Computational Fluid Dynamics Simulations of an In-line Slot and Tooth Rotor-Stator Mixer

Unlike conventional stirred tanks, rotor-stator mixers provide high deformation rates to a relatively limited volume, resulting in a region in which intensive mixing, milling, and/or dispersion operations can occur. FLUENT was used to conduct three-dimensional CFD simulations of the IKA prototype mixer, an in-line slot and tooth rotor-stator device, for a low-speed low-flow condition and a high-speed high-flow condition. The main objective of this project was to develop a CFD model of the IKA prototype mixer with the necessary refinement in the shear gap to accurately resolve these high shear values. A grid independence study was conducted to quantify the influence of shear gap grid resolution on the computed flow solution and determine the grid level most suitable for further detailed investigation. Convergence in highly-directed regions was shown to be faster than in more-open regions. Velocity and total deformation fields in the stator slots and the shear gap were examined for both operating scenarios. Differences in the fluid behaviour between the two scenarios are discussed

Analysis and design of a modular multilevel converter with trapezoidal modulation for medium and high voltage DC-DC transformers

Conventional dual active bridge topologies provide galvanic isolation and soft-switching over a reasonable operating range without dedicated resonant circuits. However, scaling the two-level dual active bridge to higher dc voltage levels is impeded by several challenges among which the high dv/dt stress on the coupling transformer insulation. Gating and thermal characteristics of series switch arrays add to the limitations. To avoid the use of standard bulky modular multilevel bridges, this paper analyzes an alternative modulation technique where staircase approximated trapezoidal voltage waveforms are produced; thus alleviating developed dv/dt stresses. Modular design is realized by the utilization of half-bridge chopper cells. Therefore, the analyzed converter is a modular multi-level converter operated in a new mode with no common-mode dc arm currents as well as reduced capacitor size, hence reduced cell footprint. Suitable switching patterns are developed and various design and operation aspects are studied. Soft switching characteristics will be shown to be comparable to those of the two-level dual active bridge. Experimental results from a scaled test rig validate the presented concept

Influence of Constraining Barrier on the 5th Lumbar and 1st Sacral joint Compressive Force during Manual Lifting

The purpose of this study was to examine the mechanical stresses on the lower back as the response of different heights of constraining barrier. Ten male subjects lifted a load from the floor to the knuckle height under the non-constrained and the constrained conditions with 4 different heights of constraining barrier (80%, 100%, 120% and 140% of knee height). The constrained condition was defined as the condition where a load was placed on the floor behind a certain level of bar. When lifting of the constrained conditions, subjects significantly increased the peak compressive forces at L5/S1 compared to the non-constrained (3868.8 ± 527.5 N, 4175.0 ± 486.0 N, 4162.4 ± 462.3 N, 4136.0 ± 553.1 N, 4079.4 ± 468.9 N for 0%, 80%, 100%, 120% and 140% barrier height conditions respectively). The subjects moved the load further from L5/S1 in the horizontal direction when lifting during the constrained conditions. While lifting during the constrained conditions subjects generated an increase in the sacral angle and a decrease of the knee flexion. The peak compressive forces at L5/S1 showed a statistically significant quadratic trend. However, the magnitude of the difference of peak compressive forces during the constrained conditions was small

Three speech sounds, one motor action: Evidence for speech-motor disparity from English flap production

The assumption that units of speech production bear a one-to-one relationship to speech motor actions pervades otherwise widely varying theories of speech motor behavior. This speech produc- tion and simulation study demonstrates that commonly occurring flap sequences may violate this assumption. In the word “Saturday,” a sequence of three sounds may be produced using a single, cyclic motor action. Under this view, the initial upward tongue tip motion, starting with the first vowel and moving to contact the hard palate on the way to a retroflex position, is under active muscular control, while the downward movement of the tongue tip, including the second contact with the hard palate, results from gravity and elasticity during tongue muscle relaxation. This sequence is reproduced using a three-dimensional computer simulation of human vocal tract biomechanics and differs greatly from other observed sequences for the same word, which employ multiple targeted speech motor actions. This outcome suggests that a goal of a speaker is to produce an entire sequence in a biomechanically efficient way at the expense of maintaining parity within the individual parts of the sequence

Vector Meson Production at HERA

We show that the lowest-order QCD calculation in a simple model of elastic vector-meson production does reproduce correctly the ratios of cross sections for rho, phi and J/psi, both in photoproduction and in high-Q2 quasi-elastic scattering. The dependence of the slopes on the mass of the vector meson is reproduced as well. We examine the lower-energy data, and find that the energy dependence of the cross section does not depend on Q2, but may depend on the vector-meson mass.Comment: 12 pages, Latex, 6 figures. Shortened version of the previous paper, which also includes a clearer criticism of the work by Martin, Ryskin and Teubner, hep-ph/960944

Defoliation frequency and season affected radiation use efficiency and dry matter partitioning to roots of lucerne (Medicago sativa L.) crops

