1,134 research outputs found
Academic Performance of New Jersey's Public Schools
Data from the 1992 National Assessment of Educational Progress are used to compare the performance of New Jersey public school children with those from other participating states. The comparisons are made with the raw means scores and after standardizing all state scores to a common (National U.S.) demographic mixture. It is argued that for most plausible questions about the performance of public schools the standardized scores are more useful. Also, it is shown that if New Jersey is viewed as an independent nation, its students finished sixth among all the nations participating in the 1991 International Mathematics Assessment
Pregled znanstvenih napredaka u učinskoj elektronici usmjerenih ka osiguravanju efikasnog rada i dužeg životnog vijeka PEMgorivih ćelija
This article focuses on the main issues that affect the lifetime and performance of proton-exchange membrane fuel cells. The short lifespans of these fuel cells represent a barrier to their massive commercialization and usage in mobile and stationary applications. As fuel cell is a very complex system, a lot of knowledge of different areas is required, such as chemistry, electricity and mechanics, in order to completely understand its operation and all the problems that can occur during it. It is for this reason that an interdisciplinary approach needs to be taken when designing fuel-cell energy systems. This paper focuses on identifying and solving those issues that negatively affect the lifetime and performance of fuel cells. It is hoped that this article would be a valuable aid for power electronics’ researchers and engineers for better understanding the presented issues and a useful guide for solving them with the use of proper power electronic-devices. Initially, the basic operation and structure of a proton-exchange membrane fuel cell is explained. Three main issues that can occur during operation of a mobile or stationary fuel cell energy system are pointed out and discussed in details, on the basis of the state-of-the-art on fuel cell technology. These issues are poor water management, reactant gas starvation and fuel cell current ripple. This article provides answers as to why they occur, how they affect the fuel cell, how they can be mitigated, and what are the future trends within this research field.Članak se osvrće na ključna pitanja koja utječu na vrijeme rada i performanse gorivih ćelija s polimernom membranom kao elektrolitom. Kratak životni vijek gorivih ćelija takve vrste prepreka je njihovoj komercijalizaciji i masovnoj upotrebi u mobilnim i stacionarnim stanicama. Budući da su gorive ćelije komplicirani sustavi potrebno je znanje iz raznih područja kemije, elektrotehnike i mehanike da bi se u potpunosti mogao razumjeti njihov način rada i problemi koji se događaju. Upravo je zbog toga multidisciplinarni pristup nužnost pri razvoju sustava koji koriste gorive ćelije. Ovaj je članak usmjeren prema identifikaciji i rješavanju onih problema koji negativno utječu na životni vijek i performanse gorivih ćelija. Autori se nadaju da će se članak pokazati kao korisna pomoć i vodič istraživačima i inženjerima u domeni učinske elektronike pri susretu s navedenim problemima. Objašnjen je način rada i struktura gorive ćelije s polimernom membranom kao elektrolitom. Izložena su, i diskutirana do u detalje, tri glavna problema sa stajališta trenutačnih spoznaja u području učinske elektronike. Ti problemi su: loše upravljanje vodom, nestanak reaktantnog plina i strujni trzaji u gorivim ćelijama. Objašnjeno je zašto se ovi problemi događaju, kako utječu na gorivu ćeliju, kako ih se može spriječiti i koje su buduće perspektive istraživanja
The Logos of the Blogosphere: Flooding the Zone, Invention, and Attention in the Lott Imbroglio
The World on Mercator's projection / J. & C. Walker sculpt. Mercator's projection
Relief shown by hachures. Shows 6 world continents, some political divisions, major cities, the Chinese Empire and Russian America; Spitsbergen and Nova Zemlia north of Europe, "Independent Tartary" in southwest Asia, and "Nueva California" as the southwest portion of North America. "Published by and under the superintendence of the Society for the Diffusion of Useful Knowledge Charles Knight & Co. 22 Ludgate Street." Outline color. Differs from 1841 version; lacks date information.Colo
Approaching the Wharf, Memphis, Tenn.
https://egrove.olemiss.edu/rayburn/1986/thumbnail.jp
Bila anda menghadapi masalah hukum hak anda saat; digeledah, disita, ditangkap, ditahan, didakwa, dipenjara
x.; 179 hal.; ill.; 19 c
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