Simple model of big-crunch/big-bang transition

We present classical and quantum dynamics of a test particle in the compactified Milne space. Background spacetime includes one compact space dimension undergoing contraction to a point followed by expansion. Quantization consists in finding a self-adjoint representation of the algebra of particle observables. Our model offers some insight into the nature of the cosmic singularity.Comment: 17 pages, no figures, RevTeX4, accepted for publication in Class. Quantum Gra

Turning big bang into big bounce: II. Quantum dynamics

We analyze the big bounce transition of the quantum FRW model in the setting of the nonstandard loop quantum cosmology (LQC). Elementary observables are used to quantize composite observables. The spectrum of the energy density operator is bounded and continuous. The spectrum of the volume operator is bounded from below and discrete. It has equally distant levels defining a quantum of the volume. The discreteness may imply a foamy structure of spacetime at semiclassical level which may be detected in astro-cosmo observations. The nonstandard LQC method has a free parameter that should be fixed in some way to specify the big bounce transition.Comment: 14 pages, no figures, version accepted for publication in Class. Quant. Gra

Reduced phase space approach to Kasner universe and the problem of time in quantum theory

We apply the reduced phase space quantization to the Kasner universe. We construct the kinematical phase space, find solutions to the Hamilton equations of motion, identify Dirac observables and arrive at physical solutions in terms of Dirac observables and an internal clock. We obtain the physical Hilbert space, which is the carrier space of the self-adjoint representation of the Dirac observables. Then we discuss the problem of time. We demonstrate that the inclusion of evolution in a gravitational system, at classical level as well as at quantum level, leads respectively to canonically and unitarily inequivalent theories. The example of Hubble operator in two different clock variables and with two distinct spectra is given.Comment: 24 page

Detection of maturity and ligament injury using magic angle directional imaging

Purpose: To investigate whether magnetic field–related anisotropies of collagen may be correlated with postmortem findings in animal models. Methods: Optimized scan planning and new MRI data‐processing methods were proposed and analyzed using Monte Carlo simulations. Six caprine and 10 canine knees were scanned at various orientations to the main magnetic field. Image intensities in segmented voxels were used to compute the orientation vectors of the collagen fibers. Vector field and tractography plots were computed. The Alignment Index was defined as a measure of orientation distribution. The knees were subsequently assessed by a specialist orthopedic veterinarian, who gave a pathological diagnosis after having dissected and photographed the joints. Results: Using 50% less scans than reported previously can lead to robust calculation of fiber orientations in the presence of noise, with much higher accuracy. The 6 caprine knees were found to range from very immature ( 3 years). Mature specimens exhibited significantly more aligned collagen fibers in their patella tendons compared with the immature ones. In 2 of the 10 canine knees scanned, partial cranial caudal ligament tears were identified from MRI and subsequently confirmed with encouragingly high consistency of tractography, Alignment Index, and dissection results. Conclusion: This method can be used to detect injury such as partial ligament tears, and to visualize maturity‐related changes in the collagen structure of tendons. It can provide the basis for new, noninvasive diagnostic tools in combination with new scanner configurations that allow less‐restricted field orientations

Uwalnianie biologicznie szkodliwych związków chemicznych z dostępnych na rynkach Europy i USA ortodontycznych systemów adhezyjnych — badania in vitro

The study assessed the chemical stability of ConTec LC, Resilence, Light Bond and Transbond XT orthodontic adhesive resins. The subject of the analysis was the release of HEMA (2-hydroxyethylmethacrylate), TEGDMA (triethylene glycol dimethacrylate), EGDMA (ethylene glycol dimethacrylate), UDMA (urethane dimethacrylate) and BPA (bisphenol A) monomers from test sample materials in successive time intervals, using HPLC (high pressure liquid chromatography). The study confirmed the presence of methacrylate monomers and bisphenol A in eluates of the assessed materials regardless of the observation period. The results show that orthodontic adhesive systems polymerized with visible light are chemically unstable, releasing biologically harmful ingredients to the external environment for a long time. Dental materials containing polymer network based on methacrylates require structure modification or elimination of harmful components in order to increase safety of their application.Oceniano stabilność chemiczną ortodontycznych żywic adhezyjnych ConTec LC, Resilence, Light Bond oraz Transbond XT. Metodą wysokociśnieniowej chromatografii cieczowej (HPLC) analizowano uwalnianie z próbek badanych materiałów monomerów: HEMA (metakrylan 2-hydroksyetylu), TEGDMA (dimetakrylan triglikolu etylenowego), EGDMA (dimetakrylan glikolu etylenowego), UDMA (dimetakrylan uretanu) i BPA (bisfenol A) w kolejnych przedziałach czasowych. Badania potwierdziły obecność monomerów metakrylanowych i bisfenolu A w eluatach ocenianych materiałów, niezależnie od czasu obserwacji. Uzyskane wyniki wskazują, że polimeryzowane światłem widzialnym ortodontyczne systemy adhezyjne są niestabilne chemicznie i w ciągu długiego czasu emitują do środowiska zewnętrznego składniki biologicznie szkodliwe. Materiały stomatologiczne zawierające usieciowane metakrylany wymagają modyfikacji struktury lub eliminacji szkodliwych komponentów w celu zwiększenia bezpieczeństwa ich stosowania

