Quantum Physics

A criterion for localization of electron states in disordered materials is presented. Applications to binary alloys, made using the self-energy calculated in the coherent- potential approximation, confirm the Mott-Cohen-Fritzsche-Ovshinsky model in detail. Mobility edges occur inside the band edges. A mobility gap can appear within the band. The band can split into sub-bands, each with mobility edges. Below a critical concen- tration, an Anderson transition, where the minority sub-band becomes entirely localized, can occur. Considerable effort has recently been devoted to calculation of the densities of states in differ- ent disordered materials. ' 3 In particular, the

In this study we present the dependence of electrical properties of copper phthalocyanine (CuPc) and metal free phthalocyanine (H 2 Pc) bulk heterojunction structure under different illumination levels. To fabricate the device on ITO coated glass substrate the bulk heterojunction thin film of CuPc and H 2 Pc with thickness varying from 100 nm to 300 nm are deposited by thermal evaporator. Aluminum thin film was deposited by thermal evaporation as a top contact. The optical properties of the fabricated device are investigated using UV-vis spectroscopy. The current-voltage characteristics in dark and under illumination show that the device is sensitive towards visible light. The absorption spectrum describes its photo sensitivity in the range of wavelength from 200 nm to 850 nm. Simulation of current-intensity of light curve is carried out and experimental results are found in good agreement with simulated ones.

We propose an approach to efficiently generate and multiplex optical orbital angular momentum (OAM) modes in a fiber with a ring refractive index profile by using multiple coherent inputs from a Gaussian mode. By controlling the phase relationship of the multiple inputs, one can selectively generate OAM modes of different states l. By controlling both the amplitude and phase of the multiple inputs, multiple OAM modes can be generated simultaneously without additional loss coming from multiplexing. We show, by simulation, the generation of OAM modes (OAM state jlj < 3) with mode purity greater than 99%. The power loss of generating and multiplexing seven modes is about 35%. A transmitter for an OAM-based mode-division multiplexing system is proposed based on the discrete Fourier transform between the data carried by the multiple inputs and the data carried by the OAM modes. The experimental implementation of the proposed approach could be achieved by integrating ring fiber, multicore fiber, and photonic integrated circuit technology.

We propose a fiber structure of a square core and ring refractive index profile that converts an input circular polarized Gaussian mode into optical orbital angular momentum (OAM) modes. By breaking the circular symmetry of the waveguide, the input circularly polarized fundamental mode in the square core can be coupled into the ring region to generate higher-order OAM modes, corresponding to the transference of spin angular momentum and orbital angular momentum. We show, by using simulation, the generation of OAM modes with a topological charge l up to 9 using <10 mm long fiber. The mode purity is above 96.4% and the extinction ratio can be 30 dB.

Electronic properties of individual CdSe colloidal nanodots have been investigated by conductive-tip atomic force microscopy (AFM). Submonolayer-thick films of the colloidal nanodots were fabricated on a self-assembled monolayer of alkanethiol molecules formed on Au(1 1 1) surfaces for single dot measurements. First, we simultaneously imaged the topography and conductivity of isolated single dots by AFM operating in contact mode with a conductive tip under appropriate bias voltages. In the current image, it is found that the dot regions have higher electric resistances due to tunneling resistance through the CdSe dots. We found a 10-nm scale electric inhomogeneity around the dots, which may correspond to the previously reported etch-pits of Au(1 1 1) surfaces formed during the deposition of the alkanethiol molecules. Then, current-voltage characteristics were measured with the conductive tip positioned on the single dots; large changes in the conductivity which suggest resonant tunneling through the quantized energy level in the dot were observed even at room temperature.

Electronic properties of individual CdSe colloidal nanodots have been investigated by conductive-tip atomic force microscopy (AFM). Submonolayer-thick films of the colloidal nanodots were fabricated on a self-assembled monolayer of alkanethiol molecules formed on Au(1 1 1) surfaces for single dot measurements. First, we simultaneously imaged the topography and conductivity of isolated single dots by AFM operating in contact mode with a conductive tip under appropriate bias voltages. In the current image, it is found that the dot regions have higher electric resistances due to tunneling resistance through the CdSe dots. We found a 10-nm scale electric inhomogeneity around the dots, which may correspond to the previously reported etch-pits of Au(1 1 1) surfaces formed during the deposition of the alkanethiol molecules. Then, current-voltage characteristics were measured with the conductive tip positioned on the single dots; large changes in the conductivity which suggest resonant tunneling through the quantized energy level in the dot were observed even at room temperature.

