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Academic literature on the topic 'LasR'

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Published: 4 June 2021
Last updated: 19 February 2022

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Journal articles on the topic "LasR"

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Storey, Douglas G., Eva E. Ujack, Harvey R. Rabin, and Ian Mitchell. "Pseudomonas aeruginosa lasRTranscription Correlates with the Transcription of lasA,lasB, and toxA in Chronic Lung Infections Associated with Cystic Fibrosis." Infection and Immunity 66, no. 6 (June 1, 1998): 2521–28. http://dx.doi.org/10.1128/iai.66.6.2521-2528.1998.

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ABSTRACT The role of Pseudomonas aeruginosa quorum-sensing systems in the lung infections associated with cystic fibrosis (CF) has not been examined. The purpose of this study was to determine if genes regulated by the LasR-LasI quorum-sensing system were coordinately regulated by the P. aeruginosa populations during the lung infections associated with CF. We also wanted to ascertain if there was a relationship between the expression of lasR, a transcriptional regulator, and some P. aeruginosa virulence factors during these infections. We extracted RNAs from the bacterial populations of 131 sputa taken from 23 CF patients. These RNAs were blotted and hybridized with probes to P. aeruginosa lasA,lasB, and toxA. The hybridization signals from each probe were ranked, and the rankings were analyzed by a Spearman rank correlation to determine if there was an association between the population transcript accumulations for the three genes. The correlations between the transcript accumulation patterns of pairs of the genes suggested that lasA, lasB, andtoxA might be coordinately regulated during CF lung infections. To determine if this coordinate regulation might be due to regulation by LasR, we probed RNAs, extracted from 84 sputa, with thelasR, lasA, lasB, toxA, and algD probes. Statistical analysis indicated thatlasR transcript accumulation correlated tolasA, lasB, toxA, andalgD transcript accumulations. These results indicated thatlasR may at least partially regulate or be coordinately regulated with lasA, lasB, toxA, and algD during the lung infections associated with CF. These results also suggested that the LasR-LasI quorum-sensing system may control the expression of at least some virulence factors in the lungs of patients with CF.
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Kiratisin, Pattarachai, Kenneth D. Tucker, and Luciano Passador. "LasR, a Transcriptional Activator of Pseudomonas aeruginosa Virulence Genes, Functions as a Multimer." Journal of Bacteriology 184, no. 17 (September 1, 2002): 4912–19. http://dx.doi.org/10.1128/jb.184.17.4912-4919.2002.

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ABSTRACT The Pseudomonas aeruginosa LasR protein functions in concert with N-3-oxo-dodecanoyl-l-homoserine lactone (3O-C12-HSL) to coordinate the expression of target genes, including many genes that encode virulence factors, with cell density. We used a LexA-based protein interaction assay to demonstrate that LasR forms multimers only when 3O-C12-HSL is present. A series of LasR molecules containing internal deletions or substitutions in single, conserved amino acid residues indicated that the N-terminal portion of LasR is required for multimerization. Studies performed with these mutant versions of LasR demonstrated that the ability of LasR to multimerize correlates with its ability to function as a transcriptional activator of lasI, a gene known to be tightly regulated by the LasR-3O-C12-HSL regulatory system. A LasR molecule that carries a C-terminal deletion can function as a dominant-negative mutant in P. aeruginosa, as shown by its ability to decrease expression of lasB, another LasR-3O-C12-HSL target gene. Taken together, our data strongly support the hypothesis that LasR functions as a multimer in vivo.
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Kong, Kok-Fai, Suriya Ravi Jayawardena, Shalaka Dayaram Indulkar, Aimee del Puerto, Chong-Lek Koh, Niels Høiby, and Kalai Mathee. "Pseudomonas aeruginosa AmpR Is a Global Transcriptional Factor That Regulates Expression of AmpC and PoxB β-Lactamases, Proteases, Quorum Sensing, and Other Virulence Factors." Antimicrobial Agents and Chemotherapy 49, no. 11 (November 2005): 4567–75. http://dx.doi.org/10.1128/aac.49.11.4567-4575.2005.

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ABSTRACT In members of the family Enterobacteriaceae, ampC, which encodes a β-lactamase, is regulated by an upstream, divergently transcribed gene, ampR. However, in Pseudomonas aeruginosa, the regulation of ampC is not understood. In this study, we compared the characteristics of a P. aeruginosa ampR mutant, PAOampR, with that of an isogenic ampR + parent. The ampR mutation greatly altered AmpC production. In the absence of antibiotic, PAOampR expressed increased basal β-lactamase levels. However, this increase was not followed by a concomitant increase in the P ampC promoter activity. The discrepancy in protein and transcription analyses led us to discover the presence of another chromosomal AmpR-regulated β-lactamase, PoxB. We found that the expression of P. aeruginosa ampR greatly altered the β-lactamase production from ampC and poxB in Escherichia coli: it up-regulated AmpC but down-regulated PoxB activities. In addition, the constitutive P ampR promoter activity in PAOampR indicated that AmpR did not autoregulate in the absence or presence of inducers. We further demonstrated that AmpR is a global regulator because the strain carrying the ampR mutation produced higher levels of pyocyanin and LasA protease and lower levels of LasB elastase than the wild-type strain. The increase in LasA levels was positively correlated with the P lasA , P lasI , and P lasR expression. The reduction in the LasB activity was positively correlated with the P rhlR expression. Thus, AmpR plays a dual role, positively regulating the ampC, lasB, and rhlR expression levels and negatively regulating the poxB, lasA, lasI, and lasR expression levels.
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Kostylev, Maxim, Daniel Y. Kim, Nicole E. Smalley, Indraneel Salukhe, E. Peter Greenberg, and Ajai A. Dandekar. "Evolution of thePseudomonas aeruginosaquorum-sensing hierarchy." Proceedings of the National Academy of Sciences 116, no. 14 (March 8, 2019): 7027–32. http://dx.doi.org/10.1073/pnas.1819796116.

