The impact of stellar envelopes on the formation of merging compact-object binaries

The common envelope (CE) phase play a key role in the formation of many astrophysical systems, including merging compact-object binaries. In a tight binary system, the CE phase happens when one star overfills its Roche lobe and initiates a process of dynamically unstable mass transfer. In this scenario, the mass transfer rate increases with time, the secondary star cannot accrete all the incoming material, and the latter surrounds the entire binary. The gas surrounding the binary star is known as CE. During the CE phase, the binary system rotates at a different rate than the CE. The orbital energy decreases due to the friction between the binary system and the CE. Due to orbital energy loss, the core of the donor and the companion star spiral toward one another within the CE (spiral-in phase). The orbital semi-major axis of binary systems can shrink by orders of magnitude during the spiral-in phase. The lost fraction of orbital energy is transferred to the envelope, which heats up and expands. The CE phase can end with two different outcomes. In the first scenario, the envelope is ejected, leaving the binary system with quite small semi-major axes. In the other scenario, during the spiral-in phase, the two stars merge and become an (evolved) massive star. Self-consistent hydrodynamical simulations of CE are very complex and computationally expensive. In fast population-synthesis studies, the CE phase is simulated via the (α,λ)- formalism, where α parameterizes the fraction of orbital energy transferred to the envelope, and λ is the envelope’s binding-energy parameter. The time required for a binary system to merge is highly dependent on the α and λ parameters, so their values have a crucial impact on the interpretation of many astrophysical systems, including merging compact-object binaries. While constraining the α parameter is challenging, we can calculate the λ values and consider λ as a physical quantity instead of a parameter. In this thesis, we present new results on self-consistent calculations of the binding energy parameter for a large set of hydrogen and helium stars, using the up-todate tracks from the PARSEC stellar evolution code. We demonstrate how the definition of the core-envelope boundary, the nature of the energy sources, metallicity, stellar mass, and evolutionary stage influence the value of λ parameters. We show that the new λ values are up to one order of magnitude lower than those obtained in previous studies and we discuss the associated implication for the formation of merging compact-object binaries. We present fitting formulas for the new binding energy parameters for hydrogen and helium stars obtained in this work, and we evaluate their accuracy with respect to self-consistent data. The SEVN population-synthesis code is the ground for implementing the new bindingenergy prescriptions obtained in this thesis and for an up-to-date astrophysical interpretation of present and forthcoming gravitational-wave sources. Since the SEVN code is based on the star tracks of the PARSEC stellar evolution code, it will be self-consistent to test our new CE prescriptions and study their impact on the evolutionary pathways of binary systems. In this thesis, we focus mainly on introducing several technical improvements in the SEVN code (e.g., adaptive data loading, single and multi-node parallelization), which is the preparatory work that will be crucial to perform efficient simulations of large populations of binary stars and testing the new binding-energy prescriptions

Improve investigating gravitational-wave sources with the help of MPI and OpenMP interface

The most recent catalog of gravitational waves compiled by the LIGO-Virgo-KAGRA collaboration contains over 90 compact-binary coalescences, mostly binary black holes. The astrophysical interpretations of the detected sources are still uncertain, although the number is expected to rise significantly over the next few years. From a theoretical point of view, one of the possible explanations for the formation of merging compact binaries is the isolated binary scenario. In this instance, two stars are gravitationally bound from the moment they are formed. During stellar evolution, stars move closer to one another, and at the end of their lives, they turn into compact remnants. As a result, a formed compact binary system has the potential to merge during the lifetime of the Universe. Binary population-synthesis codes are tools that can evolve massive populations of single or binary stars from the formation moment to the compact remnants stage. They play an essential role in the investigation of this scenario. The evolution of one binary system does not require significant computational resources. However, to obtain sufficient statistics on compact object mergers, we require simulations of billions of binary systems with different initial conditions, stellar masses, evolutionary prescriptions, and metallicities. In this project, I will implement a novel parallelization method for the SEVN code, a state-of-the-art population-synthesis code developed in SISSA and at the University of Padova. The final goal is to make the SEVN code run effectively on multi-node supercomputers. To accomplish that, I will use the Message Passing Interface (MPI) for inter-node parallelization and the Open Multi-Processing (OpenMP) interface for intra-node parallelization. Furthermore, I will also implement an automatic and adaptive data loading algorithm to load input binaries in chunks. Finally, I will investigate the weak and strong scaling of the code on various computing machines. The new code is expected to significantly speed up the evolution of binary systems, giving us the chance to investigate the formation of gravitational-wave sources in different stellar environments, possibly up to the regime of galaxies (i.e., billions of binaries)

