The study of the dwarf nova ASASSN-19de from superoutburst to quiescence

Abstract. In this thesis the focus is on the study of the cataclysmic variable TCP J06373299 - 0935420 (ASASSN-19de), which was discovered in 2019. Purpose of this thesis is to find orbital and system parameters of the system and to find the secondary’s stellar type. The study in this thesis has been done with photometric and spectroscopic data obtained with various telescopes with different instruments. Photometric data are analyzed by time series analysis and spectral energy distribution. Spectroscopic data are analyzed by Doppler tomography, radial velocity analysis and by the study of absorption lines of the secondary. The study found the following orbital and system parameters: Psh = 0.0664(4) d, Porb = 0.06611(4) d, K1 = 25.4 ± 6.2 km s−1, K2 = 176.9 ± 1.7 km s−1, MWD = 0.72 ± 0.09 M, M2 = 0.1 ± 0.01 M. The spectral type of the donor is found to be M8 – L0. Due to relatively high mass of the donor, above the hydrogen burning limit of 0.07 M, and its relatively high luminosity, we conclude that the ASASSN-19de is the pre-period-minimum cataclysmic variable.Tutkimus kääpiönovan ASASSN-19de superpurkauksesta hiljaisuuteen. Tiivistelmä. Tämän opinnäytetyö painottuu kataklysmisen muuttujan TCP J06373299 - 0935420 (ASASSN-19de) tutkimukseen, joka löydettiin vuonna 2019. Tämän opinnäytetyön tarkoituksena on selvittää kohteen rata- ja järjestelmäparametrit sekä määrätä sekundaari tähden tähtityyppi. Tämän opinnäytetyön tutkimus on tehty hyödyntäen fotometrista- ja spektroskooppista dataa, jotka on kerätty käyttäen erilaisia kaukoputkia, ja jotka käyttävät erilaista teknillistä välineistöä. Fotometrinen data on analysoitu käyttäen aikasarja-analyysiä ja spektrienergian jakautumista. Spektroskooppinen data on analysoitu käyttäen hyväksi Doppler-tomografiaa, radiaalinopeuden analyysin malleja ja tutkimalla sekundääri tähden absorptioviivoja. Tutkimuksessa selvisi seuraavat rata- ja järjestelmäparametrit: Psh = 0,0664(4) d, Porb = 0,06611(4) d, K1 = 25,4 ± 6,2 km s−1, K2 = 176,9 ± 1,7 km s-1, MWD = 0,72 ± 0,09 M, M2 = 0,1 ± 0,01 M. Sekundääri tähden spektrityypiksi määritettiin luokkaväli M8 – L0. Sekundaari tähden suhteellisen suuren massan vuoksi, joka on yli vedyn palamisrajan 0,07 M, sekä sen suhteellisen korkea kirkkauden vuoksi, päättelemme, että ASASSN-19de on ennen periodiminimiä oleva kataklysminen muuttuja

The impact of export-oriented entrepreneurship on regional economic growth

Although export-oriented new ventures and the field of international entrepreneurship have received considerable attention by scholars during the last decade (Oviatt and McDougla, 2005), their potential economic impact has not been sufficiently analyzed yet. To the best of our knowledge, no studies on this issue have been carried out at regional level. Despite the increasing impact of globalization, regions have emerged as the essential and active unit of economic development process (Scott and Stopper, 2003). Regions are influential environments fostering entrepreneurship (Feldman, 2000). This is especially true for knowledge-based entrepreneurship since proximity to knowledge sources matters in order to discover opportunities and exploit them (Audretsch, 1998). Moreover, regions differ culturally and economically, and such differences encourage or discourage people to venture in entrepreneurial activity. We analyze the impact of export-oriented entrepreneurship on regional growth using data provided by the Global Entrepreneurship Monitor project and the Spanish Institute of Statistics, for 17 NUTS-2 Spanish regions over a period of six years. After controlling for catching-up effects (van Stel et al., 2005), as well as, other drivers of economic growth (e.g. change in technology capability and human capital), we found evidence that those regions with a higher percentage of adult population involved in export-oriented entrepreneurship experience a higher GDP growth. This relationship is greater as the level of foreign customers served by the entrepreneurial initiatives is substantially higher (i.e., at least 1%, 25% or 75% of customers located abroad). These results support those found at national level by Hessels and van Stel (2009). However, our paper adds to the extant literature on entrepreneurship by analyzing the role of entrepreneurial activity with different levels of export intensity on regional growth under a longitudinal context. Policy implications derived from these results suggest that trade policies for export promotion among new ventures should be carried out at regional level. Otherwise, exporting new ventures may concentrate only on certain regions, which would help to increase differences on growth within a nation.

