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Murphy B, McElliott V, Vapniarsky N, Oliver A, Rowe J. Tissue tropism and promoter sequence variation in caprine arthritis encephalitis virus infected goats. Virus Res 2010; 151:177-84. [PMID: 20466024 DOI: 10.1016/j.virusres.2010.05.002] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/18/2010] [Revised: 04/29/2010] [Accepted: 05/04/2010] [Indexed: 11/27/2022]
Abstract
Caprine arthritis encephalitis virus is a lentivirus that infects goats and is closely related to maedi-visna virus of sheep. Infection with CAEV results in multiple discrete disease manifestations in goats which can include chronic arthritis, mastitis, pneumonia or encephalomyelitis. Presently, no satisfactory mechanistic rationale for viral tropism has been put forward. We propose that specific sequences in the lentiviral promoter (U3 region of the viral long terminal repeat) are associated with viral tissue tropism and subsequent disease expression. A total of 41 distinct CAE viral promoter regions were amplified, sequenced and phylogenetically compared from the tissues of 24 CAEV-infected goats demonstrating a variety of disease manifestations. Phylogenetically, we identified no tendency for clustering of these promoter sequences into tissue-specific groups. These results therefore do not provide evidence for the study hypothesis. However, multiple motifs within the U3 promoter region were highly conserved both within the entire collection of sequences and within tissue-specific groups.
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Oliver A, Delotte J, Mialon O, Bongain A. [The different ways of medical practice]. GYNECOLOGIE, OBSTETRIQUE & FERTILITE 2010; 38:367. [PMID: 20430666 DOI: 10.1016/j.gyobfe.2010.03.011] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/29/2023]
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103
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Oliver A, Mendizabal J, Ripoll G, Albertí P, Purroy A. Predicting meat yields and commercial meat cuts from carcasses of young bulls of Spanish breeds by the SEUROP method and an image analysis system. Meat Sci 2010; 84:628-33. [DOI: 10.1016/j.meatsci.2009.10.022] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/12/2008] [Revised: 09/25/2009] [Accepted: 10/22/2009] [Indexed: 11/16/2022]
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104
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Lemus L, Guerrero J, Costamagna J, Estiu G, Ferraudi G, Lappin AG, Oliver A, Noll BC. Unfolding of the [Cu2(1,3-bis(9-methyl-1,10-phenanthrolin-2-yl)propane)2]2+ Helicate. Coupling of the Chlorocarbon Dehalogenation to the Unfolding Process. Inorg Chem 2010; 49:4023-35. [DOI: 10.1021/ic9018986] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022]
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105
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Rodríguez-Iglesias V, Peña-Rodríguez O, Silva-Pereyra HG, Rodríguez-Fernández L, Cheang-Wong JC, Crespo-Sosa A, Reyes-Esqueda JA, Oliver A. Tuning the aspect ratio of silver nanospheroids embedded in silica. OPTICS LETTERS 2010; 35:703-705. [PMID: 20195325 DOI: 10.1364/ol.35.000703] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/28/2023]
Abstract
A method is proposed to control the aspect ratio (epsilon) of elongated nanoparticles obtained by ion implantation in a transparent matrix. The procedure was tested for Ag spheroids in silica and we could accurately change epsilon in the range from the maximum value obtained by the ion implantation (around 3.0 in this case) to 1.0 (spherical shape). The values of epsilon were determined in several steps from optical extinction spectroscopy measurements, by fitting the modification and splitting of the surface plasmon resonance peak, using the T-matrix method. In the initial (maximum deformation) and final (undeformed) states, transmission electron microscopy images were obtained, showing a good agreement with the T-matrix results in both cases.