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The bacterial pathogenPseudomonas aeruginosaactivates expression of many virulence genes in a cell density-dependent manner by using an intricate quorum-sensing (QS) network. QS inP. aeruginosainvolves two acyl-homoserine-lactone circuits, LasI-LasR and RhlI-RhlR. LasI-LasR is required to activate many genes including those coding for RhlI-RhlR.P. aeruginosacauses chronic infections in the lungs of people with cystic fibrosis (CF). In these infections, LasR mutants are common, butrhlR-rhlIexpression has escaped LasR regulation in many CF isolates. To better understand the evolutionary trajectory ofP. aeruginosaQS in chronic infections, we grew LasR mutants of the well-studiedP. aeruginosastrain, PAO1, in conditions that recapitulate an environment where QS signal synthesis by other bacteria might still occur. When QS is required for growth, addition of the RhlI product butyryl-homoserine lactone (C4-HSL), or bacteria that produce C4-HSL, to LasR mutants results in the rapid emergence of a population with a LasR-independent RhlI-RhlR QS system. These evolved populations exhibit subsequent growth without added C4-HSL. The variants that emerge have mutations inmexT, which codes for a transcription factor that controls expression of multiple genes. LasR-MexT mutants have a competitive advantage over both the parent LasR mutant and a LasR-MexT-RhlR mutant. Our findings suggest a plausible evolutionary trajectory for QS inP. aeruginosaCF infections where LasR mutants arise during infection, but because these mutants are surrounded by C4-HSL–producingP. aeruginosa,variants rewired to have a LasR-independent RhlIR system quickly emerge.
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Anderson, Ronda M., Chad A. Zimprich, and Lynn Rust. "A Second Operator Is Involved in Pseudomonas aeruginosa Elastase (lasB) Activation." Journal of Bacteriology 181, no. 20 (October 15, 1999): 6264–70. http://dx.doi.org/10.1128/jb.181.20.6264-6270.1999.

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ABSTRACT Pseudomonas aeruginosa LasB elastase gene (lasB) transcription is controlled by the two-component quorum-sensing system of LasR, and the autoinducer, 3OC12-HSL (N-3-[oxododecanoyl]homoserine lactone). LasR and 3OC12-HSL-mediated lasBactivation requires a functional operator sequence (OP1) in thelasB promoter region. Optimal activation oflasB, however, requires a second sequence of 70% identity to OP1, named OP2, located 43 bp upstream of OP1. In this study, we used sequence substitutions and insertion mutations inlasBp-lacZ fusion plasmids to explore the role of OP2 in lasB activation. Our results demonstrate that (i) OP1 and OP2 synergistically mediate lasB activation; (ii) OP2, like OP1, responds to LasR and 3OC12-HSL; and (iii) the putative autoinducer-binding domain of LasR is not required for synergistic activation from OP1 and OP2.
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Cabrol, Ségolène, Anne Olliver, Gerald B. Pier, Antoine Andremont, and Raymond Ruimy. "Transcription of Quorum-Sensing System Genes inClinical and Environmental Isolates of Pseudomonasaeruginosa." Journal of Bacteriology 185, no. 24 (December 15, 2003): 7222–30. http://dx.doi.org/10.1128/jb.185.24.7222-7230.2003.

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ABSTRACT Quorum sensing (QS)-based transcriptional responses in Pseudomonas aeruginosa have been defined on the basis of increases in transcript levels of QS-controlled genes such as lasB and aprA following the hierarchical transcriptional increases of central controllers such as the lasR gene. These increases occur at high bacterial concentrations such as early-stationary-phase growth in vitro. However, the extent to which the increases occur in a variety of clinical and environmental isolates has not been determined nor is there extensive information on allelic variation in lasR genes. An analysis of the sequences of the lasR gene among 66 clinical and environmental isolates showed that 81% have a sequence either identical to that of strain PAO1 or with a silent mutation, 15% have nucleotide changes resulting in amino acid changes, and 5% have an insertion sequence in the lasR gene. Using real-time PCR to quantify transcript levels of lasR, lasB, and aprA in the early log and early stationary phases among 35 isolates from bacteremia and pneumonia cases and the environment, we found most (33 of 35) strains had increases in lasR transcripts in early stationary phase but with a very wide range of final transcript levels per cell. There was a strong correlation (r 2 = 0.84) between early-log- and early-stationary-phase transcript levels in all strains, but this finding remained true only for the 50% of strains above the median level of lasR found in early log phase. There were significant (P < 0.05) but weak-to-modest correlations of lasR transcript levels with aprA (r2= 0.2) and lasB (r 2 = 0.5) transcript levels, but again this correlation occurred only in the 50% of P. aeruginosa strains with the highest levels of lasR transcripts in early stationary phase. There were no differences in distribution of lasR alleles among the bacteremia, pneumonia, or environmental isolates. Overall, only about 50% of P. aeruginosa strains from clinical and environmental sources show a lasR-dependent increase in the transcription of aprA and lasB genes, indicating that for about 50% of clinical isolates this regulatory system may not play a significant role in pathogenesis.
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Takaya, Akiko, Fumiaki Tabuchi, Hiroko Tsuchiya, Emiko Isogai, and Tomoko Yamamoto. "Negative Regulation of Quorum-Sensing Systems in Pseudomonas aeruginosa by ATP-Dependent Lon Protease." Journal of Bacteriology 190, no. 12 (April 11, 2008): 4181–88. http://dx.doi.org/10.1128/jb.01873-07.

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ABSTRACT Lon protease, a member of the ATP-dependent protease family, regulates numerous cellular systems by degrading specific substrates. Here, we demonstrate that Lon is involved in the regulation of quorum-sensing (QS) signaling systems in Pseudomonas aeruginosa, an opportunistic human pathogen. The organism has two acyl-homoserine lactone (HSL)-mediated QS systems, LasR/LasI and RhlR/RhlI. Many reports have demonstrated that these two systems are regulated and interconnected by global regulators. We found that lon-disrupted cells overproduce pyocyanin, the biosynthesis of which depends on the RhlR/RhlI system, and show increased levels of a transcriptional regulator, RhlR. The QS systems are organized hierarchically: the RhlR/RhlI system is subordinate to LasR/LasI. To elucidate the mechanism by which Lon negatively regulates RhlR/RhlI, we examined the effect of lon disruption on the LasR/LasI system. We found that Lon represses the expression of LasR/LasI by degrading LasI, an HSL synthase, leading to negative regulation of the RhlR/RhlI system. RhlR/RhlI was also shown to be regulated by Lon independently of LasR/LasI via regulation of RhlI, an HSL synthase. In view of these findings, it is suggested that Lon protease is a powerful negative regulator of both HSL-mediated QS systems in P. aeruginosa.
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Whiteley, Marvin, and E. P. Greenberg. "Promoter Specificity Elements in Pseudomonas aeruginosa Quorum-Sensing-Controlled Genes." Journal of Bacteriology 183, no. 19 (October 1, 2001): 5529–34. http://dx.doi.org/10.1128/jb.183.19.5529-5534.2001.

