82 research outputs found
A surrogate accelerated multicanonical Monte Carlo method for uncertainty quantification
In this work we consider a class of uncertainty quantification problems where
the system performance or reliability is characterized by a scalar parameter
. The performance parameter is random due to the presence of various
sources of uncertainty in the system, and our goal is to estimate the
probability density function (PDF) of . We propose to use the multicanonical
Monte Carlo (MMC) method, a special type of adaptive importance sampling
algorithm, to compute the PDF of interest. Moreover, we develop an adaptive
algorithm to construct local Gaussian process surrogates to further accelerate
the MMC iterations. With numerical examples we demonstrate that the proposed
method can achieve several orders of magnitudes of speedup over the standard
Monte Carlo method
Enabling Full-Stack Quantum Computing with Changeable Error-Corrected Qubits
Executing quantum applications with quantum error correction (QEC) faces the
gate non-universality problem imposed by the Eastin-Knill theorem. As one
resource-time-efficient solution, code switching changes the encoding of
logical qubits to implement universal logical gates. Unfortunately, it is still
unclear how to perform full-stack fault-tolerant quantum computing (FTQC) based
on the changeable logical qubit. Specifically, three critical problems remain
unsolved: a) how to implement the dynamic logical qubit on hardware; b) how to
determine the appropriate timing for logical qubit varying; c) how to improve
the overall system performance for programs of different features. To overcome
those design problems, We propose CECQ, to explore the large design space for
FTQC based on changeable logical qubits. Experiments on various quantum
programs demonstrate the effectiveness of CECQ
Bayesian model calibration for diblock copolymer thin film self-assembly using power spectrum of microscopy data
Identifying parameters of computational models from experimental data, or
model calibration, is fundamental for assessing and improving the
predictability and reliability of computer simulations. In this work, we
propose a method for Bayesian calibration of models that predict morphological
patterns of diblock copolymer (Di-BCP) thin film self-assembly while accounting
for various sources of uncertainties in pattern formation and data acquisition.
This method extracts the azimuthally-averaged power spectrum (AAPS) of the
top-down microscopy characterization of Di-BCP thin film patterns as summary
statistics for Bayesian inference of model parameters via the pseudo-marginal
method. We derive the analytical and approximate form of a conditional
likelihood for the AAPS of image data. We demonstrate that AAPS-based image
data reduction retains the mutual information, particularly on important length
scales, between image data and model parameters while being relatively agnostic
to the aleatoric uncertainties associated with the random long-range disorder
of Di-BCP patterns. Additionally, we propose a phase-informed prior
distribution for Bayesian model calibration. Furthermore, reducing image data
to AAPS enables us to efficiently build surrogate models to accelerate the
proposed Bayesian model calibration procedure. We present the formulation and
training of two multi-layer perceptrons for approximating the
parameter-to-spectrum map, which enables fast integrated likelihood
evaluations. We validate the proposed Bayesian model calibration method through
numerical examples, for which the neural network surrogate delivers a fivefold
reduction of the number of model simulations performed for a single calibration
task
Compilation for Quantum Computing on Chiplets
Chiplet architecture is an emerging architecture for quantum computing that
could significantly increase qubit resources with its great scalability and
modularity. However, as the computing scale increases, communication between
qubits would become a more severe bottleneck due to the long routing distances.
In this paper, we trade ancillary qubits for program concurrency by proposing a
multi-entry communication highway mechanism, and building a compilation
framework to efficiently manage and utilize the highway resources. Our
evaluation shows that this framework significantly outperforms the baseline
approach in both the circuit depth and the number of operations on some typical
quantum benchmarks, leading to a more efficient and less error-prone
compilation of quantum programs
TiāCā MXene-based Schottky Photocathode for Enhanced Photoelectrochemical Sensing
Nanomaterials are vital to the realization of photoelectrochemical (PEC) sensing platfrom that provides the sensitive detection and quantification of low-abundance biological samples. Here, this work reports a Schottky junction-based BiOI/TiāCā heterostructure, used as a photocathode for PEC bioanalysis. Specially, we realize in situ growth of flower-like BiOI on 2D intrinsically negatively charged TiāCā MXene nanosheet that endows BiOI/TiāCā heterostructure with admirably combined merits, noting in particular the generation of built-in electric field and the decrease of contact resistance between BiOI and TiāCā. Under the visible light irradiation, the BiOI/TiāCā heterostructure-modified PEC platform displays superior cathodic photocurrent signal, while PEC response cuts down with the presence of L-Cysteine (L-Cys) as a representative analyte owing to the metal-S bond formation. The āsignal-offā PEC sensing strategy shows good performance in terms of sensitivity, limit of detection (LOD, 0.005 nM) and stability. This research reveals the great potentials of MXene-based heterostructure in the application field of PEC sensor establishment
Nitrogen rather than streamflow regulates the growth of riparian trees
In arid and semiarid regions, riparian forests are crucial for maintaining ecological biodiversity and sustainability, and supporting social and economic development. For the typical arid and semiarid ecosystem, streamflow variability is thought to be the dominant factor influencing the vulnerability and evolution of the riparian forests, which often leads to the neglect of other potentially important factors such as nutrient availability and transport. Here, we measured annual stable nitrogen isotopes (Ī“15N) and nitrogen concentrations (N%) in the tree rings of Populus euphratica Oliv. (Euphrates poplar) over a 90 year period (1920ā2012), collected from the lower researches of the inland Heihe River, northwestern China. Coupling with our previous dual-isotope (Ī“13C and Ī“18O) chronologies and estimated intrinsic water-use efficiency (iWUE), we examined the linkages between tree-ring Ī“15N and Ī“18O, iWUE, streamflow, and then explored the contributions of each to tree growth during the study period. Our results show that after 1975, a statistically significant correlation between tree-ring Ī“15N and river streamflow appears, indicating the river as a potential carrier of nitrogen from the upper and middle reaches to the lower research trees. In addition, the linkage between tree-ring Ī“15N and iWUE suggests substantial influence of carbon and nitrogen together on photosynthesis and transpiration of trees, although this connection become decoupled since AD 1986. The commonality analysis revealed that the nitrogen impacts indicated by tree-ring Ī“15N on tree growth cannot be ignored when evaluating riparian forest development. The fertilization effects caused by rising CO2 concentration complicate the nitrogen constraints on tree growth during the later part of the past century. Our results have potentially broad implications for identifying the limited factors for dryland forest ecosystems that are susceptible to natural water resource variations and human activities
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