A Phenomenological Study of the Contact Interaction in FCC-based Electron–Proton Collider

<div class="htmlview paragraph">The combustion process in a diesel engine was simulated using KIVA-II, a multi-dimensional computer code. The original combustion model in KIVA-II is based on chemical kinetics, and thus fails to capture the effects of turbulence on combustion. A mixing-controlled, eddy break-up combustion model was implemented into the code. Realistic diesel fuel data were also compiled. Subsequently, the sensitivity of the code to a number of parameters related to fuel injection, mixing, and combustion was studied. Spray injection parameters were found to have a strong influence on the model's predictions. Higher injection velocity and shorter injection duration result in a higher combustion rate and peak pressure and temperature. The droplet size specified at injection significantly affects the rate of spray penetration and evaporation, and thus the combustion rate. Contrary to expectation, the level of turbulence at the beginning of the calculation did not affect fuel burning rate.</div> <div class="htmlview paragraph">THE CLEAN AND EFFICIENT conversion of the chemical energy of the fuel to useful work in internal combustion (IC) engines is influenced by the in-cylinder processes and the intake and exhaust flows. Design engineers need to understand these phenomena in detail using available experimental and analytical tools. A new generation of multi-dimensional reacting flow computer models has evolved in the last fifteen years (e.g. the KIVA-II [<span class="xref">1</span>, <span class="xref">2</span>, <span class="xref">3</span> and <span class="xref">4</span>], RPM [<span class="xref">5</span>] and PHOENICS [<span class="xref">6</span>] codes). These simulations promise to be an invaluable companion to laboratory experiments.</div> <div class="htmlview paragraph">A widely used multi-dimensional program is KIVA-II [<span class="xref">1</span>, <span class="xref">2</span>, <span class="xref">3</span> and <span class="xref">4</span>], developed at Los Alamos National Laboratory. KIVA-II is a two or three-dimensional code that describes the fluid, chemical and spray processes that occur in IC engines. The model solves for the conservation of momentum, energy, and mass for an arbitrary number of species in the gaseous phase. The spray dynamics are solved using a discrete particle technique. The effects of evaporation, droplet breakup, collisions (coalescence or deflection) and viscous and turbulent interactions with the ambient gas are accounted for. The effects of turbulence are represented by a k-e model modified to include the effects of spray interaction. Chemical reactions can be specified either as equilibrium (for fast reactions) or kinetic reactions. The kinetic reaction rates are expressed in Arrhenius form.</div> <div class="htmlview paragraph">KIVA-II models the physical phenomena which occur inside the combustion chamber from first principles. Despite the sophistication of the submodels, certain assumptions must inevitably be made due to lack of knowledge about the details of the mechanisms which characterize the various processes. These simplifications often result in errors in the predictions. Invariably, some empirical calibration constants are introduced due to the simplifications. Furthermore, some of the physically meaningful parameters need to be adjusted to compensate for modeling errors. For example, the chemical reaction constants must be adjusted to account for intermediate reaction steps not included in the mechanism. Finally, some of the physical variables that must be provided as inputs to the program, as for example the size of the droplets injected, cannot be measured directly [<span class="xref">7</span>]. Therefore, the “proper” values of the modeling constants and physical parameters must be established for the code to produce realistic predictions. To achieve this goal, experimental validation and computational sensitivity studies must be performed to assess the importance of these variables on code predictions.</div> <div class="htmlview paragraph">Despite the widespread usage of KIVA-II and its predecessors CONCHAS, CONCHAS-SPRAY and KIVA, only a limited number of validation studies appear in the literature. These studies [<span class="xref">8</span>, <span class="xref">9</span>, <span class="xref">10</span> and <span class="xref">11</span>] have compared some of the model's predictions on combustion, spray characteristics, heat transfer, and emissions with experimental data; they also tested the code's sensitivity to a small number of input parameters. The objective of the present work is to conduct more comprehensive sensitivity studies to examine the effect of various parameters related to the spray, mixing, and combustion processes on the prediction of combustion in a direct injection diesel engine. Before we proceed with the presentation of our results, previous studies are summarized and the modifications we implemented in the KIVA-II code are presented.</div>

