Porting and cylinder scavenging of two-stroke engines

První část této bakalářské práce se snaží představit základní geometrii a výpočty válce, kanálů a spalovacího prostoru dvoudobého motoru. V druhé polovině jsou blíže popsaná jednotlivá provedení systému výměny náplně válců u dvoudobých motorů. V této části je snahou porovnávat je mezi sebou a zhodnotit výhody i nevýhody každého z nich. Mnohé systémy, zde uvedené, se širšího rozšíření nedočkaly, takže jsou spíše uváděny jako jeden z možných směrů vývoje v dané problematice.In the first part of this thesis are explained, main calculations for two-stroke engine cylinder, channels and combustion chamber. In the second part are described in more detail systems scavenging of cylinders. This section is an attempt to compare them with each other and evaluate their advantages and disadvantages. Many of these systems have not spread. They are listed as other possible constructions.

SANKSI HUKUM AKIBAT MELAKUKAN TINDAK PIDANA INFORMASI DAN DOKUMEN ELEKTRONIK

Tujuan dilakukannya penelitian ini untuk mengetahui pengaturan hukum mengenai bentuk-bentuk tindak pidana informasi dan dokumen elektronik dan pemberlakuan sanksi hukum akibat melakukan tindak pidana informasi dan dokumen elektronik. Dengan menggunakan metode penelitian hukum normatif, disimpulkan: 1) Bentuk-bentuk tindak pidana informasi dan dokumen elektronik, dapat menimbulkan kerugian terhadap orang lain sehingga pemberlakuan sanksi pidana terhadap para pelaku yang telah terbukti secara sah melakukan tindak pidana merupakan bagian dari upaya penegakan hukum untuk menjamin perlindungan hukum terhadap hak-hak orang lain yang telah dirugikan. Demikian pula berkaitan dengan tindak pidana yang melanggar kesusilaan dan perjudian tentunya perlu dilakukan pemeriksaan dan penindakan terhadap para pelaku untuk menjamin adanya penghortmatan terhadap harkat dan martabat manusia; 2) Sanksi hukum akibat melakukan tindak pidana informasi dan dokumen elektronik seperti sanksi pidana penjara dan pidana denda dimaksudkan untuk memberikan efek jera bagi pelaku tindak pidana dan bagi pihak-pihak lain merupakan suatu peringatan untuk tidak melakukan perbuatan yang sama karena dapat menimbulkan keresahan, bagi masyarakat dan kerugian secara pribadi bagi orang lain.Kata kunci: Sanksi hukum, tindak pidana Informasi dan dokumen elektroni

Single-cylinder Minicross Engine

V první části se tato diplomová práce zaměřuje na seznámení se s jednotlivými provedeními systému výměny náplně válců u dvoudobých motorů. Popsány jsou tu nejpoužívanější provedení. Druhá část představuje problematiku motocyklového sportu třídy minicross a jeho specifika. V poslední části je pak představena konstrukce moderního dvoudobého motoru, použitelného jako pohonná jednotka motocyklu třídy minicross. V jednotlivých kapitolách jsou přiblížena konstrukční provedení klikového mechanismu, převodů a automatické spojky. Detailní analytické výpočty jsou pak, ve formě zdrojového kódu, připojeny do příloh na konci textové části.The first part of this thesis describes the different systems of the refill cylinders in two-stroke engines The second part introduces the issue of motorcycling class minicross and its specifics. In the final part is presented the construction of a modern two-stroke engine, which can be used for motorcycle class minicross. In the individual chapters are sketched design of the crank mechanism, gears and automatic clutch. Detailed analytical calculations are attached in the appendices at the end of the text in source code form.

