Purity and entanglement of two-photon polarization states generated by spontaneous parametric down-conversion

We elucidate the dependence of purity and entanglement of two-photon states generated by spontaneous parametric down-conversion on the parameters of the source, such as crystal length, pump beam divergence, frequency bandwidth, and detectors angular aperture. The effect of crystal anisotropy is taken into account. Numerical simulations are presented for two types of commonly used source configurations. (C) 2009 Elsevier B.V. All rights reserved.

ON THE DOUBLE NATURED SOLUTIONS OF THE TWO-TEMPERATURE EXTERNAL SOFT PHOTON COMPTONIZED ACCRETION DISKS

We have analyzed pair production in the innermost region of a two-temperature external soft photon Comptonized accretion disk. We have shown that, if the viscosity parameter is greater than a critical value alpha(c), the solution to the disk equation is double valued: one, advection dominated, and the other, radiation dominated. When alpha <= alpha(c), the accretion rate has to satisfy (m) over dot(1) <= (m) over dot <= (m) over dot(c) in order to have two steady-state solutions. It is shown that these critical parameters (m) over dot(1), (m) over dot(c) are functions of r, alpha, and theta(e), and alpha(c) is a function of r and theta(e). Depending on the combination of the parameters, the advection-dominated solution may not be physically consistent. It is also shown that the electronic temperature is maximum at the onset of the thermal instability, from which results this inner region. These solutions are stable against perturbations in the electron temperature and in the density of pairs.

Thermal photon production in Au plus Au collisions: Viscous corrections in two different hydrodynamic formalisms

We calculate the spectra of produced thermal photons in Au + Au collisions taking into account the nonequilibrium contribution to photon production due to finite shear viscosity. The evolution of the fireball is modeled by second-order as well as by divergence-type 2 + 1 dissipative hydrodynamics, both with an ideal equation of state and with one based on Lattice QCD that includes an analytical crossover. The spectrum calculated in the divergence-type theory is considerably enhanced with respect to the one calculated in the second-order theory, the difference being entirely due to differences in the viscous corrections to photon production. Our results show that the differences in hydrodynamic formalisms are an important source of uncertainty in the extraction of the value of eta/s from measured photon spectra. The uncertainty in the value of eta/s associated with different hydrodynamic models used to compute thermal photon spectra is larger than the one occurring in matching hadron elliptic flow to RHIC data. (C) 2010 Elsevier B.V. All rights reserved.

Conversion of CD95 (Fas) Type II into Type I signaling by sub-lethal doses of cycloheximide

CD95 (Fas/Apo-1)-mediated apoptosis was shown to occur through two distinct pathways. One involves a direct activation of caspase-3 by large amounts of caspase-8 generated at the DISC (Type I cells). The other is related to the cleavage of Bid by low concentration of caspase-8, leading to the release of cytochrome c from mitochondria and the activation of caspase-3 by the cytochrome c/APAF-1/caspase-9 apoptosome (Type 11 cells). It is also known that the protein synthesis inhibitor cycloheximide (CHX) sensitizes Type I cells to CD95-mediated apoptosis, but it remains contradictory whether this effect also occurs in Type II cells. Here, we show that sub-lethal doses of CHX render both Type I and Type II cells sensitive to the apoptogenic effect of anti-CD95 antibodies but not to chemotherapeutic drugs. Moreover, Bcl-2-positive Type II cells become strongly sensitive to CD95-mediated apoptosis by the addition of CHX to the cell culture. This is not the result of a restraint of the anti-apoptotic effect of Bcl-2 at the mitochondrial level since CHX-treated Type II cells still retain their resistance to chemotherapeutic drugs. Therefore, CHX treatment is granting the CD95-mediated pathway the ability to bypass the mitochondria requirement to apoptosis, much alike to what is observed in Type I cells. (c) 2007 Elsevier Inc. All rights reserved.

Conversion coefficients from air kerma to personal dose equivalent in mammography

In this work, the scattered X-ray beams produced by a mammography unit with a Mo/Mo, Mo/Rh and W/Rh anode/filter combinations were applied in the evaluation of the Hp(10, 0) and mean conversion coefficients from air kerma to the personal dose equivalent ((C) over barH(p(10,0 degrees))). The higher values of H(p)(10,0 degrees) are related to the Mo/Rh combination whereas the lower ones are for the W/Rh target/filter. (C) over barH(p(10,0 degrees)) values are in the range 0.19-0.54 Sv/Gy, where the higher values comprise the W/Rh combination. (C) 2009 Elsevier Ltd. All rights reserved.

