Doctor of Philosophy

dissertationAccurate weather forecasting in complex terrain is of great importance, yet it is a challenging problem due to a number of difficulties, including sparse observations, terrain misrepresentation in numerical models, and model errors related to terrain complexity. Owing to these limitations, few previous studies in data assimilation have emphasized regions of complex terrain. This dissertation presents the first comprehensive evaluation of data assimilation methods and forecast error characteristics for near-surface atmospheric variables in complex terrain. The mesoscale community Weather Research and Forecasting (WRF) model and an advanced ensemble Kalman filter (EnKF) data assimilation system are employed. First, the capability of the advanced EnKF method in assimilating near-surface observations (2-m temperature and 10-m wind) is examined in an observing system simulation experiments framework and compared with the traditional three-dimensional variational data assimilation (3DVAR) method. Results indicated that the EnKF is able to effectively assimilate surface observations and improve the short-range weather forecasts, while the 3DVAR method has fundamental problems in assimilating surface observations. Next, the performance of the WRF model in predicting near-surface atmospheric temperature and wind conditions under various terrain and weather regimes is examined. The WRF model is able to simulate these weather phenomena reasonably well. Forecasts of near-surface variables in flat terrain generally agree well with observations. In complex terrain, forecasts not only suffer from the model's inability to reproduce accurate atmospheric conditions in the lower atmosphere but also struggle with representative issues due to mismatches between the model and the actual terrain. A statistical analysis during a 1-month period over the Dugway Proving Ground (DPG), Utah illustrates that forecast errors in near-surface variables depend strongly on the diurnal variation in surface conditions, especially when synoptic forcing is weak. Finally, the impact of observations from the recent field experiments of the Mountain Terrain Atmospheric Modeling and Observations (MATERHORN) is examined with EnKF. Results illustrated that the quality of the EnKF/WRF analysis is generally high and the short-range forecast errors are comparable to those of the National Centers for Environmental Prediction (NCEP) North American Mesoscale Model (NAM) forecasts for both 10-m wind speed and direction

Beating the Uncertainties: Ensemble Forecasting and Ensemble-Based Data Assimilation in Modern Numerical Weather Prediction

Accurate numerical weather forecasting is of great importance. Due to inadequate observations, our limited understanding of the physical processes of the atmosphere, and the chaotic nature of atmospheric flow, uncertainties always exist in modern numerical weather prediction (NWP). Recent developments in ensemble forecasting and ensemble-based data assimilation have proved that there are promising ways to beat the forecast uncertainties in NWP. This paper gives a brief overview of fundamental problems and recent progress associated with ensemble forecasting and ensemble-based data assimilation. The usefulness of these methods in improving high-impact weather forecasting is also discussed

The impact of environmental regulation on total factor productivity of firms : An analysis based on technical distance

Printed on September 2020Peer reviewe

Research on the Teaching Design Ability of Mathematics Normal Students in Local Normal Universities in China

In order to ensure the smooth development of future work, normal university students must constantly improve their ability of teaching design. This paper uses text analysis method to study the teaching design ability of mathematics normal college students. This paper investigates the mathematics teaching design ability of normal university students from six aspects: overall teaching design, teaching objectives, key points and difficult points of teaching, teaching process, homework arrangement after class and teaching reflection. The results show that the students' overall understanding of teaching design is slightly biased, and the ability of compiling teaching objectives is not ideal, they are able to grasp the key and difficult points in teaching, but unable to put forward how to deal with the key and difficult points in teaching; The teaching process design is also deficient; Normal university students do not pay attention to homework assignment and teaching reflection. Finally, the paper puts forward some suggestions on the development of teaching design ability of mathematics normal university students. Keywords: Normal mathematics student; Teaching design ability DOI: 10.7176/JEP/13-32-08 Publication date: November 30th 202

Influence of Low Load Truncation Level on Crack Growth for Al 2324-T39 and Al 7050-T7451

AbstractTests with middle-crack tension (M(T)) specimens made of Al 2324-T39 and Al 7050-T7451 are conducted to investigate the influence of low load truncation level on fatigue crack growth. The six different truncated spectra are obtained by removing the small cycles of which amplitudes are less than the specified percentages of the maximum amplitude in the basic flight-by-flight loading spectrum and the remainder of the spectrum is untouched. The tests indicate that the mean level of fatigue crack growth life (FCGL) increases as the load truncation level is enhanced. Considering both the time saving and the influence on FCGL, there is an applicable choice (i.e. spectrum S2 or spectrum S3 in this investigation) for full scale fatigue test. The scatter of FCGL becomes much larger than that under the basic spectrum when the load truncation level is increased to a specified high level, mainly due to the occurrence of crack slanting and branching under the high level truncated loading spectra

