Boron nitride nanotube peapods at ultrasonic velocity impacts: a fully atomistic molecular dynamics investigation.

Boron nitride nanotube peapods (BNNT-peapod) are composed of linear chains of C60molecules encapsulated inside BNNTs, they were first synthesized in 2003. In this work, we investigated the mechanical response and fracture dynamics of BNNT-peapods under ultrasonic velocity impacts (from 1 km s-1up to 6 km s-1) against a solid target. We carried out fully atomistic reactive molecular dynamics simulations using a reactive force field. We have considered the case of horizontal and vertical shootings. Depending on the velocity values, we observed tube bending, tube fracture, and C60ejection. Furthermore, the nanotube unzips for horizontal impacts at certain speeds, forming bi-layer nanoribbons 'incrusted' with C60molecules. The methodology used here is applicable to other nanostructures. We hope it motivates other theoretical investigations on the behavior of nanostructures at ultrasonic velocity impacts and aid in interpreting future experimental results. It should be stressed that similar experiments and simulations were carried out on carbon nanotubes trying to obtain nanodiamonds. The present study expands these investigations to include BNNT.

On the Mechanical Properties of Popgraphene-Based Nanotubes: a Reactive Molecular Dynamics Study.

Carbon-based tubular materials have sparked a great interest in future electronics and optoelectronics device applications. In this work, we computationally studied the mechanical properties of nanotubes generated from popgraphene (PopNTs). Popgraphene is a 2D carbon allotrope composed of 5-8-5 rings. We carried out fully atomistic reactive (ReaxFF) molecular dynamics for PopNTs of different chiralities ( n,0 and 0,n ) and/or diameters and at different temperatures (from 300 up to 1200 K). Results showed that the tubes are thermally stable (at least up to 1200 K). All tubes presented stress/strain curves with a quasi-linear behavior followed by an abrupt drop of stress values. Interestingly, armchair-like PopNTs ( 0,n ) can stand a higher strain load before fracturing when contrasted to the zigzag-like ones ( n,0 ). Moreover, it was obtained that Young's modulus (YMod ) (750-900 GPa) and ultimate strength (σUS ) (120-150 GPa) values are similar to the ones reported for conventional armchair and zigzag carbon nanotubes. YMod values obtained for PopNTs are not significantly temperature-dependent. While the σUS values for the 0,n showed a quasi-linear dependence with the temperature, the n,0 exhibited no clear trends.

Selection of Patients for Treatment of Brain Arteriovenous Malformations by the Transvenous Approach: Relationship with Venous Anatomy and Risk of Hemorrhagic Complications.

BACKGROUND AND PURPOSE: Intracranial hemorrhage represents a severe complication of brain arteriovenous malformation treatment. The aim of this cohort was to report the rate of hemorrhagic complications after transvenous endovascular embolization and analyze the potential angioarchitectural risk factors as well as clinical outcomes. MATERIALS AND METHODS: During an 11-year period, 57 patients underwent transvenous endovascular embolization. All cases of hemorrhagic complications were identified. We analyzed the following variables: sex, age, hemorrhagic presentation, Spetzler-Martin grade, size of the AVM before the transvenous treatment, number of venous collectors, pattern of drainage, presence of dilated veins, and technical aspects. Univariate and multivariate multiple regression analyses were performed to evaluate the potential risk factors for procedure-related hemorrhagic complications. RESULTS: Hemorrhagic complications (either intraprocedural or periprocedural) unrelated to a perforation due to micronavigation occurred in 8 (14.0%) procedures. Significant (mRS > 2) and persistent neurologic deficits were present in 2 (3.5%) patients at 6-month control. Larger nidi, especially >3 cm (P = .03), and a larger number of venous collectors have shown a statistically significant correlation with hemorrhagic complications. Only the number of venous collectors was identified as an independent predictor of hemorrhagic complications in the multivariate analysis (OR, 8.7; 95% confidence interval, 2.2-58.2) (P = .006). CONCLUSIONS: Larger nidus sizes and an increased number of venous collectors may increase the risk of hemorrhagic complications when implementing transvenous endovascular treatment of AVMs. The technique is effective and promising, especially with small nidi and single venous collectors.

Structural transformations of carbon and boron nitride nanoscrolls at high impact collisions.

The behavior of nanostructures under high strain-rate conditions has been the object of theoretical and experimental investigations in recent years. For instance, it has been shown that carbon and boron nitride nanotubes can be unzipped into nanoribbons at high-velocity impacts. However, the response of many nanostructures to high strain-rate conditions is still unknown. In this work, we have investigated the mechanical behavior of carbon (CNS) and boron nitride nanoscrolls (BNS) colliding against solid targets at high velocities, using fully atomistic reactive (ReaxFF) molecular dynamics (MD) simulations. CNS (BNS) are graphene (boron nitride) membranes rolled up into papyrus-like structures. Their open-ended topology leads to unique properties not found in their close-ended analogs, such as nanotubes. Our results show that collision products are mainly determined by impact velocities and by two orientation angles, which define the position of the scroll (i) axis and (ii) open edge relative to the target. Our MD results showed that for appropriate velocities and orientations, large-scale deformations and nanoscroll fractures could occur. We also observed unscrolling (scrolls going back to quasi-planar membranes), scroll unzipping into nanoribbons, and significant reconstruction due to breaking and/or formation of new chemical bonds. For particular edge orientations and velocities, conversion from open to close-ended topology is also possible, due to the fusion of nanoscroll walls.