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ABSTRACT The LasR-dependent and RhlR-dependent quorum-sensing systems are global regulators of gene expression in Pseudomonas aeruginosa. Previous studies have demonstrated that promoter elements of the quorum-sensing-controlled genes lasB andhcnABC are important in density-dependent regulation. We have identified LasR- and RhlR-dependent determinants in promoters of quorum-sensing-controlled genes qsc102, qsc117 (acpP), and qsc131 (phzA to -G) by in silico, deletion, point-mutational, and primer extension analyses. Each of these genes (in addition tolasI and rsaL) is activated by LasR, and qsc117 and qsc131 also respond to RhlR. Point mutations in the promoters of the LasR-specific gene, qsc102, relax specificity so that this promoter can respond to RhlR in addition to LasR. Our findings indicate that quorum-sensing-controlled promoters in P. aeruginosa are either specific for LasR or respond to both LasR and RhlR and that critical bases in the promoter elements determine specificity.
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Müh, Ute, Martin Schuster, Roger Heim, Ashvani Singh, Eric R. Olson, and E. Peter Greenberg. "Novel Pseudomonas aeruginosa Quorum-Sensing Inhibitors Identified in an Ultra-High-Throughput Screen." Antimicrobial Agents and Chemotherapy 50, no. 11 (September 11, 2006): 3674–79. http://dx.doi.org/10.1128/aac.00665-06.

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ABSTRACT The opportunistic pathogen Pseudomonas aeruginosa has two complete acyl-homoserine lactone (acyl-HSL) signaling systems, LasR-LasI and RhlR-RhlI. LasI catalyzes the synthesis of N-3-oxododecanoyl homoserine lactone (3OC12-HSL), and LasR is a transcription factor that requires 3OC12-HSL as a ligand. RhlI catalyzes the synthesis of N-butanoyl homoserine lactone (C4), and RhlR is a transcription factor that responds to C4. LasR and RhlR control the transcription of hundreds of P. aeruginosa genes, many of which are critical virulence determinants, and LasR is required for RhlR function. We developed an ultra-high-throughput cell-based assay to screen a library of approximately 200,000 compounds for inhibitors of LasR-dependent gene expression. Although the library contained a large variety of chemical structures, the two best inhibitors resembled the acyl-homoserine lactone molecule that normally binds to LasR. One compound, a tetrazole with a 12-carbon alkyl tail designated PD12, had a 50% inhibitory concentration (IC50) of 30 nM. The second compound, V-06-018, had an IC50 of 10 μM and is a phenyl ring with a 12-carbon alkyl tail. A microarray analysis showed that both compounds were general inhibitors of quorum sensing, i.e., the expression levels of most LasR-dependent genes were affected. Both compounds also inhibited the production of two quorum-sensing-dependent virulence factors, elastase and pyocyanin. These compounds should be useful for studies of LasR-dependent gene regulation and might serve as scaffolds for the identification of new quorum-sensing modulators.
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Lequette, Yannick, Joon-Hee Lee, Fouzia Ledgham, Andrée Lazdunski, and E. Peter Greenberg. "A Distinct QscR Regulon in the Pseudomonas aeruginosa Quorum-Sensing Circuit." Journal of Bacteriology 188, no. 9 (May 1, 2006): 3365–70. http://dx.doi.org/10.1128/jb.188.9.3365-3370.2006.

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ABSTRACT The opportunistic pathogen Pseudomonas aeruginosa possesses two complete acyl-homoserine lactone (acyl-HSL) signaling systems. One system consists of LasI and LasR, which generate a 3-oxododecanoyl-homoserine lactone signal and respond to that signal, respectively. The other system is RhlI and RhlR, which generate butanoyl-homoserine lactone and respond to butanoyl-homoserine lactone, respectively. These quorum-sensing systems control hundreds of genes. There is also an orphan LasR-RhlR homolog, QscR, for which there is no cognate acyl-HSL synthetic enzyme. We previously reported that a qscR mutant is hypervirulent and showed that QscR transiently represses a few quorum-sensing-controlled genes. To better understand the role of QscR in P. aeruginosa gene regulation and to better understand the relationship between QscR, LasR, and RhlR control of gene expression, we used transcription profiling to identify a QscR-dependent regulon. Our analysis revealed that QscR activates some genes and represses others. Some of the repressed genes are not regulated by the LasR-I or RhlR-I systems, while others are. The LasI-generated 3-oxododecanoyl-homoserine lactone serves as a signal molecule for QscR. Thus, QscR appears to be an integral component of the P. aeruginosa quorum-sensing circuitry. QscR uses the LasI-generated acyl-homoserine lactone signal and controls a specific regulon that overlaps with the already overlapping LasR- and RhlR-dependent regulons.
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Dissertations / Theses on the topic "LasR"

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Assis, Luiz Santiago de. "Estudo do comportamento temporal do lasr C.W. de ND:YAG usando cristais com centros de cor como absorvedores saturáveis." Universidade de São Paulo, 1994. http://www.teses.usp.br/teses/disponiveis/43/43133/tde-27022014-113956/.