Hadron production and lepton-pair production in e + e -collisions are studied with data collected with the L3 detector at LEP at centre-of-mass energies √ s = 192-208 GeV. Using a total integrated luminosity of 453 pb -1 , 36 057 hadronic events and 12 863 lepton-pair events are selected. The cross sections for hadron production and lepton-pair production are measured for the full sample and for events where no high-energy initial-state-radiation photon is emitted prior to the collisions. Lepton-pair events are further investigated and forward-backward asymmetries are measured. Finally, the differential cross sections for electron-positron pair-production is determined as a function of the scattering angle. An overall good agreement is found with Standard Model predictions.

We find the spectrum P (ω)dω of the gravitational wave background produced in the early universe in string theory. We work in the framework of the recently discussed String Driven Cosmology, whose scale factors are computed with the low-energy effective string equations as well as selfconsistent solutions of General Relativity with a gas of strings as source. The scale factor evolution is described by an early string driven inflationary stage with an instantaneous transition to a radiation dominated stage and successive matter dominated stage. This is a string cosmology expanding evolution always running on positive proper cosmic time. The spectrum of the generated gravitons is computed in the framework of Quantum Field Theory and in the appropiated effective String Cosmology context. We study and show explicitly the effect of the dilaton field, characteristic to this kind of cosmologies. We compute the spectrum for the same evolution description with three differents approachs. Some features of gravitational wave spectra, as peaks and asymptotic behaviours, are found direct consequences of the dilaton involved in the string low energy effective action and not only of the scale factor evolution. We make use of a careful treatment of the scale factor evolution and involved transitions. This allows us to compute a full prediction on the power spectrum of gravitational waves without any free-parameters. A comparative analysis of different treatments, solutions and compatibility with observational bounds or detection perspectives is made.

The chemical reactivity of SiO x species on Cu(100) and oxygen-passivated Cu(100) surfaces has been studied by means of synchrotron photoemission (PES), X-ray photoemission ( XPS), X-ray absorption ( XAS ) spectroscopies and ab initio density functional calculations. When silicon monoxide is deposited on a clean Cu(100) surface, below the equivalent coverage of ~2 A ˚, partial dismutation of Si2+ species into Si0 plus Si4+ species takes place. The presence of Si0 as patches of Si-Cu(100) surface alloy and SiO monomers and polymeric forms of Si2+ species has been explained theoretically. The observation of Si4+ species is explained by a two-step process: first the reduction of Si2+ to Si0 plus O adsorbed on the Cu(100) surface; second the adsorbed O reacts with the incorporated SiO to oxidised to Si4+. The mechanism would be similar to that proposed for the reaction CO CO 2 on O-Cu(100) surface. On the other hand, when very low coverages (equivalent thickness<0.5 A ˚) of SiO are deposited on an oxygenpassivated Cu(100) surface, only Si2+ species are stabilised, probably in an (SiO) n polymeric form. The theoretical calculations have confirmed very weak interaction between the SiO structures and the passivated surface. The Si-K absorption edge of these Si2+ species is characterised by only two peaks at 1840 and 1849 eV. They have been assigned to the p and s orbitals of the SiO bond, by similarity with the CO molecule. Preferential orientation of the SiO units parallel to the surface is found by XAS and confirmed by the theoretical calculations.