Self-propagating high temperature synthesis of pink corundum

Pigments based on pink corundum have been obtained by self-propagating high temperature synthesis in Cr2O3-Al2O3-Al system using a small amount of chromium oxide (up to 0.5 wt %) in the composition of the green mixture. Absorption bands of pink corundum in visible reflectance spectrum at λ=560 nm (17850 cm−1) and 400 nm (25000 cm−1) correspond to electron transitions 4А2g→4T2g(4F) and 4А2g→4T1g(4F). Increasing chrome oxide content to 5 wt.% in initial charge mixture leads to pigment darkening due to inclusions of Cr2O3. Synthesized pigments can be used as a component of glaze ceramic colors for porcelain

Self-propagating High Temperature Synthesis of Pink Corundum

Pigments based on pink corundum have been obtained by self-propagating high temperature synthesis in Cr2O3-Al2O3-Al system using a small amount of chromium oxide (up to 0.5 wt %) in the composition of the green mixture. Absorption bands of pink corundum in visible reflectance spectrum at λ=560 nm (17850 cm−1) and 400 nm (25000 cm−1) correspond to electron transitions 4А2g→4T2g(4F) and 4А2g→4T1g(4F). Increasing chrome oxide content to 5 wt.% in initial charge mixture leads to pigment darkening due to inclusions of Cr2O3. Synthesized pigments can be used as a component of glaze ceramic colors for porcelain

Calculation Method to Determine the Group Composition of Vacuum Distillate with High Content of Saturated Hydrocarbons

Calculation method to determine the group composition of the heavy fraction of vacuum distillate with high content of saturated hydrocarbons, obtained by vacuum distillation of the residue from the West Siberian oil with subsequent hydrotreating, are given in this research. The method is built on the basis of calculation the physico-chemical characteristics and the group composition of vacuum distillate according to the fractional composition and density considering with high content of saturated hydrocarbons in the fraction. Calculation method allows to determine the content of paraffinic, naphthenic, aromatic hydrocarbons and the resins in vacuum distillate with high accuracy and can be used in refineries for rapid determination of the group composition of vacuum distillate

Effect of the Bone Marrow Mesenchymal Stromal Cells Cytokine-Producing Activity on the Hematopoietic Ste

Hematopoietic stem cell transplantation is used to treat hemoblastoses and some other diseases. Depending on the diagnosis, autologous cells of the patient or allogeneic cells obtained from a healthy related or unrelated donor are used. A sufficient count of harvested hematopoietic progenitor cells is necessary for successful transplantation. Currently, stimulation of their egress from the bone marrow into the peripheral blood by a granulocyte colony-stimulating factor, followed by collection by leukapheresis, is widely used for their preparation. Hematopoietic stem cells leave the bone marrow niche formed by the stromal microenvironment when their holding bonds are interrupted. Mesenchymal stromal cells regulate the release of hematopoietic precursors by producing various cytokines and other biologically active substances. Therefore, the study of the functional properties of bone marrow mesenchymal cells can help in solving the problem of “poor” mobilizations that occur in patients with multiple myeloma.The aim of the study was to estimate the effectiveness of mobilization of hematopoietic stem cells depending on the cytokine-producing ability of mesenchymal stromal cells in the bone marrow of donors and patients with multiple myeloma.The yields of hematopoietic progenitors were studied in 10 donors (median age 27 years) and 18 patients with multiple myeloma (median age 57 years). In donors, the release of hematopoietic stem cells into the peripheral blood was stimulated by subcutaneous administration of G-CSF at a dose of 10 μg/kg/day. Patients with multiple myeloma received vinorelbine at a dose of 35 mg/m2 of body surface, followed by administration of G-CSF (10 μg/kg/day subcutaneously). A culture of mesenchymal stromal cells was obtained from bone marrow taken prior to mobilization and the content of interleukins IL-1β, IL-2, IL-4, IL-6, IL-8, IL-10, TNF-α and IFN-γ in supernatants was studied by enzyme-linked immunosorbent assay using kits of reagents produced by Vector-Best (Novosibirsk).Patients with multiple myeloma were characterized by high secretion of the pro-inflammatory cytokine IL-2 (4.70 pg/ml vs 3.55 pg/ml in healthy individuals, p=0.003) and low IFN-γ (0.41 pg/ml vs 2.14 pg/ml in healthy, p<0.001), but no relationship was found between these cytokines and the hematopoietic stem cells yield. The present study showed that in patients with ineffective harvesting of hematopoietic precursors, secretion of IL-8 by stromal cells was low (308.08 pg/ml vs 561.29 pg/ml in healthy individuals, p=0.04).The obtained results are consistent with the literature data on the important role of IL-8 in the mobilization of hematopoietic stem cells, which allows to consider IL-8 as an informative marker for predicting the insufficient yields of hematopoietic precursors