Upper limit on the cosmic-ray photon flux above 10(19) eV using the surface detector of the Pierre Auger Observatory

A method is developed to search for air showers initiated by photons using data recorded by the surface detector of the Auger Observatory. The approach is based on observables sensitive to the longitudinal shower development, the signal risetime and the curvature of the shower front. Applying this method to the data, tipper limits on the flux of photons of 3.8 x 10(-3), 2.5 x 10(-3), and 2.2 x 10(-3) km(-2) sr(-1) yr(-1) above 10(19) eV, 2 x 10(19) eV, and 4 x 10(19) eV are derived, with corresponding limits on the fraction of photons being 2.0%, 5.1%, and 31% (all limits at 95% c.l.). These photon limits disfavor certain exotic models of sources of cosmic rays. The results also show that the approach adopted by the Auger Observatory to calibrate the shower energy is not strongly biased by a contamination from photons. (C) 2008 Elsevier B.V. All rights reserved.

Infrared emissions, visible up-conversion, thermoluminescence and defect centres in Er(3)Al(5)O(12) phosphor obtained by solution combustion reaction

The Er(3)Al(5)O(12) phosphor powders were prepared using the solution combustion method. Formation and homogeneity of the Er(3)Al(5)O(12) phosphor powders have been verified by X-ray diffraction and energy-dispersive X-ray analysis respectively. The frequency up-conversion from Er(3)Al(5)O(12) phosphor powder corresponding to the (2)H(9/2) -> (4)I(15/2), (2)H(11/2) -> (4)I(15/2), (4)S(3/2) -> (4)I(15/2), (4)F(9/2) -> (4)I(15/2) and the infrared emission (IR) due to the (4)I(13/2) -> (4)I(15/2) transitions lying at similar to 410, similar to 524, similar to 556, 645-680 nm and at similar to 1.53 mu m respectively upon excitation with a Ti-Sapphire pulsed/CW laser have been reported. The mechanism responsible for the frequency up-conversion and IR emission is discussed in detail. Defect centres induced by radiation were studied using the techniques of thermoluminescence and electron spin resonance. A single glow peak at 430A degrees C is observed and the thermoluminescence results show the presence of a defect center which decays at high temperature. Electron spin resonance studies indicate a center characterized by a g-factor equal to 2.0056 and it is observed that this center is not related to the thermoluminescence peak. A negligibly small concentration of cation and anion vacancies appears to be present in the phosphor in accordance with the earlier theoretical predictions.

Center of mass energy and system-size dependence of photon production at forward rapidity at RHIC

We present the multiplicity and pseudorapidity distributions of photons produced in Au + Au and Cu + Cu collisions at root(s)NN = 62.4 and 200 GeV. The photons are measured in the region -3.7 < eta < -2.3 using the photon Multiplicity detector in the STAR experiment at RHIC. The number of photons produced per average number of participating nucleon pairs increases with the beam energy and is independent of (lie collision centrality. For collisions with similar average numbers of participating nucleons the photon multiplicities are observed to be similar for An + Au and Cu + Cu collisions at a given beam energy. The ratios of the number of charged particles to photons in the measured pseudorapidity range are found to be 1.4 +/- 0.1 and 1.2 +/- 0.1 for root(s)NN = 62.4 and 200 GeV, respectively. The energy dependence of this ratio could reflect varying contributions from baryons to charged particles, while mesons are the dominant contributors to photon production in the given kinematic region. The photon pseudorapidity distributions normalized by average number of participating nucleon pairs, when plotted as a function of eta-Y(beam), are found to follow a longitudinal scaling independent of centrality and colliding ion species at both beam energies. (C) 2009 Elsevier B.V. All rights reserved.