Comments on "The long-period Galactic Cepheid RS Puppis. I. A geometric distance from its light echoes"

The luminous Galactic Cepheid RS Puppis is unique in being surrounded by a dust nebula illuminated by the variable light of the Cepheid. In a recent paper in this journal, Kervella et al. (2008) report a very precise geometric distance to RS Pup, based on measured phase lags of the light variations of individual knots in the reflection nebula. In this commentary, we examine the validity of the distance measurement, as well as the reality of the spatial structure of the nebula determined by Feast (2008) based upon the phase lags of the knots. {Kervella et al. assumed that the illuminated dust knots lie, on average, in the plane of the sky (otherwise it is not possible to derive a geometric distance from direct imaging of light echoes). We consider the biasing introduced by the high efficiency of forward scattering. We conclude that most of the knots are in fact likely to lie in front of the plane of the sky, thus invalidating the Kervella et al. result. We also show that the flat equatorial disk structure determined by Feast is unlikely; instead, the morphology of the nebula is more probably bipolar, with a significant tilt of its axis with respect to the plane of the sky. Although the Kervella et al. distance result is invalidated, we show that high-resolution polarimetric imaging has the potential to yield a valid geometric distance to this important Cepheid.Comment: 10 pages, 5 figures, 1 table; accepted by Astronomy & Astrophysic

The long-period Galactic Cepheid RS Puppis - II. 3D structure and mass of the nebula from VLT/FORS polarimetry

The long-period Cepheid RS Pup is surrounded by a large dusty nebula reflecting the light from the central star. Due to the changing luminosity of the central source, light echoes propagate into the nebula. This remarkable phenomenon was the subject of Paper I.The origin and physical properties of the nebula are however uncertain: it may have been created through mass loss from the star itself, or it could be the remnant of a pre-existing interstellar cloud. Our goal is to determine the 3D structure of the nebula, and estimate its mass. Knowing the geometrical shape of the nebula will also allow us to retrieve the distance of RS Pup in an unambiguous manner using a model of its light echoes (in a forthcoming work). The scattering angle of the Cepheid light in the circumstellar nebula can be recovered from its degree of linear polarization. We thus observed the nebula surrounding RS Pup using the polarimetric imaging mode of the VLT/FORS instrument, and obtained a map of the degree and position angle of linear polarization. From our FORS observations, we derive a 3D map of the distribution of the dust, whose overall geometry is an irregular and thin layer. The nebula does not present a well-defined symmetry. Using a simple model, we derive a total dust mass of M(dust) = 2.9 +/- 0.9 Msun for the dust within 1.8 arcmin of the Cepheid. This translates into a total mass of M(gas+dust) = 290 +/- 120 Msun, assuming a dust-to-gas ratio of 1.0 +/- 0.3 %. The high mass of the dusty nebula excludes that it was created by mass-loss from the star. However, the thinness nebula is an indication that the Cepheid participated to its shaping, e.g. through its radiation pressure or stellar wind. RS Pup therefore appears as a regular long-period Cepheid located in an exceptionally dense interstellar environment.Comment: 14 pages, 21 figures. Accepted for publication in A&

Status of the profession

The number of astronomers has grown by about 40 percent over the past decade. The number of astronomers with jobs in industry, or with long-term, non-tenured, jobs has increased dramatically compared with traditional faculty positions. The increase in the number of astronomers and the declining share of the NSF budget going to astronomy has led to extreme difficulties in the NSF grant program and in support of the National Observatories. In 1989, direct NASA support of astronomers through the grants program exceeds that of NSF, although the total of the NSF grants program over decade far exceeds that of NASA. Access to major new telescopes will be important issue for the 1990s. US astronomers, who once had a monopoly on telescopes larger than 3 meters, will, by the year 2000, have access to just half of the world's optical telescope area

Light Echoes of Transients and Variables in the Local Universe

Astronomical light echoes, the time-dependent light scattered by dust in the vicinity of varying objects, have been recognized for over a century. Initially, their utility was thought to be confined to mapping out the three-dimensional distribution of interstellar dust. Recently, the discovery of spectroscopically-useful light echoes around centuries-old supernovae in the Milky Way and the Large Magellanic Cloud has opened up new scientific opportunities to exploit light echoes. In this review, we describe the history of light echoes in the local Universe and cover the many new developments in both the observation of light echoes and the interpretation of the light scattered from them. Among other benefits, we highlight our new ability to spectroscopically classify outbursting objects, to view them from multiple perspectives, to obtain a spectroscopic time series of the outburst, and to establish accurate distances to the source event. We also describe the broader range of variable objects whose properties may be better understood from light echo observations. Finally, we discuss the prospects of new light echo techniques not yet realized in practice.Comment: 18 pages, 7 figures, 1 table. Accepted for publication in PAS

