557 research outputs found

    The LHCb tracking system

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    The LHCb detector is being constructed to measure CP-violation parameters and rare B decays. The LHCb tracking system consists of silicon micro-strip detectors and straw chambers. The system is composed of four major sub-detectors: the Velo (Vertex Locator), TT (Trigger Tracker), IT (Inner Tracker) and OT (Outer Tracker). The Velo uses silicon micro-strip detectors which are placed at 8 mm from the beam, and that can be retracted during injection. The TT is a four-layer silicon strip detector that covers the full acceptance of the experiment at the entrance of the spectrometer dipole magnet. The fringe field of the magnet allows the transverse momentum of tracks to be measured by their deflection between the Velo and TT detectors for use in the trigger. The IT and OT detectors measure the tracks behind the magnet. The IT is a silicon strip detector which covers the region close to the beam pipe, while the OT is a straw tube detector which covers the rest of the acceptance. All of the detectors are currently under construction and will be ready for installation before the end of 2006. The expected performance for the tracking system is as follows; the tracking efficiency is larger than 95% and the ghost rate is smaller than 7%, for tracks with a momentum larger than 12 GeV. The momentum resolution ranges from 0.35% to 0.5% and the IP resolution reaches 14 mm for tracks with a large transverse momentum

    New insight in the Hawaiian plume swell dynamics from scaling laws

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    The formation and shape variation of the Hawaiian plume swell is re-examined numerically. Scaling laws for the plume buoyancy flux and swell width and height help gaining new insight in relationships between swell formation and relevant model parameters, like plume temperature and size, and mantle rheology. A scaling law for the plume buoyancy F = Aη0 −1.2 R p 3.5ΔT p 2.2 exp(1.3 × 10−8 EΔT p ), with background mantle viscosity η0, plume radius R p , plume excess temperature ΔT p , and activation energy E fits numerical flux measurements within 8%. Scaling laws for the swell width and height have similar forms, and their multiplication resembles the buoyancy flux scaling law within 10%. These scaling laws suggest that the background mantle viscosity plays a significant role, and that the increased Hawaiian plume intensity ∌25 Ma ago is due to a plume excess temperature increase of 50%

    Development of a radiation hard version of the Analog Pipeline Chip APC128

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    The Analog Pipeline Chip (APC) is a low noise, low power readout chip for silicon micro strip detectors with 128 channels containing an analog pipeline of 32 buffers depth. The chip has been designed for operation at HERA with a power dissipation of 300-400 muW per channel and has been used also in several other particle physics experiments. In this paper we describe the development of a radiation hard version of this chip that will be used in the H1 vertex detector for operation at the luminosity upgraded HERA machine. A 128 channel prototyping chip with several amplifier variations has been designed in the radiation hard DMILL technology and measured. The results of various parameter variations are presented in this paper. Based on this, the design choice for the final production version of the APC128-DMILL has been made.Comment: 10 pages, 10 figure

    LANDING KINEMATICS AFTER ACL RECONSTRUCTION; DO THE BIOMECHANIST AND PHYSIOTHERAPIST SEE DIFFERENT THINGS?

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    Rehabilitation following ACL reconstruction is a long process where the chance of a recurrent injury remains high. Compensatory and asymmetric landing strategies, which may lead to these re-injuries, often remain present during the rehabilitation process although not often visually identified. Therefore, the purpose of this study was to compare the visually identified asymmetries with objective inertial sensor data during the Single and Triple Hop test. The kinematic data was able to identify asymmetric kinematics that led to altered strategies that were not identified subjectively by the physiotherapist in both the Single and Triple Hop, in particular in the hip joint. It is speculated that being able to able to identify these asymmetric strategies will improve ACLR rehabilitation and reduce the chance of a re-injury

    Repeat ridge jumps associated with plume‐ridge interaction, melt transport, and ridge migration