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Existe uma família de centros de cor e cristais dopados com íons metálicos que absorvem na região de emissão do laser de neodímio. Dentre estes, os que são laser ativos são normalmente bombeados em um esquema de cavidades colineares. Eles podem também ser usados como absorvedores saturáveis para o chaveamento Q passivo, C.W. Porém, neste caso a absorção máxima intracavidade que pode ser introduzida é limitada de forma a permitir que a ação laser ocorra. Assim, no caso de ser simultaneamente utilizado como absorvedor e meio ativo existe uma limitação do ganho máximo que o meio ativamente bombeado pode alcançar. Usando-se um esquema de cavidades acopladas, estudamos o desempenho dos centros de cor KCl:T1° (1) e LiF: F POT - IND 2 , para gerar chaveamento Q c.w. passivo (Q- switching) e o travamento de modos (mode-locking) com o esquema de cavidades acima mencionada, na região espectral do infravermelho. Em particular estudamos a ação laser simultânea dos centros KCl: Tl° (1) e do laser de Nd:YAG com o esquema de cavidades acopladas citado, onde o centro de cor tinha o papel dual de absorvedor saturável e meio de ganho. Obteve-se uma alta extração do laser de KCl:Tl° (1), atingindo o limite teórico de 40%, no regime Q-switched c.w.pois a única fonte de perdas do laser de bombeio é o absorvedor saturável. Devido ao baixo ganho dos materiais mencionados e a alta intensidade de saturação foram exploradas as propriedades da cavidade com compensação astigmática, que permite uma grande focalização do feixe sobre o cristal, num regime de cavidades acopladas. Além deste esquema, usamos também um método de bombeamento colinear para a obtenção do travamento de modos ativo-passivo no regime C. W. do laser de Nd: YAG 1 usando o LiF: F POT IND 2 como elemento de modulação passiva dos pulsos. Como um absorvedor saturável lento este necessita de cavidades longas para a obtenção deste regime de operação. Os pulsos modulados (ativamente) sofrem um processo de modulação passiva, o que é dado pela mudança do seu perfil de intensidade de gaussiano para exponencial simétrica, caracterizando a mudança do travamento de modos ativo para passivo.
In general, tunable lasers are colinearlly pumped by other powerfull lasers. In the particular case of color centers, that cover the near infrared spectral region, there is a shortcoming due to the difficulty of creating high densities of centers to efficiently extract output energy. One possible way to circumvent this problem is to use intracavity pumping, but there is a limiting factor that is the maximum available gain of the pumping laser, that limits the maximum absortion that can be introduced in the pump laser cavity. A coupled cavities scheme is a solution to solve this problem. In this sense, this scheme was studied using a simple theoretical model. Two sets of experiments were performed, using LiF:F2 and KCl:T1°(1) color centers. In the first case, in which the LiF: F-2 centers were used only as saturable absorber, it was demonstrated that the coupled cavity is responsable for the temporal behavior of the main laser, and operation in the Q-switched mode was obtained, wi th pulses of 1 SJ..S duration. In the second case, KCl:Tl° (1) color centers are also laser active and simultaneous laser operation were achieved, in the Q-switched regime. The remarkable fact was that the pumping efficiency was close to the maximum theoretically allowed and the pulse duration was also totally dependent on the control cavi ty. In both cases, the pulse time duration was in good agreement with the theoretical predictions. The mode-locking regime in these scheme was also studied, using LiF: F-2 color centers, that has a decay time much longer than the cavity round trip time. By the reducing gain a partial modulation in the couple cavity scheme, we only observed a partial modulation of the laser power, indicating that other effects prevent the full modulation. In these case, the effective absortion used was 0,6 % .In order to explore the role of the saturable absorbers in the mode-locking regime, a active modulator was used to start and sustain the regime, besides the presence of the crystal inside the cavity. We clearly observed a change in the shape of the pulses from gaussian to hyperbolic secant squared that is a characteristic of the passivily mode-locked system. In the optimum case the pulse duration was reduced by a factor of 2,4.
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Oluyombo, Olubukola. "Investigation of the antimicrobial properties of the R-type pyocins of Pseudomonas aeruginosa and the role of lasR in their expression." Thesis, University of Nottingham, 2016. http://eprints.nottingham.ac.uk/38659/.

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Pseudomonas aeruginosa is an opportunistic pathogen responsible for a number of different human infections, and is the leading cause of mortality in cystic fibrosis (CF) patients. P. aeruginosa infections are difficult to treat due to a number of antibiotic resistance mechanisms and its propensity to form multicellular biofilms. It also uses a complex quorum sensing (QS) signalling mechanism to regulate virulence, but mutants in a key QS regulator (LasR) are often prevalent in CF clinical strains. Different strains of P. aeruginosa compete to dominate infections and one way they achieve this is to produce chromosomally encoded bacteriocins, called pyocins. The major classes of pyocins are the soluble (S-types) and the tailocins (R- and F-types). This study investigated the distribution of six S-type and three major groups of R-type pyocins in CF clinical isolates and their roles during strain interactions. Competition assays between strain pairs in both planktonic and biofilm modes of growth were performed between clinical strains and corresponding R-pyocin deletion mutants. Each clinical strain produced one R-pyocin but the distribution of S-pyocins was random. R-pyocins were central to strain dominance as evidenced by the reversal of competitive advantage in null-R-pyocin mutants both in planktonic and biofilm states. R-pyocins also demonstrated novel anti-biofilm activities. Genomic analysis of the most competitive strain (A026) showed that it is a lasR mutant, phylogenetically related to Liverpool Epidemic Strains (LES). Promoter fusion assays to study R-pyocin gene expression showed an increase in the expression of R-pyocin genes in a lasR mutant of PAO1 compared to the wild type. This LasR-linked pyocin expression was RecA-independent. Overall these findings establish the crucial role of R pyocins in P. aeruginosa strain competition and a link between QS and R-pyocins.
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Utpatel, Christian [Verfasser], and Wolfgang [Akademischer Betreuer] Streit. "RNA-seq based identification and biochemical characterization of the Pseudomonas Aeruginosa LasR and Quorum Sensing anti-activator PA2226 / Christian Utpatel ; Betreuer: Wolfgang Streit." Hamburg : Staats- und Universitätsbibliothek Hamburg, 2020. http://d-nb.info/1208394924/34.

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Goh, Wai Kean Chemistry Faculty of Science UNSW. "Novel antagonists of bacterial signaling pathways." Publisher:University of New South Wales. Chemistry, 2008. http://handle.unsw.edu.au/1959.4/41458.