Testing Mass Loss in Large Magellanic Cloud Cepheids using Infrared and Optical Observations II. Predictions and Tests of the OGLE-III Fundamental-Mode Cepheids

In this article, we test the hypothesis that Cepheids have infrared excesses due to mass loss. We fit a model using the mass-loss rate and the stellar radius as free parameters to optical observations from the OGLE-III survey and infrared observations from the 2MASS and SAGE data sets. The sample of Cepheids have predicted minimum mass-loss rates ranging from zero to $10^{-8}M_\odot$ $yr^{-1}$, where the rates depend on the chosen dust properties. We use the predicted radii to compute the Period-Radius relation for LMC Cepheids, and to estimate the uncertainty caused by the presence of infrared excess for determining angular diameters with the infrared surface brightness technique. Finally, we calculate the linear and non-linear Period-Luminosity (P-L) relations for the LMC Cepheids at VIJHK + IRAC wavelengths and we find that the P-L relations are consistent with being non-linear at infrared wavelengths, contrary to previous results.Comment: 17 pages, 12 figures, 5 tables, ApJ Accepte

The long-period Galactic Cepheid RS Puppis - I. A geometric distance from its light echoes

Context: The bright southern Cepheid RS Pup is surrounded by a circumstellar nebula reflecting the light from the central star. The propagation of the light variations from the Cepheid inside the dusty nebula creates spectacular light echoes that can be observed up to large distances from the star itself. This phenomenon is currently unique in this class of stars. Aims: For this relatively distant star, the trigonometric parallax available from Hipparcos has a low accuracy. A careful observation of the light echoes has the potential to provide a very accurate, geometric distance to RS Pup. Methods: We obtained a series of CCD images of RS Pup with the NTT/EMMI instrument, covering the variation period of the star (P=41.4d). This allowed us to track the progression of the light wavefronts over the nebular features surrounding the star. We measured precisely the phase lag of the photometric variation in several regions of the circumstellar nebula. Results: From our phase lag measurements, we derived a geometric distance of 1992 +/- 28 pc to RS Pup. This distance is affected by a total uncertainty of 1.4%, and corresponds to a parallax of pi = 0.502 +/- 0.007 mas and a distance modulus of mu = 11.50 +/- 0.03. Conclusions: The geometric distance we derived is by far the most accurate to a Cepheid, and among the most accurate to any star. RS Pup appears both as somewhat neglected and particularly promising to investigate the mass-loss history of Cepheids. Thanks to its highly accurate distance, it is also bound to become an important luminosity fiducial for the long period part of the period-luminosity diagram.Comment: 14 pages in electronic form. Astronomy and Astrophysics (2007) in pres

New Evidence for Mass Loss from delta Cephei from HI 21-cm Line Observations

Recently published Spitzer observations of the classical Cepheid archetype delta Cephei revealed an extended dusty nebula surrounding this star and its hot companion. The infrared emission resembles a bow shock aligned with the direction of space motion of the star, indicating that delta Cep is undergoing mass-loss through a stellar wind. Here we report HI 21-cm line observations with the VLA to search for neutral atomic hydrogen associated with this wind. Our VLA data reveal a spatially extended HI nebula (~13' or 1 pc across) surrounding the position of delta Cep. The nebula has a head-tail morphology, consistent with circumstellar ejecta shaped by the interaction between a stellar wind and the ISM. We directly measure a mass of circumstellar hydrogen M_HI\approx0.07M_odot, although the total HI mass may be larger. The HI data imply a stellar wind with an outflow velocity V_o=35.6\pm1.2 km/s and a mass-loss rate of M_dot=(1.0\pm0.8)x10**-6 M_dot/yr. We have computed theoretical evolutionary tracks that include mass loss across the instability strip and show that a mass-loss rate of this magnitude, sustained over the preceding Cepheid lifetime of delta Cep, could be sufficient to resolve a significant fraction of the discrepancy between the pulsation and evolutionary masses for this star. (abridged)Comment: ApJ, in press (January 1, 2012). Version with full resolution figures available at http://www.haystack.mit.edu/hay/staff/lmatthew/matthews_deltaCep.pd