Radiation use efficiency (RUE), and subsequent partitioning between shoots and roots were investigated for ‘Grasslands Kaituna’ lucerne crops grown in the cool temperate climate of Canterbury, New Zealand. Crops were grazed by sheep every 28 or 42 days and yielded 12 and 23 t DM/ha.year, respectively. The RUE for above ground shoots (RUEshoot) was 1.7-2.0 g DM/MJ of intercepted photosynthetically active radiation (PARᵢ) in spring but decreased systematically to ≤1.0 g DM/MJ PARᵢ in autumn. The RUE for total biomass, (RUEtotal) ranged from 1.3 to 3.1 g DM/MJ PARᵢ in response to air temperature and defoliation treatment. The lowest RUEtotal in mid summer for the treatment defoliated every 28 days was related to a 20% decline in the leaf photosynthetic capacity measured at 1000 μmol photons/m2.s (Pn1000) and at saturating light (Pmax). In turn, the reduction in Pn1000 was related to differences in specific leaf nitrogen (SLN), through changes in specific leaf weight (SLW) rather than the leaf N concentration of 4 to 6% DM. The fractional partitioning of DM to roots (proot) increased from near zero in winter/earlyspring to >0.45 in autumn, which explained the observed seasonality of RUEshoot. For the treatment defoliated each 42 days, proot increased linearly from ~0.05 to >0.45 as Pp increased from 10.5 to 16.5 h. In decreasing photoperiods proot averaged 0.45. There was a linear increase (R²=0.52) in proot with Tsoil/Tair but only in the treatment defoliated each 42 days. Agronomic treatments that result in sub optimal N reserves post grazing can be expected to produce conservative canopy characteristics but reduced photosynthetic capacity of the first 5 main stem leaves. Beyond this development stage, canopy expansion may be reduced with more conservative leaf N

From EMC- and Cronin-effects to signals of quark-gluon plasma

The EMC- and Cronin-effects are explained by a unitarized evolution equation, where the shadowing and antishadowing corrections are dynamically produced by gluon fusions. For this sake, an alternative form of the GLR-MQ-ZRS equation is derived. The resulting integrated and unintegrated gluon distributions in proton and nuclei are used to analyze the contributions of the initial parton distributions to the nuclear suppression factor in heavy ion collisions. A simulation of the fractional energy loss is extracted from the RHIC and LHC data, where the contributions of the nuclear shadowing and antishadowing effects are considered. We find a rapid crossover from week energy loss to strong energy loss at a universal critical energy of gluon jet $E_c\sim 10 GeV$.Comment: 35 pages, 13 figures, to be published in Int. J. Mod. Phys.

Breakage of Single Droplets in 2-D Inertial Flows

Droplet break-up research has traditionally focused on droplets in: 1) generally uniform flow fields (constant strain rates or constant turbulence dissipation rates) that are easier to characterize and study, and in 2) highly complex flow fields generated by mixing devices in which the evolution of an entire droplet population with time is of interest. The current work adds to the existing body of knowledge by investigating the effect of short-term high-intensity deformation events on the break-up of single large droplets in both turbulent and inertial laminar flows. This approach consists of two components: high-speed imaging of droplets as they pass through a 2-D slit orifice and CFD simulations of the orifice flow field. The experimental trajectories of the droplets are combined with the CFD-generated flow field to determine the deformation history of the droplet prior to break-up. In turbulent 2-D orifice flows, droplets and bubbles on the order of the macroscale of turbulence were studied. For these large droplets and bubbles, it was found that the product of strain rate magnitude and un-deformed diameter (essentially the velocity difference across the droplet) was a more suitable velocity scale. A new form of locally-derived, trajectory-dependent Weber number, consisting of the maximum average strain rate magnitude over an exposure time equal to 0.04 multiplied by the Stokes particle relaxation time, was used to develop a break-up probability model that can be applied to the break-up of both liquid droplets and gas bubbles. The model adds weight to the break-up interpretation of Levich (1962); break-up occurs due to the internal pressure fluctuations overcoming the interfacial stresses of the deformed droplet. In inertial laminar 2-D orifice flows, the break-up of water droplets in oil was studied at two viscosity ratios. The recommended local Weber number was again based on the maximum average strain rate magnitude over a particular exposure time, but this exposure time was instead 8 multiplied by the oscillation time scale. Using the maximum length achieved by the droplet as the length scale was also found to better represent the potential for break-up. With these modifications, and an associated capillary number-based model for predicting the drop draw ratio, two local Weber number thresholds were defined. First, the threshold for break-up is at Welocal = 30. Second, the threshold for producing large daughter droplets, termed fracturing in this work, is at Welocal = 1,000. Between these thresholds, droplets may fracture or undergo a mechanism termed erosion in this work, where a small number of tiny droplets break off from the main body of the droplet. Both of these break-up types are based on an elongative end-pinching mechanism

Z2SAL: a translation-based model checker for Z

Despite being widely known and accepted in industry, the Z formal specification language has not so far been well supported by automated verification tools, mostly because of the challenges in handling the abstraction of the language. In this paper we discuss a novel approach to building a model-checker for Z, which involves implementing a translation from Z into SAL, the input language for the Symbolic Analysis Laboratory, a toolset which includes a number of model-checkers and a simulator. The Z2SAL translation deals with a number of important issues, including: mapping unbounded, abstract specifications into bounded, finite models amenable to a BDD-based symbolic checker; converting a non-constructive and piecemeal style of functional specification into a deterministic, automaton-based style of specification; and supporting the rich set-based vocabulary of the Z mathematical toolkit. This paper discusses progress made towards implementing as complete and faithful a translation as possible, while highlighting certain assumptions, respecting certain limitations and making use of available optimisations. The translation is illustrated throughout with examples; and a complete working example is presented, together with performance data

Phenomenological description of the gamma* p cross section at low Q2

Low Q2 photon-proton cross sections are analysed using a simple, QCD-motivated parametrisation $\sigma_{\gamma^\star p}\propto 1/(Q^2+Q_0^2)$, which gives a good description of the data. The Q2 dependence of the gamma* p cross section is discussed in terms of the partonic transverse momenta of the hadronic state the photon fluctuates into.Comment: 14 pages, revtex, epsfig, 2 figure