<div class="htmlview paragraph">A model developed to analyze steady, two-dimensional, two-phase flow of Freon-12 with simultaneous heat and mass transfer in a plate type A/C evaporator is described. The results obtained for specified flow rates and qualities at entry indicate that, for given heat input at the walls, dryout conditions prevail in certain regions of the evaporator with correspondingly higher wall temperatures there. This happens particularly when the quality is high and the flow rate is low at evaporator entry. Though the model predictions are plausible, an improved understanding of the evaporation process of Freon-12 will assure greater realism in the predictions.</div> <div class="htmlview paragraph">THIS PAPER IS CONCERNED WITH numerical modeling of steady, two-phase flow with heat and mass exchange in the plate type A/C evaporator. In the geometry considered (<span class="xref">Figure 1</span>), Freon-12 of specified quality i.e. a two-phase mixture of known mass fraction of vapor (or gas), flows through the unit while receiving heat from the ambient air blowing past the outer walls. This causes further evaporation of the liquid with consequent rise in the quality as the fluid approaches the outlet. Such an increase in quality, especially when it is high initially, may affect the flow and the boiling regimes, and the heat transfer processes [<span class="xref">1</span>]<span class="xref"><sup>1</sup></span> as shown in <span class="xref">Figure 2</span>. The transition from an annular flow with entrainment pattern to a drop flow pattern reduces the inner wall heat transfer coefficient sharply to bring about a significant rise in wall temperature.</div> <div class="htmlview paragraph">Such a condition called ‘dryout’ arises when the liquid exists like a mist away from the wall in a liquid-vapor mixture. While more information is available on the onset of dryout phenomenon in water-steam flow fields, not much is known for other fluids. Robertson [<span class="xref">2</span>] suggests that dryout at modest heat fluxes occurs at qualities above 95% for fluids other than water-steam mixture.</div> <div class="htmlview paragraph">In the present model it is assumed that the evaporation process is dominated by</div> <div class="htmlview paragraph"> <ol class="list nostyle"> <li class="list-item"> <span class="li-label">(a)</span> <div class="htmlview paragraph">forced convective heat transfer through liquid film when the quality x ≤0.95; and</div> </li> <li class="list-item"> <span class="li-label">(b)</span> <div class="htmlview paragraph">dryout heat transfer in the liquid deficient region at x > 0.95.</div> </li> </ol> </div> <div class="htmlview paragraph">The respective heat transfer correlations [<span class="xref">3</span>, <span class="xref">4</span>] adopted here for the above two situations are <span class="xref">(A1)</span> and <span class="xref">(A2)</span> given in <span class="xref">Appendix A</span>. All fluid properties in those correlations were obtained from [<span class="xref">5</span>]. To account for the frictional losses, as recommended in [<span class="xref">6</span>] and [<span class="xref">7</span>], the pressure drop correlation <span class="xref">(A3)</span> was used for two-phase cross-flow past the dimples in the evaporator.</div> <div class="htmlview paragraph">In what follows, the objectives of the paper are indicated first, and they are followed by the flow specifications and boundary conditions used by the model. The mathematical formulation and computational details are then given before presenting the results and the discussions. Thereafter, the conclusions are drawn and the recommendations are made. These are followed by the references and the appendix.</div>

Recently proposed Future Circular Collider based muon-proton colliders will allow investigating lepton-hadron interactions at the highest center-of-mass energy. In this study, we investigate the potential of these colliders for a four-fermion contact interactions search. Regarding the constructive and destructive interferences of contact interactions, we estimated discovery, observation, and exclusion limits on the compositeness scale for the left-left, right-right, left-right, and right-left helicity structures. Thus, it is shown that the FCC-based $\mu p$ colliders have great potential for investigating four-fermion contact interactions.

In recent years, with the enlightenment of some issues encountered in muon colliders, muon colliders have become more feasible for the high-energy physics community. For this reason, we studied the single production of an excited muon in muon colliders via contact interactions. In addition, we assumed that the excited muon decayed into a photon and muon through gauge interactions. Then, signal and background analyses were performed in muon–antimuon collider options with center-of-mass energies of 6, 14, and 100 TeV. The attainable mass and compositeness scale limits were calculated for the excited muon in these collider options. Based on the calculations, it was concluded that muon–antimuon colliders would be a perfect collider option for excited muon investigations.