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Traditional bacterial disease therapies utilize compounds that ultimately kill the target bacteria but it exerts a strong selective pressure on the bacteria to develop multi-drug resistance mutants. The increasing occurrence of resistance in common pathogens has highlighted the need to identify new anti-microbials that target the control of bacterial pathogenicity in a non-extermination manner to reduce the incidence of bacteria resistance. One new strategy exploits the discrete signaling molecules that regulate the various bacterial signaling pathways, which are responsible for the expression of pathogenicity traits. Halogenated furanones (fimbrolides) from the marine red alga, Delisea pulchra have been shown to interfere with the key signaling pathway present in Gram-negative bacteria by competitively displacing the cognate signaling molecule from the transcription protein. This project focused on the design and synthesis of 1,5-dihydropyrrol-2-ones, a new class of fimbrolide derivatives capable of displaying strong antagonistic properties of the fimbrolides. Primary synthetic methodologies examined include the halolactamization of allenamides and the direct lactone-lactam transformation. No doubt, both methodologies yielded the lactam ring, the former failed to introduce the crucial C-5 bromomethylene group essential for bioactivity. A facile high yielding two-step lactone-lactam transformation method was developed and using this method, a wide range of substituted 5-bromomethyl- and 5-dibromomethylene-1,5-dihydropyrrol-2-ones were synthesized. Furthermore, a new class of tricyclic crown-ether type compounds with no literature precedent were discovered. To vary the diversity of the compounds, a related class of compounds, 5,6-dihydroindol-2-ones, were examined. A general versatile method for the synthesis of 7-substituted 5,6-dihydroindol-2-ones was developed. The synthetic strategy proceeds via the established Suzuki-Miyaura cross-coupling reaction of halogenated dihydroindol-2-ones with arylboronic acids/esters. The Suzuki methodology was found to be reliable in furnishing a wide range of 7-substituted products in high yields. A preliminary molecular modeling approach was used to assist in the design of new anti-microbials via the ligand-docking analyses of the TraR and LasR protein. A positive correlation was observed between the docking scores and biological activity and the methodology was further developed into an initial screening tool to filter potential active and non-active compounds. The newly synthesized compounds were analysed for their efficacy in reducing the expression of the Green Fluorescent Protein (GFP) in the presence of natural AHL signaling molecules in an AHL-monitor strain, indicative of the inhibition of bacterial phenotype expression. The dihydropyrrol-2-one class of compounds showed significant biological activity and this highlighted their potential for further development.
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Choi, Ji Yeon. "Ecriture par Laser de fonctionnalités optiques : éléments diffractifs et ONL." Phd thesis, Université Sciences et Technologies - Bordeaux I, 2010. http://tel.archives-ouvertes.fr/tel-00583861.

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A la suite de la première démonstration de l'écriture de guide d'onde au sein de verres en 1996 par laser femtoseconde, l'écriture direct par Laser Femtoseconde (Femtoseconde Direct Laser Writing - FLDW) est apparu comme une technique souple pour la fabrication de structure photonique en trois dimensions au sein de matériaux pour l'optique. La thèse a porté sur l'inscription par laser femtoseconde de fonctionnalités optiques au sein de verres. Des éléments diffractifs par modification de l'indice de réfraction et des structures présentant des propriétés de luminescence ou d'optique non linéaire d'ordre deux ont pu être obtenus au sein de matériaux vitreux et étudiés.
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Park, Sukjoon. "Comparative analysis of Pseudomonas aeruginosa LasA and LasD /." The Ohio State University, 1996. http://rave.ohiolink.edu/etdc/view?acc_num=osu1487942476405085.

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Mogedas, Vegara Alfonso. "Tratamiento de las leucoplasias orales mediante el laser de dióxido de carbono." Doctoral thesis, Universitat Autònoma de Barcelona, 2016. http://hdl.handle.net/10803/393916.

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Les leucoplàsies orals són les lesions premalignes més freqüents de la cavitat oral. La possibilitat de degeneració d'aquestes lesions a un carcinoma escamós (taxa de supervivència estimada del 30 al 40% als 5 anys), fa necessari trobar un tractament que sigui capaç de prevenir aquesta transformació maligna alhora de tenir mínims efectes secundaris. Es presenta una tesi doctoral per compendi d'articles. Els resultats es van publicar al Journal of cranio-Maxillo-Facial Surgery (IF 2,933 en 2014). S'incorpora una revisió sistemàtica sobre el tractament de les leucoplàsies orals mitjançant el làser de diòxid de carboni i un altre article versa sobre l'experiència del Servei de Cirurgia Oral i Maxil·lofacial de l'Hospital Universitari Vall d'Hebron en una mostra de 65 pacients. D'acord amb la revisió sistemàtica es pot concloure que el tractament de les lesions leucoplasiques mitjançant el làser de CO2 és una tècnica fiable, reproduïble i associada a una molt baixa taxa de complicacions (0-13,8%), amb unes taxes de recurrència i de transformació maligna que oscil·len entre el 3,1% i el 40,7% i del 0% al 15,4% respectivament. Encara que alguns autors han aportat alguns possibles factors relacionats amb les taxes de recurrència i de transformació maligna com: l'alt grau de displàsia, les eritroleucoplasias, l'hàbit de fumar, el consum d'alcohol, les leucoplasies orals no homogènies o múltiples, les lesions de 4 o més centímetres i l'antecedent de carcinoma oral de cèl·lules escamoses; en la majoria de sèries no hi ha un consens sobre la seva rellevància. Pel que fa a la nostra mostra podem concloure que les taxes de recurrència i de transformació maligna va ser del 33,8% i del 15,4% respectivament. A més la localització de les lesions a la geniva en comparació a les trobades en la llengua es va objectivar com un factor de risc en els pacients que van presentar recidives (2,84 [1,07-7,54]). Es va apreciar una tendència entre els pacients que presentaven antecedent de carcinoma oral de cèl·lules escamoses i el risc de desenvolupar una transformació maligna (2,25 [0,62-8,10]). Les complicacions associades al procés van ser 5 (7,7%).
Las leucoplasias orales son las lesiones premalignas más frecuentes de la cavidad oral. La posibilidad de degeneración de estas lesiones a un carcinoma escamoso, cuya tasa de supervivencia se estima del 30 al 40 % a los 5 años, hace necesario encontrar un tratamiento que sea capaz de prevenir esta transformación maligna a la vez de tener mínimos efectos secundarios. Se presenta una tesis doctoral por compendio de artículos cuyos resultados se publicaron en el Journal of Cranio-Maxillo-Facial Surgery( IF 2,933 en 2014). Se incorpora una revisión sistemática sobre el tratamiento de las leucoplasias orales mediante el laser de dióxido de carbono y otro artículo versa sobre la experiencia del Servicio de Cirugía Oral y Maxilofacial del Hospital Universitario Vall D´Hebron en una muestra de 65 pacientes. De acuerdo con la revisión sistemática se puede concluir que el tratamiento de las lesiones leucoplásicas mediante el láser de CO2 es una técnica fiable, reproducible y asociada a una muy baja tasa de complicaciones (0-13,8%), con unas tasas de recurrencia y de transformación maligna que oscilan entre el 3,1% y el 40,7% y del 0% al 15,4% respectivamente. Aunque algunos autores han aportado algunos posibles factores relacionados con las tasas de recurrencia y de transformación maligna como : el alto grado de displasia, las eritroleucoplasias, el hábito de fumar, el consumo de alcohol, las leucoplasias orales no homogéneas o múltiples, las lesiones de 4 o más centímetros y el antecedente de carcinoma oral de células escamosas ; en la mayoría de series no existe un consenso sobre su relevancia. Con respecto a nuestra muestra podemos concluir que las tasas de recurrencia y de transformación maligna fue del 33,8% y del 15,4% respectivamente. Además la localización de las lesiones en la encía en comparación a las encontradas en la lengua se objetivó como un factor de riesgo en los pacientes que presentaron recidivas ( 2,84 [1,07-7,54] ). Se apreció una tendencia entre los pacientes que presentaban antecedente de carcinoma oral de células escamosas y el riesgo de desarrollar una transformación maligna ( 2,25 [0,62-8,10] ). Las complicaciones asociadas al proceso fueron 5 (7,7%).
Oral leukoplakia are the most common premalignant lesions of the oral cavity. The possibility of degeneration of these lesions to squamous cell carcinoma (survival rate at 5 years 30-50%), implies the need to find a treatment to prevent this malignant transformation and at the same time with minimal side effects. A doctoral thesis by compendium of two articles which results were published in the Journal of Cranio-Maxillo-Facial Surgery (IF 2,933 in 2014) is presented. A systematic review on the treatment of oral leukoplakia with the carbon dioxide laser and the experience of the Department of Oral and Maxillofacial Surgery Vall d'Hebron University Hospital in a sample of 65 patients is presented. According to the systematic review can be concluded that the treatment of oral leukoplakia by the CO2 laser is a reliable, reproducible technique associated with a very low complication rate (0 to 13.8%). The rates of recurrence and malignant transformation range between 3.1% and 40.7% and 0% to 15.4% respectively. Although some authors have provided some possible factors related to rates of recurrence and malignant transformation as the high degree of dysplasia, eritroleukoplakia, smoking, alcohol consumption, non-homogeneous or multiple oral leukoplakia, injuries of 4 or more centimeters and the history of oral squamous cell carcinoma; in most series there is no consensus about its relevance. Regarding our sample we can conclude that the rates of recurrence and malignant transformation was 33.8% and 15.4% respectively. In addition, the location of lesions in the gums compared to those found in the tongue was observed as a risk factor in patients who had recurrences (2.84 [1.07 to 7.54]). A trend among patients with a history of oral squamous cell carcinoma and the risk of developing malignant transformation (2.25 [0.62 to 8.10]) was observed. Complications associated with the process were 5 (7.7%).
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Last, Philipp [Verfasser], Lars [Akademischer Betreuer] [Gutachter] Linsen, Martin [Gutachter] Hering-Bertram, and Andreas [Gutachter] Birk. "Analysis of Automatic Identification System Data for Maritime Safety / Philipp Last ; Gutachter: Lars Linsen, Martin Hering-Bertram, Andreas Birk ; Betreuer: Lars Linsen." Bremen : IRC-Library, Information Resource Center der Jacobs University Bremen, 2017. http://d-nb.info/1124681051/34.