NIR to visible up-conversion, infrared luminescence, thermoluminescence and defect centres in Y(2)O(3) : Er phosphor

Er(3+) doped Y(2)O(3) phosphor was prepared by the solution combustion method and characterized using powder x-ray diffraction and energy-dispersive analysis of x-ray mapping studies. Room temperature near infrared (NIR) to green up-conversion (UC) emissions in the region 520-580 nm {((2)H(11/2), (4)S(3/2)) -> (4)I(15/2)} and red UC emissions in the region 650-700 nm ((4)F(9/2) -> (4)I(15/2)) of Er(3+) ions have been observed upon direct excitation to the (4)I(11/2) level using similar to 972 nm laser radiation of nanosecond pulses. The possible mechanisms for the UC processes have been discussed on the basis of the energy level scheme, the pump power dependence as well as based on the temporal evolution. The excited state absorption is observed to be the dominant mechanism for the UC process. Y(2)O(3) : Er exhibits one thermally stimulated luminescence (TSL) peak around 367 degrees C. Electron spin resonance (ESR) studies were carried out to study the defect centres induced in the phosphor by gamma irradiation and also to identify the centres responsible for the TSL peak. Room temperature ESR spectrum of irradiated phosphor appears to be a superposition of at least three distinct centres. One of them (centre I) with principal g-values g(parallel to) = 2.0415 and g(perpendicular to) = 2.0056 is identified as O(2)(-) centre while centre II with an isotropic g-factor 2.0096 is assigned to an F(+)-centre (singly ionized oxygen vacancy). Centre III is also assigned to an F(+)-centre with a small g-factor anisotropy (g(parallel to) = 1.974 and g(perpendicular to) = 1.967). Additional defect centres are observed during thermal annealing experiments and one of them appearing around 330 degrees C grows with the annealing temperature. This centre (assigned to an F(+)-centre) seems to originate from an F-centre (oxygen vacancy with two electrons) and the F-centre appears to correlate with the observed TSL peak in Y2O3 : Er phosphor. The trap depth for this peak has been determined to be 0.97 eV from TSL data.

Performance of GEANT4 in dosimetry applications: Calculation of X-ray spectra and kerma-to-dose equivalent conversion coefficients

In order to validate the Geant4 toolkit for dosimetry applications, simulations were performed to calculate conversion coefficients h(10, alpha) from air kerma free-in-air to personal dose equivalent Hp(10, a). The simulations consisted of two parts: the production of X-rays with radiation qualities of narrow and wide spectra, and the interaction of radiation with ICRU tissue-equivalent and ISO water slab phantoms. The half-value layers of the X-ray spectra obtained by simulation were compared with experimental results. Mean energy, spectral resolution, half-value layers and conversion coefficients were compared with ISO reference values. The good agreement between results from simulation and reference data shows that the Geant4 is suitable for dosimetry applications which involve photons with energies in the range of ten to a few hundreds of keV. (C) 2008 Elsevier Ltd. All rights reserved.

Degenerate Two-Photon Absorption in All-Trans Retinal: Nonlinear Spectrum and Theoretical Calculations

In this work we investigate the degenerate two-photon absorption spectrum of all-trans retinal ill ethanol employing the Z-scan technique with femtosecond pulses, The two-photon absorption (2PA) spectrum presents a monotonous increase as the excitation wavelength approaches the one-photon absorption band and it peak at 790 nm. We attribute the 2PA hand to the mixing of states (1)B(u)+-like and vertical bar S(1)>, which are strongly allowed by one- and two-photon, respectively. We modeled the 2PA spectrum by using the sum-over-states approach and obtained spectroscopic parameters of the electronic transitions to vertical bar S >, vertical bar S(2)> (""(1)Bu(+)""), vertical bar S(3)>, and vertical bar S(4)> singlet-excited states. The results were compared with theoretical predictions of one- and two-photon transition calculations using the response Functions formalism within the density functional theory framework with the aid of the CAM-B3LYP functional.

Effect of Pre-Heating Resin Composite and Light-Curing Units on Monomer Conversion

The purpose of this study was to evaluate the effect of pre-heating resin composite photo-cured with light-curing units (LCU) by FT-IR. Twenty specimens were made in a metallic mold (4 mm diameter x 2 mm thick) from composite resin-Tetric Ceram (R) (Ivoclar/Vivadent) at room temperature (25 degrees C) and pre heated to 37, 54, and 60 degrees C. The specimens were cured with halogen curing light (QTH) and light emitted by diodes (LED) during 40 s. Then, the specimens were pulverized, pressed with KBr and analyzed with FT-IR. The data were submitted to statistical analysis of variance and Kruskal-Wallis test. Study data showed no statistically significant difference to the degree of conversion for the different light curing units (QTH and LED) (p > 0.05). With the increase of temperature there was significant increase in the degree of conversion (p < 0.05). In this study were not found evidence that the light curing unit and temperature influenced the degree of conversion.

