Showing papers by "National Nuclear Energy Commission published in 2005"

Infrared-Active Vibrational Modes of Single-Walled Carbon Nanotubes

Abstract: The IR-active vibrational modes of single-walled carbon nanotubes have been observed by optical transmission through thin films of bundled nanotubes. Because IR-active chemical functional groups, e.g., -COOH, -OH, might be attached to the tube walls and contribute additional spectral features, we have also studied the effects of chemical purification and long-term high-temperature vacuum annealing on the IR spectrum. Through comparison with theory, we are able to assign much of the sharp structure observed in our IR spectra.

Phonon-assisted excitonic recombination channels observed in DNA-wrapped carbon nanotubes using photoluminescence spectroscopy.

Abstract: By using a sample of DNA-wrapped single-wall carbon nanotubes strongly enriched in the $(6,5)$ nanotube, photoluminescence emissions observed at special excitation energy values were identified with specific mechanisms of phonon-assisted excitonic absorption and recombination processes associated with $(6,5)$ nanotubes, including one-phonon, two-phonon, and some continuous-luminescence processes. Such detailed processes are not separately identified in three-dimensional semiconducting materials. A general theoretical framework is presented to interpret the experimentally observed phonon-assisted processes in terms of excitonic states.

Screening of yeasts as probiotic based on capacities to colonize the gastrointestinal tract and to protect against enteropathogen challenge in mice.

Abstract: Probiotics are defined as viable microorganisms that exhibit a beneficial effect on the host's health when they are ingested. Two important criteria are used for selection of probiotic microorganisms: they must be able to survive in the gastrointestinal environment and to present at least one beneficial function (colonization resistance, immunomodulation or nutritional contribution). Generally, in vitro assays demonstrating these properties were used to select probiotics but it is unclear if the data can be extrapolated to in vivo conditions. In the present work, twelve Saccharomyces cerevisiae strains isolated from different environments (insect association, tropical fruit, cheese and "aguardente" production) and pre-selected for in vitro resistance to simulated gastrointestinal conditions were inoculated in germ-free mice to evaluate their real capacity to colonize the mammal digestive tract. Using these data, one of the yeasts (S. cerevisiae 905) was selected and tested in gnotobiotic (GN) and conventional (CV) mice for its capacity to protect against oral challenge with two enteropathogenic bacteria (Salmonella Typhimurium and Clostridium difficile). The yeast reached populational levels potentially functional in the gastrointestinal portions where the enteropathogens tested act. No antagonism against either pathogenic bacterium by the yeast was observed in the digestive tract of GN mice but, after challenge with S. Typhimurium, mortality was lower and liver tissue was better preserved in CV animals treated with the yeast when compared with a control group (p<0.05). Histopathological results of intestines showed that the yeast also presented a good protective effect against oral challenge with C. difficile in GN mice (p<0.05). In conclusion, among the 12 S. cerevisiae tested, strain 905 showed the best characteristics to be used as a probiotic as demonstrated by survival capacity in the gastrointestinal tract and protective effect of animals during experimental infections.

Effect of Er:YAG laser on enamel acid resistance: morphological and atomic spectrometry analysis.

Abstract: Background and Objectives This study evaluated the effect of Er:YAG laser on enamel acid resistance. Study Design/Materials and Methods Seventy human enamel slabs were randomly divided into seven groups (n = 10): G1, Er:YAG laser (Key Laser 2, KaVo, Germany) 60 mJ, 2 Hz, 33.3 J/cm2 (handpiece no. 2051, non-contact); G2, Er:YAG laser 80 mJ, 2 Hz, 44.4 J/cm2 (handpiece no. 2051, non-contact); G3, Er:YAG laser 120 mJ, 2 Hz, 66.6 J/cm2 (handpiece no. 2051, non-contact); G4, Er:YAG laser 64 mJ, 2 Hz, 20 J/cm2 (handpiece no. 2055, contact); G5, Er:YAG laser 86.4 mJ, 2 Hz, 26.9 J/cm2 (handpiece no. 2055, contact); G6, Er:YAG laser 135 mJ, 2 Hz, 42.2 J/cm2 (handpiece no. 2055, contact); G7, control. After laser irradiation, samples were submitted to an acid challenge. For both the nos. 2051 and 2055 handpieces, irradiation was performed with a water cooled spray (5.0 ml/minutes). The calcium and phosphorous ions delivered from the tooth surface were quantified by atomic emission spectrometry, and morphological analysis of the enamel surface was performed under scanning electron microscopy. Kruskal–Wallis and multiple comparisons tests were applied to distinguish significant differences among the treatments (α = 5%). Results Groups G1, G2, and G4 presented decreased demineralization. The SEM evaluation revealed different surface alterations as a result of the different energies used. Conclusion Lower energies can decrease enamel solubility without severe alterations of the enamel. Lasers Surg. Med. 00:1–7,2005. © 2005 Wiley-Liss, Inc.