Hadronic jets in electron–proton collisions at HERA have been used for some considerable time as a tool for tests of the theory of strong interactions, quantum chromodynamics. Using jet final states, basic concepts like the factorisation ansatz for cross-section calculations, the perturbative approach to the cross section and the universality of the proton parton distribution functions can be examined. More concretely, jet measurements provide ready access to the strong coupling of QCD, α s , and to the parton distributions. In this report, an overview of jet results from the HERA experiments H1 and ZEUS and their interpretation is given together with a description of the theoretical foundations of jet physics in electron–proton collisions and of the experimental environment at HERA. Special emphasis is put on extractions of α s values and on the influence of jet data on fits of the proton parton distribution functions. Where useful, the HERA results are also discussed in the light of results from other colliders like LEP, the Tevatron or the LHC. The central message from these studies is that QCD does not only describe most of the measurements very well, but that QCD at HERA has achieved the status of a precision theory. On the other hand it is shown that further understanding of problematic issues relies critically on theoretical progress in the form of improved models or of increased precision in analytical calculations.

Electron proton (ep) colliders could provide particle collisions at TeV energies with large data rates while maintaining the clean and pile up-free environment of lepton colliders, which makes them very attractive for heavy neutrino searches. Heavy (mainly sterile) neutrinos with masses around the electroweak scale are proposed in low scale seesaw models for neutrino mass generation. In this paper, we analyse two of the most promising signatures of heavy neutrinos at ep colliders, the lepton-flavour violating (LFV) lepton-trijet signature and the displaced vertex signature. In the considered benchmark model, we find that for heavy neutrino masses around a few hundred GeV, the LFV lepton-trijet signature at ep colliders yields the best sensitivity of all currently discussed heavy neutrino signatures (analysed at the reconstructed level) up to now.

<span class="fontstyle0">Poverty is one of the most crucial problems in Indonesia which is the fifth city in South-East Asia, have a poverty line around 11.2% in 2014 (BPS 2016). Moreover, poverty in Indonesia has decreased slowly from 2000 (19.1%) until 2016 (10.9%) (Smeru, 2015). It means poverty in Indonesia should be accelerated the decline. One of the things that can reduce poverty is education (Gounder and Xing 2012). Education has a relationship with household consumption per capita. That means, the higher the education of household head, the higher the consumption per capita that household get. The aim of this study is to analyze the impact of education on poverty as measured by household's consumption in West Indonesia in 2014. This study uses Two-Stage Least Square (2SLS) methods with cross-section data and obtained from IFLS (Indonesia Family Life Survey). The result shows that there is a relationship between education and other independent variables on poverty. The independent variables that significantly affect poverty are age, age squared, gender, and marital status. The implication of this study is education can increase the number of consumption per capita so that the living standard will increase and poverty will decrease.<br /><br /></span><span class="fontstyle2">JEL Classification: </span><span class="fontstyle0">I20, I21, I25<br /><br /></span><span class="fontstyle2">Keywords</span><span class="fontstyle0">: consumption per capita, cross section, education, Two Stage Least Square, poverty.</span>

The production at the LHC of exotic excited leptons of charge $Q = +2e$ is considered. Such states are predicted in composite models with extended isospin multiplets ($I_{W}=1$ and $I_{W}=3/2$). The coupling among these doubly charged leptons and Standard Model fermions may occurs either via gauge or contact interactions. In the former case the decay channels are more constrained. We study the production cross section at the LHC of $L^{++}$ ($pp \rightarrow L^{++} \, \ell^{-}$) and focus on the leptonic signature deriving from the subsequent decays $L^{++} \rightarrow W^{+} \ell^{+} \rightarrow \ell^{+} \ell^{+} \, \nu_l $. The invariant mass distribution of the like-sign dilepton exhibits a sharp end-point corresponding to excited doubly charged lepton mass $m^{*}$. A preliminary study for the production of doubly charged leptons at the future linear colliders, by considering the process $e^{-} e^{-} \rightarrow L_{e}^{--} \, \nu_{e}$, is carried out. Both the contact and gauge interaction mechanisms are investigated and compared.