We perform string quantization in anti de Sitter (AdS) spacetime. The string motion is stable, oscillatory in time with real frequencies ω n = √ n 2 + m 2 α ′2 H 2 and the string size and energy are bounded. The string fluctuations around the center of mass are well behaved. We find the mass formula which is also well behaved in all regimes. There is an infinite number of states with arbitrarily high mass in AdS (in de Sitter (dS) there is a finite number of states only). The critical dimension at which the graviton appears is D = 25, as in de Sitter space. A cosmological constant Λ = 0 (whatever its sign) introduces a fine structure effect (splitting of levels) in the mass spectrum at all states beyond the graviton. The high mass spectrum changes drastically with respect to flat Minkowski spacetime. For Λ < 0, we find < m 2 >∼| Λ | N 2 , independent of α ′ , and the level spacing grows with the eigenvalue of the number operator, N. The density of states ρ(m) as in Minkowski space), thus discarding the existence of a critical string temperature. For the sake of completeness, we also study the quantum strings in the black string background, where strings behave, in many respects, as in the ordinary black hole backgrounds. The mass spectrum is equal to the mass spectrum in flat Minkowski space.

Exact solutions of the string equations of motion and constraints are systematically constructed in de Sitter spacetime using the dressing method of soliton theory. The string dynamics in de Sitter spacetime is integrable due to the associated linear system. We start from an exact string solution q (0) and the associated solution of the linear system Ψ (0) (λ), and we construct a new solution Ψ(λ) differing from Ψ (0) (λ) by a rational matrix in λ with at least four poles λ 0 , 1/λ 0 , λ * 0 , 1/λ * 0 . The periodicity condition for closed strings restrict λ 0 to discrete values expressed in terms of Pythagorean numbers. Here we explicitly construct solutions depending on (2 + 1)-spacetime coordinates, two arbitrary complex numbers (the 'polarization vector') and two integers (n, m) which determine the string windings in the space. The solutions are depicted in the hyperboloid coordinates q and in comoving coordinates with the cosmic time T . Despite of the fact that we have a single world sheet, our solutions describe multiple (here five) different and independent strings; the world sheet time τ turns to be a multivalued function of T . (This has no analogue in flat spacetime). One string is stable (its proper size tends to a constant for T → ∞, and its comoving size contracts); the other strings are unstable (their proper sizes blow up for T → ∞, while their comoving sizes tend to constants). These solutions (even the stable strings) do not oscillate in time. The interpretation of these solutions and their dynamics in terms of the sinh-Gordon model is particularly enlighting.

We study the string propagation in the 2+1 black hole anti de Sitter background (2+1 BH-ADS). We find the first and second order fluctuations around the string center of mass and obtain the expression for the string mass. The string motion is stable, all fluctuations oscillate with real frequencies and are bounded, even at r = 0. We compare with the string motion in the ordinary black hole anti de Sitter spacetime, and in the black string background, where string instabilities develop and the fluctuations blow up at r = 0. We find the exact general solution for the circular string motion in all these backgrounds, it is given closely and completely in terms of elliptic functions. For the non-rotating black hole backgrounds the circular strings have a maximal bounded size r m , they contract and collapse into r = 0. No indefinitely growing strings, neither multi-string solutions are present in these backgrounds. In rotating spacetimes, both the 2+1 BH-ADS and the ordinary Kerr-ADS, the presence of angular momentum prevents the string from collapsing into r = 0. The circular string motion is also completely solved in the black hole de Sitter spacetime and in the black string background (dual of the 2+1 BH-ADS spacetime), in which expanding unbounded strings and multi-string solutions appear.

We consider classical and quantum strings in the conformally invariant background corresponding to the SL(2,R) WZWN model. This background is locally anti-de Sitter spacetime with non-vanishing torsion. Conformal invariance is expressed as the torsion being parallelized. The precise effect of the conformal invariance on the dynamics of both circular and generic classical strings is extracted. In particular, the conformal invariance gives rise to a repulsive interaction of the string with the background which precisely cancels the dominant attractive term arising from gravity. We perform both semi-classical and canonical string-quantization, in order to see the effect of the conformal invariance of the background on the string mass spectrum. Both approaches yield that the high-mass states are governed by m ∼ HN (N ∈ N 0 , N 'large'), where m is the string mass and H is the Hubble constant. It follows that the level spacing grows proportionally to N : d(m 2 α ′ )/dN ∼ N , while the entropy goes like S ∼ √ m. Moreover, it follows that there is no Hagedorn temperature, so that the partition function is well-defined at any positive temperature. All results are compared with the analogue results in Anti-de Sitter spacetime, which is a non conformal invariant background. Conformal invariance simplifies the mathematics of the problem but the physics remains mainly unchanged. Differences between conformal and non-conformal backgrounds only appear in the intermediate region of the string spectrum, but these differences are minor. For low and high masses, the string mass spectra in conformal and non-conformal backgrounds are identical. Interestingly enough, conformal invariance fixes the value of the spacetime curvature to be -69/(26 α ′ ).

