The Interpretation of Experimental Observation Data for the Development of Mechanisms based Creep Damage Constitutive Equations for High Chromium Steel

It is very important to design a safe factor or estimating the remain lifetime for electric power plant components of steam pipes which mostly manufacture by high chromium steels and work at high temperature and low stress level. The author will develop the mechanisms based on creep damage constitutive equations for high chromium steel under lows stress in initial stage: (1) Creep cavities mostly formed attaching with the precipitation of Laves phase or on grain boundary for high chromium steel under low stress. The Laves phase should play an active role in the nucleation of creep cavities and suggest to explore the function between cavity nucleation and the evolution of Laves phase; (2) The dominant cavity nucleation mechanism is adapted to high chromium steels under low stress level; (3) Brittle intergranluar model is appropriate for high chromium steels at high temperature under low stress level; (4) High density number of cavity of crept test high chromium steel at high temperature under low stress could be as fracture criterion

Performance Advantages of Maximum Likelihood Methods in PRBS-Modulated Time-of-flight Energy Loss Spectroscopy

This thesis describes the design, experimental performance, and theoretical simulation of a novel time-of-flight analyzer that was integrated into a high resolution electron energy loss spectrometer (TOF-HREELS). First we examined the use of an interleaved comb chopper for chopping a continuous electron beam. Both static and dynamic behaviors were simulated theoretically and measured experimentally, with very good agreement. The finite penetration of the field beyond the plane of the chopper leads to non-ideal chopper response, which is characterized in terms of an energy corruption effect and a lead or lag in the time at which the beam responds to the chopper potential. Second we considered the recovery of spectra from pseudo-random binary sequence (PRBS) modulated TOF-HREELS data. The effects of the Poisson noise distribution and the non-ideal behavior of the interleaved comb chopper were simulated. We showed, for the first time, that maximum likelihood methods can be combined with PRBS modulation to achieve resolution enhancement, while properly accounting for the Poisson noise distribution and artifacts introduced by the chopper. Our results indicate that meV resolution, similar to that of modern high resolution electron energy loss spectrometers, can be achieved with a dramatic performance advantage over conventional, serial detection analyzers. To demonstrate the capabilities of the TOF-HREELS instrument, we made measurements on a highly oriented thin film polytetrafluoroethylene (PTFE) sample. We demonstrated that the TOF-HREELS can achieve a throughput advantage of a factor of 85 compared to the conventional HREELS instrument. Comparisons were made between the experimental results and theoretical simulations. We discuss various factors which affect inversion of PRBS modulated Time of Flight (TOF) data with the Lucy algorithm. Using simulations, we conclude that the convolution assumption was good under the conditions of our experiment. The chopper rise time, Poisson noise, and artifacts of the chopper response are evaluated. Finally, we conclude that the maximum likelihood algorithms are able to gain a multiplex advantage in PRBS modulation, despite the Poisson noise in the detector

Copper Ion-Based Electron Spin Resonance Spectroscopic Rulers

This thesis describes the extension of the double electron electron resonance (DEER) technique to the case of Cu(II) and its application in biophysics. First, we demonstrate the possibility of Cu(II)-Cu(II) distance measurement using DEER on a proline-based peptide. The DEER spectra collected at four different magnetic fields do not change appreciably with magnetic field at X-band. Based on simulations, we show that the orientational effects are important in data analysis and that the proper Cu(II)-based DEER experimental procedure is to collect DEER data at many magnetic fields. Next, we examine the cause of the weak field-dependence of Cu(II) DEER data at X-band. We improve the simulation procedure by including a distribution in relative orientation of the g-tensors of the two spins. The new model is tested on two polypeptides. Subtle but detectable orientational effects are observed from DEER spectra of both peptides. Distances obained from DEER are consistent with structural models and with earlier measurements. Constraints on the relative orientation between paramagnetic centers in these two polypeptides are determined by examinations of orientational effects and simulations. We discover that the orientational selectivity is effectively reduced when the relative orientations of the two spin g-tensors display a flexibility of ~5-10°. We apply the methodology to the case of the EcoRI-DNA complex. Electron Spin Echo Envelope Modulation (ESEEM) experiments show that Cu(II) is coordinated to one of the five histidine residues in EcoRI. Cu(II)-based distance constraints are then measured using DEER to reveal this histidine. Using a triangulation procedure based on the measurement of distance constraints we show that Cu(II) binds to histidine 114 in EcoRI. The data is novel because it reveals a second metal ion binding site in EcoRI, which has traditionally been classified as a one-metal endonuclease

The Development and Validation of the Creep Damage Constitutive Equations for P91 Alloy