<p>Volcanic activity at Europa’s seafloor is one of the key question regarding the habitability of its subsurface ocean. The suitable conditions for hydrothermalism on Europa’s seafloor are conditioned by the heat released from the underlying silicate mantle, either supplied by both radiogenic and tidal heating.<span class="Apple-converted-space"> </span></p> <p>The orbital resonance between Io, Europa, and Ganymede forces their orbit and maintain non-zero eccentricities. As a consequence, Io, and to a lesser extent, Europa, undergo large tidal forcing during their journey around Jupiter. Because of its greater distance from Jupiter, a smaller mantle size<span class="Apple-converted-space">  </span>and the decoupling effect due to the presence of the subsurface water ocean [1], mechanical energy produced by tides in Europa’s mantle is much less than that produced within Io [1, 2]. However, as demonstrated by the 3D approach of Běhounková et al. [3], the combination of tidal and radiogenic heating could maintain a partially molten state within Europa’s mantle for several tens to<span class="Apple-converted-space">  </span>hundred millions of years, particularly during periods of increased eccentricity [4]. Due to inefficient melt transport through the thick lithosphere of Europa [5], melt produced during periods of enhanced eccentricity may accumulate and in turn affect the tidal heating, as it is the case for Io [e.g. 6], implying a possible runaway melt process in the silicate interior of Europa.<span class="Apple-converted-space"> </span></p> <p>In this context, the goal of this study is to evaluate the effect of melt accumulation on Europa’s mantle tidal heat production, based on the predictions from the 3D simulations of Běhounková et al. [3]. For that purpose, we follow the approach developed to model the solid tides in Io’s partially molten interior [6], taking into account the effect of melt on the viscoelastic properties of the mantle. We adapt it to the context of Europa, corresponding to a deeper asthenosphere than on Io. We use the 3D model of Běhounková et al. [3] to assess in a manner consistent with mantle dynamics the depths where melting should occur as well as the production rates, which should be seen here as minimum values, and estimate the effect of melt accumulation in Europa’s mantle on local dissipation rate and re-assess the consequences in terms of global melt production rate.</p> <p>Based on the production rates predicted by Běhounková et al. [3], a 100 km thick layer with a melt fraction of 20% would form in 140 million years. In order to evaluate the impact of such an accumulation zone of melt, we considered different thicknesses of partially molten layers (25, 50, 100, 200 km), plated at the base of the lithosphere, and investigate melt fraction from 0 to 30 %, corresponding to different degrees of accumulation of melt products. We show that, whatever the partially molten layer thickness, melt accumulation increase tidal heat production and even exceed radiogenic heating. For equivalent volume of accumulated melt, the thinner the layer, the more pronounced this effect is (Figure 1).<span class="Apple-converted-space"> </span></p> <p>Our results show that the accumulation of melt, over timescales consistent with the 3D model prediction of Běhounková et al. [3], may significantly affect the tidal dissipation amplitude and its pattern. The potential presence fo such melt accumulations may be tested by future measurements by Europa Clipper and JUICE from the combined analysis of gravimetric, altimetric and magnetic data, which might reveal long-wavelength anomalies which could be confronted to our model prediction. Future work is, however, needed to better understand the link between melt generation and extraction in the context of Europa's mantle.</p> <p><img src="" alt="" width="665" height="500" /></p> <p>Figure 1 : Tidal power produced in Europa’s mantle with a partially molten layer of 25 (blue), 50 (cyan), 100 (green) and 200 (orange) km thickness. The expected range for radiogenic heating is represented for comparison by the red dashed lines and the black dashed line corresponds to the tidal power for no melt. The melt fraction value required in order to exceed the radiogenic power (black line) for each partially molten layer thickness is indicated, with the corresponding pattern of tidal heat flux integrated over the mantle.</p> <p>[1] Tobie, G. et al., Icarus (2005).<br />[2] Sotin, C. et al. Europa (2009).<br />[3] Běhounková et al., GRL (2021).<br />[4] Hussmann and Spohn , Icarus (2004).<br />[5] Bland and Elder, GRL (2022).<br />[6] Kervazo et al., A&A (2021).</p> <p>Acknowledgements: This research received funding from the French “Agence Nationale de Recherche” A.N.R. (OASIS project, ANR-16-CE31-0023-01,( G.T., G.C., M.K., C.D.), from CNES (JUICE and Europa Clipper missions, G.T., G.C., M.K., C.D.) and from Czech Science Foundation through project No. 22-20388S (M.B.).</p>

