Spin Foam Models of Matter Coupled to Gravity

We construct a class of spin foam models describing matter coupled to gravity, such that the gravitational sector is described by the unitary irreducible representations of the appropriate symmetry group, while the matter sector is described by the finite-dimensional irreducible representations of that group. The corresponding spin foam amplitudes in the four-dimensional gravity case are expressed in terms of the spin network amplitudes for pentagrams with additional external and internal matter edges. We also give a quantum field theory formulation of the model, where the matter degrees of freedom are described by spin network fields carrying the indices from the appropriate group representation. In the non-topological Lorentzian gravity case, we argue that the matter representations should be appropriate SO(3) or SO(2) representations contained in a given Lorentz matter representation, depending on whether one wants to describe a massive or a massless matter field. The corresponding spin network amplitudes are given as multiple integrals of propagators which are matrix spherical functions.Comment: 30 pages, 9 figures, further remarks and references added. Version to appear in Class. Quant. Gra

Development of Heterogeneous Photosensitized Transition Metal Oxide Water-Splitting Catalysts on Silica Support

The research presented in this manuscript describes the development of photosensitized inexpensive catalysts based on readily available materials. The investigation covers synthesis and characterization of photosensitizers based on porphyrins, mechanical and thermal coating of solid support with semiconducting transition metal oxides, photosensitization of the semiconducting layer, and characterization of the photoelectrochemical properties displayed by the new materials. The process of water oxidation is of primary interest here, with little emphasis put on reduction of protons to gaseous hydrogen. Photoelectrochemically produced protons serve as a probe of effectiveness of the catalysts. Several systems are described, and two catalysts are identified as the most efficient

Endocrine Factors in Experimental Peptic Ulcer and Hypertension

This thesis is divided into six parts:- Part I is concerned with the peptic ulcers which develop in rabbits following the administration of pitressin. Histological and arteriographic studies establish the pathogenesis of the gastric lesions, and an increase in adrenal cortical function is suggested on the basis of a bio-assay method. Part II shows that pitressin peptic ulcers in rabbits and rats are aggravated by the simultaneous administration of cortisone or corticotrophin. Ulcers are more numerous, some perforate, and bacterial invasion is increased. Similar lesions are produced both in the presence and absence of the adrenal glands. Part III is concerned with the concept that stimulation of the pituitary and adrenal glands during stress produces ''diseases of adaptation" in the sensitized (unilateral nephrectomy and increased sodium chloride intake) rat. Following exposure to cold stress peptic ulcer is not found, but hypertension develops. It is shown that the hypertension is not the result of increased adrenal cortical function following cold exposure, but is closely related to the increased consumption of sodium chloride. Part IV is an investigation of the pathological effects of several different stressors on sensitized rats. Mild hypertension develops in very few animals and there is no voluntary increase in the consumption of sodium chloride diet. Part V demonstrates the hypertensive pathological effects of sodium-retaining steroids. It is shown that similar lesions can he produced by sodium chloride administration without hormone overdosage. The role of the kidney in this hypertensive syndrome is established and it is shown that the adrenal glands or the cortical hormones are not essential for its development. Part VI is a study of the hypertension associated with the regeneration of adrenal cortical tissue in sensitized rats. Factors relating to the pathogenesis of this syndrome are elucidated by modifying the sodium chloride intake of the animals, and by transplantation experiments in which the regenerating adrenal tissue is transplanted into different areas drained by the portal and systemic circulation. The text is presented in Volume I and the illustrations in Volume II. An Appendix of technical methods is included in Volume I

Test and evaluation of a multifunction keyboard and a dedicated keyboard for control of a flight management computer

A flight management computer (FMC) control display unit (CDU) test was conducted to compare two types of input devices: a fixed legend (dedicated) keyboard and a programmable legend (multifunction) keyboard. The task used for comparison was operation of the flight management computer for the Boeing 737-300. The same tasks were performed by twelve pilots on the FMC control display unit configured with a programmable legend keyboard and with the currently used B737-300 dedicated keyboard. Flight simulator work activity levels and input task complexity were varied during each pilot session. Half of the points tested were previously familiar with the B737-300 dedicated keyboard CDU and half had no prior experience with it. The data collected included simulator flight parameters, keystroke time and sequences, and pilot questionnaire responses. A timeline analysis was also used for evaluation of the two keyboard concepts

Dropping the mask:It takes two.