Volatile-Rich Circumstellar Gas in the Unusual 49 Ceti Debris Disk

We present Hubble Space Telescope STIS far-UV spectra of the edge-on disk around 49 Ceti, one of the very few debris disks showing sub-mm CO emission. Many atomic absorption lines are present in the spectra, most of which arise from circumstellar gas lying along the line-of-sight to the central star. We determined the line-of-sight CI column density, estimated the total carbon column density, and set limits on the OI column density. Surprisingly, no line-of-sight CO absorption was seen. We discuss possible explanations for this non-detection, and present preliminary estimates of the carbon abundances in the line-of-sight gas. The C/Fe ratio is much greater than the solar value, suggesting that 49 Cet harbors a volatile-rich gas disk similar to that of Beta Pictoris.Comment: Accepted for publication in ApJ Letters. 5 pages, 4 figure

Effect of bending parameters on bending forces and surface strains in air bending of ultra-high strength steels

Abstract. The aim of this thesis is to investigate the effects of different parameters on bending forces and strains on the outer surface, and to study the bendability of ultra-high strength steels as well as their behaviour in bending. The aim is to provide a basis for further research by testing the effect of a wide variety of parameters such as punch radius, rolling direction and punch velocity on bendability. The bendability is investigated experimentally with bending tests, utilising Digital Image Correlation (DIC) for optical strain measurement of the outer surface of the specimen. Punch radius was found to have the greatest effect on the distribution of strain on the outer surface. Smaller punches resulted in significantly higher and more localised deformation. Using punches with smaller radii than the recommended minimum for the material was found to result in shear banding and cracking on the specimen surface. The three studied steel grades, S700MC, S900MC and S1100, were found to distribute strain very differently. The S700 grade was found to distribute strain most evenly, while the S900 had the most localised strain distributions. The S1100 grade was found to be the most susceptible to fracturing, even if the strain distributions were generally wider and the maximum strains on the surface lower than in the S900. The rolling direction was found to have varying effects on each grade. For the S700 and S900, bendability was better in transversal direction. For the S1100, the bendability was either equal or slightly better in the longitudinal direction. Multi-breakage was found to affect both the bending force and strains significantly. After the sheet was observed to separate from the punch, indicating a shift from 3- to 4-point bending, the bending forces were found to start increasing and the maximum strains to start stagnating as the distribution started to grow more from the sides. Punch velocity was not found to have any measurable effect on either strain or force. Although some trends could be seen from the results, it was conceded that the sample sizes of the individual parameter combinations were small. The presented results and the measurement data are considered useful for improving bending simulation and numerical models, and as a basis for further research, through which some of the findings may be generalised and used for improving workshop instructions.Särmäysparametrien vaikutus särmäysvoimiin ja pintavenymiin ultralujien terästen särmäyksessä. Tiivistelmä. Tässä työssä tutkitaan eri työkalujen, särmäysparametrien sekä särmättävän materiaalin vaikutuksia ultralujien terästen särmäysvoimiin ja venymiin särmän ulkopinnalla. Työn tavoitteena on kartoittaa laajalla alalla eri parametrien, kuten painimen koon, valssaussuunnan ja särmäysnopeuden vaikutuksia ultralujien terästen särmäykseen, tutkia ultralujien terästen särmättävyyttä ja niille tyypillistä käyttäytymistä särmäyksessä sekä toimia pohjana jatkotutkimukselle. Työssä pyritään selvittämään näitä vaikutuksia ja syyseuraussuhteita kokeellisesti särmäyskokeiden avulla, hyödyntäen digitaalista kuvakorrelaatiota (DIC) särmän ulkopinnan venymien optiseen mittaukseen. Painimen koon todettiin vaikuttavan venymäjakaumiin eniten. Pienemmillä painimilla venymät keskittyivät pienemmille alueille, mikä johti merkittävästi suurempiin paikallisiin venymiin. Suositeltuja minimisärmäyssäteitä pienempien painimien käytön havaittiin johtavan kuroumajuovien ja säröilyn syntyyn materiaalin pinnalla. Venymän jakautumisessa pinnalla havaittiin suuri ero tarkasteltavien terästlaatujen, S700MC, S900MC ja S1100, välillä. Tasaisimmat jakaumat havaittiin S700-laadulla ja suurimmat paikalliset venymät S900-laadulla. S1100-laadun todettiin murtuvan herkimmin, vaikkakin venymäjakamat olivat sillä S900-laatua tasaisemmat. Valssaussuunnan vaikutus vaihteli tarkasteltavien materiaalien välillä. S700- ja S900-laaduilla särmättävyys oli parempi poikittaisessa suunnassa valssaussuuntaan nähden, kun taas S1100-laadulla särmättävyys oli pitkittäin yhtä hyvä tai hiukan parempi kuin poikittain. Levyn irtoamisen painimesta (ns. multi-breakage) todettiin vaikuttavan merkittävästi sekä voimiin että venymiin ultralujien terästen särmäyksessä. Levyn irrottua särmäysvoimien havaittiin nousevan ja venymäjakaumien alkavan kasvaa sivuilta. Särmäysnopeudella ei havaittu olevan vaikutusta mitattuihin voimiin tai venymiin. Tuloksista voitiin havaita tiettyjä taipumuksia ja pääsuuntia eri tekijöiden vaikutuksista, mutta kunkin parametriyhdistelmien otoskoot myönnettiin pieniksi. Tuloksia ja kerättyä mittausdataa voidaan hyödyntää särmäyssimulaatioiden ja numeeristen mallien kehityksessä, sekä jatkotutkimuksen pohjana. Jatkotutkimuksen kautta tuloksia voidaan pyrkiä yleistämään ja edelleen hyödyntämään ohjeistusten kehittämisessä