<div class="htmlview paragraph">Combustion and flow were calculated in a spark-ignited two-stroke crankcase-scavenged engine using a laminar and turbulent characteristic-time combustion submodel in the three-dimensional KIVA code. Both premixed-charge and fuel-injected cases were examined. A multi-cylinder engine simulation program was used to specify initial and boundary conditions for the computation of the scavenging process.</div> <div class="htmlview paragraph">A sensitivity study was conducted using the premixed-charge engine data. The influence of different port boundary conditions on the scavenging process was examined. At high delivery ratios, the results were insensitive to variations in the scavenging flow or residual fraction details. In this case, good agreement was obtained with the experimental data using an existing combustion submodel, previously validated in a four-stroke engine study. However, at low delivery ratios, both flow-field and combustion-model details were important, and the agreement with experiment was poor using the existing combustion submodel, which does not account for the effect of residual gas concentration.</div> <div class="htmlview paragraph">To improve the agreement between modeling and experimental results, a modified combustion submodel was introduced that includes the effect of residual gas concentration on the laminar characteristic time. With the new submodel, agreement with the experiment has been improved considerably for all cases considered in this study. These levels of agreement between experiment and computations are similar to those found in previous applications of the laminar and turbulent characteristic-time combustion submodel to four-stroke engine combustion. Further improvement of the combustion submodel was made difficult by the observed coupling between the in-cylinder flow-field and the combustion-model details at low delivery ratios.</div> <div class="htmlview paragraph">Three-dimensional computer models have been applied to predict combustion in internal combustion engines. For example, computations of spark-ignited premixed-charge combustion in research and production-type four-stroke engines have been presented by Kuo and Reitz [<span class="xref">1</span>]<span class="xref">*</span>. Spark-ignited, premixed-charge and direct-injected rotary engine computations have been presented by Abraham and Bracco [<span class="xref">2</span>,<span class="xref">3</span>]. The latter computations suggested design changes that led to approximately 6 percent improvement in efficiency in a direct-injection stratified-charge rotary engine.</div> <div class="htmlview paragraph">The above studies were conducted using a characteristic-time combustion submodel originally proposed by Abraham et al. [<span class="xref">4</span>]. In this model, chemical species approach their thermodynamic equilibrium with a rate that is a combination of the turbulent-mixing time and the laminar chemical-kinetics time. The combination is formed in such a way that the longer of the two times has more influence on the conversion rate. An additional element of the model is that the laminar-flame kinetics strongly influence the early flame development following ignition.</div> <div class="htmlview paragraph">Comparisons with experimental engine pressure measurements indicate that the model predictions agree reasonably well with measurements under normal engine operating conditions. The causes of discrepancies were discussed in detail by Kuo and Reitz [<span class="xref">1</span>,<span class="xref">5</span>] who observed that the level of agreement between the predictions and the experiments is consistent with the levels of uncertainty in the input parameters to the computations (e.g., there is some uncertainty about the gas temperature, turbulence intensity and length scale existing in the combustion chamber at the start of combustion, and also in the wall-heat-transfer and turbulence model constants).</div> <div class="htmlview paragraph">There is current interest in engines that operate under dilute conditions either with air, internal residuals, or recirculated exhaust gas. Najt and Kuo [<span class="xref">6</span>] have successfully applied the laminar and turbulent characteristic-time combustion submodel to engines diluted with air. A major goal of the present study was to investigate the performance of the combustion submodel for engines diluted with residual gas. This condition is of interest in variable-valve-actuation engines with large valve overlap, and in premixed-charge and direct-injected two-stroke engines at low delivery ratios, which have high residual gas concentrations in the combustion chamber. For this study, the model was applied to crankcase-scavenged two-stroke engine combustion for which experimental data is available.</div> <div class="htmlview paragraph">This paper is organized as follows. First, the experiments used to assess the performance of the combustion submodel are described. Then, details are given of the initial and boundary conditions, and the combustion and spray submodels. The results are divided into two parts. The first part explores the sensitivity of the results to the in-cylinder flow field and combustion model details in the premixed-charge engine. The second part presents a parametric study of the model performance in the premixed-charge and direct-injected engines.</div>

