In chapter 1, we focus on the full potential equation in an infinite nozzle with some decay cross-sections and prove the existence and stability of the transonic shock wave; which is a solution to a free boundary value problem for a quasi-linear mix-typed partial differential equation with the position of shock as a free boundary. To achieve this conclusion, we reduce it to a free boundary value problem for a quasi-linear elliptic equation in an unbounded domain. The crucial step in our analysis is to derive some uniform a priori estimates in such a domain. Then we apply the fixed point theorem to establish the existence of solutions to the full potential equation. / In chapter 2, we study the short time existence of discontinuous shock front solutions of the pressure gradient system which is the Euler system without inertial terms, where the initial data can have shock discontinuities of arbitrary strength which lie on a given smooth initial surface with arbitrary geometry. These shock solutions are constructed via a classical iteration scheme. The key step is to obtain the uniform stability for the related linearized equation by calculating the Lopatinski's determinant, which enables us to modify the technique of Majda and establish the local existence of solutions to the pressure gradient system without the structural constraints as for the full Euler system. / In this thesis we study two kinds of multi-dimensional shock phenomena for the compressible fluid dynamics. / Xie Feng. / "December 2005." / Adviser: Zhou Ping Xin. / Source: Dissertation Abstracts International, Volume: 67-11, Section: B, page: 6446. / Thesis (Ph.D.)--Chinese University of Hong Kong, 2005. / Includes bibliographical references (p. 71-80). / Electronic reproduction. Hong Kong : Chinese University of Hong Kong, [2012] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Electronic reproduction. [Ann Arbor, MI] : ProQuest Information and Learning, [200-] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Abstracts in English and Chinese. / School code: 1307.

Salmonella enterica sv. typhimurium is a major food-borne pathogen, in part because of its ability to persist and multiply at low temperatures. Adaptation to refrigerated temperatures involves induction of a multigenic cold shock response (CSR); where gene expression is co-ordinately modified, to express cold shock proteins (CSPs). Characterisation of CspA, the major cold shock protein, instigated the identification of other CspA paralogues; which are highly conserved and widespread across species. Six CspA paralogues have previously been identified in S. typhimurium and a csp null strain, lacking all CspA paralogues made. This strain is unable to grow following cold shock, demonstrating that the CspA paralogues play an essential role during low temperature adaptation. The individual CspA paralogues exhibit distinct expression profiles; including expression of CspC and CspE at optimal temperature and CspA and CspB following cold shock. This work investigates the transcriptional changes of S. typhimurium during cold shock and the role of the CspA paralogues under both optimal and cold shock conditions. Using a bacteriophage Mu transposon library (Francis and Gallagher, 1993) this study identifies 7 novel cold induced targets and analyses their native expression levels in SL1344 and the csp null strain during cold shock. This revealed that the regulation of 5 discrete loci including tRNApro2, cpxP and 3 uncharacterised ORFS are mediated by CspA paralogues. In addition, the transcriptional profiles of a highly conserved and essential set of genes encoding known cold shock proteins, NusA, IF2, RbfA, PNPase and CsdA have been characterised. Comparative Northern analysis of SL1344 and the csp null strain has identified a role for CspA paralogues in mediating low temperature induction of three of these genes, through transcription anti-termination. Taken together these results demonstrate that during adaptation to low temperature CspA paralogues regulate expression of genes involved in the translational machinery and metabolic biosynthetic pathways: possibly through a number of transcriptional and post transcriptional processing events. Furthermore this study provides in vivo evidence of the RNA binding activity of the S. typhimurium CspA paralogues. Using fusion proteins, the RNA targets of CspE at 37°C and CspA at 10°C were isolated and analysed. This work identifies 17 direct binding targets for CspE and these indicate that CspE performs a role at optimal growth temperature in regulating components of metabolic (coaA and plsX), translational (EF-Tu, EF-G and IF3) and virulence associated (hha) pathways. Functional redundancy between CspE and CspA was suggested as both paralogues bound 16s rRNA. In light of these findings, the functions of CspA & CspE at optimal and low temperature are discussed. Overall this study has revealed novel information about low temperature adaptation of S. typhimurium, expanding our knowledge of the complexity and importance of the CSR in bacterial pathogens. In addition this work enhances our comprehension of the roles of the CspA paralogues at both optimal and low temperature.

