Prompt photon processes in photoproduction at HERA

We present results for the photoproduction of inclusive prompt photons and for prompt photons accompanied by jets, measured with the ZEUS detector at HERA. Cross sections as a function of pseudorapidity and transverse energy are presented for 5 5 GeV in the centre of mass energy range 120-270 GeV. Comparisons are made with predictions from leading logarithm parton shower Monte Carlos and next-to-leading order QCD calculations using currently available models of the photon structure. NLO QCD calculations describe the shape and magnitude of the measurements reasonably well.Comment: Talk given at Photon99 Conference, Freiburg, German

Jet and hadron production in photon-photon collisions

Di-jet and inclusive charged hadron production cross-sections measured in photon-photon collisions by OPAL are compared to NLO pQCD calculations. Jet shapes measured in photon-photon scattering by OPAL, in deep-inelastic ep scattering by H1 and in photon-proton scattering by ZEUS are shown to be consistent in similar kinematic ranges. New results from TOPAZ on prompt photon production in photon-photon interactions are presented.Comment: 4 pages, submitted to Proceedings of DIS99, DESY-Zeuthen, Germany, April 199

Direct vs. resolved photon: an exercise in factorization

Direct and resolved photon interactions are shown to be intimately related through the factorization mechanism. It is argued that in theoretically consistent analysis of jet production in $\gamma$p and ep collisions the LO resolved $\gamma$ contribution must be considered together with the NLO direct $\gamma$ component. Recent data from HERA therefore do not provide a direct evidence for the former component, but should rather be interpreted as a manifestation of the $O(\alpha\alpha_s^2)$ term in $\gamma$p and, via the Weizs\"acker-Williams approximation, in ep interactions.Comment: PRA-HEP/93-07, Latex, 10 pages and 5 Postscript figures in 2 PS files appended at the end of Tex fil

Multiparton Interactions in Photoproduction at HERA

The high energy photoproduction of jets is being observed at the ep collider, HERA. It may be that the HERA centre-of-mass energy is sufficiently large that the production of more than one pair of jets per ep collision becomes possible, owing to the large number density of the probed gluons. We construct a Monte Carlo model of such multiparton interactions and study their effects on a wide range of physical observables. The conclusion is that multiple interactions could have very significant effects upon the photoproduction final state and that this would for example make extractions of the gluon density in the photon rather difficult. Total rates for the production of many (i.e. > 2) jets could provide direct evidence for the presence of multiple interactions, although parton showering and hadronization significantly affect low transverse energy jets.Comment: 21 pages, 8 figures include

An enquiry into the use of international trade measures as environmental policy instruments.

The links and overlapping areas of concern between international trade policy and environment policy are many and varied, and a number of often competing interests at stake, each of which must be accommodated. Thus far, the debate on this issue has been characterised by a distinct lack of agreement on how to proceed, due to a lack of a common analytical framework; each of the main communities in the debate have sought to impose their agendas, priorities and analyses. In light of this, the first purpose of this thesis is to determine whether or not there exists a legitimate role for international trade policy instruments in the conduct of environment policy. This enquiry takes to be indisputable that the protection and maintenance of a healthy and stable environment must be accorded a higher priority than anything else, including the international trading system, to the extent that they are otherwise irreconcilable. Therefore, Chapter 2 examines the basis on which environmental standards should be established, and the extent to which they should be harmonised. To determine whether the use of trade policy instruments to achieve the necessary environmental standards should be considered legitimate, Chapters 3, 4 and 5 present and discuss three tests. It is argued that the use of trade-related environmental policy instruments (TREPI) should be considered to be legitimate only if it meets all three of these tests. This three-part legitimacy test describes a decision-making process, and is a useful way of organising and analysing policy problems concerning the relationship between international trade policy and environment policy. Chapter 6 considers two actual disputes and a potential case to show how this legitimacy test might work. This latter case involves the analysis of significant new evidence about the commercial impact of environmental and animal welfare regulations on UK agriculture. By adopting the simple approach proposed in this thesis we seek to avoid the fundamental conflict caused by the epistemological and analytical assumptions and biases of each of the three communities: the international trade community, the environmental community, and the development community. Instead a more objective means of considering the complex of issues is proposed. The three tests are independent of any of the three communities and, in their simplicity, could be applied to a wide range of problems. Applied to the trade and environment issue, they demonstrate their objectivity by the conclusions they lead to: on some points they lend support to the interests of each of the three communities, while on others they do not. To the extent that an appropriate role for trade policy instruments in the conduct of environment policy is found, the second purpose of this enquiry is to consider whether or not, and in what ways, the current international trading system frustrates or facilitates such a use. Chapter 7 discusses, in three parts, the environmental effects of international trade liberalisation. In Chapter 8, the scope for possible amendments to the GATT system is considered by reference to the environmental provisions of the NAFTA. Finally, the use of domestic trade remedy laws as environment policy instruments is considered in Chapter 9

Determining the Gluon Distributions in the Proton and Photon from Two-Jet Production at HERA

Two-jet production from the direct photon contribution at HERA is a sensitive measure of the small-$x$ gluon in the proton. We propose measurements of ratios of the jet cross-sections which will clearly distinguish between gluons with or without singular behaviour at small $x$. Furthermore, we show that analogous ratio measurements for the resolved photon contribution provide a sensitive way of determining the gluon distribution in the photon.Comment: Rutherford Appleton Laboratory report RAL-93-071 7 pages 3 figs Fig2 and Fig3 included as psfile

