178 research outputs found
A Novel Power Flow Method for Long Term Frequency Stability Analysis
This thesis presents a novel approach for a power system to find a practical power flow solution when all the generators in the system have hit their real power output limits, such as some generator units shutting down or load outages. The approach assumes the frequency of the system is unable to be kept at the rated value (usually 60 or 50 Hz) and accordingly, the generator real power outputs are affected by the system frequency deviation.
The modification aims to include the system frequency deviation as a new state variable in the power flow so that the power system can be described in a more precise way when the generation limits are hit and the whole system is not operated under the normal condition. A new mathematical formulation for power flow is given by modified the conventional power flow mismatch equation and Jacobian matrix.
The Newton – Raphson method is particularly chose to be modified because Newton – Raphson method is most widely used and it is a fast convergent and accurate method. The Jacobian matrix will be augmented by adding a column and a row.
Matlab is used as a programming tool to implement the Power Flow for Long Term Frequency Stability (PFLTFS) method for a simple 4-bus system and the IEEE 118-bus system. And PSS/E Dynamic simulation is used to verify the steady state solution from PFLTFS is reasonable. The PSS/E Dynamic Simulation plots are used to analyze the long term frequency response.
The PFLTFS method provides a technique for solving an abnormal state system power flow. From the results we can conclude that the PFLTFS method is reasonable for solving power flow of a real power unbalanced system
Assessment of putative protein targets derived from the SARS genome
AbstractThe ability to rapidly and reliably develop hypotheses on the function of newly discovered protein sequences requires systematic and comprehensive analysis. Such an analysis, embodied within the DS GeneAtlasâ„¢ pipeline, has been used to critically evaluate the severe acute respiratory syndrome (SARS) genome with the goal of identifying new potential targets for viral therapeutic intervention. This paper discusses several new functional hypotheses on the roles played by the constituent gene products of SARS, and will serve as an example of how such assignments can be developed or extended on other systems of interest
Oxygen dissociation on the C3N monolayer: A first-principles study
The oxygen dissociation and the oxidized structure on the pristine C3N
monolayer in exposure to air are the inevitably critical issues for the C3N
engineering and surface functionalization yet have not been revealed in detail.
Using the first-principles calculations, we have systematically investigated
the possible O2 adsorption sites, various O2 dissociation pathways and the
oxidized structures. It is demonstrated that the pristine C3N monolayer shows
more O2 physisorption sites and exhibits stronger O2 adsorption than the
pristine graphene. Among various dissociation pathways, the most preferable one
is a two-step process involving an intermediate state with the chemisorbed O2
and the barrier is lower than that on the pristine graphene, indicating that
the pristine C3N monolayer is more susceptible to oxidation than the pristine
graphene. Furthermore, we found that the most stable oxidized structure is not
produced by the most preferable dissociation pathway but generated from a
direct dissociation process. These results can be generalized into a wide range
of temperatures and pressures using ab initio atomistic thermodynamics. Our
findings deepen the understanding of the chemical stability of 2D crystalline
carbon nitrides under ambient conditions, and could provide insights into the
tailoring of the surface chemical structures via doping and oxidation.Comment: 23 pages,8 figure
Development of high performance catalysts for CO oxidation using data-based modeling
Abstract This paper presents a model-aided approach to the development of catalysts for CO oxidation. This is in contrast to the traditional methodology whereby experiments are guided based on experience and intuition of chemists. The proposed approach operates in two stages. To screen a promising combination of active phase, promoter and support material, a powerful "space-filling" experimental design (specifically, Hammersley sequence sampling) was adopted. The screening stage identified Au-ZnO/Al 2 O 3 as a promising recipe for further optimization. In the second stage, the loadings of Au and ZnO were adjusted to optimize the conversion of CO through the integration of a Gaussian process regression (GPR) model and the technique of maximizing expected improvement. Considering that Au constitutes the main cost of the catalyst, we further attempted to reduce the loading of Au with the aid of GPR, while keeping the low-temperature conversion to a high level. Finally we obtained 2.3%Au-5.0%ZnO/Al 2 O 3 with 21 experiments. Infrared reflection absorption spectroscopy and hydrogen temperature-programmed reduction confirmed that ZnO significantly promotes the catalytic activity of Au