Quasinormal ringing of acoustic black holes in Laval nozzles: Numerical simulations

Quasinormal ringing of acoustic black holes in Laval nozzles is discussed. The equation for sounds in a transonic flow is written into a Schr\"{o}dinger-type equation with a potential barrier, and the quasinormal frequencies are calculated semianalytically. From the results of numerical simulations, it is shown that the quasinormal modes are actually excited when the transonic flow is formed or slightly perturbed, as well as in the real black hole case. In an actual experiment, however, the purely-outgoing boundary condition will not be satisfied at late times due to the wave reflection at the end of the apparatus, and a late-time ringing will be expressed as a superposition of "boxed" quasinormal modes. It is shown that the late-time ringing damps more slowly than the ordinary quasinormal ringing, while its central frequency is not greatly different from that of the ordinary one. Using this fact, an efficient way for experimentally detecting the quasinormal ringing of an acoustic black hole is discussed.Comment: 9 pages, 8 figures, accepted for publication in Physical Review

The Large Ultraviolet/Optical/Infrared Surveyor

Astronomy crossed a threshold three decades ago with the discovery of planets around other stars. Compared to scientists' previous expectations set by the Solar System, exoplanets are wonderfully abundant and varied. Indirect planet discovery techniques have shown that small rocky planets residing in stellar habitable zones, where such planets may have liquid water on their surfaces, are not rare. This revelation drives us to ask more ambitious and fundamental questions, that fascinate scientists and the public alike: are there other truly Earth-like planets out there and do any of them harbour life? Today, exoplanets are largely small black shadows' to us, with measurements of orbits, sizes and masses (all three in the best cases).The upcoming James Webb Space Telescope and future 30-m-class ground-based telescopes will characterize the atmospheres of habitable planet candidates orbit in glow-mass M dwarf stars. However, deeply probing atmospheres of the exoplanets most similar to the Earth, those around Sun-like stars, remains out of reach for currently planned observatories. Bringing them within our grasp is a primary motivation for the Large UV/Optical/Infrared Surveyor(LUVOIR) mission concept, currently the focus of a three-year NASA study

Constructing hyperbolic systems in the Ashtekar formulation of general relativity

Hyperbolic formulations of the equations of motion are essential technique for proving the well-posedness of the Cauchy problem of a system, and are also helpful for implementing stable long time evolution in numerical applications. We, here, present three kinds of hyperbolic systems in the Ashtekar formulation of general relativity for Lorentzian vacuum spacetime. We exhibit several (I) weakly hyperbolic, (II) diagonalizable hyperbolic, and (III) symmetric hyperbolic systems, with each their eigenvalues. We demonstrate that Ashtekar's original equations form a weakly hyperbolic system. We discuss how gauge conditions and reality conditions are constrained during each step toward constructing a symmetric hyperbolic system.Comment: 15 pages, RevTeX, minor changes in Introduction. published as Int. J. Mod. Phys. D 9 (2000) 1

Phase statistics of seismic coda waves

We report the analysis of the statistics of the phase fluctuations in the coda of earthquakes recorded during a temporary experiment deployed at Pinyon Flats Observatory, California. The practical measurement of the phase is discussed and the main pitfalls are underlined. For large values, the experimental distributions of the phase first, second and third derivatives obey universal power-law decays whose exponents are remarkably well predicted by circular Gaussian statistics. For small values, these distributions are flat. The details of the transition between the plateau and the power-law behavior are governed by the wavelength. The correlation function of the first phase derivative along the array shows a simple algebro-exponential decay with the mean free path as the only length scale. Although only loose bounds are provided in this study, our work suggests a new method to estimate the degree of heterogeneity of the crComment: 4 figures, submitted to Physical Review Letter

Fluctuation scaling of quotation activities in the foreign exchange market

We study the scaling behavior of quotation activities for various currency pairs in the foreign exchange market. The components’ centrality is estimated from multiple time series and visualized as a currency pair network. The power-law relationship between a mean of quotation activity and its standard deviation for each currency pair is found. The scaling exponent α and the ratio between common and specific fluctuations η increase with the length of the observation time window Δt. The result means that although for Δt=1(min), the market dynamics are governed by specific processes, and at a longer time scale Δt>100(min) the common information flow becomes more important. We point out that quotation activities are not independently Poissonian for Δt=1(min), and temporally or mutually correlated activities of quotations can happen even at this time scale. A stochastic model for the foreign exchange market based on a bipartite graph representation is proposed