3,515 research outputs found
Recommendations for Counselor Education and Supervision Programs to Improve Gatekeeping Processes Developed from Doctoral Student Experiences
The purpose of this qualitative study was to explore the experiences of eleven doctoral students at three CACREP accredited programs to address issues in counselor education and supervision programs and faculty face regarding gatekeeping. The information was used to develop and provide recommendations for gatekeeping procedures that can be implemented at the departmental and classroom levels. Ways programs can improve the training of doctoral students for gatekeeping roles and responsibilities, steps faculty can take to create an environment which supports gatekeeping at their institution, as well as support doctoral students as they grow into future gatekeepers of the profession are discussed
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An implicit free surface algorithm for geodynamical simulations
Identifying the dominant controls on Earth’s surface topography is of critical importance to understanding both the short- and long-term evolution of geological processes and past- and present-day dynamics of Earth’s coupled mantle–lithosphere system. The ability to simulate a stress free — or a so-called ‘free surface’ — boundary condition is required to examine such processes via numerical models. However, at present, geodynamical models incorporating a free surface are limited, as most underlying free surface algorithms place severe restrictions on the computational timestep. Consequently, the simulations are often intractable. In this study, we introduce a new approach for incorporating a free surface within geodynamical models: an algorithm, in which free surface elevation is treated as an independent variable and is solved for in conjunction with the momentum and continuity equation, using implicit time integration. We demonstrate that the method is straightforward to implement in existing models and, using a series of analytical and benchmark comparisons, we show that it does not suffer from the timestep constraints of previous schemes. Furthermore, the scheme can be made second order accurate in time, at no additional cost. The method therefore dramatically improves the computational efficiency of geodynamical simulations including a free surface, whilst maintaining solution accuracy
On the unimportance of memory for the time non-local components of the Kadanoff-Baym equations
The generalized Kadanoff-Baym ansatz (GKBA) is an approximation to the
Kadanoff-Baym equations (KBE), that neglects certain memory effects that
contribute to the Green's function at non-equal times. Here we present
arguments and numerical results to demonstrate the practical insignificance of
the quantities neglected when deriving the GKBA at conditions at which KBE and
GKBA are appropriate. We provide a mathematical proof that places a scaling
bound on the neglected terms, further reinforcing that these terms are
typically small in comparison to terms that are kept in the GKBA. We perform
calculations in a range of models, including different system sizes and filling
fractions, as well as experimentally relevant non-equilibrium excitations. We
find that both the GKBA and KBE capture the dynamics of interacting systems
with moderate and even strong interactions well. We explicitly compute terms
neglected in the GKBA approximation and show, in the scenarios tested here,
that they are orders of magnitude smaller than the terms that are accounted
for, i.e., they offer only a small correction when included in the full
Kadanoff-Baym equations.Comment: 14 pages, 3 figures, Supplemental information with 10 figure
Coupled aeroelastic shape and topology optimization of wings
This paper presents a method for simultaneous optimization of the outer shape
and internal topology of aircraft wings, with the objective of minimizing drag
subject to lift and compliance constraints for multiple load cases. The physics
are evaluated by the means of a source-doublet panel method for the aerodynamic
response and linear elastic finite elements for the structural response, which
are one way coupled. At each design iteration a mapping procedure is applied to
map the current wing shape and corresponding pressure loads to the unfitted
finite element mesh covering the design domain. Wings of small fixed-wing
airplanes both, with and without a stiffening strut, are optimized. The
resulting wings show internal topologies with struts and wall-truss
combinations, depending on the design freedom of the shape optimization. The
lift distributions of the optimized wings show patterns similar to the ones
obtained when performing optimization of wing shapes with constraints on the
bending moment at the root
High frequency, single/dual phases, large AC/DC signal power characterization for two phase on-silicon coupled inductors
In this work, a new set-up is presented to characterize the large signal electrical parameters of on-Silicon integrated coupled inductors for Power Supply on Chip. The proposed system is suitable to perform the measurements under different large-signal test conditions given by the dc bias current up to 2 A and ac current through one or both windings, with amplitudes ranging from 0 A to 0.5 A at frequencies up to 120 MHz. Since a key issue when measuring at high-frequencies is the error due to the attenuation and time skew between the channels, an additional test is performed to characterize the measurement system and compensate the voltage and current waveforms
The mantle wedge's transient 3-D flow regime and thermal structure
Arc volcanism, volatile cycling, mineralization, and continental crust formation are likely regu-lated by the mantle wedge’s flow regime and thermal structure. Wedge flow is often assumed to follow a regular corner-flow pattern. However, studies that incorporate a hydrated rheology and thermal buoyancy predict internal small-scale-convection (SSC). Here, we systematically explore mantle-wedge dynamics in 3-