Widespread subsonic turbulence in Ophiuchus North 1
Supersonic motions are common in molecular clouds. (Sub)sonic turbulence is
usually detected toward dense cores and filaments. However, it remains unknown
whether (sub)sonic motions at larger scales (1~pc) can be present in
different environments or not. Located at a distance of about 110 pc, Ophiuchus
North 1 (Oph N1) is one of the nearest molecular clouds that allows in-depth
investigation of its turbulence properties by large-scale mapping observations
of single-dish telescopes. We carried out the CO () and CO
() imaging observations toward Oph N1 with the Purple Mountain
Observatory 13.7 m telescope. The observations have an angular resolution of
55\arcsec (i.e., 0.03~pc). Most of the whole CO emitting regions
have Mach numbers of 1, demonstrating the large-scale (sub)sonic
turbulence across Oph N1. Based on the polarization measurements, we estimate
the magnetic field strength of the plane-of-sky component to be
9~G. We infer that Oph N1 is globally sub-Alfv{\'e}nic, and is
supported against gravity mainly by the magnetic field. The steep velocity
structure function can be caused by the expansion of the Sh~2-27 H{\scriptsize
II} region or the dissipative range of incompressible turbulence. Our
observations reveal a surprising case of clouds characterised by widespread
subsonic turbulence and steep size-linewidth relationship. This cloud is
magnetized where ion-neutral friction should play an important role.Comment: 16 pages, 12 figures, accepted for publication in A&
pLMFPPred: a novel approach for accurate prediction of functional peptides integrating embedding from pre-trained protein language model and imbalanced learning
Functional peptides have the potential to treat a variety of diseases. Their
good therapeutic efficacy and low toxicity make them ideal therapeutic agents.
Artificial intelligence-based computational strategies can help quickly
identify new functional peptides from collections of protein sequences and
discover their different functions.Using protein language model-based
embeddings (ESM-2), we developed a tool called pLMFPPred (Protein Language
Model-based Functional Peptide Predictor) for predicting functional peptides
and identifying toxic peptides. We also introduced SMOTE-TOMEK data synthesis
sampling and Shapley value-based feature selection techniques to relieve data
imbalance issues and reduce computational costs. On a validated independent
test set, pLMFPPred achieved accuracy, Area under the curve - Receiver
Operating Characteristics, and F1-Score values of 0.974, 0.99, and 0.974,
respectively. Comparative experiments show that pLMFPPred outperforms current
methods for predicting functional peptides.The experimental results suggest
that the proposed method (pLMFPPred) can provide better performance in terms of
Accuracy, Area under the curve - Receiver Operating Characteristics, and
F1-Score than existing methods. pLMFPPred has achieved good performance in
predicting functional peptides and represents a new computational method for
predicting functional peptides.Comment: 20 pages, 5 figures,under revie
Hierarchical Multi-scale Attention Networks for action recognition
Recurrent Neural Networks (RNNs) have been widely used in natural language
processing and computer vision. Among them, the Hierarchical Multi-scale RNN
(HM-RNN), a kind of multi-scale hierarchical RNN proposed recently, can learn
the hierarchical temporal structure from data automatically. In this paper, we
extend the work to solve the computer vision task of action recognition.
However, in sequence-to-sequence models like RNN, it is normally very hard to
discover the relationships between inputs and outputs given static inputs. As a
solution, attention mechanism could be applied to extract the relevant
information from input thus facilitating the modeling of input-output
relationships. Based on these considerations, we propose a novel attention
network, namely Hierarchical Multi-scale Attention Network (HM-AN), by
combining the HM-RNN and the attention mechanism and apply it to action
recognition. A newly proposed gradient estimation method for stochastic
neurons, namely Gumbel-softmax, is exploited to implement the temporal boundary
detectors and the stochastic hard attention mechanism. To amealiate the
negative effect of sensitive temperature of the Gumbel-softmax, an adaptive
temperature training method is applied to better the system performance. The
experimental results demonstrate the improved effect of HM-AN over LSTM with
attention on the vision task. Through visualization of what have been learnt by
the networks, it can be observed that both the attention regions of images and
the hierarchical temporal structure can be captured by HM-AN
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