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Wazen, Paul. "Laser NH moyen-infrarouge continu pompe optiquement par lase CO laser et amplificateur de puissance de type Raman, laser à inversion de population accordable en fréquence par effet stark /." Grenoble 2 : ANRT, 1987. http://catalogue.bnf.fr/ark:/12148/cb376106932.

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König, Kristian Lars [Verfasser], Wilfried [Akademischer Betreuer] Nörtershäuser, and Thorsten [Akademischer Betreuer] Kröll. "Laser-Based High-Voltage Metrology with ppm Accuracy / Kristian Lars König ; Wilfried Nörtershäuser, Thorsten Kröll." Darmstadt : Universitäts- und Landesbibliothek Darmstadt, 2019. http://d-nb.info/1178672670/34.

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Books on the topic "LasR"

1

Power, Jo-Ann. The last Duchess of Wolff's Lair. New York: Zebra Books, 1993.

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Reichholf, Josef. Las: Ekologia laso w s rodkowoeuropejskich. Warszawa: S wiat Ksia ·z ki, 1999.

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Lahr lahr. Lāhaur: Kārvān-i Adab, 1989.

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A, Andreev Alexander, Institut lazernoĭ fiziki SO RAN., Russia (Federation). Ministerstvo nauki i tekhnologiĭ., Technische Zentrum Nord (Germany), Thomson-CSF, Jenoptik AG, and Society of Photo-optical Instrumentation Engineers., eds. Superstrong laser fields and applications: Laser Optics '98 : 22-26 June 1998, St. Petersburg, Russia. Bellingham, Wash., USA: SPIE, 1998.

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Hemsworth, Ethan J. Laser-induced plasmas: Theory and applications. Hauppauge, N.Y: Nova Science Publishers, 2010.

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Laser microanalysis. New York: Wiley, 1989.

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Japan-U, S. Seminar on Physics of High Power Laser Matter Interactions (1992 Kyoto Japan). Japan-U.S. Seminar on Physics of High Power Laser Matter Interactions, Kyoto, Japan, 9-13 March 1992. Singapore: World Scientific, 1992.

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Maazel, Fiona. Last last chance. New York: Farrar, Straus and Giroux, 2008.

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Zhijiang, Wang, and Zhang Zhiming, eds. Proceedings of the Topical Meeting on Laser Materials and Laser Spectroscopy: A satellite meeting of IQEC '88, Shanghai, China, July, 25-27, 1988. Singapore: World Scientific, 1989.

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Grigorʹi͡ant͡s, A. G. Osnovy lazernoĭ obrabotki materialov. Moskva: "Mashinostroenie", 1989.

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Book chapters on the topic "LasR"

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Wang, Xiaofeng, Jiayang Sun, and Kath Bogie. "Spatial-temporal data mining procedure: LASR." In Institute of Mathematical Statistics Lecture Notes - Monograph Series, 213–31. Beachwood, Ohio, USA: Institute of Mathematical Statistics, 2006. http://dx.doi.org/10.1214/074921706000000707.

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Krivoruchko, V., V. Tarenkov, M. Savosta, and I. Danilenko. "Nanoscale Magnetism and Magnetotransport Phenomena of (LaSr)MnO Compact." In Mixed Ionic Electronic Conducting Perovskites for Advanced Energy Systems, 225–30. Dordrecht: Springer Netherlands, 2004. http://dx.doi.org/10.1007/978-1-4020-2349-1_20.

