56 research outputs found
Spare me the details: How the type of information about automated interviews influences applicant reactions
Applicants seem to react negatively to artificial intelligence-based automated systems in personnel selection. This study investigates the impact of different pieces of information to alleviate applicant reactions in an automated interview setting. In a 2 (no process information vs. process information) Ă— 2 (no process justification vs. process justification) between-subjects design, participants (N = 124) received respective information and watched a video showing an automated interview. Testing mediation effects via different applicant reaction variables indicated that process justification is better than process information which can even impair applicant reactions. However, information did not increase organizational attractiveness compared to not receiving any information. This study sheds light on what type of information contributes to positive and negative applicant reactions to automated systems
Collisions of inhomogeneous pre-planetesimals
In the framework of the coagulation scenario, kilometre-sized planetesimals
form by subsequent collisions of pre-planetesimals of sizes from centimetre to
hundreds of metres. Pre-planetesimals are fluffy, porous dust aggregates, which
are inhomogeneous owing to their collisional history. Planetesimal growth can
be prevented by catastrophic disruption in pre-planetesimal collisions above
the destruction velocity threshold. We develop an inhomogeneity model based on
the density distribution of dust aggregates, which is assumed to be a Gaussian
distribution with a well-defined standard deviation. As a second input
parameter, we consider the typical size of an inhomogeneous clump. These input
parameters are easily accessible by laboratory experiments. For the simulation
of the dust aggregates, we utilise a smoothed particle hydrodynamics (SPH) code
with extensions for modelling porous solid bodies. The porosity model was
previously calibrated for the simulation of silica dust, which commonly serves
as an analogue for pre-planetesimal material. The inhomogeneity is imposed as
an initial condition on the SPH particle distribution. We carry out collisions
of centimetre-sized dust aggregates of intermediate porosity. We vary the
standard deviation of the inhomogeneous distribution at fixed typical clump
size. The collision outcome is categorised according to the four-population
model. We show that inhomogeneous pre-planetesimals are more prone to
destruction than homogeneous aggregates. Even slight inhomogeneities can lower
the threshold for catastrophic disruption. For a fixed collision velocity, the
sizes of the fragments decrease with increasing inhomogeneity.
Pre-planetesimals with an active collisional history tend to be weaker. This is
a possible obstacle to collisional growth and needs to be taken into account in
future studies of the coagulation scenario.Comment: 12 pages, 9 figures, 4 table
The four-populations model: a new classification scheme for pre-planetesimal collisions
Within the collision growth scenario for planetesimal formation, the growth
step from centimetre sized pre-planetesimals to kilometre sized planetesimals
is still unclear. The formation of larger objects from the highly porous
pre-planetesimals may be halted by a combination of fragmentation in disruptive
collisions and mutual rebound with compaction. However, the right amount of
fragmentation is necessary to explain the observed dust features in late T
Tauri discs. Therefore, detailed data on the outcome of pre-planetesimal
collisions is required and has to be presented in a suitable and precise
format. We propose and apply a new classification scheme for pre-planetesimal
collisions based on the quantitative aspects of four fragment populations: the
largest and second largest fragment, a power-law population, and a
sub-resolution population. For the simulations of pre-planetesimal collisions,
we adopt the SPH numerical scheme with extensions for the simulation of porous
solid bodies. By means of laboratory benchmark experiments, this model was
previously calibrated and tested for the correct simulation of the compaction,
bouncing, and fragmentation behaviour of macroscopic highly porous silica dust
aggregates. It is shown that previous attempts to map collision data were much
too oriented on qualitatively categorising into sticking, bouncing, and
fragmentation events. We show that the four-populations model encompasses all
previous categorisations and in addition allows for transitions. This is
because it is based on quantitative characteristic attributes of each
population such as the mass, kinetic energy, and filling factor. As a
demonstration of the applicability and the power of the four-populations model,
we utilise it to present the results of a study on the influence of collision
velocity in head-on collisions of intermediate porosity aggregates.Comment: 14 pages, 11 figures, 5 tables, to be published in Astronomy and
Astrophysic
The Physics of Protoplanetesimal Dust Agglomerates. IV. Towards a Dynamical Collision Model
Recent years have shown many advances in our knowledge of the collisional
evolution of protoplanetary dust. Based on a variety of dust-collision
experiments in the laboratory, our view of the growth of dust aggregates in
protoplanetary disks is now supported by a deeper understanding of the physics
involved in the interaction between dust agglomerates. However, the parameter
space, which determines the collisional outcome, is huge and sometimes
inaccessible to laboratory experiments. Very large or fluffy dust aggregates
and extremely low collision velocities are beyond the boundary of today's
laboratories. It is therefore desirable to augment our empirical knowledge of
dust-collision physics with a numerical method to treat arbitrary aggregate
sizes, porosities and collision velocities. In this article, we implement
experimentally-determined material parameters of highly porous dust aggregates
into a Smooth Particle Hydrodynamics (SPH) code, in particular an
omnidirectional compressive-strength and a tensile-strength relation. We also
give a prescription of calibrating the SPH code with compression and
low-velocity impact experiments. In the process of calibration, we developed a
dynamic compressive-strength relation and estimated a relation for the shear
strength. Finally, we defined and performed a series of benchmark tests and
found the agreement between experimental results and numerical simulations to
be very satisfactory. SPH codes have been used in the past to study collisions
at rather high velocities. At the end of this work, we show examples of future
applications in the low-velocity regime of collisional evolution.Comment: accepted by The astrophysical Journa
Numerical Simulations of Highly Porous Dust Aggregates in the Low-Velocity Collision Regime
A highly favoured mechanism of planetesimal formation is collisional growth.