Effect of Spray-Dryer Operating Variables on the Whole Milk Powder Quality

Abstract: This work aims at identifying the effects of the main operational spray-dryer variables on the milk powder quality. Experiments have been performed in a pilot spray-dryer following the full-factorial design technique to provide data and correlations that predict the whole powder properties as function of the main operational variables of the spray-dryer. The emulsion feed flow rate, the atomization rotation and the inlet air temperature have been chosen as the independent variables while the residual moisture content, the tapped bulk density, the cohesion force enhancement between particles as well as size distribution of agglomerate and its morphology are the response variables that quantify the powder quality. Correlations obtained are analyzed and incorporated into a mathematical model previously developed for simulating the spray-drying of whole milk emulsion.

Electro-oxidation of ethylene glycol on PtRu/C and PtSn/C electrocatalysts prepared by alcohol-reduction process

Abstract: PtRu/C and PtSn/C electrocatalysts were prepared by the alcohol-reduction process with different atomic ratios. The electrocatalysts were characterized by EDAX, XRD, TEM and cyclic voltammetry and the electro-oxidation of ethylene glycol was studied by cyclic voltammetry and chronoamperometry using the thin porous coating technique. PtRu/C and PtSn/C electrocatalysts were found to be active for ethylene glycol oxidation, which starts at lower potentials by increasing the ruthenium and tin content. In the region of interest for direct alcohol fuel cell applications PtSn/C electrocatalysts were more active than PtRu/C electrocatalysts.

Determination of the geographical origin of green coffee by principal component analysis of carbon, nitrogen and boron stable isotope ratios

Abstract: In this study we show that the continental origin of coffee can be inferred on the basis of coupling the isotope ratios of several elements determined in green beans. The combination of the isotopic fingerprints of carbon, nitrogen and boron, used as integrated proxies for environmental conditions and agricultural practices, allows discrimination among the three continental areas producing coffee (Africa, Asia and America). In these continents there are countries producing 'specialty coffees', highly rated on the market that are sometimes mislabeled further on along the export-sale chain or mixed with cheaper coffees produced in other regions. By means of principal component analysis we were successful in identifying the continental origin of 88% of the samples analyzed. An intra-continent discrimination has not been possible at this stage of the study, but is planned in future work. Nonetheless, the approach using stable isotope ratios seems quite promising, and future development of this research is also discussed.

Influence of vegetable shortening and emulsifiers on the unfrozen water content and textural properties of frozen French bread dough

Abstract: The influence of vegetable shortening (VS) and emulsifiers (calcium stearoyl-2-lactylate (CSL) and polysorbate 80 (PS80)) on frozen French bread dough has been studied. Eight formulations without yeast were used with different quantities of VS, CSL and PS80. Dough was prepared by mixing all ingredients in a dough mixer at two speeds. The fresh dough was divided into 60 g pieces and molded. Fresh dough samples were also collected for water content and textural analyses. The dough pieces were packed, frozen in a freezer at −30°C and stored at −18°C up to 56 days. After 2, 7, 21, 28 and 56 days of frozen storage, samples were removed from the freezer, thawed at ambient temperature and textural analyses were conducted. The enthalpy of freezable water on fresh bread dough was determined by Differential Scanning Calorimetry (DSC) at the heating rate of 3°C/min, temperature range of −40°C to 20°C. The value of unfrozen water was 0.30–0.34 g H 2 O/g solids and additives used during the storage up to 56 days significantly affected the textural properties of frozen dough.