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106
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Camps T, Oliver A, Oliver M, Amat M, Mariotti V, Le Brech S, Ruiz J, Manteca X. Can behavioral problems lead to neurological abnormalities? A case report. J Vet Behav 2010. [DOI: 10.1016/j.jveb.2009.09.018] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
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107
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Lladó X, Oliver A, Freixenet J, Martí R, Martí J. A textural approach for mass false positive reduction in mammography. Comput Med Imaging Graph 2009; 33:415-22. [PMID: 19406614 DOI: 10.1016/j.compmedimag.2009.03.007] [Citation(s) in RCA: 42] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/31/2008] [Revised: 03/25/2009] [Accepted: 03/26/2009] [Indexed: 10/20/2022]
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108
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Edwards ED, Powell CVE, Mason BW, Oliver A. Prospective cohort study to test the predictability of the Cardiff and Vale paediatric early warning system. Arch Dis Child 2009; 94:602-6. [PMID: 18812403 DOI: 10.1136/adc.2008.142026] [Citation(s) in RCA: 69] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/03/2022]
Abstract
OBJECTIVE To develop and test the predictability of a paediatric early warning score to identify children at risk of developing critical illness. DESIGN Prospective cohort study. SETTING Admissions to all paediatric wards at the University Hospital of Wales. OUTCOME MEASURES Respiratory arrest, cardiac arrest, paediatric high-dependency unit admission, paediatric intensive care unit admission and death. RESULTS Data were collected on 1000 patients. A single abnormal observation determined by the Cardiff and Vale paediatric early warning system (C&VPEWS) had a 89.0% sensitivity (95% CI 80.5 to 94.1), 63.9% specificity (95% CI 63.8 to 63.9), 2.2% positive predictive value (95% CI 2.0 to 2.3) and a 99.8% negative predictive value (95% CI 99.7 to 99.9) for identifying children who subsequently had an adverse outcome. The area under the receiver operating characteristic curve for the C&VPEWS score was 0.86 (95% CI 0.82 to 0.91). CONCLUSION Identifying children likely to develop critical illness can be difficult. The assessment tool developed from the advanced paediatric life support guidelines on identifying sick children appears to be sensitive but not specific. If the C&VPEWS was used as a trigger to activate a rapid response team to assess the child, the majority of calls would be unnecessary.
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109
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López-Suárez A, Torres-Torres C, Rangel-Rojo R, Reyes-Esqueda JA, Santana G, Alonso JC, Ortiz A, Oliver A. Modification of the nonlinear optical absorption and optical Kerr response exhibited by nc-Si embedded in a silicon-nitride film. OPTICS EXPRESS 2009; 17:10056-10068. [PMID: 19506657 DOI: 10.1364/oe.17.010056] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/27/2023]
Abstract
We studied the absorptive and refractive nonlinearities at 532 nm and 26 ps pulses for silicon-nitride films containing silicon nanoclusters (nc-Si) prepared by remote plasma-enhanced chemical vapor deposition (RPECVD). Using a self-diffraction technique, we measured for the as-grown sample beta=7.7x10(-9)m/W, n(2)=1.8x10(-16)m(2)/W, and /chi(3)1111/ = 4.6x10(-10)esu; meanwhile, when the sample was exposed to an annealing process at 1000 degrees C during one hour in a nitrogen atmosphere, we obtained beta=-5x10(-10)m/W, n2=9x10(-17)m(2)/W, and /chi(3)1111/=1.1x10(-10)esu. A pure electronic nonlinear refraction was identified and a large threshold ablation of 41 J/cm(-2) was found for our films. By fitting nonlinear optical transmittance measurements, we were able to estimate that the annealed sample exhibits a response time close to 1 fs. We report an enhancement in the photoluminescence (PL) signal after the annealing process, as well as a red-shift due to an increment in size of the nc-Si during the thermal process.
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Monroy BM, Santana G, Benami A, Ortiz A, Alonso JC, Fandiño J, Cruz-Gandarilla F, Aguilar-Hernández J, Contreras-Puente G, López-Suárez A, Oliver A. Photoluminescence of as-grown silicon nanocrystals embedded in silicon nitride: influence of atomic hydrogen abundance. JOURNAL OF NANOSCIENCE AND NANOTECHNOLOGY 2009; 9:2902-2909. [PMID: 19452947 DOI: 10.1166/jnn.2009.204] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/27/2023]
Abstract
Silicon nanocrystals embedded in silicon nitride films were grown by direct plasma enhanced chemical vapor deposition at 300 degrees C, using mixtures of SiH2Cl2/NH3/H2/Ar. The films composition and chemical stability was tested by Fourier Transform Infrared Spectroscopy and Rutherford Backscattering Spectroscopy. The influence of hydrogen abundance during the deposition process on the photoluminescence of as-grown samples was studied as a function of the radiofrequency power and hydrogen dilution flow rate. In situ Optical Emission Spectroscopy allowed the diagnostic of the species in the plasma region and their general trends as a function of the radiofrequency power. The changes in the hydrogen content and silicon incorporation to the film as a function of the radiofrequency power were discussed in terms of silicon nanocrystals formation and growth in the silicon nitride matrix. The photoluminescence emission from the as-grown samples was found to red-shift with increasing hydrogen abundance. This observation is consistent with the increase in silicon content associated to nc-Si of larger size. On the other hand, the photoluminescence intensity was observed to decrease for very high radiofrequency powers and hydrogen dilutions. High Resolution Transmission Electron Microscopy confirmed the presence of silicon nanocrystals embedded in the amorphous silicon nitride matrix and allowed the correlation between the nanocrystals size and the photoluminescence emission energy using the quantum confinement model.
