403 research outputs found
Towards Interpretable Deep Learning Models for Knowledge Tracing
As an important technique for modeling the knowledge states of learners, the
traditional knowledge tracing (KT) models have been widely used to support
intelligent tutoring systems and MOOC platforms. Driven by the fast
advancements of deep learning techniques, deep neural network has been recently
adopted to design new KT models for achieving better prediction performance.
However, the lack of interpretability of these models has painfully impeded
their practical applications, as their outputs and working mechanisms suffer
from the intransparent decision process and complex inner structures. We thus
propose to adopt the post-hoc method to tackle the interpretability issue for
deep learning based knowledge tracing (DLKT) models. Specifically, we focus on
applying the layer-wise relevance propagation (LRP) method to interpret
RNN-based DLKT model by backpropagating the relevance from the model's output
layer to its input layer. The experiment results show the feasibility using the
LRP method for interpreting the DLKT model's predictions, and partially
validate the computed relevance scores from both question level and concept
level. We believe it can be a solid step towards fully interpreting the DLKT
models and promote their practical applications in the education domain
Modules for Experiments in Stellar Astrophysics (MESA): Giant Planets, Oscillations, Rotation, and Massive Stars
We substantially update the capabilities of the open source software package
Modules for Experiments in Stellar Astrophysics (MESA), and its one-dimensional
stellar evolution module, MESA Star. Improvements in MESA Star's ability to
model the evolution of giant planets now extends its applicability down to
masses as low as one-tenth that of Jupiter. The dramatic improvement in
asteroseismology enabled by the space-based Kepler and CoRoT missions motivates
our full coupling of the ADIPLS adiabatic pulsation code with MESA Star. This
also motivates a numerical recasting of the Ledoux criterion that is more
easily implemented when many nuclei are present at non-negligible abundances.
This impacts the way in which MESA Star calculates semi-convective and
thermohaline mixing. We exhibit the evolution of 3-8 Msun stars through the end
of core He burning, the onset of He thermal pulses, and arrival on the white
dwarf cooling sequence. We implement diffusion of angular momentum and chemical
abundances that enable calculations of rotating-star models, which we compare
thoroughly with earlier work. We introduce a new treatment of
radiation-dominated envelopes that allows the uninterrupted evolution of
massive stars to core collapse. This enables the generation of new sets of
supernovae, long gamma-ray burst, and pair-instability progenitor models. We
substantially modify the way in which MESA Star solves the fully coupled
stellar structure and composition equations, and we show how this has improved
MESA's performance scaling on multi-core processors. Updates to the modules for
equation of state, opacity, nuclear reaction rates, and atmospheric boundary
conditions are also provided. We describe the MESA Software Development Kit
(SDK) that packages all the required components needed to form a unified and
maintained build environment for MESA. [Abridged]Comment: Accepted for publication in The ApJ Supplement Series. Extra
informations required to reproduce the calculations in this paper are
available at http://mesastar.org/results/mesa
Strain and correlation of self-organized Ge_(1-x)Mn_x nanocolumns embedded in Ge (001)
We report on the structural properties of Ge_(1-x)Mn_x layers grown by
molecular beam epitaxy. In these layers, nanocolumns with a high Mn content are
embedded in an almost-pure Ge matrix. We have used grazing-incidence X-ray
scattering, atomic force and transmission electron microscopy to study the
structural properties of the columns. We demonstrate how the elastic
deformation of the matrix (as calculated using atomistic simulations) around
the columns, as well as the average inter-column distance can account for the
shape of the diffusion around Bragg peaks.Comment: 9 pages, 7 figure
Can Parity Violation in Neutrino Transport Lead to Pulsar Kicks?