Pinning down the Glue in the Proton

The latest measurements of $F_2$ at HERA allow for a {\it combination} of gluon and sea quark distributions at small $x$ that is significantly different from those of existing parton sets. We perform a new global fit to deep-inelastic and related data. We find a gluon distribution which is larger for x \lapproxeq 0.01, and smaller for $x \sim 0.1$, and a flatter input sea quark distribution than those obtained in our most recent global analysis. The new fit also gives $\alpha_s(M_Z^2) = 0.114$. We study other experimental information available for the gluon including, in particular, the constraints coming from fixed-target and collider prompt $\gamma$ production data.Comment: 8 pages, LATEX, 6 figs available as .uu fil

Significant Phonon Drag Enables High Power Factor in the AlGaN/GaN Two-Dimensional Electron Gas

In typical thermoelectric energy harvesters and sensors, the Seebeck effect is caused by diffusion of electrons or holes in a temperature gradient. However, the Seebeck effect can also have a phonon drag component, due to momentum exchange between charge carriers and lattice phonons, which is more difficult to quantify. Here, we present the first study of phonon drag in the AlGaN/GaN two-dimensional electron gas (2DEG). We find that phonon drag does not contribute significantly to the thermoelectric behavior of devices with ~100 nm GaN thickness, which suppress the phonon mean free path. However, when the thickness is increased to ~1.2 $\mu$m, up to 32% (88%) of the Seebeck coefficient at 300 K (50 K) can be attributed to the drag component. In turn, the phonon drag enables state-of-the-art thermoelectric power factor in the thicker GaN film, up to ~40 mW m$^{-1}$ K$^{-2}$ at 50 K. By measuring the thermal conductivity of these AlGaN/GaN films, we show that the magnitude of the phonon drag can increase even when the thermal conductivity decreases. Decoupling of thermal conductivity and Seebeck coefficient could enable important advancements in thermoelectric power conversion with devices based on 2DEGs

Hepatic transcriptome analysis of inter-family variability in flesh n-3 long-chain polyunsaturated fatty acid content in Atlantic salmon

Background: Genetic selection of Atlantic salmon families better adapted to alternative feed formulations containing high levels of vegetable ingredients has been suggested to ensure sustainable growth of aquaculture. The present study aimed to identify molecular pathways that could underlie phenotypic differences in flesh n-3 long-chain polyunsaturated fatty acid (LC-PUFA) levels when fish are fed vegetable oil diets. Liver transcriptome was analyzed and compared in four families presenting higher or lower n-3 LC-PUFA contents at two contrasting flesh total lipid levels. Results: The main effect of n-3 LC-PUFA contents was in the expression of immune response genes (38% of all significantly affected genes), broadly implicated in the modulation of inflammatory processes and innate immune response. Although genetic evaluations of traits used in the breeding program revealed that the chosen families were not balanced for viral disease resistance, this did not fully explain the preponderance of immune response genes in the transcriptomic analysis. Employing stringent statistical analysis no lipid metabolism genes were detected as being significantly altered in liver when comparing families with high and low n-3 LC-PUFA flesh contents. However, relaxing the statistical analysis enabled identification of potentially relevant effects, further studied by RT-qPCR, in cholesterol biosynthesis, lipoprotein metabolism and lipid transport, as well as eicosanoid metabolism particularly affecting the lipoxygenase pathway.Total lipid level in flesh also showed an important effect on immune response and 8% of significantly affected genes related to lipid metabolism, including a fatty acyl elongase (elovl2), an acyl carrier protein and stearoyl-CoA desaturase. Conclusions: Inter-family differences in n-3 LC-PUFA content could not be related to effects on lipid metabolism, including transcriptional modulation of the LC-PUFA biosynthesis pathway. An association was found between flesh adiposity and n-3 LC-PUFA in regulation of cholesterol biosynthesis, which was most likely explained by variation in tissue n-3 LC-PUFA levels regulating transcription of cholesterol metabolism genes through srebp2. A preponderance of immune response genes significantly affected by n-3 LC-PUFA contents could be potentially associated with disease resistance, possibly involving anti-inflammatory actions of tissue n-3 LC-PUFA through eicosanoid metabolism. This association may have been fortuitous, but it is important to clarify if this trait is included in future salmon breeding programmes

New Parton Distribution Functions for the Photon

We present new improved parton distributions for the photon. We fit {\bf all} available data on the photon structure function, $F^{\gamma}_{2}(x,Q^2)$, with $Q^2\ge 3$ GeV$^2$, in order to determine the quark distributions. We also pay particular attention to the gluon distribution in the photon, $g^{\gamma}(x,Q^2)$, which has been poorly constrained in earlier analyses which only include structure function data. We use large $p_T$ jet production in $\gamma \gamma$ collisions from TRISTAN to constrain $g^\gamma$. We also see what information can be gleaned from $\gamma p$ collisions at HERA on $g^{\gamma}$ and on the quark distributions at large $x$, where there are no structure function data. We review future prospects of elucidating the parton distributions of the photon.Comment: 33 pages, 8 figures, uses eps