Double-lumen central venous catheters impregnated with chlorhexidine and silver sulfadiazine to prevent catheter colonisation in the intensive care unit setting: a prospective randomised study.

Antimicrobial- and antiseptic-impregnated catheters are strategies recommended to prevent central venous catheter (CVC) colonisation. Few data regarding chlorhexidine/silver sulfadiazine-impregnated catheters in intensive care unit (ICU) patients have been reported. We performed a prospective, randomised study comparing the colonisation rates of chlorhexidine/silver sulfadiazine-impregnated CVCs (group 1) against standard CVCs (group 2). In order to assess catheter colonisation rates, a 4cm segment from the tips of aseptically removed catheters was cultured by the roll-plate method. In all, 109 patients were enrolled with successful catheter insertion, 51 of them in group 1 and 58 in group 2. There were no statistically significant differences between the two groups with regards to age, Sequential Organ Failure Assessment (SOFA) score, ICU admission diagnosis, infection risk, catheter insertion sites or catheter length of stay. The colonisation rates were 29.4% (15 catheters) for group 1 and 34.5% (20 catheters) for group 2 (P=0.50). Double-lumen CVCs impregnated with chlorhexidine and silver sulfadiazine were not effective in reducing the incidence of catheter colonisation in ICU patients.

Effects of raloxifene on the urethra of adult castrated female rats.

OBJECTIVE: The objective of this study was to evaluate the effects of raloxifene on the weight and epithelial thickness of the urethra of castrated female rats. METHODS: Forty castrated female rats were randomly separated into two groups: group I (control, n = 20) received only the vehicle, and group II (raloxifene, n = 20) received 750 microg/day of raloxifene for 30 days. On the 31st day, the animals were sacrificed and the urethras were removed for the study. A model for categorical data using the weighted minimum mean square error method and Student's t test were used for the data analysis (p < 0.05). RESULTS: The mean weights of the urethras in groups I and II were 22 +/- 1.6 mg and 24 +/- 1.7 mg, respectively (p = 0.371). There was an increase in the mean epithelial thickness of the distal segments in group II compared to group I (50.7 +/- 1.9 microm vs. 45.3 +/- 1.6 microm, respectively) (p < 0.04). No statistically significant difference was found in the mean epithelial thickness of the proximal urethra between the two groups (p = 0.187). CONCLUSION: Raloxifene administered to castrated female rats for 30 days increased the distal urethral epithelial thickness and did not alter the weight of the urethra.

A fluorimetric method based on changes in membrane potential for screening paralytic shellfish toxins in mussels.

To prevent the consumption of bivalves contaminated with paralytic shellfish poisoning (PSP), toxin levels in seafood products are estimated by using the official mouse bioassay. Because of the limitations of this bioassay other methods of monitoring toxins are clearly needed. We have developed a test to screen for PSP toxins based on its functional activity; the toxins bind to the voltage-gated Na+ channels and block their activity. The method is a fluorimetric assay that allows quantitation of the toxins by detecting changes in the membrane potential of human excitable cells. This assay gives an estimate of toxicity, since each toxin present in the sample binds to sodium channels with an affinity which is proportional to its intrinsic toxic potency. The detection limits for paralytic shellfish toxins were found to be 1 ng saxitoxin equivalents/ml compared to the regulatory limit threshold of 400 ng/ml (equivalent to 80 microg/100 g) used in most countries. Our results indicate that this fluorescent assay is a specific, very sensitive, rapid, and reliable method of monitoring PSP toxin levels in samples from seafood products and toxic algae.

Histamine and cadaverine production by bacteria isolated from fresh and frozen albacore (Thunnus alalunga).