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Grabski, H. V., and S. G. Tiratsuyan. "Interaction of Quercetin with LasR of Pseudomonas aeruginosa: Mechanistic Insights of the Inhibition of Virulence Through Quorum Sensing." In IFMBE Proceedings, 585–88. Cham: Springer International Publishing, 2019. http://dx.doi.org/10.1007/978-3-030-31866-6_104.

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Alagely, Ali, Sathish Rajamani, and Max Teplitski. "Luminescent Reporters and Their Applications for the Characterization of Signals and Signal-Mimics that Alter LasR-Mediated Quorum Sensing." In Methods in Molecular Biology, 113–30. Totowa, NJ: Humana Press, 2010. http://dx.doi.org/10.1007/978-1-60761-971-0_9.

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Feng, J., Q. B. Bo, P. Che, J. P. Wang, M. F. Lu, J. F. Liu, Xue Qiang Cao, and Jian Meng. "Effect of Substitution of Magnetic Metal Ions on Magnetic and Magnetoresistance Properties in LaSr2Mn2O7." In Materials Science Forum, 2227–30. Stafa: Trans Tech Publications Ltd., 2005. http://dx.doi.org/10.4028/0-87849-960-1.2227.

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Eichler, Jürgen, and Hans Joachim Eichler. "Licht, Atome, Moleküle, Festkörper." In Laser, 1–27. Berlin, Heidelberg: Springer Berlin Heidelberg, 2010. http://dx.doi.org/10.1007/978-3-642-10462-6_1.

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Eichler, Jürgen, and Hans Joachim Eichler. "Halbleiterlaser." In Laser, 179–215. Berlin, Heidelberg: Springer Berlin Heidelberg, 2010. http://dx.doi.org/10.1007/978-3-642-10462-6_10.

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Eichler, Jürgen, and Hans Joachim Eichler. "FELs, kohärente Röntgen- und Atomstrahlen." In Laser, 217–29. Berlin, Heidelberg: Springer Berlin Heidelberg, 2010. http://dx.doi.org/10.1007/978-3-642-10462-6_11.

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Eichler, Jürgen, and Hans Joachim Eichler. "Ausbreitung von Lichtwellen." In Laser, 231–63. Berlin, Heidelberg: Springer Berlin Heidelberg, 2010. http://dx.doi.org/10.1007/978-3-642-10462-6_12.

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Eichler, Jürgen, and Hans Joachim Eichler. "Optische Resonatoren." In Laser, 265–80. Berlin, Heidelberg: Springer Berlin Heidelberg, 2010. http://dx.doi.org/10.1007/978-3-642-10462-6_13.

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Conference papers on the topic "LasR"

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Hussain, Ishrar, Olga Ormandjieva, and Leila Kosseim. "LASR: A tool for large scale annotation of software requirements." In 2012 IEEE Second International Workshop on Empirical Requirements Engineering (EmpiRE). IEEE, 2012. http://dx.doi.org/10.1109/empire.2012.6347683.

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Waltz, Cory, Donald R. Jedlovec, Michael C. Hardy, Dawn Shaughnessy, Narek Gharibyan, and Cal A. Smith. "Large area solid radiochemistry (LASR) collector at the National Ignition Facility." In Target Diagnostics Physics and Engineering for Inertial Confinement Fusion VI, edited by Jeffrey A. Koch and Gary P. Grim. SPIE, 2017. http://dx.doi.org/10.1117/12.2272640.

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Dandekar, Ajai, Kaia Sappington, Ken-Ichi Oinuma, and E. P. Greenberg. "Pseudomonas Aeruginosa Quorum Sensing: The Transcription Factor LasR Is Formed As A Functional Apo-protein And Is Reversibly Activated By Its Cognate Signal In Vivo." In American Thoracic Society 2010 International Conference, May 14-19, 2010 • New Orleans. American Thoracic Society, 2010. http://dx.doi.org/10.1164/ajrccm-conference.2010.181.1_meetingabstracts.a3188.

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Kubota, M. "Phase separation between novel Bi-stripe order and CE-type charge order in half-doped bilayer manganite LaSr[sub 2]Mn[sub 2]O[sub 7]." In Physics in local lattice distortions. AIP, 2001. http://dx.doi.org/10.1063/1.1363109.

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Aldajah, Saud, Oyelayo O. Ajayi, George R. Fenske, Claude B. Reed, and Zhiyue Xu. "Effect of Laser Glazing and Laser Shock Peening on Tribological Performance of 1080 Carbon Steel." In ASME/STLE 2004 International Joint Tribology Conference. ASMEDC, 2004. http://dx.doi.org/10.1115/trib2004-64047.

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High-power laser surface treatments in the form of glazing, shock peening, cladding, and alloying can significantly affect material tribology. In this paper, effects of laser glazing, laser shock peening, and their combination on the tribological behavior of 1080 carbon steel were investigated. Laser glazing is a process in which a high-power laser beam melts the top layer of the surface, followed by rapid cooling and resolidification. This results in a new surface layer microstructure and properties. Laser shock peening, on the other hand, is a mechanical process in which a laser generates pressure pulses on the surface of the metal, similar to shot peening. Five conditions were evaluated: untreated (baseline), laser shock peened only (PO), laser-glazed only (GO), laser-glazed then shock peened last (GFPL), and laser shock peened then glazed last (PFGL). In pin-on-disc testing, all laser-treated surfaces reduced dry friction, with the GFPL surface having maximum friction reduction of 43%. Under lubricated conditions, all laser-treated surfaces except the PO sample lowered friction. Similarly, all glazed samples reduced wear by a factor of 2–3, while the PO sample did not change wear significantly. These tribological results are associated with changes in the near-surface microstructure and properties.
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Madajian, Jonathan A., Alexander Cohen, Rebecca Hwang, Chase Bishman, Rachel Reyes, Miguel Bautista, Ryan Tsukamoto, et al. "LAST: Laser Array Space Telescope." In SPIE Optical Engineering + Applications, edited by Gary B. Hughes. SPIE, 2016. http://dx.doi.org/10.1117/12.2238453.

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Raje, Shreya, Amir Sajjadi, Kunal Mitra, and Michael S. Grace. "Ablation of Subsurface Tumors Using 1552 nm Ultra-Short Pulse Laser." In ASME 2008 Summer Bioengineering Conference. American Society of Mechanical Engineers, 2008. http://dx.doi.org/10.1115/sbc2008-192415.

