circumstellar density. It increases the expected s/p ratio substantially and flattens its spectrum to an almost energy-independent form for energies larger than 100 GeV/n if the supernovae explode on average into a hot dilute medium with hydrogen number density $N_H=0.003$cm$^{-3}$. The contribution of CR spallation inside SNRs to the s/p ratio increases with increasing circumstellar density and becomes dominant for N_H\gsim 1 cm$^{-3}$, leading at high energies to a flat s/p ratio which is only by a factor of three lower than in the case of the hot medium. Measurements of the boron to carbon ratio at energies above 100 GeV/n could be used in comparison with the values predicted here as a consistency test for the supernova origin of the GCRs.Comment: 11 pages, 6 figures, accepted for publication in Astronomy and Astrophysic