Two hundred twenty-seven bacterial strains were isolated from fresh and frozen albacore stored either at -18 or -25 degrees C and investigated for their abilities to produce biogenic amines. As a preliminary screening, all 227 strains were tested in either Niven or Niven modified medium, which allowed the selection of 25 presumptive histamine-producing strains. High-pressure liquid chromatography revealed that only 10 of the 25 strains selected were able to produce low histamine concentrations (<25 ppm) in tryptic soy broth medium supplemented with 2% histidine. None of the 25 strains tested produced putrescine or spermine, whereas 6 strains produced spermidine. Histamine production by Stenotrophomonas maltophilia strain 25MC6 was not prevented at 4 degrees C, and the levels of this amine reached concentrations of 25.8 ppm after 6 days. Three S. maltophilia strains showed strong lysine-decarboxylating activity. Their cadaverine formation capacity was determined by high-pressure liquid chromatography in tryptic soy broth supplemented with 1% lysine; this revealed that the three S. maltophilia strains tested produced more than 700 ppm of cadaverine during the first 24 h of incubation at 37 degrees C. S. maltophilia strain 15MF, initially obtained from fresh albacore tuna, produced up to 2,399 ppm and 4,820 ppm of cadaverine after 24 and 48 h of incubation at 37 degrees C, respectively. To our knowledge, this is the first report on histamine and cadaverine production by strains of the species S. maltophilia, previously known as Pseudomonas and Xanthomonas maltophilia, isolated from fresh and frozen albacore tuna.

A fluorescent microplate assay for microcystin-LR.

A fluorescent enzyme inhibition assay for microcystin-LR was developed using a new fluorescent substrate of protein phosphatases 1 (PP1) and 2A (PP2A), 6,8-difluoro-4-methylumbelliferyl phosphate. The PP1 and PP2A inhibition assay for microcystin-LR was performed in a microtiter plate and the fluorescence yielded by the enzymatic hydrolysis of the substrate was quantified in a fluorescence plate reader. The concentration of microcystin-LR causing 50% inhibition of PP1 and PP2A activity (IC50) was 0.01 nM for PP1 and 0.08 nM for PP2A. The measurable range of microcystin-LR was 800 to 0.08 pg/well for both enzymes. The described assay is fast and very sensitive for the detection of microcystin-LR. Furthermore, this assay can be successfully applied to the study of toxins that inhibit PP1 or PP2A.

Changes in biogenic amines and microbiological analysis in albacore (Thunnus alalunga) muscle during frozen storage.

Albacore specimens of extra quality were analyzed for their biogenic amine contents after 1, 3, 6, and 9 months of frozen storage at -18 degrees C or -25 degrees C. A high-performance liquid chromatography method involving a linear elution gradient was optimized for the identification and determination of putrescine, cadaverine, histamine, spermidine, and spermine in albacore tuna. Putrescine was the biogenic amine that showed the highest increase, reaching concentrations of 59.04 ppm (815% of the initial level) and 68.26 ppm (942% of the initial level) in the white muscle of albacore after 9 months of frozen storage at -18 and -25 degrees C, respectively. Cadaverine, histamine, and spermidine concentrations were below 3, 5, and 11 ppm, respectively, after 9 months of frozen storage, while spermidine underwent a significant decrease at both storage temperatures. Microbiological analysis confirmed the absence of species of Enterobacteriaceae in 75% of the albacore specimens after 9 months of frozen storage; coliforms were always below 3 CFU/g. The survival rate of the psychrotrophic microorganisms after 9 months of frozen storage at -25 degrees C was 4.6%, while 38.9 and 92.1% of the aerobic mesophiles present in the white muscle of albacore before freezing survived 9 months of storage at -18 and -25 degrees C, respectively.

A fluorescent microplate assay for diarrheic shellfish toxins.

A fluorescent enzyme inhibition assay for okadaic acid using 4-methylumbelliferyl phosphate and fluorescein diphosphate as substrates for the enzyme phosphatase 2A was developed. In the inhibition assay, performed in a microtiter plate, the PP2A was inhibited by adding okadaic acid and the resulting fluorescence enhancement derived from enzymatic hydrolysis of the substrate was quantified in a fluorescence plate reader. The measurable range of okadaic acid was 3.2 to 3200 pg/ml with an IC50 = 0.1 nM. The detection limit of okadaic acid was 2.56 pg/well in buffer solutions and 12.8 ng/g hepatopancreas in shellfish extracts. The coefficient of variation (CV, n = 22) for each point ranged from 18.80 to 37.90% (mean 28.35%). The proposed method is very convenient, rapid, and sensitive by using the enzyme inhibition assay system and fluorescent reaction as a detection system. This work demonstrates that the fluorescent assay can be used to quantify the amount of okadaic acid in shellfish samples and also is valid for very dilute samples, such as phytoplankton samples.

Nodular regenerative hyperplasia of the liver and the Budd-Chiari syndrome. Case report, review of the literature and reappraisal of pathogenesis.

We report a case of nodular regenerative hyperplasia (NRH) of the liver associated with the Budd-Chiari syndrome in a patient whose clinical and radiological presentation suggested a diagnosis of multiple liver tumours. Based on both our study and a review of the literature, it appears that, in a number of cases of NRH associated with various clinical conditions, blood stasis at the sinusoidal level is the common denominator. We postulate that, in this situation, the prolonged exposure of hepatocytes to blood-borne hepatotrophic substances, such as hepatopoietins, glucagon and insulin, in combination with functional loss due to pressure injury within the congested areas, may be one of the mechanisms leading to the development of NRH.