Comments on the Stress-Energy Tensor Operator in Curved Spacetime

 The technique based on a *-algebra of Wick products of field operators in curved spacetime, in the local covariant version proposed by Hollands and Wald, is strightforwardly generalized in order to define the stress-energy tensor operator in curved globally hyperbolic spacetimes. In particular, the locality and covariance requirement is generalized to Wick products of differentiated quantum fields. Within the proposed formalism, there is room to accomplish all of the physical requirements provided that known problems concerning the conservation of the stress-energy tensor are assumed to be related to the interface between the quantum and classical formalism. The proposed stress-energy tensor operator turns out to be conserved and reduces to the classical form if field operators are replaced by classical fields satisfying the equation of motion. The definition is based on the existence of convenient counterterms given by certain local Wick products of differentiated fields. These terms are independent from the arbitrary length scale (and any quantum state) and they classically vanish on solutions of the Klein-Gordon equation. Considering the averaged stress-energy tensor with respect to Hadamard quantum states, the presented definition turns out to be equivalent to an improved point-splitting renormalization procedure which makes use of the nonambiguous part of the Hadamard parametrix only that is determined by the local geometry and the parameters which appear in the Klein-Gordon operator. In particular, no extra added-by-hand term g _αβQ and no arbitrary smooth part of the Hadamard parametrix (generated by some arbitrary smooth term ``ω ₀ ') are involved. The averaged stress-energy tensor obtained by the point-splitting procedure also coincides with that found by employing the local ζ-function approach whenever that technique can be implemented. Received: 24 September 2001/Accepted: 14 May 2002 Published online: 22 November 2002     

Matrix-element corrections to parton shower simulations for Higgs hadroproduction

We implement matrix-element corrections to HERWIG parton shower simulations for Standard Model Higgs boson production at hadron colliders. We study the Higgs transverse momentum distribution and compare different versions of HERWIG and resummed calculations. The HERWIG results exhibit a remarkable improvement as many more events are generated at large transverse momentum after the inclusion of matrix-element corrections.     

W ± + 4jet irreducible background events from QCD in top and Higgs searches at the Next Linear Collider

Irreducible background effects due to e ⁺ e ^? → W ^± + bbjj and e ⁺ e ^? → W ^± + jjjj events produced via QCD in top-antitop production and heavy Higgs searches in the bremsstrahlung channel are studied at the Next Linear Collider. Various distributions relevant to phenomenological analyses are given and compared to those expected from top and Higgs signals in the decay channel bb?W ⁺ W ^? → bb?W ^± jj. This analysis follows similar ones previously carried out for the case of the irreducible background proceeding via electroweak interactions     

Confirmation of anabolic hormone residues in bovine blood by micro-HPLC–ion spray–tandem mass spectrometry

Sensitive, specific analytical methods for the determination of an-abolics in biological matrices are essential to control the illegal use of these substances in food-producing animals. Programs of residue control are performed annually in Italy for the determination of endogenous sex hormones (17β-estradiol, progesterone, testoster-one) for which maximum physiological levels have been established. At present the methods used in the Italian programs to determine natural hormones in bovine blood are based on the sensitive radio-immunoassay (RIA), due to relatively low levels of these substances in plasma/serum. In this study, we report a new method based on tandem mass spectrometry with on-line micro-high performance liquid chromatography (micro-HPLC-MS-MS) using an atmos-pheric pressure ionization (API) source and an ion spray (IS) interface for the specific direct detection of natural (progesterone and testosterone), and synthetic (17β19-nortestosterone and me-droxyprogesterone) hormone residues in bovine serum. 17-Methyl-testosterone was used as the internal standard. Analytes were extracted with acetate buffer, purified on C18 Solid Phase Extrac-tion (SPE) cartridge and separated on a reverse phase C18 micro-HPLC column (300 mm × 1 mm, 5 μm), using acetonitrile-water, 80:20 (v/v) containing 2mM ammonium acetate as the mobile phase, at a flow rate of 10 μl/min. When anabolic hormones were ionized in the IS interface operating in the positive ion mode, only the protonated molecules, [M+H]⁺, were generated, without evidence of any fragmentation. These served as precursor ions for collision induced dissociation (CID) and Diagnostic daughter ions for each analyte were identified in order to carry out analysis by micro-HPLC-MS-MS in the selected reaction monitoring (SRM) mode. For the analytes in question, the response of the mass detector was related linearly to the quantity of each analyte injected between 10 and 300 pg, in the SRM mode. The limit of detection, based on a 3:1 signal-to-noise ratio, is 6–7 pg for the hormones. Recoveries were higher than 83% for 17β-19-nortestosterone, testosterone, and 17-methyltestosterone, and 72% for the medroxyprogesterone, and progesterone. The micro-HPLC-MS-MS method for the determi-nation of anabolic hormones in bovine blood requires no sample derivatization, minimal sample preparation, and provides a sensi-tive, selective, rapid alternative to the existing purification, separa-tion, and detection techniques. At present this very sensitive method is being successfully applied to measure bovine serum concentra-tions of natural hormones, such as testosterone and progesterone, in order to then confirm any illegal administration of these sub-stances.     