An Analysis of Mode III Doubly Periodic Crack-Tip Field of Orthotropic Composite Materials

The mechanical behavior near the doubly periodic crack tips for orthotropic composite materials plate subjected to antiplane shear loading is studied. This is done by complex function theory and conformal mapping of the Jacobi elliptic function with the help of boundary conditions. The analytical solution of the crack-tips stress intensity factor and the expression of stress fields are obtained. Numerical examples are given to analyze the impact of the different transverse spacing, longitudinal spacing, and the ratio of cracks periods on stress intensity factors. The results show that the crack-tip field increases with reducing either the transverse spacing or the longitudinal spacing. At the same time, the crack-tip field increases with the decrease of the ratio of cracks periods. This shows that the distribution form makes an important effect on the crack-tip field, but the crack density parameter is not the only cause

ARGONAUTE PIWI domain and microRNA duplex structure regulate small RNA sorting in Arabidopsis.

Small RNAs (sRNAs) are loaded into ARGONAUTE (AGO) proteins to induce gene silencing. In plants, the 5'-terminal nucleotide is important for sRNA sorting into different AGOs. Here we show that microRNA (miRNA) duplex structure also contributes to miRNA sorting. Base pairing at the 15th nucleotide of a miRNA duplex is important for miRNA sorting in both Arabidopsis AGO1 and AGO2. AGO2 favours miRNA duplexes with no middle mismatches, whereas AGO1 tolerates, or prefers, duplexes with central mismatches. AGO structure modelling and mutational analyses reveal that the QF-V motif within the conserved PIWI domain contributes to recognition of base pairing at the 15th nucleotide of a duplex, while the DDDE catalytic core of AtAGO2 is important for recognition of the central nucleotides. Finally, we rescued the adaxialized phenotype of ago1-12, which is largely due to miR165 loss-of-function, by changing miR165 duplex structure which we predict redirects it to AGO2

Multiple distinct small RNAs originate from the same microRNA precursors

Abstract Background MicroRNAs (miRNAs), which originate from precursor transcripts with stem-loop structures, are essential gene expression regulators in eukaryotes. Results We report 19 miRNA precursors in Arabidopsis that can yield multiple distinct miRNA-like RNAs in addition to miRNAs and miRNA*s. These miRNA precursor-derived miRNA-like RNAs are often arranged in phase and form duplexes with an approximately two-nucleotide 3'-end overhang. Their production depends on the same biogenesis pathway as their sibling miRNAs and does not require RNA-dependent RNA polymerases or RNA polymerase IV. These miRNA-like RNAs are methylated, and many of them are associated with Argonaute proteins. Some of the miRNA-like RNAs are differentially expressed in response to bacterial challenges, and some are more abundant than the cognate miRNAs. Computational and expression analyses demonstrate that some of these miRNA-like RNAs are potentially functional and they target protein-coding genes for silencing. The function of some of these miRNA-like RNAs was further supported by their target cleavage products from the published small RNA degradome data. Our systematic examination of public small-RNA deep sequencing data from four additional plant species (Oryza sativa, Physcomitrella patens, Medicago truncatula and Populus trichocarpa) and four animals (Homo sapiens, Mus musculus, Caenorhabditis elegans and Drosophila) shows that such miRNA-like RNAs exist broadly in eukaryotes. Conclusions We demonstrate that multiple miRNAs could derive from miRNA precursors by sequential processing of Dicer or Dicer-like proteins. Our results suggest that the pool of miRNAs is larger than was previously recognized, and miRNA-mediated gene regulation may be broader and more complex than previously thought

3-(10-Chloro-9-anthr­yl)-5-[3-(prop-2-yn­yloxy)phenoxy­meth­yl]isoxazole

In the title mol­ecule, C27H18ClNO3, the anthracene mean plane forms dihedral angles of 67.43 (2) and 15.75 (3)° with the isoxazole and benzene rings, respectively. In the crystal structure, C—H⋯π inter­actions link mol­ecules into centrosymmetric dimers, which are further linked by weak inter­molecular C—H⋯N hydrogen bonds into ribbons propagating in the [110] direction