Influence of different light sources and photo-activation methods on degree of conversion and polymerization shrinkage of a nanocomposite resin

The purpose of this study was to evaluate the influence of different light sources and photo-activation methods on degree of conversion (DC%) and polymerization shrinkage (PS) of a nanocomposite resin (Filtek (TM) Supreme XT, 3M/ESPE). Two light-curing units (LCUs), one halogen-lamp (QTH) and one light-emitting-diode (LED), and two different photo-activation methods (continuous and gradual) were investigated in this study. The specimens were divided in four groups: group 1-power density (PD) of 570 mW/cm(2) for 20 s (QTH); group 2-PD 0 at 570 mW/cm(2) for 10 s + 10 s at 570 mW/cm(2) (QTH); group 3-PD 860 mW/cm(2) for 20 s (LED), and group 4-PD 125 mW/cm(2) for 10 s + 10 s at 860 mW/cm(2) (LED). A testing machine EMIC with rectangular steel bases (6 x 1 x 2 mm) was used to record the polymerization shrinkage forces (MPa) for a period that started with the photo-activation and ended after two minutes of measurement. For each group, ten repetitions (n = 40) were performed. For DC% measurements, five specimens (n = 20) for each group were made in a metallic mold (2 mm thickness and 4 mm diameter, ISO 4049) and them pulverized, pressed with bromide potassium (KBr) and analyzed with FT-IR spectroscopy. The data of PS were analyzed by Analysis of Variance (ANOVA) with Welch`s correction and Tamhane`s test. The PS means (MPa) were: 0.60 (G1); 0.47 (G2); 0.52 (G3) and 0.45 (G4), showing significant differences between two photo-activation methods, regardless of the light source used. The continuous method provided the highest values for PS. The data of DC% were analyzed by Analysis of Variance (ANOVA) and shows significant differences for QTH LCUs, regardless of the photo-activation method used. The QTH provided the lowest values for DC%. The gradual method provides lower polymerization contraction, either with halogen lamp or LED. Degree of conversion (%) for continuous or gradual photo-activation method was influenced by the LCUs. Thus, the presented results suggest that gradual method photo-activation with LED LCU would suffice to ensure adequate degree of conversion and minimum polymerization shrinkage.

Two-Photon Polymerization for Fabricating Structures Containing the Biopolymer Chitosan

Two-photon polymerization is a powerful tool for fabricating three-dimensional micro/nano structures for applications ranging from nanophotonics to biology. To tailor such structure for specific purposes it is often important to dope them. In this paper we report on the fabrication of structures, with nanometric surface features (resolution of approximately 700 nm), using two-photon polymerization of an acrylic resin doped with the biocompatible polymer chitosan using a guest-host scheme. The fluorescence background in the Raman spectrum indicates the presence of chitosan throughout the structure. Mechanical characterization reveals that chitosan does not affect the mechanical properties of the host acrylic resin and, consequently, the structures exhibit excellent integrity. The approach presented in this work can be used in the fabrication of micro- and nanostructures containing biopolymers for biomedical applications.

Two-photon absorption of perylene derivatives: Interpreting the spectral structure

This work investigates the two-photon absorption spectrum of perylene tetracarboxylic derivatives using the white-light continuum Z-scan technique. Perylene derivatives present relatively high two-photon absorption cross-section, which makes them attractive for applications in photonics. Because of the spectral resolution of the white-light continuum Z-scan, we were able to observe a well defined structure in the two-photon absorption spectrum, composed by two distinct peaks. These peaks, as well as the resonant enhancement of the nonlinearity, were modeled using the sum-over-states approach considering a four-level energy diagram with two final two-photon states. The existence of such states was confirmed using the response function formalism within the DFT framework. (C) 2009 Elsevier B.V. All rights reserved.