On the dynamics of the general Bianchi IX spacetime near the singularity

We show that the complex dynamics of the general Bianchi IX universe in the vicinity of the spacelike singularity can be approximated by a simplified system of equations. Our analysis is mainly based on numerical simulations. The properties of the solution space can be studied by using this simplified dynamics. Our results will be useful for the quantization of the general Bianchi IX model.Comment: 20 pages, 5 figures, minor change

Comparing the dynamics of diagonal and general Bianchi IX spacetime

We make comparison of the dynamics of the diagonal and nondiagonal Bianchi IX models in the evolution towards the cosmological singularity. Apart from the original variables, we use the Hubble normalized ones commonly applied in the examination of the dynamics of homogeneous models. Applying the dynamical systems method leads to the result that in both cases the continuous space of critical points is higher dimensional and they are of the nonhyperbolic type. This is a generic feature of the dynamics of both cases and seems to be independent on the choice of phase space variables. The topologies of the corresponding critical spaces are quite different. We conjecture that the nondiagonal case may carry a new type of chaos different from the one specific to the usually examined diagonal one.Comment: 25 pages, 2 figures, version including numerical simulations of dynamic

Classical and quantum cosmology of Born-Infeld type models

We discuss Born-Infeld type fields (tachyon fields) in classical and quantum cosmology. We first partly review and partly extend the discussion of the classical solutions and focus in particular on the occurrence of singularities. For quantization, we employ geometrodynamics. In the case of constant potential, we discuss both Wheeler-DeWitt quantization and reduced quantization. We are able to give various solutions and discuss their asymptotics. For the case of general potential, we transform the Wheeler-DeWitt equation to a form where it leads to a difference equation. Such a difference equation was previously found in the quantization of black holes. We give explicit results for the cases of constant potential and inverse squared potential and point out special features possessed by solutions of the difference equation.Comment: 14 pages, 8 figures, published versio

Quantum Fate of Singularities in Anisotropic Cosmological Models

This thesis studies the possibility of the quantum avoidance of gravitational singularities in anisotropic cosmological models. For that purpose, we review the fundamentals of spatially homogeneous cosmological models and quantum cosmology based on the Wheeler-DeWitt equation in minisuperspace. Furthermore, we introduce a generalized dynamical system which is designed to emulate some of the main features of the cosmological models. After studying its geometric properties, we start to investigate how one can approach the canonical quantization of such a system. The main focus of our analysis is on the factor ordering problem in the Wheeler-DeWitt equation. The considerations motivate us to formulate criteria for singularity avoidance, that respect the conformal geometry of the con�guration space of the spatially homogeneous models. We then go on by studying some speci�c models with and without matter. In particular we examine classical and quantum properties of the Bianchi type I, II and IX and the Kantowski-Sachs universe. The criteria we developed previously are applied to see under which circumstances singularities can be avoided. If the potential terms are negligible when compared against the velocity terms in the gravitational action, the approach towards the singularity is called asymptotically velocity term dominated. We �nd that such singularities can be resolved, if the dimension of the minisuperspace is suffciently large. The underlying mechanism is a spreading of wave packets in minisuperspace. We also consider the non-diagonal Bianchi IX model with tilted dust. This model is relevant in the context of the BKL scenario. We pay particular attention to the asymptotic regime close to the singularity and the temporal behavior of curvature invariants in this regime

Investigations Of Low Pressure Two-Phase Steam-Water Injector

Vapor-liquid injector is a passive device in which thermal energy of vapor is used to compress and heat a cold liquid. In the past such injectors were used extensively for feeding water into boilers, especially of steam engines. Recently an interest in the two-phase injectors revived with new proposals of their application in thermal engineering, refrigeration and air conditioning. Low-pressure steam-water injectors may be applied as thermal driven liquid pump in absorption and steam ejection refrigeration systems. In this paper a close attention is paid to steam-water injectors in which superheated steam of relatively low pressure is the driving medium. Paper presents selected results of experimental and theoretical studies of a such type of steam-water injector. Experimental research was conducted on a laboratory scale injector made of transparent material. The measured parameters were the pressure and temperature distributions in the injector as well as inlet mass flow rates of both fluids. The measurements were conducted for constant inlet flow conditions during the injector stable operation. Between the measurements, inlet water flow rate and/or outlet back-pressure varied. Experimental flow characteristics of a low-pressure steam-water injector is presented. In theoretical part of the study, recorded distributions of pressure and temperature in the injector mixing chamber were used to evaluate the heat transfer coefficient for the vapour-liquid condensing flow. In the paper, also attention was paid to the evaluation of heat transfer coefficient during condensation in the mixing chamber