In cold temperatures, the survival of Salmonella enterica serovar Typhimurium (S. Typhimurium) requires the action of cold shock protein A (CspA) paralogues. These are thought to melt misfolded ribonucleic acids, facilitating their translation at low temperatures. However, through phenotypic analysis of our SL1344 csp null mutant (lacking all CspA paralogues), it has been shown that CspA paralogues function during other environmental stresses, outwith temperature reduction, and play an essential role in colony formation of an SL1344 rpoS mutant at 37°C. The general stress σ subunit, RpoS, plays an important role in adapting cells to a number of stresses including oxidative stress, temperature changes, low pH and stationary phase. Under such conditions, RpoS acts as an ‘emergency co-ordinator’, subsequently inducing the transcription of necessary stress response genes. In Escherichia coli, RpoS is regulated posttranscriptionally by at least three small RNAs (sRNAs): OxyS, DsrA and RprA; that require interactions with the Sm-like RNA chaperone, Hfq. In S. Typhimurium, the stability of the RpoS protein itself is regulated by ClpXP, an ATP-dependent protease responsible for RpoS degradation, and a specific recognition factor that targets RpoS to this protease, MviA. The present study has shown that the CspA paralogues of S. Typhimurium are involved in the expression of RpoS and aims to elucidate the role of these proteins in RpoS production. Comparative phenotypic tests were carried out in strains carrying mutations in rpoS, hfq and the csp genes to gain insight into the interactions of Hfq and CspA paralogues, with respect to RpoS expression. Both significant phenotypic overlaps, such as peroxide sensitivity, and phenotypes unique to certain mutant strains, such as cold acclimation in the csp null strain, were observed. CspA paralogues and Hfq are functionally distinct, not only in their involvement in RpoS expression, but also in RpoS-independent processes, such as cold acclimation, motility and to some extent, growth at 37°C. The roles of Hfq and the CspA paralogues, in RpoS expression, were also assessed at the molecular level. A combination of qRT-PCR analysis, transcriptional fusions and immunoblotting (with anti-σ antibodies) has shown that DsrA and RprA are not essential for RpoS expression in S. Typhimurium, during stationary phase or exponential cold shock, and do not require Hfq under these conditions. Contrary to reports in E. coli, DsrA is not induced upon cold shock in SL1344. Northern blots have shown that neither Hfq nor the CspA paralogues are involved in regulating rpoS transcription during either stationary phase at 37°C or cold shock in exponential phase. Immunoblotting and translational fusions have identified different pathways for the regulation of RpoS during stationary phase at 37°C and cold shock in exponential phase. Hfq is involved during the former condition only, whilst CspA paralogues are involved in both. Protein stability experiments have shown that the CspA paralogues do not play a major role in stabilising RpoS protein against degradation. Together, these results have pointed to a role for both the CspA paralogues and Hfq in facilitating the efficient translation of rpoS mRNA. An SL1344 csp null rpoS mutant is unable to form colonies on LB agar at 37°C, a phenomenon found when introducing combinations of mutations to SL1344 for phenotypic assessment. A conditional rpoS mutant revealed that the SL1344 csp null rpoS strain is viable but non-culturable. From the csp gene family, only cspA and cspB were able to restore colony forming ability to the rpoS mutant. Further complementation experiments pointed to faulty cell division, due to abnormal RNase E activity, as the cause.

