2,163 research outputs found
Asymmetric matrix sensing by gradient descent with small random initialization
We study matrix sensing, which is the problem of reconstructing a low-rank
matrix from a few linear measurements. It can be formulated as an
overparameterized regression problem, which can be solved by factorized
gradient descent when starting from a small random initialization.
Linear neural networks, and in particular matrix sensing by factorized
gradient descent, serve as prototypical models of non-convex problems in modern
machine learning, where complex phenomena can be disentangled and studied in
detail. Much research has been devoted to studying special cases of asymmetric
matrix sensing, such as asymmetric matrix factorization and symmetric positive
semi-definite matrix sensing.
Our key contribution is introducing a continuous differential equation that
we call the . We prove that the perturbed
gradient flow converges quickly to the true target matrix whenever the
perturbation is sufficiently bounded. The dynamics of gradient descent for
matrix sensing can be reduced to this formulation, yielding a novel proof of
asymmetric matrix sensing with factorized gradient descent. Compared to
directly analyzing the dynamics of gradient descent, the continuous formulation
allows bounding key quantities by considering their derivatives, often
simplifying the proofs. We believe the general proof technique may prove useful
in other settings as well
Unexpected Scaling of the Performance of Carbon Nanotube Transistors
We show that carbon nanotube transistors exhibit scaling that is
qualitatively different than conventional transistors. The performance depends
in an unexpected way on both the thickness and the dielectric constant of the
gate oxide. Experimental measurements and theoretical calculations provide a
consistent understanding of the scaling, which reflects the very different
device physics of a Schottky barrier transistor with a quasi-one-dimensional
channel contacting a sharp edge. A simple analytic model gives explicit scaling
expressions for key device parameters such as subthreshold slope, turn-on
voltage, and transconductance.Comment: 4 pages, 4 figure
Multidrug Resistance in Breast Cancer: From In Vitro Models to Clinical Studies
The development of multidrug resistance (MDR) and subsequent relapse on therapy is a widespread problem in breast cancer, but our understanding of the underlying molecular mechanisms is incomplete. Numerous studies have aimed to establish the role of drug transporter pumps in MDR and to link their expression to response to chemotherapy. The ATP-binding cassette (ABC) transporters are central to breast cancer MDR, and increases in ABC expression levels have been shown to correlate with decreases in response to various chemotherapy drugs and a reduction in overall survival. But as there is a large degree of redundancy between different ABC transporters, this correlation has not been seen in all studies. This paper provides an introduction to the key molecules associated with breast cancer MDR and summarises evidence of their potential roles reported from model systems and clinical studies. We provide possible explanations for why despite several decades of research, the precise role of ABC transporters in breast cancer MDR remains elusive
MODIS Cloud Optical Property Retrieval Uncertainties Derived from Pixel-Level VNIR/SWIR Radiometric Uncertainties
Moderate Resolution Imaging Spectroradiometer (MODIS) retrievals of optical thickness and effective particle radius for liquid water and ice phase clouds employ a well-known VNIR/ SWIR solar reflectance technique. For this type of algorithm, we evaluate the quantitative uncertainty in simultaneous retrievals of these two cloud parameters to pixel-level radiometric calibration estimates and other fundamental (and tractable) error sources
The Use of Interacting Marketing Models as Framework for Research
The recent emphasis on consumers as the raison d\u27etre of the business firm has led marketers to neglect or deemphasize the roles of the other participants in the marketing system. Yet, an understanding of the marketing system requires the development of a comprehensive marketing model focusing on the consumers, distributive institutions, manufacturers, and other participants involved in the marketing of the given product(s)
Single-Walled Carbon Nanotubes as Shadow Masks for Nanogap Fabrication
We describe a technique for fabricating nanometer-scale gaps in Pt wires on
insulating substrates, using individual single-walled carbon nanotubes as
shadow masks during metal deposition. More than 80% of the devices display
current-voltage dependencies characteristic of direct electron tunneling. Fits
to the current-voltage data yield gap widths in the 0.8-2.3 nm range for these
devices, dimensions that are well suited for single-molecule transport
measurements
Diffusion of New Products in Heterogeneous Populations: Incorporating Stochastic Coefficients
Diffusion models have had a major impact on the literature and practice of marketing science. Following the pioneering work of Bass (1969), which suggested a deterministic model for homogeneous populations, the basic diffusion model has been extended to incorporate: changes in the market potential over time (Mahajan & Peterson 1978); complimentarity, substitutability, contigent & independent relations of the new product with other brands in the market place (Peterson & Mahajan 1978); spatial diffusion pattern (Mahajan & Peterson 1979); varying word-of-mouth effects (Easingwood, Mahajan & Muller 1983); various marketing mix effects including the effect of price on both innovation and imitation coefficients (Robinson and Lakhani 1975) or advertising effect on the innovation coefficient (Horsky and Simon 1983). competitive effects (Eliashberg & Jeuland 1982, Fershtman, Mahajan and Muller 1983
Implicit regularization in AI meets generalized hardness of approximation in optimization -- Sharp results for diagonal linear networks
Understanding the implicit regularization imposed by neural network
architectures and gradient based optimization methods is a key challenge in
deep learning and AI. In this work we provide sharp results for the implicit
regularization imposed by the gradient flow of Diagonal Linear Networks (DLNs)
in the over-parameterized regression setting and, potentially surprisingly,
link this to the phenomenon of phase transitions in generalized hardness of
approximation (GHA). GHA generalizes the phenomenon of hardness of
approximation from computer science to, among others, continuous and robust
optimization. It is well-known that the -norm of the gradient flow of
DLNs with tiny initialization converges to the objective function of basis
pursuit. We improve upon these results by showing that the gradient flow of
DLNs with tiny initialization approximates minimizers of the basis pursuit
optimization problem (as opposed to just the objective function), and we obtain
new and sharp convergence bounds w.r.t.\ the initialization size. Non-sharpness
of our results would imply that the GHA phenomenon would not occur for the
basis pursuit optimization problem -- which is a contradiction -- thus implying
sharpness. Moreover, we characterize minimizer of the
basis pursuit problem is chosen by the gradient flow whenever the minimizer is
not unique. Interestingly, this depends on the depth of the DLN
Spin dependent transport of ``nonmagnetic metal/zigzag nanotube encapsulating magnetic atoms/nonmagnetic metal'' junctions
Towards a novel magnetoresistance (MR) device with a carbon nanotube, we
propose ``nonmagnetic metal/zigzag nanotube encapsulating magnetic
atoms/nonmagnetic metal'' junctions. We theoretically investigate how
spin-polarized edges of the nanotube and the encapsulated magnetic atoms
influence on transport. When the on-site Coulomb energy divided by the
magnitude of transfer integral, , is larger than 0.8, large MR effect
due to the direction of spins of magnetic atoms, which has the magnitude of the
MR ratio of about 100%, appears reflecting such spin-polarized edges.Comment: 4 pages, 3 figures, accepted for publication in Synth. Metal
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