D simulations. We find that longitudinal ‘‘Richter-rolls’’ of SSC (with trench-perpendicular axes) commonly occur if wedge hydration reduces viscosities to ≤1 ∙ 10^19 Pa s, although transient transverse rolls (with trench-parallel axes) can dominate at viscosities of ~5 ∙ 10^18 - 1 ∙ 10^19 Pa s. Rolls below the arc and back arc differ. Subarc rolls have similar trench-parallel and trench-perpendicular dimensions of 100–150 km and evolve on a 1–5 Myr time-scale. Subback-arc instabilities, on the other hand, coalesce into elongated sheets, usually with a preferential trench-perpendicular alignment, display a wavelength of 150–400 km and vary on a 5–10 Myr time scale. The modulating influence of subback-arc ridges on the subarc system increases
with stronger wedge hydration, higher subduction velocity, and thicker upper plates. We find that trench-parallel averages of wedge velocities and temperature are consistent with those predicted in 2-D models. However, lithospheric thinning through SSC is somewhat enhanced in 3-D, thus expanding hydrous melting regions and shifting dehydration boundaries. Subarc Richter-rolls generate time-dependent trench-parallel temperature variations of up to ~150 K, which exceed the transient 50–100 K variations predicted in 2-D
and may contribute to arc-volcano spacing and the variable seismic velocity structures imaged beneath some arcs
Dynamic Mode Decomposition for Extrapolating Non-equilibrium Green's Functions Dynamics
The HF-GKBA offers an approximate numerical procedure for propagating the
two-time non-equilibrium Green's function(NEGF). Here we compare the HF-GKBA to
exact results for a variety of systems with long and short-range interactions,
different two-body interaction strengths and various non-equilibrium
preparations. We find excellent agreement between the HF-GKBA and exact time
evolution in models when more realistic long-range exponentially decaying
interactions are considered. This agreement persists for long times and for
intermediate to strong interaction strengths. In large systems, HF-GKBA becomes
prohibitively expensive for long-time evolutions. For this reason, look at the
use of dynamical mode decomposition(DMD) to reconstruct long-time NEGF
trajectories from a sample of the initial trajectory. Using no more than 16\%
of the total time evolution we reconstruct the total trajectory with high
fidelity. Our results show the potential for DMD to be used in conjunction with
HF-GKBA to calculate long time trajectories in large-scale systems
Interaction of subducted slabs with the mantle transition-zone: A regime diagram from 2-D thermo-mechanical models with a mobile trench and an overriding plate
Transition zone slab deformation influences Earth's thermal, chemical, and tectonic evolution. However, the mechanisms responsible for the wide range of imaged slab morphologies remain debated. Here we use 2-D thermo-mechanical models with a mobile trench, an overriding plate, a temperature and stress-dependent rheology, and a 10, 30, or 100-fold increase in lower mantle viscosity, to investigate the effect of initial subducting and overriding-plate ages on slab-transition zone interaction. Four subduction styles emerge: (i) a "vertical folding" mode, with a quasi-stationary trench, near-vertical subduction, and buckling/folding at depth (VF); (ii) slabs that induce mild trench retreat, which are flattened/"horizontally deflected" and stagnate at the upper-lower mantle interface (HD); (iii) inclined slabs, which result from rapid sinking and strong trench retreat (ISR); (iv) a two-stage mode, displaying backward-bent and subsequently inclined slabs, with late trench retreat (BIR). Transitions from regime (i) to (iii) occur with increasing subducting plate age (i.e., buoyancy and strength). Regime (iv) develops for old (strong) subducting and overriding plates. We find that the interplay between trench motion and slab deformation at depth dictates the subduction style, both being controlled by slab strength, which is consistent with predictions from previous compositional subduction models. However, due to feedbacks between deformation, sinking rate, temperature, and slab strength, the subducting plate buoyancy, overriding plate strength, and upper-lower mantle viscosity jump are also important controls in thermo-mechanical subduction. For intermediate upper-lower mantle viscosity jumps (×30), our regimes reproduce the diverse range of seismically imaged slab morphologies
Reconciling mantle wedge thermal structure with arc lava thermobarometric determinations in oceanic subduction zones
Subduction zone mantle wedge temperatures impact plate interaction, melt generation, and chemical recycling. However, it has been challenging to reconcile geophysical and geochemical constraints on wedge thermal structure. Here we chemically determine the equilibration pressures and temperatures of primitive arc lavas from worldwide intraoceanic subduction zones and compare them to kinematically driven thermal wedge models. We find that equilibration pressures are typically located in the lithosphere, starting just below the Moho, and spanning a wide depth range of ∼25 km. Equilibration temperatures are high for these depths, averaging ∼1300°C. We test for correlations with subduction parameters and find that equilibration pressures correlate with upper plate age, indicating overriding lithosphere thickness plays a role in magma equilibration. We suggest that most, if not all, thermobarometric pressure and temperature conditions reflect magmatic reequilibration at a mechanical boundary, rather than reflecting the conditions of major melt generation. The magma reequilibration conditions are difficult to reconcile, to a first order, with any of the conditions predicted by our dynamic models, with the exception of subduction zones with very young, thin upper plates. For most zones, a mechanism for substantially thinning the overriding plate is required. Most likely thinning is localized below the arc, as kinematic thinning above the wedge corner would lead to a hot fore arc, incompatible with fore-arc surface heat flow and seismic properties. Localized subarc thermal erosion is consistent with seismic imaging and exhumed arc structures. Furthermore, such thermal erosion can serve as a weakness zone and affect subsequent plate evolutio
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