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Over last two decades lasers have been used for the treatment of subsurface tumors. Various techniques such as Laser-induced Hyperthermia, Laser Interstitial Thermal Therapy (LITT), and Laser Immunotherapy have been developed for the successful ablation of subsurface tumors by different researchers. All these techniques use photo-thermal mechanism for tumor ablation by delivering thermal energy at the tumor site. In all these existing techniques, either continuous wave (CW) or long pulse laser source has been used, which often produces larger heat affected zone as compared to that produced by short pulse laser. Moreover, the delivery of laser beam at the target site is achieved through fiber optic probes which often require perforation of the skin. These drawbacks can be eliminated if a converging laser beam from a short pulse laser source is directly focused at the subsurface location to ablate the tumor.
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Orazi, Leonardo, Alessandro Fortunato, Giovanni Tani, Giampaolo Campana, Alessandro Ascari, and Gabriele Cuccolini. "A New Computationally Efficient Method in Laser Hardening Modeling." In ASME 2008 International Manufacturing Science and Engineering Conference collocated with the 3rd JSME/ASME International Conference on Materials and Processing. ASMEDC, 2008. http://dx.doi.org/10.1115/msec_icmp2008-72501.

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Laser hardening is a laser assisted process devoted to the surface hardening of the mechanical components. This process is highly suitable for medium carbon steels with carbon content comprised between 0.2 – 0.6% or for low alloy steels which are usually surface hardened during their manufacturing process. Laser hardening technology is gaining a great industrial interest in the last years in fact, the possibility of integrating the heating source directly on the production line, together with the absence of the quenching medium, meets the production needs of modern industries. Laser hardening optimization could be complex especially when tempering due to multiple passes effects must be considered. Many research studies have been proposed in the last years aimed at predicting the optimal laser process parameters such as beam power density, beam velocity and scanning strategies. Many Authors agree with the assumption that the whole austenite resulting from the heating is transformed into martensite during the quenching. This is a valid approximation for single pass but could be a rough hypothesis in multiple-passes when the cooling rate could be not so high. Moreover hysteresis phenomena, due to the severe heat cycle occurring in laser hardening, should be taken into account for pearlite to austenite and martensite to austenite transformations during heating and for martensite tempering during multiple passes. In this paper the crucial problems to be faced regarding laser surface hardening modeling are discussed with respect to current literature. In particular, partial austenitization of the pearlite is suggested as a solution of the hardness prediction of the profile depth. Then three transformation parameters are proposed in order to take into account the hysteresis phenomena in martensite and pearlite transformations into austenite and in martensite tempering. Finally several experimental examples are proposed in order to validate the mentioned assumptions.
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Hoxie, Stephen W., James W. Ness, Harry Zwick, and Bruce E. Stuck. "Laser accident and incident register (LAIR)." In BiOS '99 International Biomedical Optics Symposium, edited by Pascal O. Rol, Karen M. Joos, Fabrice Manns, Bruce E. Stuck, and Michael Belkin. SPIE, 1999. http://dx.doi.org/10.1117/12.350603.

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Dutta, Ashim, Megan Kramer, Molly Fahey, Kunal Mitra, and Michael S. Grace. "Comparison of Thermal and Non-Thermal Ablation of Tumor Using Focused Short Pulse Laser Beam." In ASME 2007 Summer Bioengineering Conference. American Society of Mechanical Engineers, 2007. http://dx.doi.org/10.1115/sbc2007-176225.

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For last few decades laser-induced tumor ablation has attracted significant attention of researchers. The accessibility of tumors located deep inside the body organ using fiber-optic probe without any major surgical resection has made this method an alternative for conventional surgical resection. Various minimally invasive techniques have been developed are used to ablate the tumor successfully with minimum collateral damages [1, 2]. All these techniques utilize the photo-thermal mechanism where conversion of laser energy (mainly from CW or long pulsed laser source) to heat energy leads to necrosis of the tissue through photocoagulation. Since, the necrosis of tumor is achieved by volumetric heating of the whole tumor there remains a significant chance of heat spreading out of the tumor volume damaging surrounding healthy tissue. Therefore, precise control of treatment parameters (laser pulse width, laser power, and irradiation time) is required to restrict the heat spread to the healthy tissue surrounding the tumor.
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Reports on the topic "LasR"

1

Siegman, A. E. Laser Physics and Laser Techniques. Fort Belvoir, VA: Defense Technical Information Center, November 1991. http://dx.doi.org/10.21236/ada247326.

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Chen, Pisin. Longitudinal Laser Shaping in Laser Wakefield Accelerators. Office of Scientific and Technical Information (OSTI), August 2001. http://dx.doi.org/10.2172/787215.

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IIichev, Nikolay. Laser with Wavelength 589nm - Sodium Wavelength Laser. Fort Belvoir, VA: Defense Technical Information Center, January 2000. http://dx.doi.org/10.21236/ada379010.

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Peterson, O. G. Laser neutralization. Office of Scientific and Technical Information (OSTI), June 1986. http://dx.doi.org/10.2172/5111417.

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Reynolds, Kelsey. Laser Sharp. Ames: Iowa State University, Digital Repository, February 2013. http://dx.doi.org/10.31274/itaa_proceedings-180814-597.

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Caskey, G. W., C. J. Jr Fronczek, and S. D. Phillips. Laser trackers:. Gaithersburg, MD: National Institute of Standards and Technology, 1997. http://dx.doi.org/10.6028/nist.ir.6061.

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Komashko, A. Laser-Material Interaction of Powerful Ultrashort Laser Pulses. Office of Scientific and Technical Information (OSTI), January 2003. http://dx.doi.org/10.2172/15005034.

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Sheehy B. Energy Recovery Linac: Laser and Laser Light Transport. Office of Scientific and Technical Information (OSTI), January 2010. http://dx.doi.org/10.2172/1061950.

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Joggerst, Raymond. Laser Safety: Laser Alignment Hands-On #41250 Student Handout. Office of Scientific and Technical Information (OSTI), September 2017. http://dx.doi.org/10.2172/1392841.

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Siegman, A. E. Research in Laser Oscillation Physics and Laser Device Performance. Fort Belvoir, VA: Defense Technical Information Center, June 1995. http://dx.doi.org/10.21236/ada296836.

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