HAL is a multi-disciplinary open access archive for the deposit and dissemination of scientific research documents, whether they are published or not. The documents may come from teaching and research institutions in France or abroad, or from public or private research centers. L'archive ouverte pluridisciplinaire HAL, est destinée au dépôt et à la diffusion de documents scientifiques de niveau recherche, publiés ou non, émanant des établissements d'enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.

Sterile neutrinos with mass in the range of one to a few keV are important as extensions of the Standard Model of particle physics and are serious dark matter (DM) candidates. This DM mass scale (warm DM) is in agreement with both cosmological and galactic observations. We study the role of a keV sterile neutrino through its mixing with a light active neutrino in Rhenium 187 and Tritium beta decays. We pinpoint the energy spectrum of the beta particle, 0 Te (Q β -ms), as the region where a sterile neutrino could be detected and where its mass ms could be measured. This energy region is at least 1 keV away from the region suitable to measure the mass of the light active neutrino, located near the endpoint Q β . The emission of a keV sterile neutrino in a beta decay could show up as a small kink in the spectrum of the emitted beta particle. With this in view, we perform a careful calculation of the Rhenium and Tritium beta spectra and estimate the size of this perturbation by means of the dimensionless ratio R of the sterile neutrino to the active neutrino contributions. We comment on the possibility of searching for sterile neutrino signatures in two experiments which are currently running at present, MARE and KATRIN, focused on the Rhenium 187 and Tritium beta decays respectively.

HAL is a multi-disciplinary open access archive for the deposit and dissemination of scientific research documents, whether they are published or not. The documents may come from teaching and research institutions in France or abroad, or from public or private research centers. L'archive ouverte pluridisciplinaire HAL, est destinée au dépôt et à la diffusion de documents scientifiques de niveau recherche, publiés ou non, émanant des établissements d'enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.

We uncover the general mechanism and the nature of the today dark energy (DE). This is only based on well known quantum physics and cosmology. We show that the observed DE today originates from the cosmological quantum vacuum of light particles which provides a continuous energy distribution able to reproduce the data. Bosons give positive contributions to the DE while fermions yield negative contributions. As usual in field theory, ultraviolet divergences are subtracted from the physical quantities. The subtractions respect the symmetries of the theory and we normalize the physical quantities to be zero for the Minkowski vacuum. The resulting finite contributions to the energy density and the pressure from the quantum vacuum grow as log a(t) where a(t) is the scale factor, while the particle contributions dilute as 1/a 3 (t), as it must be for massive particles. We find the explicit today dark energy equation of state P = w(z) H: It turns to be slightly w(z) < -1 with w(z) asymptotically reaching the value -1 from below. A scalar particle can produce the observed dark energy through its quantum cosmological vacuum provided: (i) Its mass is of the order of 10 -3 eV = 1 meV, (ii) It is very weakly coupled, and (iii) it is stable on the time scale of the age of the universe. The axion vacuum thus appears as a natural candidate. The neutrino vacuum (especially the lightest mass eigenstate) can give negative contributions to the dark energy. We find that w(z = 0) is slightly below -1 by an amount ranging from (-1.5 × 10 -3 ) to (-8 × 10 -3 ) and we predict the axion mass be in the range between 4 and 5 meV . We find that the universe will expand in the future faster than the de Sitter universe, as an exponential in the square of the cosmic time. Dark energy today arises from the quantum vacuum of light particles in FRW cosmological space-time in an analogous way to the Casimir vacuum effect of quantum fields in Minkowski space-time with non-trivial boundary conditions. (+) passed away (a): Contents I. Introduction and Results 2 II. Scalar Fields in Cosmological Space-Times III. Fermion Fields in Cosmological Space-Times IV. The Cosmological Quantum Vacuum. V. Vacuum Energy Density and Pressure for Late Times VI. The Quantum Nature of the Cosmological Vacuum. VII. Dark Energy from the Cosmological Quantum Vacuum. VIII. Neutrino Mass Eigenstates IX. Light Particle Masses and the Dark Energy Density Today X. The Future Evolution of the Universe XI. Discussion XII. Conclusions A. Dimensional and Cutoff Regularization of the Vacuum Energy References I. INTRODUCTION AND RESULTS Since the discovery of the dark energy in the present universe [1], [2], an intense observational activity has improved our knowledge about it [3], [4], [5], and more activity is expected to provide new data and understanding eg. [6], [7]. Many different approachs and models have been proposed to explain the dark energy [8], [9], [10], [11], [12]. For reviews and approachs on the dark energy see for example Refs. [10], [8], [9], [11, 12].