Single dust grains, which follow gas flows in the protoplanetary disc, hit each
other, stick due to van der Waals forces and form fluffy aggregates up to
centimetre size. The mechanism of further growth is unclear since the outcome
of aggregate collisions in the relevant velocity and size regime cannot be
investigated in the laboratory under protoplanetary disc conditions. Realistic
statistics of the result of dust aggregate collisions beyond decimetre size is
missing for a deeper understanding of planetary growth. Joining experimental
and numerical efforts we want to calibrate and validate a computer program that
is capable of a correct simulation of the macroscopic behaviour of highly
porous dust aggregates. After testing its numerical limitations thoroughly we
will check the program especially for a realistic reproduction of various
benchmark experiments. We adopt the smooth particle hydrodynamics (SPH)
numerical scheme with extensions for the simulation of solid bodies and a
modified version of the Sirono porosity model. Experimentally measured
macroscopic material properties of silica dust are implemented. We calibrate
and test for the compressive strength relation and the bulk modulus. SPH has
already proven to be a suitable tool to simulate collisions at rather high
velocities. In this work we demonstrate that its area of application can not
only be extended to low-velocity experiments and collisions. It can also be
used to simulate the behaviour of highly porous objects in this velocity regime
to a very high accuracy.The result of the calibration process in this work is
an SPH code that can be utilised to investigate the collisional outcome of
porous dust in the low-velocity regime.Comment: accepted by Astronomy & Astrophysic
Broad emission lines for negatively spinning black holes
We present an extended scheme for the calculation of the profiles of emission
lines from accretion discs around rotating black holes. The scheme includes
discs with angular momenta which are parallel and antiparallel with respect to
the black hole's angular momentum, as both configurations are assumed to be
stable (King et al., 2005). We discuss line shapes for such discs and present a
code for modelling observational data with this scheme in X-ray data analysis
programs. Based on a Green's function approach, an arbitrary radius dependence
of the disc emissivity and arbitrary limb darkening laws can be easily taken
into account, while the amount of precomputed data is significantly reduced
with respect to other available models.Comment: 7 pages, 6 figures; accepted by MNRAS for Publication, now matches
the proof read versio
Simulations of eccentric disks in close binary systems
We study the development of finite eccentricity in accretion disks in close
binary systems using a two-dimensional grid-based numerical scheme. We perform
detailed parameter studies to explore the dependence on viscosity, disk aspect
ratio, the inclusion of a mass-transfer stream and the role of the boundary
conditions. We consider mass ratios 0.05<q<0.3 appropriate to superoutbursting
cataclysmic binary systems.
Instability to the formation of a precessing eccentric disk that attains a
quasi-steady state with mean eccentricity in the range 0.3-0.5 occurs readily.
The shortest growth times are ~15 binary orbits for the largest viscosities and
the instability mechanism is for the most part consistent with the
mode-coupling mechanism associated with the 3:1 resonance proposed by Lubow.
However, the results are sensitive to the treatment of the inner boundary and
to the incorporation of the mass-transfer stream. In the presence of a stream
we found a critical viscosity below which the disk remains circular.
Incorporation of a mass-transfer stream tends to impart stability for small
enough viscosity (or, equivalently, mass-transfer rate through the disk) and
does assist in obtaining a prograde precession rate that is in agreement with
observations. For the larger q the location of the 3:1 resonance is pushed
outwards towards the Roche lobe where higher-order mode couplings and
nonlinearity occur. It is likely that three-dimensional simulations that
properly resolve the disk's vertical structure are required to make significant
progress in this case.Comment: 19 pages, 27 Figures, accepted by A&
A comparative study of disc-planet interaction
We perform numerical simulations of a disc-planet system using various
grid-based and smoothed particle hydrodynamics (SPH) codes. The tests are run
for a simple setup where Jupiter and Neptune mass planets on a circular orbit
open a gap in a protoplanetary disc during a few hundred orbital periods. We
compare the surface density contours, potential vorticity and smoothed radial
profiles at several times. The disc mass and gravitational torque time
evolution are analyzed with high temporal resolution. There is overall
consistency between the codes. The density profiles agree within about 5% for
the Eulerian simulations while the SPH results predict the correct shape of the
gap although have less resolution in the low density regions and weaker
planetary wakes. The disc masses after 200 orbital periods agree within 10%.
The spread is larger in the tidal torques acting on the planet which agree
within a factor 2 at the end of the simulation. In the Neptune case the
dispersion in the torques is greater than for Jupiter, possibly owing to the
contribution from the not completely cleared region close to the planet.Comment: 32 pages, accepted for publication in MNRA
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