Ocena stopnia konwersji ortodontycznych żywic adhezyjnych na bazie polimerów

Degree of conversion (DC) of selected currently used orthodontic adhesive materials, after their polymerization with dental curing light, were investigated in laboratory conditions. Samples of four orthodontic adhesives (Contec LC, Transbond XT, Transbond Plus and Resilience) were prepared in Teflon matrices and then formed into the thickness of 1 mm. After the baseline measurement of crosslinking of the materials with Fourier transform infrared spectroscopy (FT-IR) the samples were cured with treatment light, and then 1 and 24 h after the completion of the photopolymerization process, the values of DC were evaluated. The results were analyzed using the Statistica 8.0 software package. In the process of hypothesis testing the level of significance was assumed at α = 0.05. The statistical analysis yielded significant differences between DC values of orthodontic adhesives tested in both time periods and a significant increase after 24 h storage of the studied orthodontic adhesive systems. It was stated that DC values of the visible light-cured orthodontic adhesives assessed in the present study depend of the type of the composite material. A significant increase in DC occurring with extended period of observation proves that polymerization of dental adhesive materials is a long-term process.Przeprowadzono w warunkach laboratoryjnych badania stopnia konwersji (DC) wybranych, stosowanych współcześnie ortodontycznych materiałów adhezyjnych po ich polimeryzacji pod wpływem światła widzialnego lampy stomatologicznej. Próbki czterech klejów ortodontycznych (Contec LC, Transbond XT, Transbond Plus i Resilience) przygotowano w teflonowych matrycach, a następnie uformowano do grubości 1 mm. Po wykonaniu za pomocą spektroskopii w podczerwieni z transformacją Fouriera (FT-IR) pomiaru początkowego usieciowania próbek, poddawano je działaniu lampy zabiegowej, a następnie po 1 i 24 h od zakończenia procesu fotopolimeryzacji wyznaczano wartości DC. Uzyskane wyniki analizowano korzystając z pakietu statystycznego Statistica 8.0. W procesie testowania hipotez statystycznych przyjęto poziom istotności α = 0,05. Analiza statystyczna wykazała istotne różnice pomiędzy wartościami DC badanych klejów ortodontycznych wyznaczonymi po upływie 1 i 24 h oraz istotny wzrost DC podczas 24-godzinnego przechowywania ocenianych próbek. Stwierdzono, że wartość DC ocenianych układów adhezyjnych polimeryzowanych światłem widzialnym zależy od rodzaju materiału. Istotny wzrost wartości DC zachodzący wraz z wydłużeniem czasu obserwacji może świadczyć o tym, że polimeryzacja stomatologicznych materiałów adhezyjnych jest procesem długotrwałym

The Effect of Glow Discharge Nitriding on the Corrosion Resistance of Stainless Steel Orthodontic Arches in Artificial Saliva Solution

The oral cavity due to its temperature fluctuations, changing pH, high humidity, action of mechanical forces and the presence of microorganisms is a favorable environment for degradation of dental materials. The paper presents comparative results on orthodontic arch-wires AISI304 steel before and after low temperature plasma nitriding carried out at cathodic potential (conventional) and at plasma potential, i.e. in a process incorporating an active screen. Corrosion resistance test on nitrided layers produced on stainless steel were carried out via electrochemical impedance spectroscopy (EIS) and the potentiodynamic method in non-deaerated artificial saliva solution at 37°C. The results were complemented with analysis of the structure, surface topography and microhardness. The results showed an increase in corrosion resistance of AISI304 steel after conventional glow-discharge nitriding