The essential features underlying the top-down scenarii for UHECR are discussed, namely, the stability (or lifetime) imposed to the heavy objects (particles) whatever they be: topological and non-topological solitons, X-particles, cosmic defects, microscopic black-holes, fundamental strings. We provide an unified formula for the quantum decay rate of all these objects as well as the particle decays in the standard model. The key point in the top-down scenarii is the necessity to adjust the lifetime of the heavy object to the age of the universe. This ad-hoc requirement needs a very high dimensional operator to govern its decay and/or an extremely small coupling constant. The natural lifetimes of such heavy objects are, however, microscopic times associated to the GUT energy scale (∼ 10 -28 sec. or shorter). It is at this energy scale (by the end of inflation) where they could have been abundantly formed in the early universe and it seems natural that they decayed shortly after being formed.

The transfer function T (k) of dark matter (DM) perturbations during matter domination is obtained by solving the linearized collisionless Boltzmann-Vlasov equation. We provide an exact expression for T (k) for arbitrary distribution functions of decoupled particles and initial conditions, which can be systematically expanded in a Fredholm series. An exhaustive numerical study of thermal relics for different initial conditions reveals that the first two terms in the expansion of T (k) provide a remarkably accurate and simple approximation valid on all scales of cosmological relevance for structure formation in the linear regime. The natural scale of suppression is the free streaming wavevector at matter-radiation equality, important ingredient is a non-local kernel determined by the distribution functions of the decoupled particles which describes the memory of the initial conditions and gravitational clustering and yields a correction to the fluid description. This correction is negligible at large scales k ≪ k f s (teq) but it becomes important at small scales k ≥ k f s (teq). Distribution functions that favor the small momentum region yield longer-range memory kernels and lead to an enhancement of power at small scales k > k f s (teq). Fermi-Dirac and Bose-Einstein statistics lead to long-range memory kernels, with longer range for bosons, both resulting in enhancement of T (k) at small scales. For DM thermal relics that decoupled while ultrarelativistic we find k f s (teq) ≃ 0.003 (g d /2) , where g d is the number of degrees of freedom at decoupling. For WIMPS we obtain k f s (teq) = 5.88 (g d /2 ) where C = O(1) and independent of statistics for thermal relics. We provide simple and accurate fits for T (k) in a wide range of small scales k > k f s (teq) for thermal relics and different initial conditions. The numerical and analytic results for arbitrary distribution functions and initial conditions allow an assessment of DM candidates through their impact on structure formation. A. The free streaming length. B. Exact results from Gilbert's equation C. Thermal and Gilbert's initial conditions D. Solution of the Gilbert equation in powers of k. E. Gilbert's equation as an integro-differential equation. F. The exact transfer function and its Fredholm expansion.

Vicinal Si(100) (4°) shows perfectly ordered terraces with a width of 4 nm separated by double steps. Adsorption of Au at 800°C results in a dramatic change of the step morphology: the surface decomposes into areas which are perfectly flat with a (100)orientation and [119]-facets, which compensate the macroscopic miscut. Macroscopic super terraces with a width of 400 nm up to 4 mm are formed, which are extremely straight with a length limited only by the size of the sample.