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Oliver A, Awala AO, Skidmore C, Cahill DJ. Recognition and reduction of the impact of inheritable causes of ovarian failure. J OBSTET GYNAECOL 2009; 29:445. [DOI: 10.1080/01443610902954352] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/20/2022]
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112
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Mena A, Smith EE, Burns JL, Speert DP, Moskowitz SM, Perez JL, Oliver A. Genetic adaptation of Pseudomonas aeruginosa to the airways of cystic fibrosis patients is catalyzed by hypermutation. J Bacteriol 2008; 190:7910-7. [PMID: 18849421 PMCID: PMC2593214 DOI: 10.1128/jb.01147-08] [Citation(s) in RCA: 174] [Impact Index Per Article: 10.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/14/2008] [Accepted: 10/01/2008] [Indexed: 11/20/2022] Open
Abstract
In previous work (E. E. Smith, D. G. Buckley, Z. Wu, C. Saenphimmachack, L. R. Hoffman, D. A. D'Argenio, S. I. Miller, B. W. Ramsey, D. P. Speert, S. M. Moskowitz, J. L. Burns, R. Kaul, and M. V. Olson, Proc. Natl. Acad. Sci. USA 103:8487-8492, 2006) it was shown that Pseudomonas aeruginosa undergoes intense genetic adaptation during chronic respiratory infection (CRI) in cystic fibrosis (CF) patients. We used the same collection of isolates to explore the role of hypermutation in this process, since one of the hallmarks of CRI is the high prevalence of DNA mismatch repair (MMR) system-deficient mutator strains. The presence of mutations in 34 genes (many of them positively linked to adaptation in CF patients) in the study collection of 90 P. aeruginosa isolates obtained longitudinally from 29 CF patients was not homogeneous; on the contrary, mutations were significantly concentrated in the mutator lineages, which represented 17% of the isolates (87% MMR deficient). While sequential nonmutator lineages acquired a median of only 0.25 mutation per year of infection, mutator lineages accumulated more than 3 mutations per year. On the whole-genome scale, data for the first fully sequenced late CF isolate, which was also shown to be an MMR-deficient mutator, also support these findings. Moreover, for the first time the predicted amplification of mutator populations due to hitchhiking with adaptive mutations in the course of natural human infections is clearly documented. Interestingly, increased accumulation of mutations in mutator lineages was not a consequence of overrepresentation of mutations in genes involved in antimicrobial resistance, the only adaptive trait linked so far to hypermutation in CF patients, demonstrating that hypermutation also plays a major role in P. aeruginosa genome evolution and adaptation during CRI.
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Torres-Torres C, López-Suárez A, Tamayo-Rivera L, Rangel-Rojo R, Crespo-Sosa A, Alonso JC, Oliver A. Thermo-optic effect and optical third order nonlinearity in nc-Si embedded in a silicon-nitride film. OPTICS EXPRESS 2008; 16:18390-18396. [PMID: 18958117 DOI: 10.1364/oe.16.018390] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/27/2023]
Abstract
Using a self-diffraction experiment with 7ns pulses at 532nm we studied a silicon nitride film containing silicon nanoclusters (nc-Si) of 3.1+/-0.37 nm mean size. The sample was prepared by remote plasma-enhanced chemical vapor deposition (RPECVD), and we found that its nonlinearity consists of a combination of electronic and thermal contributions. By varying the repetition rate of the laser, we discriminated the responsible mechanisms for the nonlinear response. Using this procedure we determined a total /chi((3))1111/ = 3.3x10(-10)esu, n2 = 2.7x10(-16) m(2)/W, beta = 1x10(-9) m/W and dn/dT =1x10(-4) degrees C(-1) for our sample. We also show results for the optical Kerr effect using 80 fs pulses at 820 nm. The purely electronic nonlinearity measured is characterized by /chi((3))1111/=9.5 x10(-11) esu.
