Morse code

Morse code is a method used in telecommunication to encode text characters as standardized sequences of two different signal durations, called dots and dashes, or dits and dahs. Morse code is named after Samuel Morse, one of the inventors of the telegraph. International Morse code encodes the 26 basic Latin letters through , one accented Latin letter (), the Arabic numerals, and a small set of punctuation and procedural signals (prosigns). There is no distinction between upper and lower case letters. Each Morse code symbol is formed by a sequence of dits and dahs. The dit duration is the basic unit of time measurement in Morse code transmission. The duration of a dah is three times the duration of a dit. Each dit or dah within an encoded character is followed by a period of signal absence, called a space, equal to the dit duration. The letters of a word are separated by a space of duration equal to three dit

Experimental testing and simulation of bolted beam-column connections having thick extended endplates and multiple bolts per row

Luís Costa Borges, Shyam Khadka, Alain Nussbaumer, Gary Scott Prinz

Retrofit of existing steel buildings often requires strengthening of the connection regions. One common connection, the bolted beam-column connection, is often strengthened in design using stiffened extended endplates, or with continuity plates welded between the column flanges. In a retrofit scenario, adding stiffeners to the endplate is difficult due to the concrete slab and metal deck, and excessive field welding of continuity plates may be uneconomical. Simplifying retrofit efforts, and for economy, connection strength may be improved by simply adding more bolts to the connection. Current code methods, broadly generalized to all connection configurations, are currently based on component experiments having only one bolt on either side of the column web. This study experimentally investigates strengthening of bolted beam-column connections, having no column web stiffeners, using more than one bolt on either side of the column web. Six full-scale bolted beam-column connections are tested, representing exterior beam column connections (beams attached to only one column flange). Connections with both extended and flush endplates are considered. Two column sections (HE300A and HE300B) are tested along with HE300B beams creating both equal-column-beam, and weak-column strong-beam scenarios. Analytical simulations provide insight into local connection demands, and experimental results are compared with current code methods. The experiments indicate that closer inner-bolt spacing relative to the column web increases connection moment capacity but decreases rotation capacity (connection ductility) due to increased bolt prying forces from column flange distortions. The outer bolt of multiple-bolt-per-row configurations contributes very little to the connection resistance when column web stiffeners are not considered. With the exception of specimen T-3B which failed through bolt-thread shear after 0.02 rad, all connections with multiple bolts per row still achieved rotations greater than 0.06 rad. The Eurocode 3 component method and adapted Eurocode 3 procedures conservatively predicted the connection strength of each test specimen, including weak-column strong-beam assemblies, and accurately identified the initial connection limit states.

Elsevier2014

Building Efficient Query Engines using High-Level Languages

Ioannis Klonatos

We are currently witnessing a shift towards the use of high-level programming languages for systems development. These approaches collide with the traditional wisdom which calls for using low-level languages for building efficient software systems. This shift is necessary as billions of dollars are spent annually on the maintenance and debugging of performance-critical software. High-level languages promise faster development of higher-quality software; by offering advanced software features, they help to reduce the number of software errors of the systems and facilitate their verification. Despite these benefits, database systems development seems to be lagging behind as DBMSes are still written in low-level languages. The reason is that the increased productivity offered by high-level languages comes at the cost of a pronounced negative performance impact. In this thesis, we argue that it is now time for a radical rethinking of how database systems are designed. We show that, by using high-level languages, it is indeed possible to build databases that allow for both productivity and high performance. More concretely, in this thesis we follow this abstraction without regret vision and use high-level languages to address the following two problems of database development. First, the introduction of a new storage or memory technology typically requires the development of new versions of most out-of-core algorithms employed by the database system. Given the increasing popularity of hardware specialization, this leads to an arms race for the developers. To make things even worse, there exists no clear methodology for creating such algorithms and we must rely on significant creative effort to serve our need for out-of-core algorithms. To address this issue, we present the OCAS framework for the automatic synthesis of efficient out-of-core algorithms. The developer provides two independent inputs: 1) a memory-hierarchy-oblivious algorithm, expressed using a high-level specification language; and 2) a description of the target memory hierarchy. Using these specifications, our system is then able to automatically synthesize memory-hierarchy and storage-device-aware algorithms for tasks such as joins and sorting. The framework is extensible and quickly synthesizes custom out-of-core algorithms as new storage technologies become available. Second, from a software engineering point of view, years of performance-driven DBMS development have led to complicated, monolithic, low-level code bases, which are hard to maintain and extend. In particular, the introduction of new innovative approaches can be a very time-consuming task. To overcome such limitations, we present LegoBase, a query engine written in the high-level language, Scala. LegoBase realizes the abstraction without regret vision in the domain of analytical query processing. We show how by offering sufficiently powerful abstractions our system allows to easily implement a broad spectrum of optimizations which are difficult to achieve with existing approaches. Then, the key technique to regain efficiency is to apply generative programming and source-to-source compile the entire high-level Scala code to specialized, low-level C code. Our architecture significantly outperforms a commercial in-memory database system and an existing query compiler. LegoBase is the first step towards providing a full DBMS written in a high-level language.

EPFL2017

Experimental testing and simulation of bolted beam-column connections having thick extended endplates and multiple bolts per row

Luís Costa Borges, Shyam Khadka, Alain Nussbaumer, Gary Scott Prinz

Elsevier2014

Building Efficient Query Engines using High-Level Languages

Ioannis Klonatos

EPFL2017

Précontrainte et armature pour contrôler l'ouverture résiduelle des fissures

Experimental testing and simulation of bolted beam-column connections having thick extended endplates and multiple bolts per row

Building Efficient Query Engines using High-Level Languages

Experimental testing and simulation of bolted beam-column connections having thick extended endplates and multiple bolts per row

Building Efficient Query Engines using High-Level Languages

Précontrainte et armature pour contrôler l'ouverture résiduelle des fissures