Results are reported from a search for new physics processes in events containing a single isolated high-transverse-momentum lepton (electron or muon), energetic jets, and large missing transverse momentum. The analysis is based on a 4.98 fb -1 sample of proton-proton collisions at a center-of-mass energy of 7 TeV, obtained with the CMS detector at the LHC. Three separate background estimation methods, each relying primarily on control samples in the data, are applied to a range of signal regions, providing complementary approaches for estimating the background yields. The observed yields are consistent with the predicted standard model backgrounds. The results are interpreted in terms of limits on the parameter space for the constrained minimal supersymmetric extension of the standard model, as well as on cross sections for simplified models, which provide a generic description of the production and decay of new particles in specific, topology based final states.

The top-quark mass is measured in proton-proton collisions at √ s = 7 TeV using a data sample corresponding to an integrated luminosity of 5.0 fb -1 collected by the CMS experiment at the LHC. The measurement is performed in the dilepton decay channel tt → ( + ν b) ( -ν b), where = e, μ. Candidate top-quark decays are selected by requiring two leptons, at least two jets, and imbalance in transverse momentum. The mass is reconstructed with an analytical matrix weighting technique using distributions derived from simulated samples. Using a maximum-likelihood fit, the top-quark mass is determined to be 172.5 ± 0.4 (stat.) ± 1.5 (syst.) GeV.

The first LHC pp collisions at centre-of-mass energies of 0.9 and 2.36 TeV were recorded by the CMS detector in December 2009. The trajectories of charged particles produced in the collisions were reconstructed using the all-silicon Tracker and their momenta were measured in the 3.8 T axial magnetic field. Results from the Tracker commissioning are presented including studies of timing, efficiency, signal-to-noise, resolution, and ionization energy. Reconstructed tracks are used to benchmark the performance in terms of track and vertex resolutions, reconstruction of decays, estimation of ionization energy loss, as well as identification of photon conversions, nuclear interactions, and heavy-flavour decays.

The possible existence of the bound states of the interacting two-dimensional (2D) magnetoexcitons in the lowest Landau levels (LLLs) approximation was investigated using the Landau gauge description. The magnetoexcitons taking part in the formation of the bound state with resultant wave vector 0 k  have

The origin of the g-factor of the two-dimensional (2D) electrons and holes moving in the periodic crystal lattice potential with the perpendicular magnetic and electric fields is discussed. The Pauli equation describing the Landau quantization accompanied by the Rashba spin-orbit coupling (RSOC) and Zeeman splitting (ZS) for 2D heavy holes with nonparabolic dispersion law is solved exactly. The solutions have the form of the pairs of the Landau quantization levels due to the spinor-type wave functions. The energy levels depend on amplitudes of the magnetic and electric fields, on the g-factor h g , and on the parameter of nonparabolicity C . The dependences of two energy levels in any pair on the Zeeman parameter 0 4 h h h m Z g m  , where h m is the hole effective mass, are nonmonotonous and without intersections. The smallest distance between them at 0 C  takes place at the value / 2 h Z n  , where n is the order of the chirality terms determined by the RSOC and is the same for any quantum number of the Landau quantization.

In this article, the author partly uses metaphors to explore multiverses in the omniverse, quantum tunneling & conformal cyclic cosmology in a revelatory eschatology and genesis.
The Holographic Universe is addressed in conjunction with a revisitation of 11-dimensional supermembrane theory, with its five 10-dimensional superstring classes reinterpreted in the form of a Twin Bipolaron Gravitation Center (TBPGC). A parallel lightpath cosmology of dimensionally separated spheroidal de Sitter dS and hyperbolic Anti-de Sitter AdS cosmic expansion models is introduced to enable the cancellation of curvatures in the context of the AdS-CFT correspondence and the emergence of a multiverse defined in phase-shifted universes from a seedling cyclic protoverse oscillating as Bohmian standing waves between maximized even and minimized odd Hubble Event Horizon nodes as TBP parameters of the cosmogenesis.

