11,001 research outputs found
Carbon Nanotube Gas Sensor Using Neural Networks
The need to identify the presence and quantify the concentrations of gases and vapors is ubiquitous in NASA missions and societal applications. Sensors for air quality monitoring in crew cabins and ISS have been actively under development (Ref. 1). In particular, measuring the concentration of CO2 and NH3 is important because high concentrations of these gases pose a risk to ISS crew health. Detection of fuel and oxidant leaks in crew vehicles is critical for ensuring mission safety. Accurate gas and vapor concentrations can be measured, but this typically requires bulky and expensive instrumentation. Recently, inexpensive sensors with low power demands have been fabricated for use on the International Space Station (ISS). Carbon Nanotube (CNT) based chemical sensors are one type of these sensors. CNT sensors meet the requirements for low cost and ease of fabrication for deployment on the ISS. However, converting the measured signal from the sensors to human readable indicators of atmospheric air quality and safety is challenging. This is because it is difficult to develop an analytical model that maps the CNT sensor output signal to gas concentration. Training a neural network on CNT sensor data to predict gas concentration is more effective than developing an analytic approach to calculate the concentration from the same data set. With this in mind a neural network was created to tackle this challenge of converting the measured signal into CO2 and NH3 concentration values
Generating 3D faces using Convolutional Mesh Autoencoders
Learned 3D representations of human faces are useful for computer vision
problems such as 3D face tracking and reconstruction from images, as well as
graphics applications such as character generation and animation. Traditional
models learn a latent representation of a face using linear subspaces or
higher-order tensor generalizations. Due to this linearity, they can not
capture extreme deformations and non-linear expressions. To address this, we
introduce a versatile model that learns a non-linear representation of a face
using spectral convolutions on a mesh surface. We introduce mesh sampling
operations that enable a hierarchical mesh representation that captures
non-linear variations in shape and expression at multiple scales within the
model. In a variational setting, our model samples diverse realistic 3D faces
from a multivariate Gaussian distribution. Our training data consists of 20,466
meshes of extreme expressions captured over 12 different subjects. Despite
limited training data, our trained model outperforms state-of-the-art face
models with 50% lower reconstruction error, while using 75% fewer parameters.
We also show that, replacing the expression space of an existing
state-of-the-art face model with our autoencoder, achieves a lower
reconstruction error. Our data, model and code are available at
http://github.com/anuragranj/com
Nonlinear interaction of spin and charge currents in graphene
We describe a nonlinear interaction between charge currents and spin currents
which arises from the energy dependence of the conductivity. This allows
nonmagnetic contacts to be used for measuring and controlling spin signals. We
choose graphene as a model system to study these effects and predict its
magnitudes in nonlocal spin valve devices. The ambipolar behavior of graphene
is used to demonstrate amplification of spin accumulation in p-n junctions by
applying a charge current through nonmagnetic contacts.Comment: minor changes, 4 pages, 3 figure
Environmental triage decisions during a drought
The Murray Darling Basin Current is currently in drought. There are low water levels in most dams, and increased uncertainty about future rainfall. As a result management of the ecosystems in the basin that depend on river flows involves some hard decisions about what assets to save and what assets to let go. This paper models this triage problem using a stochastic and dynamic programming approach. This model is used to identify how optimal management is affected by hysteretic and irreversible effects of drought on ecosystem assets and uncertainty about future climate.Triage, irreversibility, climate change, Environmental Economics and Policy,
Non-linear spin Seebeck effect due to spin-charge interaction in graphene
The abilities to inject and detect spin carriers are fundamental for research
on transport and manipulation of spin information. Pure electronic spin
currents have been recently studied in nanoscale electronic devices using a
non-local lateral geometry, both in metallic systems and in semiconductors. To
unlock the full potential of spintronics we must understand the interactions of
spin with other degrees of freedom, going beyond the prototypical electrical
spin injection and detection using magnetic contacts. Such interactions have
been explored recently, for example, by using spin Hall or spin thermoelectric
effects. Here we present the detection of non-local spin signals using
non-magnetic detectors, via an as yet unexplored non-linear interaction between
spin and charge. In analogy to the Seebeck effect, where a heat current
generates a charge potential, we demonstrate that a spin current in a
paramagnet leads to a charge potential, if the conductivity is energy
dependent. We use graphene as a model system to study this effect, as recently
proposed. The physical concept demonstrated here is generally valid, opening
new possibilities for spintronics
Capture, Learning, and Synthesis of 3D Speaking Styles
Audio-driven 3D facial animation has been widely explored, but achieving
realistic, human-like performance is still unsolved. This is due to the lack of
available 3D datasets, models, and standard evaluation metrics. To address
this, we introduce a unique 4D face dataset with about 29 minutes of 4D scans
captured at 60 fps and synchronized audio from 12 speakers. We then train a
neural network on our dataset that factors identity from facial motion. The
learned model, VOCA (Voice Operated Character Animation) takes any speech
signal as input - even speech in languages other than English - and
realistically animates a wide range of adult faces. Conditioning on subject
labels during training allows the model to learn a variety of realistic
speaking styles. VOCA also provides animator controls to alter speaking style,
identity-dependent facial shape, and pose (i.e. head, jaw, and eyeball
rotations) during animation. To our knowledge, VOCA is the only realistic 3D
facial animation model that is readily applicable to unseen subjects without
retargeting. This makes VOCA suitable for tasks like in-game video, virtual
reality avatars, or any scenario in which the speaker, speech, or language is
not known in advance. We make the dataset and model available for research
purposes at http://voca.is.tue.mpg.de.Comment: To appear in CVPR 201
Many-body localization in incommensurate models with a mobility edge
We review the physics of many-body localization in models with incommensurate
potentials. In particular, we consider one-dimensional quasiperiodic models
with single-particle mobility edges. Although a conventional perspective
suggests that delocalized states act as a thermalizing bath for the localized
states in the presence of of interactions, there is evidence that such systems
can display non-ergodicity. This is in part due to the fact that the
delocalized states do not have any kind of protection due to symmetry or
topology and are thus susceptible to localization. A study of non-interacting
incommensurate models shows that they admit extended, partially extended, and
fully localized many-body states. These models cannot thermalize dynamically
and remain localized upon the introduction of interactions. In particular, for
a certain range of energy, the system can host a non-ergodic extended (i.e.