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    Repeated shifts, or jumps, of mid-ocean ridge segments toward nearby hot spots can produce large, long-term changes to the geometry and location of the tectonic plate boundaries. Ridge jumps associated with hot spot–ridge interaction are likely caused by several processes including shear on the base of the plate due to expanding plume material as well as reheating of lithosphere as magma passes through it to feed off-axis volcanism. To study how these processes influence ridge jumps, we use numerical models to simulate 2-D (in cross section) viscous flow of the mantle, viscoplastic deformation of the lithosphere, and melt migration upward from the asthenospheric melting zone, laterally along the base of the lithosphere, and vertically through the lithosphere. The locations and rates that magma penetrates and heats the lithosphere are controlled by the time-varying accumulation of melt beneath the plate and the depth-averaged lithospheric porosity. We examine the effect of four key parameters: magmatic heating rate of the lithosphere, plate spreading rate, age of the seafloor overlying the plume, and the plume-ridge migration rate. Results indicate that the minimum value of the magmatic heating rate needed to initiate a ridge jump increases with plate age and spreading rate. The time required to complete a ridge jump decreases with larger values of magmatic heating rate, younger plate age, and faster spreading rate. For cases with migrating ridges, models predict a range of behaviors including repeating ridge jumps, much like those exhibited on Earth. Repeating ridge jumps occur at moderate magmatic heating rates and are the result of changes in the hot spot magma flux in response to magma migration along the base of an evolving lithosphere. The tendency of slow spreading to promote ridge jumps could help explain the observed clustering of hot spots near the Mid-Atlantic Ridge. Model results also suggest that magmatic heating may significantly thin the lithosphere, as has been suggested at Hawaii and other hot spots

    Subsidence of the West Siberian Basin: Effects of a mantle plume impact

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    Comparison of modeling results with observed subsidence patterns from the West Siberian Basin provides new insight into the origin of the Siberian Traps, and constrains the temperature, size, and depth of an impacting mantle plume head during and after the eruption of the Siberian Traps at the Permian-Triassic boundary (250 Ma). We compare subsidence patterns from one-dimensional conductive heat flow models to observed subsidence from backstripping studies of wells in the basin. This results in a best-fit scenario with a 50-km-thick initial plume head with a temperature of 1500 °C situated 50 km below the surface, and an initial regional crustal thickness of 34 km, in agreement with published values. Backstripping and modeling results agree very well, including a 60–90 m.y. delay between the rifting phase and the first regional sedimentation. Regional subsidence patterns indicate that the plume head was present across a minimum area of ∌2.5 × 106 km2. These results re-emphasize the viability of a mantle plume origin for the Siberian Traps, provide important constraints on the dynamics of mantle plume heads, and suggest a thermal control for the subsidence of the West Siberian Basin

    The Bs -> Ds pi and Bs -> Ds K selections

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    The decay channels Bs->Dspi and Bs->DsK will be used to extract the physics parameters Δms\Delta m_s, ΔΓs\Delta\Gamma_s and Îł+ϕs\gamma + \phi_s. Simulation studies based on Monte Carlo samples produced in 2004 and 2005 show that a total of 140k Bs->Dspi and 6.2k Bs->DsK events are expected to be triggered, reconstructed and selected in 2fb−12fb^{-1} of data (107s10^7s of data taking at a luminosity of 2\times 10^{32}\unit{cm^{-2}s^{-1}}). The combinatorial background-over-signal ratio originating from inclusive bb events is expected to be B/SDspiwhereas,forBs−>DsK,thelimitisB/S Dspi whereas, for Bs->DsK, the limit is B/S < 0.18~\at~90\%$~CL

    Relamination of mafic subducting crust throughout Earth’s history

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    Earth has likely cooled by several hundred degrees over its history, which has probably affected subduction dynamics and associated magmatism. Today, the process of compositional buoyancy driven upwelling, and subsequent underplating, of subducted materials (commonly referred to as “relamination”) is thought to play a role in the formation of continental crust. Given that Archean continental crust formation is best explained by the involvement of mafic material, we investigate the feasibility of mafic crust relamination under a wide range of conditions applicable to modern and early Earth subduction zones, to assess if such a process might have been viable in an early Earth setting. Our numerical parametric study illustrates that the hotter, thicker-crust conditions of the early Earth favour the upward relamination of mafic subducting crust. The amount of relaminating subducting crust is observed to vary significantly, with subduction convergence rate having the strongest control on the volume of relaminated material. Indeed, removal of the entire mafic crust from the subducting slab is possible for slow subduction (∌2 cm/yr) under Archean conditions. We also observe great variability in the depth at which this separation occurs (80–120 km), with events corresponding to shallower detachment being more voluminous, and that relaminating material has to remain metastably buoyant until this separation depth, which is supported by geological, geophysical and geodynamical observations. Furthermore, this relamination behaviour is commonly episodic with a typical repeat time of approximately 10 Myrs, similar to timescales of episodicity observed in the Archean rock record. We demonstrate that this relamination process can result in the heating of considerable quantities of mafic material (to temperatures in excess of 900 °C), which is then emplaced below the over-riding lithosphere. As such, our results have implications for Archean subduction zone magmatism, for continental crust formation in the early Earth, and provide a novel explanation for the secular evolution of continental crust
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