In this dialogue with Francois Laruelle Anne-Françoise Schmid suggests that Laruelle's nonphilosophy, which begins with an indecision, could be conceived as something that in the history of painting has been called figura serpentinata, "serpentine line". This line, which produces a kind of music by the use of concepts, is visible according her trough his whole work: from his first book on Ravaisson, Phenomenon and Difference (1971), through to his last one, The Last Humanity: A New Ecological Science, published in French in 2015 and expected to appear in English in 2018.

Propagation of a light through a one-dimensional photonic crystal containing a defect layer doped with a Raman gain medium is discussed. We demonstrate all-optically controlled switching from normal to anomalous dispersion in such a structure. A group delay for the transmitted probe (Raman) pulse is investigated. We show that the group velocity of a Raman pulse can be tuned from subluminal to superluminal by varying the intensity of the pump field.

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We consider the class of physical theories whose dynamics are given by natural equations, which are partial differential equations determined by a functor from the category of n manifolds, for some n, to the category of fiber bundles, satisfying certain further conditions. We show how the theory of natural equations clarifies several important foundational issues, including the status and meaning of minimal coupling, symmetries of theories, and background structure. We also state and prove a fundamental result about the initial value problem for natural equations.

I consider the sense in which teleparallel gravity and symmetric teleparallel gravity may be understood as gauge theories of gravity. I first argue that both theories have surplus structure. I then consider the relationship between Yang-Mills theory and Poincaré Gauge Theory and argue that though these use similar formalisms, there are subtle disanalogies in their interpretation.

Spinel type Co 3 O 4 (100) is successfully grown on Ag(100) at ultrahigh vacuum conditions and its structure, electronic and chemical properties are compared with those of Co 3 O 4 (111) grown on Ir(100). We find that the Co 3 O 4 (100) is unreconstructed. In contrast to the defect free Co 3 O 4 (111) surface the Co 3 O 4 (100) surface contains a high concentration of defects that we assign to subsurface cation vacancies analogous to those observed for Fe 3 O 4 (100). Our photoemission and absorption spectroscopy experiments reveal a very similar electronic structure of the Co 3 O 4 (111) and Co 3 O 4 (100) surfaces. The similar electronic structure of the two surfaces is reflected in the CO adsorption properties at low temperatures, as we observe adsorption of molecular CO as well as the formation of carbonate (CO 3 ) species on both surfaces upon CO exposure at 85 K.

The aim of this paper is to present a direct observation by means of Brewster angle microscopy of Langmuir films made of C6o along the process of their compression. We found coexistence of a gas and a condensed phase at low area densities. Our results agree with the formation of multilayers even at low area densities. We made compressions of the films at several speeds, with rapid compressions we found that the condensed phase formed foam-like structures and circular domains of different sizes at very small area densities.

Conformal scalar fields coupled to the dilaton appear naturally in two-dimensional models of black hole evaporation. We show that their trace anomaly is (1/24π)[R -6(∇φ) 2 -2✷φ]. It follows that an RST-type counterterm appears naturally in the one-loop effective action.

The wave function of the universe is usually taken to beafunctional of the three-metric on a spacelike section, , which is measured. It is sometimes better, however, to work in the conjugate representation, where the wave function depends on a quantity related to the second fundamental form of . This makes it possible to ensure that is part of a Lorentzian universe by requiring that the argument of the wave function bepurely imaginary. We demonstrate the advantages of this formalism rst in the well-known examples of the nucleation of a d e Sitter or a Nariai universe. We then use it to calculate the pair creation rate for sub-maximal black holes in de Sitter space, which had been thought t o v anish semi-classically.

It is shown that in classical general relativity, if space-time is nonempty at one time, it will be nonempty at all times provided that the energy momentum tensor of the matter satisfies a physically reasonable condition. The apparent contradiction with the quantum predictions for the creation and annihilation of matter particles by gravitons is discussed and is shown to arise from the lack of a good energy momentum operator for the matter in an unquantised curved space-time metric.

For a large class of quantum models of mean-field type the thermodynamic limit of the free energy density is proved to be given by the Gibbs variational principle. The latter is shown to be equivalent to a noncommutative version of Varadhan's asymptotic formula.