<div class="htmlview paragraph">This paper presents results of a study conducted to apply and evaluate the In-Vehicle Information System (IVIS) DEMAnD Model developed recently by the Virginia Polytechnic University's Center for Transportation Research for the Federal Highway Administration. This software-based model allows vehicle design engineers to predict the effects an in-vehicle information system might have on driver performance. The model was exercised under nine different driver attention task levels ranging from simple, such as glancing into a side view mirror, to complex, such as operating an in-vehicle navigation system. The nine driver tasks were evaluated using three different vehicle configurations and two levels of driver-roadway complexity. In addition, real-world information on driver visual performance was also collected during four different tasks for comparison with model predictions of these same functions. The comparison of model prediction for maximum number of glances, total task performance time, and a model-rating feature called <i>figure of demand</i> for each of the tasks indicated:</div> <div class="htmlview paragraph"> <ol class="list nostyle"> <li class="list-item"><span class="li-label">1</span><div class="htmlview paragraph">Driver task performance behavior is influenced substantially more by differences in the level of driver/roadway/traffic combinations, than by differences in test vehicle configurations.</div></li> <li class="list-item"><span class="li-label">2</span><div class="htmlview paragraph">The driver performance data collected under actual driving conditions compared very well with the model predictions.</div></li> <li class="list-item"><span class="li-label">3</span><div class="htmlview paragraph">Overall, the IVIS DEMAnD model appears to be a good early attempt at modeling the effect on driver performance of in-vehicle IT (Information Technology) systems in general.</div></li> </ol> </div>

<div class="htmlview paragraph">The general trend in the IC engine design has been towards reduction in fuel consumption since the 1973 oil embargo. The improvement in combustion process has contributed greatly to a better fuel economy of today's engine and there are many challenges ahead on the GDI front towards the 3L/100km engine [<span class="xref">1</span>].</div> <div class="htmlview paragraph">One of the biggest windows of opportunity in achieving higher engine fuel efficiency together with an acceptable emissions level is to reduce its friction. To achieve these an accurate method of assessing friction levels through the concept, design and development is paramount. Translation of friction torque to the total drive cycle's fuel consumption is carried out using Ford's in-house CAE analytical packages.</div> <div class="htmlview paragraph">A new method of directly measuring camshaft friction has been developed, which offers both exceptional accuracy and unprecedented convenience. The advantage of this methodology over previous techniques is that it can be run simultaneously with other engine development tests on either motored or fired engines, with little effort and no specialized testing equipment. The method uses strain-gauges to measure the torque exerted upon the cam-sprockets whilst running at constant speed, on motored or fired engines. The system was statically calibrated and validated dynamically. It has been validated by two dynamic tests: a direct co-axial motoring test carried out on Ford's friction rig in Cologne, and a tear-down engine friction test performed in Dunton. Readings are found to be repeatable to within 1%, and the technique is accurate to the nearest 0.05 Nm. The measured data were then compared to the analytical predictions of ESA, ENFAS and VTF4 models [<span class="xref">2</span>, <span class="xref">3</span> &<span class="xref">4</span>].</div> <div class="htmlview paragraph">The acquired signal was also used to determine the rotational vibration modes of the total valve-train system. Case studies into the variation of valve-train friction with engine speed, load and oil temperature have been carried out as well as a comparison between motored and fired valve-train friction and an evaluation of the benefits of low-friction oil.</div> <div class="htmlview paragraph">This method shows good correlation with the existing methods and its capability of measuring absolute friction torque in firing engines makes it suitable to be used as an integral part of the engine development process. The method developed was presented and recommended for all further valve-train friction measurement as an integral part of the engine design and development process.</div>

Results on J/ ψ production at HERA

Cross sections for elastic production of J/Psi mesons in photoproduction and electroproduction are measured in electron proton collisions at HERA using an integrated luminosity of 55 pb^{-1}. Results are presented for photon virtualities Q^2 up to 80 GeV^2. The dependence on the photon-proton centre of mass energy W_{gamma p} is analysed in the range 40 < \Wgp < 305 GeV in photoproduction and 40 < \Wgp < 160 GeV in electroproduction. The \Wgp dependences of the cross sections do not change significantly with Q^2 and can be described by models based on perturbative QCD. Within such models, the data show a high sensitivity to the gluon density of the proton in the domain of low Bjorken x and low Q^2. Differential cross sections d\sigma/dt, where t is the squared four-momentum transfer at the proton vertex, are measured in the range |t|<1.2 GeV^2 as functions of \Wgp and Q^2. Effective Pomeron trajectories are determined for photoproduction and electroproduction. The J/Psi production and decay angular distributions are consistent with s-channel helicity conservation. The ratio of the cross sections for longitudinally and transversely polarised photons is measured as a function of Q^2 and is found to be described by perturbative QCD based models.

Search for contact interactions in [formula omitted] collisions at HERA