Ho, Sin Chu. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2008. / Includes bibliographical references (leaves 112-135). / Abstracts in English and Chinese. / Abstract --- p.i / 摘要 --- p.ii / Acknowledgement --- p.iii / Table of Contents --- p.iv / List of Abbreviations --- p.vii / List of Figures --- p.x / List of Tables --- p.xii / Chapter Chapter 1 --- Introduction --- p.1 / Chapter 1.1 --- Test Organisms: Daphnia magna and Moina macrocopa --- p.1 / Chapter 1.2 --- Biomarkers --- p.2 / Chapter 1.3 --- Heat shock protein (HSP) --- p.4 / Chapter 1.3.1 --- Regulation of hsp70 gene expression --- p.5 / Chapter 1.3.2 --- Review of studies on hsp70 of various species --- p.6 / Chapter 1.3.3 --- Review of studies using molecular methods in Daphnia and Moina --- p.7 / Chapter 1.4 --- Environmental stress studied --- p.9 / Chapter 1.5 --- Objectives --- p.11 / Chapter Chapter 2 --- Materials and Methods --- p.12 / Chapter 2.1 --- Experimental organisms --- p.12 / Chapter 2.2 --- "The effects of temperature, metals and nutritional stress on cladocerans" --- p.13 / Chapter 2.3 --- Demographic measurement --- p.15 / Chapter 2.4 --- Cloning and sequencing of D. magna and M. macrocopa hsp70 --- p.17 / Chapter 2.4.1 --- Acute heat shock --- p.17 / Chapter 2.4.2 --- Total RNA extraction --- p.17 / Chapter 2.4.3 --- Reverse transcription and polymerase chain reaction (PCR) --- p.18 / Chapter 2.4.4 --- Degenerative PCR --- p.21 / Chapter 2.4.5 --- Cloning and sequencing of hsp70 partial sequence --- p.25 / Chapter 2.4.6 --- Rapid amplification of cDNA ends (RACE) --- p.28 / Chapter 2.4.7 --- Confirmation of D. magna and M. macrocopa hsp70 sequences --- p.30 / Chapter 2.5 --- Molecular measurements - heat shock protein 70 gene expression --- p.31 / Chapter 2.5.1 --- Sample collection --- p.31 / Chapter 2.5.2 --- Quantification of cDNA level by real-time PCR --- p.32 / Chapter 2.5.2.1 --- Primer design --- p.32 / Chapter 2.5.2.2 --- Validation of real-time PCR conditions --- p.32 / Chapter 2.5.2.3 --- Determination of hsp70 gene expression levels --- p.35 / Chapter 2.6 --- Statistical analysis --- p.36 / Chapter Chapter 3 --- Results --- p.37 / Chapter 3.1 --- Demographic measurements --- p.37 / Chapter 3.1.1 --- Effects of temperature on life history parameters of M macrocopa --- p.37 / Chapter 3.1.2 --- Effects of temperature on life history parameters of D. magna --- p.40 / Chapter 3.1.3 --- Effects of Metals on life history parameters of M. macrocopa --- p.42 / Chapter 3.1.4 --- Effects of Anabaena on life history parameters of M. macrocopa --- p.47 / Chapter 3.2 --- Cloning and sequencing of hsp70 --- p.50 / Chapter 3.2.1 --- Partial sequences of D. magna and M. macrocopa hsp70 --- p.50 / Chapter 3.2.2 --- Sequences of 3´ة and 5´ة RACE amplified products --- p.53 / Chapter 3.2.3 --- Full sequences of D. magna and M. macrocopa hsp70 --- p.53 / Chapter 3.2.4 --- Phylogenetic relationships of the hsp70 gene --- p.60 / Chapter 3.3 --- Molecular measurements - heat shock protein 70 gene expression --- p.71 / Chapter 3.3.1 --- Validation of real-time PCR conditions --- p.71 / Chapter 3.3.2 --- Effect of temperature stress on hsp70 gene expression levels --- p.76 / Chapter 3.3.3 --- Effect of metals on hsp70 gene expression levels --- p.78 / Chapter 3.3.4 --- Effect of Anabaena on Hsp70 Gene Expression Levels --- p.83 / Chapter Chapter 4 --- Discussion --- p.85 / Chapter 4.1 --- Demographic responses of M. macrocopa and D. magna by different stress --- p.85 / Chapter 4.1.1 --- Effects of temperature on life history parameters --- p.85 / Chapter 4.1.2 --- Effects of metal stress on life history parameters --- p.87 / Chapter 4.1.3 --- Effects of Anabaena on life history parameters --- p.89 / Chapter 4.2 --- Characterization of hsp70 of M. macrocopa and D. magna --- p.92 / Chapter 4.3 --- Hsp70 gene expression in response to different stress --- p.94 / Chapter 4.3.1 --- Effect of temperature stress on hsp70 gene expression levels --- p.94 / Chapter 4.3.2 --- Effect of metals on Hsp70 gene expression levels --- p.97 / Chapter 4.3.3 --- Effect of Anabaena on hsp70 gene expression levels --- p.101 / Chapter 4.4 --- Comparison of demographic and molecular measurements --- p.102 / Chapter 4.5 --- Performance of hsp70 gene expression as a biomarker of environmental stress --- p.106 / Chapter 4.6 --- Conclusion --- p.111 / References --- p.112 / Appendix --- p.136