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Kraus C, Shahan J, Hsieh Y, Rothman R, Oliver A, Gamiel J, Laeyendecker O, Quinn T, Kelen G. 41: Seroprevalence of HSV-2 Infection Among an Urban Emergency Department Patient Population. Ann Emerg Med 2008. [DOI: 10.1016/j.annemergmed.2008.06.106] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022]
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115
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Kraus C, Shahan J, Rothman R, Hsieh Y, Laeyendecker O, Oliver A, Gamiel J, Quinn T, Kelen G. 2: Twenty Years Experience With HIV Testing among Emergency Department Patients at the Johns Hopkins Hospital. Ann Emerg Med 2008. [DOI: 10.1016/j.annemergmed.2008.06.067] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/21/2022]
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116
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Gamba C, Fernández E, Oliver A, Tirado M, Baeza C, López-Parra A, Arroyo-Pardo E. Population genetics and DNA preservation in ancient human remains from Eastern Spain. FORENSIC SCIENCE INTERNATIONAL GENETICS SUPPLEMENT SERIES 2008. [DOI: 10.1016/j.fsigss.2007.10.037] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2022]
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117
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Bragonzi A, Paroni M, Montanari S, Oliver A, Döring G, Tümmler B. PSEUDOMONAS AERUGINOSA PATHOGENICITY WITHIN CLONAL STRAINS FROM PATIENTS WITH CYSTIC FIBROSIS. J Cyst Fibros 2008. [DOI: 10.1016/s1569-1993(08)60535-4] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/21/2022]
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118
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Oliver A, Alarcón T, Caballero E, Cantón R. Procedimientos en microbiología clínica (número 28, 2.ª edición 2008). Enferm Infecc Microbiol Clin 2008. [DOI: 10.1016/s0213-005x(08)72717-4] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
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119
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Oliver A, Freixenet J, Martí R, Pont J, Pérez E, Denton ERE, Zwiggelaar R. A novel breast tissue density classification methodology. ACTA ACUST UNITED AC 2008; 12:55-65. [PMID: 18270037 DOI: 10.1109/titb.2007.903514] [Citation(s) in RCA: 176] [Impact Index Per Article: 11.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
It has been shown that the accuracy of mammographic abnormality detection methods is strongly dependent on the breast tissue characteristics, where a dense breast drastically reduces detection sensitivity. In addition, breast tissue density is widely accepted to be an important risk indicator for the development of breast cancer. Here, we describe the development of an automatic breast tissue classification methodology, which can be summarized in a number of distinct steps: 1) the segmentation of the breast area into fatty versus dense mammographic tissue; 2) the extraction of morphological and texture features from the segmented breast areas; and 3) the use of a Bayesian combination of a number of classifiers. The evaluation, based on a large kappa = 0.81 and 0.67 for the two data sets) between automatic and expert-based Breast Imaging Reporting and Data System mammographic density assessment.