Crystallization on films of PHB/PEG blends: Evaluation by DSC

Abstract: The degradation kinetics of a linear (LPC) and a branched polycarbonate (BPC) was investigated by means of thermogravimetric analysis. The samples were heated from 30 to 900°C in nitrogen atmosphere, with three different heating rates: 5, 10 and 20°C min -1 . The Vyazovkin model-free kinetics method was applied to calculate the activation energy ( E ) of the degradation process as a function of conversion and temperature. The LPC shows that starts to loose mass slightly over 350°C and the BPC, slightly over 400°C. This shows that the BPC has more thermal resistance than LPC, and E for BPC was bigger than E for LPC.

Alkali-metal-doping dynamics and anomalous lattice contraction of individual debundled carbon nanotubes

Abstract: The dynamics of K doping of thin films of semiconducting debundled single-walled carbon nanotubes (SWNTs) on a $\mathrm{Si}∕{\mathrm{SiO}}_{2}$ substrate is followed using in situ Raman scattering. Similar to the behavior we observed in the Cs doping of bundled SWNTs, four distinct intervals during doping can be distinguished via the behavior of the high frequency tangential band (or G-band) scattering. We therefore find that the character of the time evolution of the frequency and linewidth of the most prominent G band with alkali-metal doping is almost identical for debundled and bundled tubes. This includes the observation of an anomalous upturn in the G-band frequency during the third interval of doping that is consistent with a contraction of the $\mathrm{C}\mathrm{C}$ bond within the tube wall. We conclude that this anomalous contraction is not associated with doping-induced changes in the tube-tube interaction within a bundle, but is an intrinsic, and yet unexplained, consequence of an upshifting Fermi level in debundled $n$-doped SWNTs. A long induction period between when doping conditions are established and when changes in the Raman spectrum occur is observed and remains unexplained.

A comparative study of the in vitro corrosion behavior and cytotoxicity of a superferritic stainless steel, a Ti‐13Nb‐13Zr alloy, and an austenitic stainless steel in Hank's solution

Abstract: In this study, the in vitro corrosion resistance of a superferritic stainless steel in naturally aerated Hank's solution at 37 degrees C has been determined to evaluate the steel for use as a biomaterial. The potentiodynamic polarization method and electrochemical impedance spectroscopy (EIS) were used to determine the corrosion resistance. The polarization results showed very low current densities at the corrosion potential and electrochemical behavior typical of passive metals. At potentials above 0.75 V (SCE), and up to that of the oxygen evolution reaction, the superferritic steel exhibited transpassive behavior followed by secondary passivation. The superferritic stainless steel exhibited high pitting resistance in Hank's solution. This steel did not reveal pits even after polarization to 3000 mV (SCE). The EIS results indicated high impedance values at low frequencies, supporting the results obtained from the polarization measurements. The results obtained for the superferritic steel have been compared with those of the Ti-13Nb-13Zr alloy and an austenitic stainless steel, as Ti alloys are well known for their high corrosion resistance and biocompatibility, and the austenitic stainless steel is widely used as an implant material. The cytotoxicity tests indicated that the superferritic steel, the austenitic steel, and the Ti-13Nb-13Zr alloy were not toxic. Based on corrosion resistance and cytotoxicity results, the superferritic stainless steel can be considered as a potential biomaterial.

99mTc‐HYNIC‐Bombesin (7‐14)NH2: Radiochemical Evaluation with Co‐ligands EDDA (EDDA = Ethylenediamine‐N,N′‐diacetic Acid), Tricine, and Nicotinic Acid

Abstract: Bombesin (BBN) is a peptide exhibiting high affinity for the gastrin releasing peptide receptor (GRPr), which is over‐expressed on a variety of human tumors including breast, prostate, lung and pancreatic cancers. The specific aim of this study was to identify a new 99mTc‐radiolabeled BBN analogue based upon the bifunctional chelating ligand HYNIC (2‐hydrazinonicotinamide) that might be used as a noninvasive tool for diagnosis of GRP receptor‐positive tumors. In this study, HYNIC‐β‐Ala‐BBN(7‐14)NH2 and HYNIC‐5‐Ava‐BBN(7‐14)NH2 were synthesized using traditional solid phase peptide synthetic techniques. The newly‐formed conjugates were radiolabeled using 99mTc in the presence of different coligands including tricine, ethylenediamine diacetic acid (EDDA), tricine/EDDA, and tricine/nicotinic acid. Radiolabeling conditions (i.e., pH, temperature, and reaction time) were optimized and evaluated by ITLC and reversed‐phase HPLC. This material is the result of work supported with resources and the use of faciliti...