Tuning the aspect ratio of silver nanospheroids embedded in silica

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.

Prospective cohort study to test the predictability of the Cardiff and Vale paediatric early warning system

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.

Modification of the nonlinear optical absorption and optical Kerr response exhibited by nc-Si embedded in a silicon-nitride film

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.

Photoluminescence of as-grown silicon nanocrystals embedded in silicon nitride: influence of atomic hydrogen abundance

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.

Genetic adaptation of Pseudomonas aeruginosa to the airways of cystic fibrosis patients is catalyzed by hypermutation

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.

Thermo-optic effect and optical third order nonlinearity in nc-Si embedded in a silicon-nitride film

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.

A novel breast tissue density classification methodology

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.

Higher risk of ischaemic stroke associated with factor XI levels in dyslipidaemic patients

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.

Nosocomial spread of Pseudomonas aeruginosa producing the metallo-β-lactamase VIM-2 in a Spanish hospital: clinical and epidemiological implications

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.

Absorptive and refractive nonlinearities by four-wave mixing for Au nanoparticles in ion-implanted silica

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.

Molecular epidemiology of methicillin-resistant Staphylococcus aureus in Majorcan hospitals: high prevalence of the epidemic clone EMRSA-15

Clinical isolates (n = 389) of methicillin-resistant Staphylococcus aureus (MRSA) recovered from 371 patients between January 2003 and June 2004 at the three major public hospitals on the island of Majorca, Spain were studied. The clonal relatedness of MRSA isolates was determined by pulsed-field gel electrophoresis (PFGE) after digestion with SmaI. During the study period, MRSA was found in 31% of patients with S. aureus-positive cultures. PFGE analysis identified three predominant clones, affecting 94% of the patients. The three clones had been detected since 1999 in one hospital, and were designated as clones A, B and C. Whereas clones A and B (multidrug-resistant) were related to the two most prevalent clones in Spain at this time, clone C was identical to EMRSA-15, currently one of the most common MRSA clones in UK hospitals and also detected in other countries, but rarely in Spanish hospitals. This imported epidemic clone was detected in c. 10% of patients admitted to one of the three hospitals in 2002, but its prevalence has increased significantly (32% of the patients investigated in the three hospitals in the present study), and this clone also accounted for 44% of the isolates from non-hospitalised patients. Even though EMRSA-15 showed the least multidrug resistance of the three major clones, it was apparently more virulent, since it was associated significantly (p 0.001) with bacteraemia, and positive blood cultures were documented for 21% of the patients infected by this clone, compared with only 10% and 7% of patients infected with clones A and B, respectively.

Influence of high mutation rates on the mechanisms and dynamics of in vitro and in vivo resistance development to single or combined antipseudomonal agents

We studied the mechanisms and dynamics of the development of resistance to ceftazidime (CAZ) alone or combined with tobramycin (TOB) or ciprofloxacin (CIP) in vitro and in vivo (using a mouse model of lung infection with human antibiotic regimens). Pseudomonas aeruginosa strain PAO1 and its hypermutable derivative PAODeltamutS were used, and the results were compared with those previously obtained with CIP, TOB, and CIP plus TOB (CIP-TOB) under the same conditions. An important (200-fold) amplification of the number of resistant mutant cells was documented for PAODeltamutS-infected mice that were under CAZ treatment compared to the number for mice that received placebo, whereas the median number of resistant mutant cells was below the detection limits for mice infected by PAO1. These results were intermediate between the high amplification with CIP (50,000-fold) and the low amplification with TOB (10-fold). All CAZ-resistant single mutant cells selected in vitro or in vivo hyperproduced AmpC. On the other hand, the three combinations studied were found to be highly effective in the prevention of in vivo resistance development in mice infected with PAODeltamutS, although the highest therapeutic efficacy (in terms of mortality and total bacterial load reduction) compared to those of the individual regimens was obtained with CIP-TOB and the lowest was with CAZ-CIP. Nevertheless, mutant cells that were resistant to the three combinations tested were readily selected in vitro for PAODeltamutS (mutation rates from 1.2 x 10(-9) to 5.8 x 10(-11)) but not for PAO1, highlighting the potential risk for antimicrobial resistance development associated with the presence of hypermutable strains, even when combined therapy was used. All five independent CAZ-TOB-resistant PAODeltamutS double mutants studied presented the same resistance mechanism (AmpC hyperproduction plus an aminoglycoside resistance mechanism not related to MexXY), whereas four different combinations of resistance mechanisms were documented for the five CAZ-CIP-resistant double mutants.