metallic) phase in which the energy eigenstates violate the eigenstate
thermalization hypothesis (ETH) but the entanglement entropy obeys volume-law
scaling. The level statistics and entanglement growth also indicate the lack of
ergodicity in these models. The phenomenon of localization and non-ergodicity
in a system with interactions despite the presence of single-particle
delocalized states is closely related to the so-called "many-body proximity
effect" and can also be observed in models with disorder coupled to systems
with delocalized degrees of freedom. Many-body localization in systems with
incommensurate potentials (without single-particle mobility edges) have been
realized experimentally, and we show how this can be modified to study the the
effects of such mobility edges. Demonstrating the failure of thermalization in
the presence of a single-particle mobility edge in the thermodynamic limit
would indicate a more robust violation of the ETH.Comment: 17 pages, 14 figures, Review articl
Isoflurane Modulates Cardiac Mitochondrial Bioenergetics by Selectively Attenuating Respiratory Complexes
Mitochondrial dysfunction contributes to cardiac ischemia–reperfusion (IR) injury but volatile anesthetics (VA) may alter mitochondrial function to trigger cardioprotection. We hypothesized that the VA isoflurane (ISO) mediates cardioprotection in part by altering the function of several respiratory and transport proteins involved in oxidative phosphorylation (OxPhos). To test this we used fluorescence spectrophotometry to measure the effects of ISO (0, 0.5, 1, 2 mM) on the time-course of interlinked mitochondrial bioenergetic variables during states 2, 3 and 4 respiration in the presence of either complex I substrate K+-pyruvate/malate (PM) or complex II substrate K+-succinate (SUC) at physiological levels of extra-matrix free Ca2 + (~ 200 nM) and Na+ (10 mM). To mimic ISO effects on mitochondrial functions and to clearly delineate the possible ISO targets, the observed actions of ISO were interpreted by comparing effects of ISO to those elicited by low concentrations of inhibitors that act at each respiratory complex, e.g. rotenone (ROT) at complex I or antimycin A (AA) at complex III. Our conclusions are based primarily on the similar responses of ISO and titrated concentrations of ETC. inhibitors during state 3. We found that with the substrate PM, ISO and ROT similarly decreased the magnitude of state 3 NADH oxidation and increased the duration of state 3 NADH oxidation, ΔΨm depolarization, and respiration in a concentration-dependent manner, whereas with substrate SUC, ISO and ROT decreased the duration of state 3 NADH oxidation, ΔΨm depolarization and respiration. Unlike AA, ISO reduced the magnitude of state 3 NADH oxidation with PM or SUC as substrate. With substrate SUC, after complete block of complex I with ROT, ISO and AA similarly increased the duration of state 3 ΔΨm depolarization and respiration. This study provides a mechanistic understanding in how ISO alters mitochondrial function in a way that may lead to cardioprotection
Enhanced charge-independent Mitochondrial Free Ca\u3csup\u3e2+\u3c/sup\u3e and Attenuated ADP-induced NADH Oxidation by Isoflurane: Implications for Cardioprotection
Modulation of mitochondrial free Ca2 + ([Ca2 +]m) is implicated as one of the possible upstream factors that initiates anesthetic-mediated cardioprotection against ischemia–reperfusion (IR) injury. To unravel possible mechanisms by which volatile anesthetics modulate [Ca2 +]m and mitochondrial bioenergetics, with implications for cardioprotection, experiments were conducted to spectrofluorometrically measure concentration-dependent effects of isoflurane (0.5, 1, 1.5, 2 mM) on the magnitudes and time-courses of [Ca2 +]m and mitochondrial redox state (NADH), membrane potential (ΔΨm), respiration, and matrix volume. Isolated mitochondria from rat hearts were energized with 10 mM Na+- or K+-pyruvate/malate (NaPM or KPM) or Na+-succinate (NaSuc) followed by additions of isoflurane, 0.5 mM CaCl2 (≈ 200 nM free Ca2 + with 1 mM EGTA buffer), and 250 μM ADP. Isoflurane stepwise: (a) increased [Ca2 +]m in state 2 with NaPM, but not with KPM substrate, despite an isoflurane-induced slight fall in ΔΨm and a mild matrix expansion, and (b) decreased NADH oxidation, respiration, ΔΨm, and matrix volume in state 3, while prolonging the duration of state 3 NADH oxidation, respiration, ΔΨm, and matrix contraction with PM substrates. These findings suggest that isoflurane\u27s effects are mediated in part at the mitochondrial level: (1) to enhance the net rate of state 2 Ca2 + uptake by inhibiting the Na+/Ca2 + exchanger (NCE), independent of changes in ΔΨm and matrix volume, and (2) to decrease the rates of state 3 electron transfer and ADP phosphorylation by inhibiting complex I. These direct effects of isoflurane to increase [Ca2 +]m, while depressing NCE activity and oxidative phosphorylation, could underlie the mechanisms by which isoflurane provides cardioprotection against IR injury at the mitochondrial level
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