I study a dusty plasma produced in a DC glow discharge device. The chamber is a stainless steel cylinder 0.6 m in diameter and 0.9 m long. A stainless steel disk 3.2 cm in diameter acts as the anode and the walls act as the cathode. The discharge current is set between 1 - 10 mA and the voltage at the anode between 250 - 300 V. Dust is initially on a tray beneath the anode, and becomes trapped in the anode glow naturally with high discharge current. A secondary cloud can be made at a different location using a biased mesh. I make experimental observations of the dynamics of the secondary cloud as well as the unique interaction of the dust with a wire loop near the anode. First, I describe the interaction of the secondary cloud with a wire when it the cloud is released to flow back to the primary cloud. A detached bow shock is observed as the cloud encounters an obstacle, and an elongated teardrop shaped void is formed downstream of the obstacle. Second, a continuous flow is set up using at biased ring. The potentials of the ring and anode create a converging-diverging electrostatic potential structure which accelerates dust particles into a thin stream in the diverging section. The interaction of this stream and a wire obstacle is described. Finally, the potentials of the mesh and anode are suddenly switched to float simultaneously to observe the secondary cloud expansion in the afterglow plasma. The rate of expansion is shown to depend inversely on the background pressure in the range of 100-200mTorr. The expansion shows a separation in the cloud and possible Yukawa-like expansion where the center of the cloud does not respond initially to the removal of confinement.

No description available.

Thesis (Ph. D.)--University of Missouri-Columbia, 2007. / The entire dissertation/thesis text is included in the research.pdf file; the official abstract appears in the short.pdf file (which also appears in the research.pdf); a non-technical general description, or public abstract, appears in the public.pdf file. Title from title screen of research.pdf file (viewed on December 6, 2007) Vita. Includes bibliographical references.

Even though the elastic deformations that occur during the impact of colliding bodies may be small in comparison to their actual dimensions, they play an important role in mechanical collisions. During the time the bodies are in contact, elastic, friction, and inertia properties combine to produce a complex variation of sliding and sticking throughout the contact surface. Detailed analysis of this interaction is quite tedious, but would seem to be necessary for accurately predicting the impulse and velocity changes that occur during contact. However, a considerably-simplified model captures the essential characteristics of the elastic-friction interaction during contact, leading to predictions of impulse and velocity changes that agree well with those of more detailed analyses of a number of different collisions. The model's simplicity enables an examination of parameters that affect a general class of collisions. For planar collisions, the model contains five dimensionless parameters; the effects of four of these on the rebound velocity are examined here. In addition, comparisons are made with a previously-used, somewhat simpler model, which neglects the tangential compliance in the region of contact. / Graduation date: 1993

