39 research outputs found
Near-field spectroscopy of bimodal size distribution of InAs/AlGaAs quantum dots
We report on high-resolution photoluminescence (PL) spectroscopy of spatial
structure of InAs/AlGaAs quantum dots (QDs) by using a near-field scanning
optical microscope (NSOM). The double-peaked distribution of PL spectra is
clearly observed, which is associated with the bimodal size distribution of
single QDs. In particular, the size difference of single QDs, represented by
the doublet spectral distribution, can be directly observed by the NSOM images
of PL.Comment: 3pages, 3figue
Homotopy-based training of NeuralODEs for accurate dynamics discovery
Conceptually, Neural Ordinary Differential Equations (NeuralODEs) pose an
attractive way to extract dynamical laws from time series data, as they are
natural extensions of the traditional differential equation-based modeling
paradigm of the physical sciences. In practice, NeuralODEs display long
training times and suboptimal results, especially for longer duration data
where they may fail to fit the data altogether. While methods have been
proposed to stabilize NeuralODE training, many of these involve placing a
strong constraint on the functional form the trained NeuralODE can take that
the actual underlying governing equation does not guarantee satisfaction. In
this work, we present a novel NeuralODE training algorithm that leverages tools
from the chaos and mathematical optimization communities - synchronization and
homotopy optimization - for a breakthrough in tackling the NeuralODE training
obstacle. We demonstrate architectural changes are unnecessary for effective
NeuralODE training. Compared to the conventional training methods, our
algorithm achieves drastically lower loss values without any changes to the
model architectures. Experiments on both simulated and real systems with
complex temporal behaviors demonstrate NeuralODEs trained with our algorithm
are able to accurately capture true long term behaviors and correctly
extrapolate into the future.Comment: 12 pages, 6 figures, submitted to ICLR202
Optimization of Force Sensitivity in Q-Controlled Amplitude-Modulation Atomic Force Microscopy
We present control of force sensitivity in Q-controlled amplitude-modulation atomic force microscopy (AM-AFM) that is based on the high-Q quartz tuning-fork. It is found that the phase noise is identical to the amplitude noise divided by oscillation amplitude in AM-AFM. In particular, we observe that while Q-control does not compromise the signal-to-noise ratio, it enhances the detection sensitivity because the minimum detectable force gradient is inversely proportional to the effective quality factor for large bandwidths, which is due to reduction of frequency noise. This work demonstrates Q-control in AM-AFM is a useful technique for enhancement of the force sensitivity with increased Q or improvement of the scanning speed with decreased Q