Properties of highly magnetized neutron stars from X-ray timing analysis on different time scales

Massive stars end their lives either by collapsing directly into a black hole or by exploding as a supernova, leaving behind their collapsed core, a black hole or a neutron star (NS). NSs are a showcase of extremities: their density competes with that of the atomic nucleus and their magnetic fields are the strongest in the universe. As such, they present a unique opportunity for studying the fundamental forces of nature. When the NS inhabits a binary system, it may accrete matter from its companion star, and accretion is a highly effective way of transforming potential energy into radiation. This means that NSs reveal themselves to us through various interactions of matter and radiation, appearing as X-ray sources to our satellites. How the X-rays vary in time and photon energy carries information of the physical processes in the NS system. Of these processes, the interaction of accreted matter with the NS’s extremely strong magnetic field is the theme of this thesis. First, matter slowly spirals in the accretion disc, until it is forced to follow the magnetic field lines in the vicinity of the NS and onto the NS’s magnetic poles. Such a dramatic transformation of an accretion flow does not remain without consequences, but rather, writes itself into the details of mass density fluctuations which modulate the observed flux. Therefore, this thesis turns to timing analysis, offering a view to the different time scales of accretion: from low frequencies mapping the slow outer accretion disc to the high frequencies revealing what happens when the accretion disc encounters the magnetosphere of the NS. The standard assumptions of magnetic field structure are relaxed in light of the results

Magnetospheric truncation of an accretion disk around the unique X-ray pulsar GRO J1744-28

Neutron stars are very massive yet compact objects, where both quantum mechanical and relativistic effects play a role. Many of them have magnetic fields which are many orders of magnitude stronger than what mankind can achieve in laboratories. In systems where a neutron star accretes matter from its binary companion, the magnetic fields affect the accretion process. If the accreted matter forms an accretion disk around the neutron star, the disk will be truncated and the matter guided onto the magnetic poles by the magnetic field. How this truncation happens and how the magnetic field shapes the resulting X-ray emission, depend on complex interactions between matter and radiation in these extreme fields. Thus observations of these nature's high-energy laboratories are crucial to the development of up-to-date physical models. In my thesis, I examined observations of a unique accreting highly magnetized neutron star GRO J1744-28, also known as Bursting Pulsar. The pulsar reaches very high luminosities, at which its accretion disk might have a radiation pressure dominated inner zone, a feature which hasn't been directly observed in any other accreting X-ray pulsar. This could explain the rare type II bursts which are seen in this source and have been suggested to arise in a radiation-dominated accretion disk. Random fluctuations are present in light curves of every accreting X-ray source and they are shaped at different timescales by various stochastic processes in the accretion disk. A natural way to inspect the fluctuations is a power density spectrum, which is a Fourier transform of the light curve data from time domain into frequency domain. In the present thesis, this method of timing analysis was utilized extensively and power density spectra were used for probing the conditions in the accretion disk at different luminosities. Theoretical framework was provided by the "perturbation propagation" model, which can explain how the shape of power spectra depend on the size and structure of the accretion disk. According to the perturbation propagation model, we should see a break in the power spectrum at high frequencies, where the break frequency corresponds to the Keplerian orbital frequency of the inner disk edge. Using the break frequencies in power spectra, we can then deduce the size of the magnetosphere at different luminosities. The observed dependency of the break frequency on the luminosity is discussed in the frame of this perturbation propagation model and the dependency is shown to be inconsistent with a standard gas-pressure dominated inner disk at high luminosities. The shape of the power spectrum is calculated for an accretion disk which has a radiation-pressure dominated inner zone and compared to the data. We show that the data is consistent with the picture that the inner accretion disk is radiation pressure dominated

Negation in Old English Prose : Corpus studies in constituent negation, negative raising and negators as equivalents of clauses

The author defended his doctoral dissertation Negation in Old English Prose: Corpus studies in constituent negation, negative raising, and negators as equivalents of clauses at the Faculty of Arts, University of Helsinki, on 24 September 2020. The opponent was Professor Ursula Lenker (Ludwig-Maximilians-Universitat Munchen) and the custos was Professor Minna Palander-Collin.Peer reviewe

Negators in Contrastive Constructions in Old English

The purpose of this article is to find out the factors that explain the variation among the different negators in contrastive constructions, X (and) not Y and not X but Y, in Old English prose and glosses. An attempt is also made to answer the question why such structures are used, and why they are more common in some texts than in others. The data consists of a select corpus. The results indicate that in early West Saxon the negators in such constructions are mainly nalles and naes, while the negator na occurs less frequently. The exclusive use of the negator na by aelfric simplifies the system of negators in late West Saxon. Contrastive constructions are mainly employed as rhetorical means for emphasis. They are favoured in texts that are intended to influence people. The results suggest that the variation is partly idiolectal and genre-based, and partly diachronic.Peer reviewe

Negation in Old English Prose:: Corpus studies in constituent negation, negative raising and negators as equivalents of clauses

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Immaterial rewarding in knowledge work environment:literature review and managerial suggestions

Abstract. This thesis is set out to map the current state of immaterial reward and incentive research in knowledge work context. Thesis is made to illustrate the current knowledge through literature review. Purpose of this thesis is to increase understanding of immaterial rewarding and its function in knowledge work. This is done by examining the theoretical consensus regarding immaterial rewarding and knowledge work. Thesis also illustrates what are the current practical applications of immaterial rewarding in knowledge work organizations. Method of the thesis is literature review and sources compose of material searched through academic portals. This thesis uses wide variety of search words to widen scope of possible results and method of material selection is personal evaluation. Selected material is then examined and portrayed in general manner regarding the practical applications. This thesis also examines and discusses the problems and contradictions within the literature. Regarding the literature review, this thesis finds out that immaterial rewarding in knowledge work is a complex and conjoined topic. It positions itself in the intersection of humanistic sciences (psychology, sociology) and economics. During the literature review it also becomes apparent that this topic lacks uniform consensus and frameworks to shape and understand this subject. This thesis proposes some categorizations to create structure within the topic. Regarding the practical applications and managerial suggestions, this thesis proposes two major points. First, both employees and employers need to understand the nature of knowledge work and knowledge worker, and treat knowledge workers as assets, not costs. Second, individual preferences and surrounding environment guide knowledge worker’s reward perception and thus shape the reward experience

On tensor decompositions and algebraic structure of the mixed and transverse ray transforms

The geodesic ray transform, the mixed ray transform and the transverse ray transform of a tensor field on a manifold can all be seen as what we call mixing ray transforms, compositions of the geodesic ray transform and an invertible linear map on tensor fields. We show that the characterization of the kernel and the stability of a mixing ray transform can be reduced to the same properties of any other mixing ray transform. Our approach applies to various geometries and ray transforms, including the light ray transform. In particular, we extend studies in de Hoop--Saksala--Zhai (2019) from compact simple surfaces to orientable surfaces with solenoidally injective geodesic ray transform. Our proofs are based on algebraic arguments.Comment: 26 pages, minor changes and correction

Four Passages to Information Use Related Phenomena in Bachelor Theses at the Finnish Universities of Applied Sciences

Peer reviewe