In situ Raman spectroscopy allows for a detailed and time-resolved investigation of the kinetics of complex physical or chemical processes. Oxidation has become a frequently used method for the ...removal of disordered carbon species from carbon nanotubes. Oxidation, however, can also induce damage to the tubes and destroy most of the sample. We conducted an in situ Raman spectroscopy study of the oxidation of double- and single-walled carbon nanotubes (DWCNT and SWCNT) under isothermal and nonisothermal conditions to identify the temperature range in which the oxidation of amorphous carbon occurs without any changes with respect to the tubes and their structure. In situ Raman spectroscopy analysis of the oxidation of DWCNTs showed a decrease in the intensity of the D band starting around 370 °C, followed by complete D band elimination at 440 °C. Oxidation studies of SWCNTs showed a similar decrease in the D band intensity, but the D band was not completely eliminated. Furthermore, in situ measurements allow us to determine the different contributions to the D band feature and show the relationship between the D band, G band, and RBM Raman modes in the Raman spectra of DWCNT upon heating. Isothermal oxidation provides an efficient purification method for DWCNTs and SWCNTs, which is also selective to tube diameter. After oxidation, tubes show clean surfaces without disordered or amorphous carbon impurities.
Nanodiamond-reinforced aluminum metal matrix composites (ND–Al MMC) powders were synthesized by means of high energy ball milling. We present a systematic study of the effect of various milling ...conditions on the structure and properties of the resulting MMC powders. The described method can be used to control important powder characteristics, including particle size and shape, Al crystal size and residual strain, and structural integrity and dispersion of the nanoparticle inclusions, a crucial requirement for subsequent powder consolidation. Raman spectroscopy was utilized for the first time to directly verify the structural integrity and the dispersion of ND in the Al matrix. For low ball-to-powder ratios (BPR), average particle size and size range of the ND–Al composite powders were found to decrease during milling, while the hardness increases. A BPR of 10:1, a milling time of 10h, and a ND content of 10wt.% were most effective in obtaining small powder particle sizes, small Al crystal sizes, and improved mechanical properties reaching a hardness of 3.46GPa, a 210% increase over the pristine, untreated Al powder (1.10GPa). Finally, we demonstrate that the as-produced composite powders are well-suited for low-temperature consolidation processing by fabricating the first cold-sprayed ND–Al MMC coating.
Here, we present a comprehensive study analyzing early stages of the transformation of detonation nanodiamond (ND) powder to graphitic carbon onions via thermal annealing in argon atmosphere. Raman ...spectroscopy was employed to monitor this transformation, starting with the sp³-to-sp² conversion of the ND surface at the onset of the graphitization process. Additionally, transmission electron microscopy, x-ray diffraction, and thermogravimetric analysis were used to supplement the structural information obtained from Raman spectroscopy and allow for an accurate interpretation of the obtained Raman data. The effect of the annealing time on the transformation process was also studied to determine the kinetics of the conversion at low temperatures. The results presented in this study complement previous work on ND annealing and provide deeper insight into the nanodiamond-to-carbon onion conversion mechanism, in particular the time and size dependence. We present further evidence for the existence of a disordered sp² phase as an intermediate step in the transformation process.
A dense nanodiamond–aluminum (ND–Al) composite coating was successfully produced by low pressure cold spray (CS) deposition of ball-milled powders containing 10wt% ND. High-energy ball milling is a ...feasible means for the synthesis of composite feedstock powders as it provides excellent control over particle size distribution, crystal size, and the dispersion of ND agglomerates. The resulting CS coatings were characterized with respect to deposition efficiency, particle velocity and mechanical properties. It was found that the CS deposition produced dense, ND–Al composite coatings with increases in both hardness and elastic modulus as compared to the feedstock powders. The coating hardness of the 0.5h-milled ND–Al composite that has the highest DE (14.2%) in ND–Al composites is 3.02GPa, an 175% increase over the pristine as-received Al (1.10GPa). The highest elastic modulus of the composite coatings is 98.3GPa, a 51.5% increase over the as-received Al powder.
In this Letter, we present an in situ Raman spectroscopy study of oxidation-induced changes in the structure and composition of double-wall carbon nanotubes (DWCNTs). Above 480
°C, the intensity of ...the D band decreases to less than 0.01% of the G band intensity, when measured using the 780
nm laser excitation. The D band was absent from the Raman spectra recorded with the 514.5
nm excitation. Thermogravimetric analysis and high-resolution transmission electron microscopy are used to explain the observed results. We conclude that oxidation provides a purification method for the DWCNT which leads to a sample containing tubes having nearly clean surfaces without disordered carbon.
