A dc to dc converter

The object of the invention is to provide an improved converter for converting one direct current voltage to another. A plurality of phased square wave voltages are provided from a ring counter through amplifiers to a like plurality of output transformers. Each of these transformers has two windings, and S(1) winding and an S(2) winding. The S(1) windings are connected in series, then the S(2) windings are connected in series, and finally, the two sets of windings are connected in series. One of six SCRs is connected between each two series connected windings to a positive output terminal and one of diodes is connected between each set of two windings of a zero output terminal. By virtue of this configuration, a quite high average direct current voltage is obtained, which varies between full voltage and two-thirds full voltage rather than from full voltage to zero. Further, its variation, ripple frequency, is reduced to one-sixth of that present in a single phase system. Application to raising battery voltage for an ion propulsion system is mentioned

Ambitious STS-7 mission to feature first landing at Kennedy

The STS-7 press briefing schedule, NASA select television schedule; launch preparations, countdown and liftoff; major countdown milestones; launch window; STS-7 flight sequence of events, landing timeline; STS-7 flight timeline; landing and post landing operations; flight objectives; Telesat's ANIK-C 2; PALAPA-B; STS-7 experiments; and spacecraft tracking and data network are presented

New Modeling of the Lensing Galaxy and Cluster of Q0957+561: Implications for the Global Value of the Hubble Constant

The gravitational lens 0957+561 is modeled utilizing recent observations of the galaxy and the cluster as well as previous VLBI radio data which have been re-analyzed recently. The galaxy is modeled by a power-law elliptical mass density with a small core while the cluster is modeled by a non-singular power-law sphere as indicated by recent observations. Using all of the current available data, the best-fit model has a reduced chi-squared of approximately 6 where the chi-squared value is dominated by a small portion of the observational constraints used; this value of the reduced chi-squared is similar to that of the recent FGSE best-fit model by Barkana et al. However, the derived value of the Hubble constant is significantly different from the value derived from the FGSE model. We find that the value of the Hubble constant is given by H_0 = 69 +18/-12 (1-K) and 74 +18/-17 (1-K) km/s/Mpc with and without a constraint on the cluster's mass, respectively, where K is the convergence of the cluster at the position of the galaxy and the range for each value is defined by Delta chi-squared = reduced chi-squared. Presently, the best achievable fit for this system is not as good as for PG 1115+080, which also has recently been used to constrain the Hubble constant, and the degeneracy is large. Possibilities for improving the fit and reducing the degeneracy are discussed.Comment: 22 pages in aaspp style including 6 tables and 5 figures, ApJ in press (Nov. 1st issue

Supply chain disruptions : managing risks vs. managing crises

Thesis (M. Eng. in Logistics)--Massachusetts Institute of Technology, Engineering Systems Division, 2007.This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.Includes bibliographical references (leaves 74-76).This thesis looks at two back-to-back disruptive supply chain events, one due to a sole-supplier's bankruptcy and the other caused by Hurricane Rita, that occurred at a specialty chemical company, and uses these examples to demonstrate how managing crises is more costly than managing risks. In examining the events surrounding the sole-supplier bankruptcy, managing a crisis cost this specialty chemical company 45% more money than managing a risk. Through the findings of these two disruptive events, a framework, the Eye of Providence, is created to manage supply chain risks. First, an organization must determine how developed its risk-management protocol is. Next, by studying past disruptive events and determining the key impact factors, an organization could calculate and learn about the opportunity cost of managing crisis. Then, by continuously evaluating its suppliers and rigorously applying those key impact factors to the analysis of its supply chain practice, an organization could evaluate and identify its current vulnerabilities.(cont.) Finally, by proactively monitoring event-based warning signals, or disruption indicators, an organization could assess its potential supply chain risks, and plan accordingly. Whether a company is low on the risk-maturity level or has already integrated risk management into its corporate culture, the process developed in this thesis serves as a versatile tool that can help businesses structure a more dynamic, resilient supply chain.by Garrett J. Lee [and] Zen-Lee M. Chang.M.Eng.in Logistic