100 research outputs found
Chlorine and Bromine Isotope Fractionation of Halogenated Organic Pollutants on Gas Chromatography Columns
Compound-specific chlorine/bromine isotope analysis (CSIA-Cl/Br) has become a
useful approach for degradation pathway investigation and source appointment of
halogenated organic pollutants (HOPs). CSIA-Cl/Br is usually conducted by gas
chromatography-mass spectrometry (GC-MS), which could be negatively impacted by
chlorine and bromine isotope fractionation of HOPs on GC columns. In this
study, 31 organochlorines and 4 organobromines were systematically investigated
in terms of Cl/Br isotope fractionation on GC columns using GC-double focus
magnetic-sector high resolution MS (GC-DFS-HRMS). On-column chlorine/bromine
isotope fractionation behaviors of the HOPs were explored, presenting various
isotope fractionation modes and extents. Twenty-nine HOPs exhibited inverse
isotope fractionation, and only polychlorinated biphenyl-138 (PCB-138) and
PCB-153 presented normal isotope fractionation. And no observable isotope
fractionation was found for the rest four HOPs, i.e., PCB-101,
1,2,3,7,8-pentachlorodibenzofuran, PCB-180 and 2,3,7,8-tetrachlorodibenzofuran.
The isotope fractionation extents of different HOPs varied from below the
observable threshold (0.50%) to 7.31% (PCB-18). The mechanisms of the on-column
chlorine/bromine isotope fractionation were tentatively interpreted with the
Craig-Gordon model and a modified two-film model. Inverse isotope effects and
normal isotope effects might contribute to the total isotope effects together
and thus determine the isotope fractionation directions and extents. Proposals
derived from the main results of this study for CSIA-Cl/Br research were
provided for improving the precision and accuracy of CSIA-Cl/Br results. The
findings of this study will shed light on the development of CSIA-Cl/Br methods
using GC-MS techniques, and help to implement the research using CSIA-Cl/Br to
investigate the environmental behaviors and pollution sources of HOPs.Comment: 30 pages, 5 figure
Holocene vegetational and climatic history of the Xuguo Co catchment in the central Tibetan Plateau
A 101-cm core was taken from a large lake in the central Tibetan Plateau. Its pollen and loss-on-ignition analyses provide a Holocene vegetational, climatic, and environmental history of the lake catchment. Pollen analysis shows that: dense steppe dominated regional vegetation in the early Holocene (9,200–8,000 cal. yr BP); regional vegetation coverage gradually decreased in the middle Holocene (8,000–4,100 cal. yr BP); and marsh meadow grew on the lake edge and sparse steppe occupied the lake catchment after 4,100 cal. yr BP. Our result also reveals that: 9,200–8,000 cal. yr BP witnessed summer temperature, monsoonal rainfall, and lake-level maxima, as well as few winter and spring aeolian activities and frequent wildfires; 8,000–4,100 cal. yr BP saw a nonlinear decline in temperature, rainfall, lake level, and wildfires; and modern climatic and environmental conditions were established after 4,100 cal. yr BP. Three major monsoon-weakening events at ca. 6,700, 5,800, and 4,100 cal. yr BP were detected by pollen signals and proxies of the climate and environment
Improving Gender Fairness of Pre-Trained Language Models without Catastrophic Forgetting
Existing studies addressing gender bias of pre-trained language models,
usually build a small gender-neutral data set and conduct a second phase
pre-training on the model with such data. However, given the limited size and
concentrated focus of the gender-neutral data, catastrophic forgetting would
occur during second-phase pre-training. Forgetting information in the original
training data may damage the model's downstream performance by a large margin.
In this work, we empirically show that catastrophic forgetting occurs in such
methods by evaluating them with general NLP tasks in GLUE. Then, we propose a
new method, GEnder Equality Prompt (GEEP), to improve gender fairness of
pre-trained models with less forgetting. GEEP freezes the pre-trained model and
learns gender-related prompts with gender-neutral data. Empirical results show
that GEEP not only achieves SOTA performances on gender fairness tasks, but
also forgets less and performs better on GLUE by a large margin.Comment: This paper has been accepted at the 61st Annual Meeting of the
Association for Computational Linguistics (ACL 2023
Asymptotic CRB Analysis of Random RIS-Assisted Large-Scale Localization Systems
This paper studies the performance of a randomly RIS-assisted multi-target
localization system, in which the configurations of the RIS are randomly set to
avoid high-complexity optimization. We first focus on the scenario where the
number of RIS elements is significantly large, and then obtain the scaling law
of Cram\'er-Rao bound (CRB) under certain conditions, which shows that CRB
decreases in the third or fourth order as the RIS dimension increases. Second,
we extend our analysis to large systems where both the number of targets and
sensors is substantial. Under this setting, we explore two common RIS models:
the constant module model and the discrete amplitude model, and illustrate how
the random RIS configuration impacts the value of CRB. Numerical results
demonstrate that asymptotic formulas provide a good approximation to the exact
CRB in the proposed randomly configured RIS systems
Policy Optimization for Markov Games: Unified Framework and Faster Convergence
This paper studies policy optimization algorithms for multi-agent
reinforcement learning. We begin by proposing an algorithm framework for
two-player zero-sum Markov Games in the full-information setting, where each
iteration consists of a policy update step at each state using a certain matrix
game algorithm, and a value update step with a certain learning rate. This
framework unifies many existing and new policy optimization algorithms. We show
that the state-wise average policy of this algorithm converges to an
approximate Nash equilibrium (NE) of the game, as long as the matrix game
algorithms achieve low weighted regret at each state, with respect to weights
determined by the speed of the value updates. Next, we show that this framework
instantiated with the Optimistic Follow-The-Regularized-Leader (OFTRL)
algorithm at each state (and smooth value updates) can find an
approximate NE in iterations, and a
similar algorithm with slightly modified value update rule achieves a faster
convergence rate. These improve over the
current best rate of symmetric policy
optimization type algorithms. We also extend this algorithm to multi-player
general-sum Markov Games and show an
convergence rate to Coarse Correlated Equilibria (CCE). Finally, we provide a
numerical example to verify our theory and investigate the importance of smooth
value updates, and find that using "eager" value updates instead (equivalent to
the independent natural policy gradient algorithm) may significantly slow down
the convergence, even on a simple game with layers
A Wi-Fi Signal-Based Human Activity Recognition Using High-Dimensional Factor Models
Passive sensing techniques based on Wi-Fi signals have emerged as a promising
technology in advanced wireless communication systems due to their widespread
application and cost-effectiveness. However, the proliferation of low-cost
Internet of Things (IoT) devices has led to dense network deployments,
resulting in increased levels of noise and interference in Wi-Fi environments.
This, in turn, leads to noisy and redundant Channel State Information (CSI)
data. As a consequence, the accuracy of human activity recognition based on
Wi-Fi signals is compromised. To address this issue, we propose a novel CSI
data signal extraction method. We established a human activity recognition
system based on the Intel 5300 network interface cards (NICs) and collected a
dataset containing six categories of human activities. Using our approach,
signals extracted from the CSI data serve as inputs to machine learning (ML)
classification algorithms to evaluate classification performance. In comparison
to ML methods based on Principal Component Analysis (PCA), our proposed
High-Dimensional Factor Model (HDFM) method improves recognition accuracy by
6.8%
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