The effects of vacuum annealing and oxidation in air on the structure of multi-walled carbon nanotubes (MWCNTs) produced by a large-scale catalytic chemical vapor deposition (CCVD) process are ...studied using Raman spectroscopy and transmission electron microscopy (TEM). A detailed Raman spectroscopic study of as-produced nanotubes has also been conducted. While oxidation in air up to 400°C removes disordered carbon, defects in tube walls are produced at higher temperatures. TEM reveals that MWCNTs annealed at 1,800°C and above become more ordered than as-received tubes, while the tubes annealed at 2,000°C exhibit polygonalization, mass transfer and over growth. The change in structure is observable by the separation of the Raman G and D' peaks, a lower R-value (I ^sub D^/I ^sub G^ ratio), and an increase in the intensity of the second order peaks. Using wavelengths from the deep ultraviolet (UV) range (5.08 eV) extending into the visible near infrared (IR) (1.59 eV), the Raman spectra of MWCNTs reveal a dependence of the D-band position proportional to the excitation energy of the incident laser energies.PUBLICATION ABSTRACT
Background
Evidence for the association of atrial fibrillation (AF) present on the ECG and cardiovascular outcomes in AF patients is limited.
Objective
To investigate the prognostic significance of ...AF on a single surface ECG for cardiovascular outcomes in AF patients.
Methods
A total of 3642 AF patients were prospectively enrolled. Main exclusion criteria were rhythms other than sinus rhythm (SR) or AF. The primary end‐point was a composite of all‐cause death and hospitalizations for congestive heart failure (CHF). Secondary end‐points were all‐cause death, CHF hospitalizations, cardiovascular death, myocardial infarction, any stroke and stroke subtypes. Associations were assessed with multivariable Cox proportional hazards models.
Results
Mean age was 71 years, 28% were female, and mean follow‐up was 3.4 years. Patients with SR on the ECG at study enrolment (56%) were younger (69 vs. 74 years, P < 0.0001), had more often paroxysmal AF (73 vs. 18%, P < 0.0001) and fewer comorbidities. The incidence of the primary end‐point was 1.8 and 3.1 per 100 person‐years in patients with SR and AF, respectively. The multivariable‐adjusted hazard ratio was 1.4 (95% confidence intervals 1.1; 1.7; P = 0.001) for patients with AF on the ECG compared to patients with SR. The hazard ratios (95% confidence intervals) were 1.4 (1.1; 1.8; P = 0.006) for all‐cause death, 1.5 (1.2; 1.9; P = 0.001) for CHF and 1.6 (1.1; 2.2; P = 0.006) for cardiovascular death. None of the other associations were statistically significant.
Conclusions
The presence of AF in a single office ECG had significant prognostic implications with regard to mortality and CHF hospitalizations in patients with AF. These patients present a high‐risk group and might benefit from intensified treatment.
The control of the crystal size in nanodiamond (ND) powder is crucial, since most of its physical and chemical properties are size-related. In this work we demonstrate a simple method for increasing ...the crystal size of ND powder by selective oxidation in air. We analyze the oxidized powders by high-resolution transmission electron microscopy, X-ray diffraction and Raman spectroscopy in order to monitor changes in the average crystal size distribution and identify the limitations of these techniques for crystal size measurements. Our studies show that none of these techniques alone is able to provide sufficiently accurate information on size distributions, but can produce complementary results for better understanding of the properties of ND powder.
High-sensitivity cardiac troponin T (hs-cTnT) blood concentrations were shown to exhibit a diurnal rhythm, characterized by gradually decreasing concentrations throughout daytime, rising ...concentrations during nighttime and peak concentrations in the morning. We aimed to investigate whether this also applies to (h)s-cTnI assays and whether it would affect diagnostic accuracy for acute myocardial infarction (AMI).
Blood concentrations of cTnI were measured at presentation and after 1 h using four different cTnI assays: three commonly used sensitive (s-cTnI Architect, Ultra and Accu) and one experimental high-sensitivity assay (hs-cTnI Accu) in a prospective multicenter diagnostic study of patients presenting to the emergency department with suspected AMI. These concentrations and their diagnostic accuracy for AMI (quantified by the area under the curve (AUC)) were compared between morning (11 p.m. to 2 p.m.) and evening (2 p.m. to 11 p.m.) presenters.
Among 2601 patients, AMI was the final diagnosis in 17.6% of patients. Concentrations of (h)s-cTnI as measured using all four assays were comparable in patients presenting in the morning versus patients presenting in the evening. Diagnostic accuracy for AMI of all four (h)s-cTnI assays were high and comparable between patients presenting in the morning versus presenting in the evening (AUC at presentation: 0.90 vs 0.93 for s-cTnI Architect; 0.91 vs 0.94 for s-cTnI Ultra; 0.89 vs 0.94 for s-cTnI Accu; 0.91 vs 0.94 for hs-cTnI Accu).
Cardiac TnI does not seem to express a diurnal rhythm. Diagnostic accuracy for AMI is very high and does not differ with time of presentation.
NCT00470587, http://clinicaltrials.gov/show/NCT00470587
•There is no difference in cTnI concentrations between patients presenting in the morning and in the evening in all assessed diagnostic groups.•The diagnostic accuracy for AMI is very high and similar for all patients, irrespective of the time of presentation.•In the important subgroup of early presenting patients, the same results could be shown.•These findings indicate that (h)s-cTnI expresses no circadian rhythm and is safe in use at all time of the day.
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