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120
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Couto-Parada X, Lee A, Ushiro-Lumb I, Anderson J, Baily G, Limb S, Noble H, Orkin C, Reeves I, Oliver A, Clark D. Evaluation of Roche Cobas Taqman Quantitative HIV-1 RNA PCR against other HIV-1 commercial viral load tests to examine potential under-quantification. J Int AIDS Soc 2008. [DOI: 10.1186/1758-2652-11-s1-p203] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022] Open
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121
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Borrell M, Tirado I, Mateo J, Oliver A, Santamaria A, Fontcuberta J. IgM anti-protein S antibodies as a risk factor for venous thrombosis. Haematologica 2008; 93:1115-7. [DOI: 10.3324/haematol.12575] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022] Open
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122
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Santamaría A, Oliver A, Borrell M, Belvís R, Martí-Fábregas J, Mateo J, Fontcuberta J. Higher risk of ischaemic stroke associated with factor XI levels in dyslipidaemic patients. Int J Clin Pract 2007; 61:1819-23. [PMID: 17511793 DOI: 10.1111/j.1742-1241.2007.01388.x] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/29/2022] Open
Abstract
BACKGROUND Ischaemic stroke (IS) is a complex disease that involves genetic and environmental factors. The role of factor XI (FXI) in arterial thrombosis is unclear. We have investigated the risk of IS related to FXI levels in a case-control study. METHODS We studied 445 individuals: 218 diagnosed with IS and 227 age-gender-ethnic matched control subjects. We measured factor VIIIc, fibrinogen and factor XIc levels. FXI < 144% was taken as the reference group in the statistical analysis. RESULTS There were 104 women and 114 men in the IS group and 108 women and 119 men in the control group. The crude odds ratio (OR) of IS in dyslipidaemic patients with high levels of FXI was 4.2 [95% confidence interval (CI): 1.2-14.8] compared with dyslipidaemic controls and low levels of FXI, but the OR in the non-dyslipidaemic with high levels of FXI subgroup was 1.2 (95% CI: 0.4-3.2). The adjusted OR of IS in dyslipidaemic patients with high levels of FXI was 6.4 (95% CI: 1.6-26.1) compared with dyslipidaemic controls, but the OR in non-dyslipidaemic subgroup with high levels of FXI was 0.6 (95% CI: 0.2-2.1). CONCLUSION We found almost a sixfold higher risk of IS in patients with dyslipidaemia and high levels of FXI. Further studies should elucidate the role of FXI in IS and therapeutic approaches should become apparent for patients with dyslipidaemia and high-FXI plasma levels.
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Peña C, Suarez C, Tubau F, Gutierrez O, Domínguez A, Oliver A, Pujol M, Gudiol F, Ariza J. Nosocomial spread of Pseudomonas aeruginosa producing the metallo-β-lactamase VIM-2 in a Spanish hospital: clinical and epidemiological implications. Clin Microbiol Infect 2007; 13:1026-9. [PMID: 17651449 DOI: 10.1111/j.1469-0691.2007.01784.x] [Citation(s) in RCA: 33] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
Abstract
Thirty-four isolates of pan-resistant Pseudomonas aeruginosa producing VIM-2 metallo-beta-lactamase (MBL) were detected at a university hospital in Spain (July 2004-September 2006). Eleven (32%) patients had clinically significant infections, and three (27%) of these patients died. A single clone of MBL-producing P. aeruginosa was identified by pulsed-field gel electrophoresis. A cluster of isolates associated with the vascular surgery ward involved ten patients and appeared as a series of low-grade, sustained and misdiagnosed endemic infections in the hospital. The identification of MBL-positive P. aeruginosa should be considered mandatory in the surveillance of pan-resistant P. aeruginosa and requires a high index of suspicion in the context of endemic infections with a low attack rate.
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Maciá MD, Mena A, Borrell N, Pérez JL, Oliver A. Increased susceptibility to colistin in hypermutable Pseudomonas aeruginosa strains from chronic respiratory infections. Antimicrob Agents Chemother 2007; 51:4531-2. [PMID: 17893154 PMCID: PMC2168005 DOI: 10.1128/aac.00981-07] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
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125
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Torres-Torres C, Khomenko AV, Cheang-Wong JC, Rodríguez-Fernández L, Crespo-Sosa A, Oliver A. Absorptive and refractive nonlinearities by four-wave mixing for Au nanoparticles in ion-implanted silica. OPTICS EXPRESS 2007; 15:9248-9253. [PMID: 19547266 DOI: 10.1364/oe.15.009248] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/28/2023]
Abstract
We report a theoretical and experimental study on the real and imaginary part of the third-order nonlinear optical susceptibility at 532 nm and 7 ns pulse for high-purity silica samples containing Au nanoparticles prepared by ion implantation. We present a method for measuring the magnitude and sign of refractive and absorptive nonlinearities based on four-wave mixing (FWM). This method is derived from a comparison of the light intensities of incident and self-diffracted polarized waves. In the nanosecond regime the samples exhibit saturable absorption and it seems that a thermal effect is the mechanism responsible of nonlinearity of index.
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