In magnetized proto-neutron stars, neutrino cross sections depend
asymmetrically on the neutrino momenta due to parity violation. However, these
asymmetric opacities do not induce any asymmetric flux in the bulk interior of
the star where neutrinos are nearly in thermal equilibrium. Consequently,
parity violation in neutrino absorption and scattering can only give rise to
asymmetric neutrino flux above the neutrino-matter decoupling layer. The kick
velocity is substantially reduced from previous estimates, requiring a dipole
field ~G to get of order a few hundred km~s.Comment: REVTEX, 4 pages, no figures. Submitted to Phys. Rev. Letter
R-modes in Neutron Stars with Crusts: Turbulent Saturation, Spin-down, and Crust Melting
Rossby waves (r-modes) have been suggested as a means to regulate the spin
periods of young or accreting neutron stars, and also to produce observable
gravitational wave radiation. R-modes involve primarily transverse,
incompressive motions of the star's fluid core. However, neutron stars gain
crusts early in their lives: therefore, r-modes also imply shear in the fluid
beneath the crust. We examine the criterion for this shear layer to become
turbulent, and derive the rate of dissipation in the turbulent regime. Unlike
dissipation from a viscous boundary layer, turbulent energy loss is nonlinear
in mode energy and can therefore cause the mode to saturate at amplitudes
typically much less than unity. This energy loss also reappears as heat below
the crust. We study the possibility of crust melting as well as its
implications for the spin evolution of low-mass X-ray binaries. Lastly, we
identify some universal features of the spin evolution that may have
observational consequences.Comment: 12 pages, 4 figures, submitted to Ap
Cooling of young stars growing by disk accretion
In the initial formation stages young stars must acquire a significant
fraction of their mass by accretion from a circumstellar disk that forms in the
center of a collapsing protostellar cloud. Throughout this period mass
accretion rates through the disk can reach 10^{-6}-10^{-5} M_Sun/yr leading to
substantial energy release in the vicinity of stellar surface. We study the
impact of irradiation of the stellar surface produced by the hot inner disk on
properties of accreting fully convective low-mass stars, and also look at
objects such as young brown dwarfs and giant planets. At high accretion rates
irradiation raises the surface temperature of the equatorial region above the
photospheric temperature T_0 that a star would have in the absence of
accretion. The high-latitude (polar) parts of the stellar surface, where disk
irradiation is weak, preserve their temperature at the level of T_0. In
strongly irradiated regions an almost isothermal outer radiative zone forms on
top of the fully convective interior, leading to the suppression of the local
internal cooling flux derived from stellar contraction (similar suppression
occurs in irradiated ``hot Jupiters''). Properties of this radiative zone
likely determine the amount of thermal energy that gets advected into the
convective interior of the star. Total intrinsic luminosity integrated over the
whole stellar surface is reduced compared to the non-accreting case, by up to a
factor of several in some systems (young brown dwarfs, stars in quasar disks,
forming giants planets), potentially leading to the retardation of stellar
contraction. Stars and brown dwarfs irradiated by their disks tend to lose
energy predominantly through their cool polar regions while young giant planets
accreting through the disk cool through their whole surface.Comment: 14 pages, 6 figures, submitted to Ap
Transgenic analysis of the Leishmania MAP kinase MPK10 reveals an auto-inhibitory mechanism crucial for stage-regulated activity and parasite viability
Protozoan pathogens of the genus Leishmania have evolved unique signaling mechanisms that can sense changes in the host environment and trigger adaptive stage differentiation essential for host cell infection. The signaling mechanisms underlying parasite development remain largely elusive even though Leishmania mitogen-activated protein kinases (MAPKs) have been linked previously to environmentally induced differentiation and virulence. Here, we unravel highly unusual regulatory mechanisms for Leishmania MAP kinase 10 (MPK10). Using a transgenic approach, we demonstrate that MPK10 is stage-specifically regulated, as its kinase activity increases during the promastigote to amastigote conversion. However, unlike canonical MAPKs that are activated by dual phosphorylation of the regulatory TxY motif in the activation loop, MPK10 activation is independent from the phosphorylation of the tyrosine residue, which is largely constitutive. Removal of the last 46 amino acids resulted in significantly enhanced MPK10 activity both for the recombinant and transgenic protein, revealing that MPK10 is regulated by an auto-inhibitory mechanism. Over-expression of this hyperactive mutant in transgenic parasites led to a dominant negative effect causing massive cell death during amastigote differentiation, demonstrating the essential nature of MPK10 auto-inhibition for parasite viability. Moreover, phosphoproteomics analyses identified a novel regulatory phospho-serine residue in the C-terminal auto-inhibitory domain at position 395 that could be implicated in kinase regulation. Finally, we uncovered a feedback loop that limits MPK10 activity through dephosphorylation of the tyrosine residue of the TxY motif. Together our data reveal novel aspects of protein kinase regulation in Leishmania, and propose MPK10 as a potential signal sensor of the mammalian host environment, whose intrinsic pre-activated conformation is regulated by auto-inhibition
Bulk viscosity in the nonlinear and anharmonic regime of strange quark matter
The bulk viscosity of cold, dense three-flavor quark matter is studied as a
function of temperature and the amplitude of density oscillations. The study is
also extended to the case of two different types of anharmonic oscillations of
density. We point several qualitative effects due to the anharmonicity,
although quantitatively they appear to be relatively small. We also find that,
in most regions of the parameter space, with the exception of the case of a
very large amplitude of density oscillations (i.e. 10% and above), nonlinear
effects and anharmonicity have a small effect on the interplay of the
nonleptonic and semileptonic processes in the bulk viscosity.Comment: 14 pages, 6 figures; v2: Appendix B is omitted, a few new discussions
added and some new references adde
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