This paper presents research on the validation of a set of creep damage constitutive equations for P91 alloy under multi-axial states of stress, and its applicability under lower stress level. Creep damage is one of the serious problems for the high temperature industries and computational creep damage has been developed and used, complementary to the experimental approach, to assist safe operation. In creep damage mechanics, a set of constitutive equations needs to be developed and validated. Recently, a mechanism based approach for the developing creep damage constitutive equation for this type of high Cr alloy has merged and several versions of creep damage constitutive equations have been proposed. However, so far, they are limited to uni-axial case under medium to high stress level. In fact, multi-axial states of stress and lower stress level are more pertinent to the real industrial applications. That is the objective of this research. This paper contributes to the methodology and specific knowledge

The relative significance of internal damage mechanisms on the overall creep damage and ultimate failure of P91 steel

This paper reports research on the study of the relative significance of various internal creep damage mechanisms on the overall creep damage and lifetime of P91 steel. The study is essentially parametric investigation based on the individual internal creep damage mechanisms and phenomenological modelling of creep cavity damage. The simulated results do show the importance of the cavity damage among all the creep damage mechanisms. However, more importantly, it also points out the deficiency in the latest approach of phenomenological approach of modelling cavity damage over a wider stress range, and addresses the necessity of considering and incorporating the micromechanics/mechanism of nucleation, growth, coalescence into the creep damage constitutive modelling work. This paper contributes to the knowledge and method for creep damage mechanics

Dys-regulated Gene Expression Networks by Meta-Analysis of Microarray Data on Oral Squamous Cell Carcinoma

Background: Oral squamous cell carcinoma (OSCC) is the sixth most common type of carcinoma worldwide. Development of OSCC is a multi-step process involving genes related to cell cycle, growth control, apoptosis, DNA damage response and other cellular regulators. The pathogenic pathways involved in this tumor are mostly unknown and therefore a better characterization of OSCC gene expression profile would represent a considerable advance. The availability of publicly available gene expression datasets has opened up new challenges especially for the integration of data generated by different research groups and different array platforms with the purpose of obtaining new insights on the biological process investigated.

Results: In this work we performed a meta-analysis on four microarray and four datasets of gene expression data on OSCC in order to evaluate the degree of agreement of the biological results obtained by these different studies and to identify common regulatory pathways that could be responsible of tumor growth. Sixteen dys-regulated pathways implicated in OSCC were mined out from the four published datasets, and most importantly three pathways were first reported. Those regulatory pathways and biological processes which are significantly enriched have been investigated by means of literatures and meanwhile, four genes of the maximally altered pathways, ECM-receptor interaction, were validated and identified by qRT-PCR as a possible candidate of aggressiveness of OSCC.

Conclusion: we have developed a robust method for analyzing pathways altered in OSCC using three expression array data sets. This study sets a stage for the further discovery of the basic mechanisms that may underlie a diseased state and would help in identifying critical nodes in the pathway that can be targeted for diagnosis and therapeutic intervention. In addition, those who are interested in our approach can obtain the software package (MATLAB platform) by email freely

As-Li electrides under high pressure: superconductivity, plastic, and superionic states

Inorganic electrides are a new class of compounds catering to the interest of scientists due to the multiple usages exhibited by interstitial electrons in the lattice. However, the influence of the shape and distribution of interstitial electrons on physical properties and new forms of physical states are still unknown. In this work, crystal structure search algorithms are employed to explore the possibility of forming new electrides in the As-Li system, where interstitial electrons behave as 1D electron chains (1D electride) in Pmmm phase of AsLi$_7$ and transform into 0D electron clusters (0D electride) in P6/mmm phase at 80 GPa. The P6/mmm phase has relatively high superconductivity at 150 GPa (Tc=38.4K) than classical electrides, even at moderate pressure with Tc=16.6K. The novel superconducting properties are conjectured to be possibly due to three Van Hove singularities at the Fermi level. In addition, a Dirac cone in the band has been observed, expanding the sources of Dirac materials. The survival of AsLi$_7$ at room temperature is confirmed by molecular dynamics simulation at 300 K. At 1000 K, the As atoms in the system act like solid, while a portion of the Li atoms cycle around the As atoms, and another portion of the Li atoms flow freely like liquid, showing the novel physical phenomenon of the coexistence of the plastic and superionic states. This suggests that the superionic and plastic states cannot only be found in hydrides but also in the electride. Our results indicate that superconducting electride AsLi$_7$ with superionic and plastic states can exist in Earth's interior

Using tweets to help sentence compression for news highlights generation

We explore using relevant tweets of a given news article to help sentence com-pression for generating compressive news highlights. We extend an unsupervised dependency-tree based sentence compres-sion approach by incorporating tweet in-formation to weight the tree edge in terms of informativeness and syntactic impor-tance. The experimental results on a pub-lic corpus that contains both news arti-cles and relevant tweets show that our pro-posed tweets guided sentence compres-sion method can improve the summariza-tion performance significantly compared to the baseline generic sentence compres-sion method.