Structural and Dipole-Relaxation Processes in Epoxy-Multilayer Graphene Composites with Low Filler Content.

Multilayered graphene nanoplatelets (MLGs) were prepared from thermally expanded graphite flakes using an electrochemical technique. Morphological characterization of MLGs was performed using scanning electron microscopy (SEM), X-ray diffraction analysis (XRD), Raman spectroscopy (RS), and the Brunauer-Emmett-Teller (BET) method. DGEBA-epoxy-based nanocomposites filled with synthesized MLGs were studied using Static Mechanical Loading (SML), Thermal Desorption Mass Spectroscopy (TDMS), Broad-Band Dielectric Spectroscopy (BDS), and Positron Annihilation Lifetime Spectroscopy (PALS). The mass loading of the MLGs in the nanocomposites was varied between 0.0, 0.1, 0.2, 0.5, and 1% in the case of the SML study and 0.0, 1.0, 2, and 5% for the other measurements. Enhancements in the compression strength and the Young's modulus were obtained at extremely low loadings (C≤ 0.01%). An essential increase in thermal stability and a decrease in destruction activation energy were observed at C≤ 5%. Both the dielectric permittivity (ε1) and the dielectric loss factor (ε2) increased with increasing C over the entire frequency region tested (4 Hz-8 MHz). Increased ε2 is correlated with decreased free volume when increasing C. Physical mechanisms of MLG-epoxy interactions underlying the effects observed are discussed.

Revealing new measles virus transmission routes by use of sequence analysis of phosphoprotein and hemagglutinin genes.

With improved measles virus (MV) control, the genetic variability of the MV-nucleoprotein hypervariable region (NP-HVR) decreases. Thus, it becomes increasingly difficult to determine the origin of a virus using only this part of the genome. During outbreaks in Europe and Africa, we found MV strains with identical NP-HVR sequences. However, these strains showed considerable diversity within a larger sequencing window based on concatenated MV phosphoprotein and hemagglutinin genes (P/H pseudogenes). In Belarus, Germany, Russia, and the Democratic Republic of Congo, the P/H pseudogenes provided insights into chains of transmission, whereas identical NP-HVR provided none. In Russia, for instance, the P/H pseudogene identified temporal clusters rather than geographical clusters, demonstrating the circulation and importation of independent variants rather than large local outbreaks lasting for several years, as suggested by NP-HVR. Thus, by extending the sequencing window for molecular epidemiology, a more refined picture of MV circulation was obtained with more clearly defined links between outbreaks and transmission chains. Our results also suggested that in contrast to the P gene, the H gene acquired fixed substitutions that continued to be found in subsequent outbreaks, possibly with consequences for its antigenicity. Thus, a longer sequencing window has true benefits both for the epidemiological surveillance of measles and for the better monitoring of viral evolution.

High genetic diversity of measles virus, World Health Organization European Region, 2005-2006.

During 2005-2006, nine measles virus (MV) genotypes were identified throughout the World Health Organization European Region. All major epidemics were associated with genotypes D4, D6, and B3. Other genotypes (B2, D5, D8, D9, G2, and H1) were only found in limited numbers of cases after importation from other continents. The genetic diversity of endemic D6 strains was low; genotypes C2 and D7, circulating in Europe until recent years, were no longer identified. The transmission chains of several indigenous MV strains may thus have been interrupted by enhanced vaccination. However, multiple importations from Africa and Asia and virus introduction into highly mobile and unvaccinated communities caused a massive spread of D4 and B3 strains throughout much of the region. Thus, despite the reduction of endemic MV circulation, importation of MV from other continents caused prolonged circulation and large outbreaks after their introduction into unvaccinated and highly mobile communities.

Genotyping of recent measles virus strains from Russia and Vietnam by nucleotide-specific multiplex PCR.

The nucleoprotein genes of 49 measles virus (MV) strains circulating in Russia between 2000 and 2006 and in Vietnam in 2003 were analyzed by genotype-specific PCR and the results were compared with their sequences. The sequences revealed the presence of genotypes H1 and H2 in the center (Nha Trang) and the north (Hanoi) of Vietnam, respectively. The relative diversity of the H2 strains suggested an endemic circulation of these viruses in the capital. In contrast genotype H1 strains from Nha Trang were homogenous genetically, which may indicate a recent importation. The strains obtained from 12 different regions of the Russian Federation were assigned to the genotypes H1, D4, and D6. Most strains (81.4%) were correctly genotyped by a multiplex PCR method which was sensitive to genotype-specific mutations [Kremer et al. (2004): J Clin Microbiol 42: 3017-3022]. Ambiguous or negative results for some clade H and genotype D6 strains were due to point mutations in the type-specific primer binding sites. After exchanging a single nucleotide in both the clade H- and the genotype D6-specific primers, all strains were assigned correctly to their genotype. A simplified procedure for use in Vietnam was developed to distinguish directly between genotypes H1 and H2 and any non-H genotype. These results demonstrate that our multiplex PCR method can be adapted easily to new sequence variants or specific epidemiological situations, and thus be very useful for rapid genotyping of large number of samples even in laboratories which do not have sequencing facilities.