In some social situations, autistic people feel pressure to modify their innate social behaviour (i.e. camouflage), while in other social situations they feel free to engage in ways that feel authentic or true to themselves. To date, the latter aspect of autistic people’s experience has rarely been explored. Using an online qualitative survey, this study examined 133 autistic people’s experiences and perspectives of socialising in ways that felt authentic to them, with a particular focus on mixed-neurotype interactions and the role of nonautistic people. Using reflexive thematic analysis, four themes were generated: (1) embracing diverse communication styles, interests and perspectives; (2) creating a more inclusive mixed-neurotype social environment together; (3) minimising and managing mixed-neurotype miscommunication in mutually beneficial ways; and (4) enjoyable interactions involving reduced anxiety and exhaustion as well as genuine connection and rapport. These findings are discussed with reference to theory and research involving the construct of authenticity both inside and outside the field of autism research. The knowledge generated in this study illuminates a previously underexplored aspect of autistic people’s experience and elucidates potential avenues through which to enhance the social experiences and well-being of this group

An algebraic interpretation of the Wheeler-DeWitt equation

We make a direct connection between the construction of three dimensional topological state sums from tensor categories and three dimensional quantum gravity by noting that the discrete version of the Wheeler-DeWitt equation is exactly the pentagon for the associator of the tensor category, the Biedenharn-Elliott identity. A crucial role is played by an asymptotic formula relating 6j-symbols to rotation matrices given by Edmonds.Comment: 10 pages, amstex, uses epsf.tex. New version has improved presentatio

Positivity in Lorentzian Barrett-Crane Models of Quantum Gravity

The Barrett-Crane models of Lorentzian quantum gravity are a family of spin foam models based on the Lorentz group. We show that for various choices of edge and face amplitudes, including the Perez-Rovelli normalization, the amplitude for every triangulated closed 4-manifold is a non-negative real number. Roughly speaking, this means that if one sums over triangulations, there is no interference between the different triangulations. We prove non-negativity by transforming the model into a ``dual variables'' formulation in which the amplitude for a given triangulation is expressed as an integral over three copies of hyperbolic space for each tetrahedron. Then we prove that, expressed in this way, the integrand is non-negative. In addition to implying that the amplitude is non-negative, the non-negativity of the integrand is highly significant from the point of view of numerical computations, as it allows statistical methods such as the Metropolis algorithm to be used for efficient computation of expectation values of observables.Comment: 13 page

Spin Foam Models of Yang-Mills Theory Coupled to Gravity

We construct a spin foam model of Yang-Mills theory coupled to gravity by using a discretized path integral of the BF theory with polynomial interactions and the Barret-Crane ansatz. In the Euclidian gravity case we obtain a vertex amplitude which is determined by a vertex operator acting on a simple spin network function. The Euclidian gravity results can be straightforwardly extended to the Lorentzian case, so that we propose a Lorentzian spin foam model of Yang-Mills theory coupled to gravity.Comment: 10 page

3+1 spinfoam model of quantum gravity with spacelike and timelike components

We present a spinfoam formulation of Lorentzian quantum General Relativity. The theory is based on a simple generalization of an Euclidean model defined in terms of a field theory over a group. The model is an extension of a recently introduced Lorentzian model, in which both timelike and spacelike components are included. The spinfoams in the model, corresponding to quantized 4-geometries, carry a natural non-perturbative local causal structure induced by the geometry of the algebra of the internal gauge (sl(2,C)). Amplitudes can be expressed as integrals over the spacelike unit-vectors hyperboloid in Minkowski space, or the imaginary Lobachevskian space.Comment: 16 pages, 1 figur