Search results for "Compression ratio"
showing 10 items of 17 documents
On parsing optimality for dictionary-based text compression—the Zip case
2013
Dictionary-based compression schemes are the most commonly used data compression schemes since they appeared in the foundational paper of Ziv and Lempel in 1977, and generally referred to as LZ77. Their work is the base of Zip, gZip, 7-Zip and many other compression software utilities. Some of these compression schemes use variants of the greedy approach to parse the text into dictionary phrases; others have left the greedy approach to improve the compression ratio. Recently, two bit-optimal parsing algorithms have been presented filling the gap between theory and best practice. We present a survey on the parsing problem for dictionary-based text compression, identifying noticeable results …
The rightmost equal-cost position problem.
2013
LZ77-based compression schemes compress the input text by replacing factors in the text with an encoded reference to a previous occurrence formed by the couple (length, offset). For a given factor, the smallest is the offset, the smallest is the resulting compression ratio. This is optimally achieved by using the rightmost occurrence of a factor in the previous text. Given a cost function, for instance the minimum number of bits used to represent an integer, we define the Rightmost Equal-Cost Position (REP) problem as the problem of finding one of the occurrences of a factor whose cost is equal to the cost of the rightmost one. We present the Multi-Layer Suffix Tree data structure that, for…
Reliable TDC position determination: a comparison of different thermodynamic methods through experimental data and simulations
2008
It is known to internal combustion researcher that the correct determination of the crank position when the piston is at Top Dead Centre (TDC) is very important, since an error of 1 crank angle degree (CAD) can cause up to a 10% evaluation error on indicated mean effective pressure (IMEP) and a 25% error on the heat released by the combustion: the TDC position should be then known within a precision of 0.1 CAD. This task can be accomplished by means of a dedicated capacitive sensor, which allows a measurement within the required 0.1 degrees precision. Such a sensor has a substantial cost and its use is not really fast; a different approach can be followed using a thermodynamic method, whose…
American College of Cardiology/ European Society of Cardiology international study of angiographic data compression phase III. Measurement of image q…
2000
Objectives We sought to investigate up to which level of Joint Photographic Experts Group (JPEG) data compression the perceived image quality and the detection of diagnostic features remain equivalent to the quality and detectability found in uncompressed coronary angiograms. Background Digital coronary angiograms represent an enormous amount of data and therefore require costly computerized communication and archiving systems. Earlier studies on the viability of medical image compression were not fully conclusive. Methods Twenty-one raters evaluated sets of 91 cine runs. Uncompressed and compressed versions of the images were presented side by side on one monitor, and image quality differe…
Calibration of a knock prediction model for the combustion of a gasoline-natural gas mixture
2009
Gaseous fuels, such as Liquefied Petroleum Gas (LPG) and Natural Gas (NG), thank to their good mixing capabilities, allow complete and cleaner combustion than normal gasoline, resulting in lower pollutant emissions and particulate matter. Moreover natural gas, which is mainly constituted by methane, whose molecule has the highest hydrogen/carbon ratio, leads also to lower ozone depleting emissions. The authors in a previous work (1) experienced the simultaneous combustion of gasoline and natural gas in a bi-fuel S.I. engine, exploiting so the high knock resistance of methane to run the engine with an ‘overall stoichiometric’ mixture (thus lowering fuel consumption and emissions) and better …
Experimental Determination of Liquefied Petroleum Gas–Gasoline Mixtures Knock Resistance
2014
The results of previous experimental researches showed that great advantages can be achieved, both in terms of fuel consumption and pollutant emissions, in bifuel vehicles by means of the double-fuel combustion, i.e., the simultaneous combustion of gasoline and a gaseous fuel, such as liquefied petroleum gas (LPG) or natural gas (NG). The substantial increase in knock resistance pursued by adding LPG to gasoline, which allowed to maintain an overall stoichiometric proportion with air also at full load, is not documented in the scientific literature and induced the authors to perform a proper experimental campaign. The motor octane number (MON) of LPG–gasoline mixtures has been hence determi…
Statistical atmospheric parameter retrieval largely benefits from spatial-spectral image compression
2021
The infrared atmospheric sounding interferometer (IASI) is flying on board of the Metop satellite series, which is part of the EUMETSAT Polar System. Products obtained from IASI data represent a significant improvement in the accuracy and quality of the measurements used for meteorological models. Notably, the IASI collects rich spectral information to derive temperature and moisture profiles, among other relevant trace gases, essential for atmospheric forecasts and for the understanding of weather. Here, we investigate the impact of near-lossless and lossy compression on IASI L1C data when statistical retrieval algorithms are later applied. We search for those compression ratios that yield…
An NTC zone compliant knock onset prediction model for spark ignition engines
2015
Abstract Pollutant emissions reduction and energy saving policies increased the production of Spark Ignition (SI) engines operated with gaseous fuels. Natural Gas (NG) and Liquefied Petroleum Gas (LPG), thanks to their low cost and low environmental impact represent the best alternative. Bi-fuel engines, which may run either with gasoline or with gas (NG or LPG), widely spread in many countries thanks to their versatility, high efficiency and low pollutant emissions: gas fueled vehicles, as example, are allowed to run in many limited traffic zones. In the last years, supercharged SI engines fueled with either gasoline or gaseous fuel, spread in the market. Thermodynamic simulations, widely …
Performance Prevision of a Turbocharged Natural Gas Fuelled S.I. Engine
2008
Natural gas represents today maybe the most valid alternative to conventional fuels for road vehicles propulsion. The main constituent of natural gas, methane, is characterized by a high autoignition temperature, which makes the fuel highly resistant to knocking: this allows a considerable downsizing of the engine by means of supercharging even under high compression ratio. Starting from these considerations, the authors realized a thermodynamic model of a 4-cilynder s.i. engine for the prevision of in-cylinder pressure, employing a two-zone approach for the combustion and adding sub-models to account for gas properties change and knocking occurrence. An extensive experimental campaign has …
Lossless and near-lossless image compression based on multiresolution analysis
2013
There are applications in data compression, where quality control is of utmost importance. Certain features in the decoded signal must be exactly, or very accurately recovered, yet one would like to be as economical as possible with respect to storage and speed of computation. In this paper, we present a multi-scale data-compression algorithm within Harten's interpolatory framework for multiresolution that gives a specific estimate of the precise error between the original and the decoded signal, when measured in the L"~ and in the L"p (p=1,2) discrete norms. The proposed algorithm does not rely on a tensor-product strategy to compress two-dimensional signals, and it provides a priori bound…