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PublicationLight Rail Transit Systems: A Definition and Evaluation(1972-10-01) Vuchic, Vukan RRail transit represents a family of modes ranging from light rail to regional rapid transit systems and it can be utilized in a number of different cities and types of applications. Many European cities of medium size employ very successfully light rail mode for gradual upgrading of transit service into partially or fully separated high speed, reliable transit systems. Analysis of these cities show that with population densities and auto ownership very similar to those in the United States cities, their transit systems offer a superior service and have much better usage than our cities. Many modern features of light rail technology are not known in this country. Wider use of different rail systems, greatly increased transit financing, introduction of more qualified personnel into transit industry and improved transit planning and implementation procedures are recommended to close the gap in urban transportation between some more progressive European cities and their counterparts in this country. PublicationSkip-Stop Operation as a Method for Transit Speed Increase(1973-04-01) Vuchic, Vukan RIncrease of transit speeds is one of the most effective ways of increasing the attractiveness of transit for urban travel. While surface transit in particular suffers from low speed, the desirability of higher speeds is not limited to it. Rapid transit has adequate speed for short to medium-distance trips in urban areas. However, for longer trips, particularly when there is a competing freeway facility, the requirement for speed is rather high. Since many station spacings are adopted on the basis of area coverage, high operating speed of the trains often cannot be achieved. Thus, typical lines of urban rapid transit with average interstation spacings of approximately one-half mile have only limited length on which their speeds are satisfactory; for distances longer than, typically, 5-7 miles, they often become too slow. This is becoming an increasing problem with the spatial spread of cities. This article describes the main alternative solutions to this problem and then focuses on the skip-stop operation, presenting a methodology for its analysis and evaluation of its applicability. Although the article discusses rail services, the basic aspects of the problem are common for any technology. For example, there are a number of bus services for which skip-stop service could be considered utilizing the methodology developed here. PublicationTransit Federation -- A Solution for Service Integration(1972) Homburger, Wolfgang S; Vuchic, Vukan RInadequate organization of public transport services in urban areas, particularly in the large ones, is one of the major reasons for the unsatisfactory level of service and economic problems of the operating companies. Despite the current trend toward mergers of transit operators into large public agencies, the services in most cities remain fragmented in various degrees; integration is often not in sight due to organizational problems which appear insurmountable. Losses to the users, the operators, and the city from this situation are often very significant. This article briefly analyzes the reasons for this situation, explores its consequences and their importance. A number of solutions for the problem are possible, but none of them is simple and easy to achieve. The federation of transit organizations introduced recently in Hamburg, Germ any, has proved to be so successful that it has received wide attention in international professional circles. This solution therefore deserves a careful study by transit operators as well as government officials of metropolitan areas in the United States and other countries. PublicationDirectory Construction and Decoding in a Generalized File Structure(1970-08-01) Desiato, Barbara MA generalized file structure consists of a file and its directory from which some of the existing file structures such as inverted, index-sequential, and multilist files can be derived and specialized. The directory acts as a reference for information within the file. It consists of keywords (i.e., attribute-value pairs) and addresses of records which are characterized by these keywords. The directory and its access routines simulate an associative memory in that records can be located in the file by merely providing the keywords which are associated with the records. The directory is initialized when the file is created and is updated for each addition of a keyword or a record to the file. For a given attribute, directory decoding can be done for one specific value or a range of values. Decoding involves the search of the keywords within the directory and the addresses of the records characterized by these keywords. PublicationRapid Transit Automation and the Last Crew Member(1973-10-01) Vuchic, Vukan RRapid transit systems in many cities are being automated, but most transit officials reject the idea of operation without crews on the train as idealistic. At the same time large resources are spent on development of full automation for numerous new systems such as PRT, many of which have no defined role in urban transportation programmed train movement eliminates any possible improper driving practices. However, nearly all rapid transit vehicles have indirect controls which prevent the driver from improper acceleration and assist him in braking. Thus improvement through A TO is again not significant. PublicationUrban Transportation Policy: Time for Reorientation(1975-03-22) Vuchic, Vukan RWritten testimony from Vukan Vuchic to the Transportation Committee of the National Conference of Democratic Mayors in New Orleans on March 22, 1975. PublicationOn the Stability of Electric Arc Discharges(1976-06-07) Whitman, A. M.; Ayyaswamy, Portonovo S.; Cohen, Ira M.The stability of electric arc discharges has been explored through the use of an energy balance coupled with charge conservation. In order to facilitate this analysis, a new model for the electrical conductivity function has been proposed. Asymptotic solutions for the arc governing equations have been obtained. Stability criteria have been developed from both the linear theory (infinitesimal size disturbance) and from a minimizing solution point of view for finite size disturbances. The results delineate an open region in the stability diagram where arc instabilities may be possible. PublicationThe PDPMAP Assembly System(1967) Johnson, Thomas H; Wolfberg, Michael SThis report describes the PDPMAP Assembly System which is used to assemble symbolic programs written for a Digital Equipment Corporation PDP-8 or DEC-338 with up to 16-K memory 1ocations. The system is implemented at the University of Pennsylvania on an IBM 7040 and DEC PDP-8 connected by a high-speed data channel (IBM 7904 and DEC DM03). The PDPMAP System uses the powerful assembler of a larger computer (IBM 7040 MAP Assembler) to quickly assemble programs for a small computer. PublicationCalculation of the Positions of the α- and β-bands in the Electronic Spectra of Benzenoid Hydrocarbons Using the Method of Limited Configuration Interaction(1963) Koutecký, Josef; Paldus, Josef; Vitek, VaclavThe positions of the α- and β-bands in the electronic absorption spectra of twenty aromatic benzenoid hydrocarbons were calculated by the semiempirical method of limited configuration interaction in the π-electron approximation using the Huckel molecular orbitals. The agreement of the experimental and calculated values is good for the β-band whereas a systematic deviation is observed for the α-band. This deviation cannot be removed by extending the configuration interaction of the monoexcited states constructed from the molecular orbitals considered. However, the consideration of electronic repulsion enables us to explain the character of the dependences of the experimental excitation energies on the excitation energies obtained by the simple Huckel method of molecular orbitals. Using a suitable choice of semiempirical parameters different for various electronic transitions (showing no large mutual differences) yields semiempirical interpolation formulas for the; p-, α-, and β-bands which give very good agreement with the corresponding experimental excitation energies for the compounds studied. PublicationThermal and electrical characteristics of a two‐dimensional tanh‐conductivity arc(1978) Ayyaswamy, Portonovo S.; Das, G. C.; Cohen, Ira M.The two-dimensional variable-property arc has been studied through the use of the tanh-conductivity model. Results that describe the thermal and electric arc characteristics for various values of the electrode temperatures and aspect ratios are given. The numerical evaluation is carried out by the use of a Galerkin technique. The results exhibit several novel and interesting features depending on the arc parameters. For large aspect ratios (ratio of the interelectrode distance to that between the bounding walls) and small electrode temperatures, the current---electric-field characteristics tend toward those of a slender arc. However, at a given aspect ratio with large enough electrode temperatures, the distinct minimum noted in the slender-arc characteristics does not occur. Also, for a given aspect ratio and large enough differences in electrode potential, the electric-field-current characteristic is nearly linear and is independent of the electrode temperature. The transverse electrostatic potential is found to have no significant variation in cross-sectional planes. The qualitative nature of the thermal characteristics are similar to those of a constant-property arc although significant differences in quantitative results exist. Wall and electrode heat transfer rates are provided.