Time Fractional Diffusion: A Discrete Random Walk Approach

The time fractional diffusion equation is obtained from the standarddiffusion equation by replacing the first-order time derivative with afractional derivative of order (0, 1). From a physicalview-point this generalized diffusion equation is obtained from afractional Fick law which describes transport processes with longmemory. The fundamental solution for the Cauchy problem is interpretedas a probability density of a self-similar non-Markovian stochasticprocess related to a phenomenon of slow anomalous diffusion. By adoptinga suitable finite-difference scheme of solution, we generate discretemodels of random walk suitable for simulating random variables whosespatial probability density evolves in time according to this fractionaldiffusion equation.     

Experimental analysis of thermal fields in horizontally eccentric cylindrical annuli

This paper presents new experimental results on thermal field and heat transfer in a two-dimensional annulus between horizontally eccentric cylinders. The study is conducted by means of optical techniques, for 1.07×10⁴≤Ra _L≤8.27×10⁴ and a wide eccentricity range. The horizontal eccentricity of the inner cylinder substantially alters the thermal field and the geometry of the plume, but, in analogy to the behaviour for vertical eccentricity, the average Nu is slightly affected in the investigated range of eccentricity. The concentric geometry is also considered mainly to validate the experimental technique and evaluate the accuracy of the adopted methodology by comparison with available results. Both shearing interferometer and reference beam interferometer are obtained by means of Wollaston prisms with appropriate splitting angles, so that the temperature and local Nu distributions may be evaluated quantitatively from the original pictures via digital image processing.     

Singlet Heterofission in Tetracene–Pentacene Thin-Film Blends

Heterofission is a photophysical process of fundamental and applied interest whereby an excited singlet state is converted into two triplets on chemically distinct chromophores. The potential of this process lies in the tuning of both the optical band gap and the splitting between singlet and triplet energies. Herein, we report the time-domain observation of heterofission in mixed thin films of the prototypical singlet fission chromophores pentacene and tetracene using excitation wavelengths above and below the tetracene band gap. We found a time constant of 26 ps for endothermic heterofission of a singlet exciton on pentacene in blends with low pentacene fractions, which was outcompeted by pentacene homofission for increasing pentacene concentrations. Direct excitation of tetracene lead to fast energy transfer to pentacene and subsequent singlet fission, which prevented homo- or heterofission of a singlet exciton on tetracene.     

Relationship between the Auger parameter and the ground state valence charge at the core-ionized site

A simple semi-empirical model that correlates the Auger parameter to the ground state valence charge of the core-ionized atom with closed valence shell configuration, and which was previously applied to Cu(I) (3d¹⁰) compounds, is extended to Ba (II) (5d¹⁰), Pb (II) (5d¹⁰4s²), and Zn (II) (3d¹⁰) compounds (halides and chalcogenides). Until now, the Auger parameter was employed to separate initial and final state effects that influence the core electron binding energy. In agreement with our model, a linear relationship is found between the Auger parameter shift and the ground state Bader valence charge obtained by density functional theory (DFT) calculations.     

High‐Performing Red‐Light‐Emitting Pyrotechnic Illuminants through the Use of Perchlorate‐Free Materials

The development of perchlorate‐free M662 40 mm illuminating pyrotechnic compositions is described. On the bases of cost, performance, and sensitivity, potassium periodate was determined to be most effective potassium perchlorate replacement in the compositions tested. The optimal periodate‐based composition exceeded the performance of the perchlorate‐containing control, exhibited low sensitivity values to impact, friction, and electrostatic discharge, and had high thermal onset temperatures.