Upon encountering stress conditions, cells must rapidly alter their gene expression and re-model their RNA complement to deal with the changing environment. As a consequence, both new RNA transcription as well as RNA degradation must take place. Accordingly, the RNA degradative machinery may adjust to the changes in RNA metabolism. Thus, a study of the response of the three major degradative exoribonucleases in Escherichia coli, polynucleotide phosphorylase, RNase II, and RNase R, to stress is of significant importance. RNase R, a processive 3' to 5' exoribonuclease, is unique among the known E. coli exoribonucleases in its ability to digest through RNAs containing extensive secondary structure without the aid of a helicase. In vivo, RNase R plays important roles in quality control of stable RNA, decay of mRNA with extensive repetitive extragenic palindromic (REP) sequences, cell-cycle regulated degradation of tmRNA in Caulobacter crescentus, as well as processing of rRNA under low temperature in P. syringae. In this dissertation, RNase R was shown to be unusual among the E. coli exoribonucleases in its dramatic response to a variety of stress conditions. Elevation of RNase R activity by as much as 10-fold was observed in response to entry into stationary phase, starvation and cold shock, and an ~3-fold increase was seen during growth in minimal medium compared to rich medium. The elevation in RNase R activity was associated with an increase in RNase R protein. Phenotypes of rnr mutants were also investigated, and RNase R was found to contribute to cell growth and viability. Further investigation of the regulation of RNase R during stress, primarily in stationary phase, revealed a novel regulation mechanism. Despite the large increase in RNase R protein and activity in stationary phase, rnr message actually decreased to only ~14% of its level in exponential phase. Further study revealed that RNase R is highly unstable in exponential phase and becomes stabilized during stationary phase, cold shock, and in minimal medium. Investigation of proteolysis on the unusual instability of RNase R indicated that both Lon and ClpXP play a role. In the absence of Lon, RNase R stability is increased ~10-fold. Based on these results, I propose that the increase in RNase R during stress is due to its enhanced stability under those conditions.

Shock absorbers are crucial components of a vehicle’s chassis responsible for the trade-off between stability, handling, and passenger comfort. The aim of the thesis is to investigate the physical behavior of an advanced automotive racing shock absorber, known as TTR, developed by Öhlins Racing AB. This goal is achieved by developing a detailed lumped parameter numerical model of the entire TTR suspension in the advanced 1D simulation tool, AMESim. The shock absorber is mainly composed of the main cylinder with through-rod piston design and the gas reservoir located at the low pressure hydraulic line, which connects the compression and rebound sides. The mentioned sides are identical in terms of the components which are a High Speed Adjuster, a Low Speed Adjuster, and a check valve mounted in parallel. The adjusters are special hydraulic valves, which can be modified in terms of flow metering characteristics by means of external accessible screws. Adjustment is done in a series of discrete numbers called ‘clicks’. A fixed orifice and a spring-loaded poppet valve are responsible for controlling the piston low and high speed regions respectively. The developed AMESim numerical model is capable of capturing the physics behind the real shock absorber damping characteristics, under both static and dynamic conditions. The model is developed mainly using the standard AMESim mechanical, hydraulic and hydraulic component design libraries and allows discovering the impact of each single hydraulic component on the TTR overall behavior. In particular, the 1D model is presented in two levels of progressive physical complexity in order to improve the dynamic damping characteristics. Several physical phenomena are considered, such as the hydraulics volumes pressure dynamics, the contribution of external spring and pressure forces to the dynamic balance of the moving elements, the static and viscous frictions, and the elastic deformations induced by solid boundaries pressure. In this thesis, progressive model validation with different types of measurements is as well presented, covering the individual hydraulic components models as well as the entire shock absorber model. The measurements have been performed on the flow benches and dynamometers available at the Öhlins Racing measurements laboratory. These comparisons, deeply discussed in the thesis, allow discovering the impact of specific physical effects on the low and high speed hydraulic valves static performance and on the shock absorber dynamic behavior. Numerical results show good agreement, especially at low and medium frequencies and symmetric ‘click’ adjustments on compression and rebound sides. Further model development is necessary in the other areas, for example by considering more complex models of the valve dynamics and fluid flow patterns, i.e. flow forces, together with more advanced models of the sealing elements viscous friction, and thermal effects. Finally, the AMESim environments offered a good level of flexibility in designing the TTR hydro-mechanical system, by allowing the user to choose between different levels of model complexity.