TGF-β inhibitor Smad7 regulates dendritic cell-induced autoimmunity

TGF-β is an anti-inflammatory cytokine whose signaling is negatively controlled by Smad7. Previously, we established a role for Smad7 in the generation of autoreactive T cells; however, the function of Smad7 in dendritic cells (DCs) remains elusive. Here, we demonstrate that DC-specific Smad7 deficiency resulted in elevated expression of the transcription factors Batf3 and IRF8, leading to increased frequencies of CD8(+)CD103(+) DCs in the spleen. Furthermore, Smad7-deficient DCs expressed higher levels of indoleamine 2,3-dioxygenase (IDO), an enzyme associated with tolerance induction. Mice devoid of Smad7 specifically in DCs are resistant to the development of experimental autoimmune encephalomyelitis (EAE) as a result of an increase of protective regulatory T cells (Tregs) and reduction of encephalitogenic effector T cells in the central nervous system. In agreement, inhibition of IDO activity or depletion of Tregs restored disease susceptibility. Intriguingly, when Smad7-deficient DCs also lacked the IFN-γ receptor, the mice regained susceptibility to EAE, demonstrating that IFN-γ signaling in DCs mediates their tolerogenic function. Our data indicate that Smad7 expression governs splenic DC subset differentiation and is critical for the promotion of their efficient function in immunity

Interferon-γ Regulates the Proliferation and Differentiation of Mesenchymal Stem Cells via Activation of Indoleamine 2,3 Dioxygenase (IDO)

The kynurenine pathway (KP) of tryptophan metabolism is linked to antimicrobial activity and modulation of immune responses but its role in stem cell biology is unknown. We show that human and mouse mesenchymal and neural stem cells (MSCs and NSCs) express the complete KP, including indoleamine 2,3 dioxygenase 1 (IDO) and IDO2, that it is highly regulated by type I (IFN-β) and II interferons (IFN-γ), and that its transcriptional modulation depends on the type of interferon, cell type and species. IFN-γ inhibited proliferation and altered human and mouse MSC neural, adipocytic and osteocytic differentiation via the activation of IDO. A functional KP present in MSCs, NSCs and perhaps other stem cell types offers novel therapeutic opportunities for optimisation of stem cell proliferation and differentiation

T Cells Specifically Targeted to Amyloid Plaques Enhance Plaque Clearance in a Mouse Model of Alzheimer's Disease

Patients with Alzheimer's disease (AD) exhibit substantial accumulation of amyloid-β (Aβ) plaques in the brain. Here, we examine whether Aβ vaccination can facilitate the migration of T lymphocytes to specifically target Aβ plaques and consequently enhance their removal. Using a new mouse model of AD, we show that immunization with Aβ, but not with the encephalitogenic proteolipid protein (PLP), results in the accumulation of T cells at Aβ plaques in the brain. Although both Aβ-reactive and PLP-reactive T cells have a similar phenotype of Th1 cells secreting primarily IFN-γ, the encephalitogenic T cells penetrated the spinal cord and caused experimental autoimmune encephalomyelitis (EAE), whereas Aβ T cells accumulated primarily at Aβ plaques in the brain but not the spinal cord and induced almost complete clearance of Aβ. Furthermore, while a single vaccination with Aβ resulted in upregulation of the phagocytic markers triggering receptors expressed on myeloid cells-2 (TREM2) and signal regulatory protein-β1 (SIRPβ1) in the brain, it caused downregulation of the proinflammatory cytokines TNF-α and IL-6. We thus suggest that Aβ deposits in the hippocampus area prioritize the targeting of Aβ-reactive but not PLP-reactive T cells upon vaccination. The stimulation of Aβ-reactive T cells at sites of Aβ plaques resulted in IFN-γ-induced chemotaxis of leukocytes and therapeutic clearance of Aβ

Brain antigens in functionally distinct antigen-presenting cell populations in cervical lymph nodes in MS and EAE

Drainage of central nervous system (CNS) antigens to the brain-draining cervical lymph nodes (CLN) is likely crucial in the initiation and control of autoimmune responses during multiple sclerosis (MS). We demonstrate neuronal antigens within CLN of MS patients. In monkeys and mice with experimental autoimmune encephalomyelitis (EAE) and in mouse models with non-inflammatory CNS damage, the type and extent of CNS damage was associated with the frequencies of CNS antigens within the cervical lymph nodes. In addition, CNS antigens drained to the spinal-cord-draining lumbar lymph nodes. In human MS CLN, neuronal antigens were present in pro-inflammatory antigen-presenting cells (APC), whereas the majority of myelin-containing cells were anti-inflammatory. This may reflect a different origin of the cells or different drainage mechanisms. Indeed, neuronal antigen-containing cells in human CLN did not express the lymph node homing receptor CCR7, whereas myelin antigen-containing cells in situ and in vitro did. Nevertheless, CLN from EAE-affected CCR7-deficient mice contained equal amounts of myelin and neuronal antigens as wild-type mice. We conclude that the type and frequencies of CNS antigens within the CLN are determined by the type and extent of CNS damage. Furthermore, the presence of myelin and neuronal antigens in functionally distinct APC populations within MS CLN suggests that differential immune responses can be evoked