A three-dimensional (3D) ring-shaped laser trap has been built using axicons. The diameter of this laser trap ranges from 70 to 140 m and is adjusted by simply changing the position of one axicon in the optical path. Parallel 3D trapping of 5 m silica microspheres and 3D confinement of cells along the ring are demonstrated. In this system the special optical properties of axicons are used to create a continuous annular trap with high power efficiency and a constant numerical aperture. This new approach, without any mechanical scanning, offers significant potential for applications in cell motility analysis and biotropism studies.

An alternative interpretation of the conformal transformations of the metric is discussed according to which the latter can be viewed as a mapping among Riemannian and Weyl-integrable spaces. A novel aspect of the conformal transformation's issue is then revealed: these transformations relate complementary geometrical pictures of a same physical reality, so that, the question about which is the physical conformal frame, does not arise. In addition, arguments are given which point out that, unless a clear statement of what is understood by "equivalence of frames" is made, the issue is a semantic one. For definiteness, an intuitively "natural" statement of conformal equivalence is given, which is associated with conformal invariance of the field equations. Under this particular reading, equivalence can take place only if the metric is defined up to a conformal equivalence class. A concrete example of a conformal-invariant theory of gravity is then explored. Since Brans-Dicke theory is not conformally invariant, then the Jordan's and Einstein's frames of the theory are not equivalent. Otherwise, in view of the alternative approach proposed here, these frames represent complementary geometrical descriptions of a same phenomenon. The different points of view existing in the literature are critically scrutinized on the light of the new arguments.

(LB) films of w-tricosenoic acid are deposited onto side-polished optical fibers, resulting in wavelength-selective elements. The wavelength response is shown to be strongly dependent on film thickness, giving a shift in central wavelength with film thickness of AAO/Ad = 2.4, in agreement with a simple phasematching model. It is demonstrated that an alternative polishing technique, requiring no substrates or epoxy, allows more repeatable LB deposition and produces devices with similar characteristics. This is the only technique that will allow deposition of more complex electro-optic LB film-forming molecules.

An overlay material was deposited by the Langmuir -Blodgett technique onto a single-mode optical fiber containing a long-period grating. The long-period grating exhibits characteristic attenuation bands in its transmission spectrum whose central wavelengths were observed to depend on the optical thickness of the overlay material, even for materials that have a refractive index higher than that of silica.

The fabrication of an optical cavity at the distal end of an optical fiber has been achieved by Langmuir-Blodgett (LB) deposition of tricosanoic acid, the technique allowing nanometer-scale control over the cavity length to a total thickness of ca. 0.5 m. The cavity has been shown to act interferometrically and, thus, has potential sensing applications.

A passive signal-processing technique for addressing a miniature low-f inesse f iber Fabry -Perot interferometric sensor with a multimode laser diode is reported. Two modes of a multimode laser diode separated by 3 nm are used to obtain quadrature outputs from an ϳ20-mm cavity. Wavelength-division demultiplexing combined with digital signal processing is used to recover the measurand-induced phase change. The technique is demonstrated for the measurement of vibration. The signal-to-noise ratio is ϳ70 dB at 500 Hz for ϳp͞2 rad displacement of the mirror, which results in a minimum detectable signal of ϳ200 mrad Hz 21/2 . A quantitative discussion of miscalibration and systematic errors is presented.

Long-period gratings (LPG's) written in commercially available boron-codoped fibers operating at wavelengths of ,1.1 mm are shown to exhibit high temperature and bending sensitivities. Each resonant attenuation band of such LPG's was observed to split in two when the LPG's were bent. The split attenuation bands' separation increased significantly with increasing bend curvature, and the central wavelengths of the split bands provided a measure of temperature. We exploit this effect to allow for simultaneous measurement of temperature and bending in smart-structure applications. The demonstrated novel sensor system is simple and low cost.

A liquid-level sensor based on the refractive-index sensitivity of long-period fiber-optic gratings is proposed and demonstrated. The form of the transmission spectrum of the long-period grating is dependent on the fraction of the length of the long-period grating that is surrounded by the liquid. The sensor shows a large linear range, with sensitivity of 4.8% change in transmission per millimeter, for a long-period grating with a length of 40 mm and a periodicity of 400 mm.