The conformational evolution of elongated polymer solutions tailors the polarization of light-emission from organic nanofibers

Polymer fibers are currently exploited in tremendously important technologies. Their innovative properties are mainly determined by the behavior of the polymer macromolecules under the elongation induced by external mechanical or electrostatic forces, characterizing the fiber drawing process. Although enhanced physical properties were observed in polymer fibers produced under strong stretching conditions, studies of the process-induced nanoscale organization of the polymer molecules are not available, and most of fiber properties are still obtained on an empirical basis. Here we reveal the orientational properties of semiflexible polymers in electrospun nanofibers, which allow the polarization properties of active fibers to be finely controlled. Modeling and simulations of the conformational evolution of the polymer chains during electrostatic elongation of semidilute solutions demonstrate that the molecules stretch almost fully within less than 1 mm from jet start, increasing polymer axial orientation at the jet center. The nanoscale mapping of the local dichroism of individual fibers by polarized near-field optical microscopy unveils for the first time the presence of an internal spatial variation of the molecular order, namely the presence of a core with axially aligned molecules and a sheath with almost radially oriented molecules. These results allow important and specific fiber properties to be manipulated and tailored, as here demonstrated for the polarization of emitted light.Comment: 45 pages, 10 figures, Macromolecules (2014

Defect Induced Photoluminescence from Dark Excitonic States in Individual Single-Walled Carbon Nanotubes

We show that new low-energy photoluminescence (PL) bands can be created in semiconducting single-walled carbon nanotubes by intense pulsed excitation. The new bands are attributed to PL from different nominally dark excitons that are "brightened" due to defect-induced mixing of states with different parity and/or spin. Time-resolved PL studies on single nanotubes reveal a significant reduction of the bright exciton lifetime upon brightening of the dark excitons. The lowest energy dark state has longer lifetimes and is not in thermal equilibrium with the bright state.Comment: 4 pages, 3 figure

Efficient formation of deeply bound ultracold molecules probed by broadband detection

Using a non-selective broadband detection scheme we discovered an efficient mechanism of formation of ultracold Cs$_2$ molecules in deeply bound levels ($v=1-9$) of their electronic ground state X$^1 \Sigma_g^+$. They are formed by a one-photon photoassociation of ultracold cesium atoms in a manifold of excited electronic states, followed by a two-step spontaneous emission cascade. We were able to form about $10^5-10^6$ molecules per second in these low vibrational levels of the ground state. This detection scheme could be generalized to other molecular species for the systematic investigation of cold molecule formation mechanisms.Comment: 4 page

Calibration of a new spectrometry setup for in vivo lung monitoring

The Anthropogammametry Laboratory of SCK-CEN has the objective to screen workers of nuclear facilities (SCK-CEN and other companies) for internal contamination, because they can be contaminated from inhaling or swallowing radioactive material. Routine measurements, carried out daily, are whole body counting and lung monitoring. In lung monitoring, the objective is to screen if plutonium has been inhaled from the people and, to do this, 241Am peak energy (59 keV) is searched by using three germanium detectors, which are chosen for their high resolution, especially at low energy. To increase the measurement efficiency a new set of bigger Germaniun detectors were mounted in the SCK-CEN antropogammametry laboratory. The objective of this study was to calibrate and optimize a new setup for in-vivo lung monitoring in the Antropogammametry Laboratory at SCK-CEN. This new setup, made of two HPGe, had to be more efficient and more comfortable for the people doing measurements than the actual setup used (two LEGe detectors). To reach these goals, some background measurements of the bunker and studies of the best position of the detectors had to be done. MCNP code was the tool used to simulate the performances of the detectors in different position to find the one that would give the best efficiency for the measurements. After that, efficiency curves depending on the CWT were established through multiple measurements and it is possible to see a really improved efficiency for the energy of interest, almost doubled. As the calibration was done with a phantom, also the uncertainties in these curves had to be taken into account , because a person is really different from a phantom, either for the composition either because he can move during the measurements (50 minutes). It has been found that the sum of the uncertainties is about 16% (k=1).Other studies of uncertainties were done with MCNP, using an anthropomorphic phantom model. With this new setup what we expect is a decrease of MDA and then improved performances

Acute glyphosate exposure does not condition the response of microbial communities to a dry-rewetting disturbance in a soil with long history of glyphosate-based herbicides

Dry-rewetting perturbations are natural disturbances in the edaphic environment and particularly in dryland cultivation areas. The interaction of this disturbance with glyphosate-based herbicides (GBHs) deserves special attention in the soil environment due to the intensification of agricultural practices and the acceleration of climate change with an intensified water cycle. The objective of this study was to assess the response of microbial communities in a soil with long history of GBHs to a secondary imposed perturbation (a single dry-rewetting event). A factorial microcosm study was conducted to evaluate the potential conditioning effect of an acute glyphosate exposure on the response to a following dry-rewetting event. A Respiratory Quotient (RQ) based on an ecologically relevant substrate (p-coumaric acid) and basal respiration was used as physiological indicator. Similarly, DNA-based analyses were considered, including quantitative PCR (qPCR) of functional sensitive microbial groups linked to cycles of carbon (Actinobacteria) and nitrogen (ammonia-oxidizing microorganisms), qPCR of total bacteria and denaturing gradient gel electrophoresis (DGGE) of ammonia-oxidizing bacteria (AOB). Significant effects of Herbicide and of Dry-rewetting perturbations were observed in the RQ and in the copy number of amoA gene of AOB, respectively. However, no significant interaction was observed between them when analyzing the physiological indicator and the copy number of the evaluated genes. PCR-DGGE results were not conclusive regarding a potential effect of Dry-rewetting × Herbicide interaction on AOB community structure, suggesting further analysis by deep sequencing of amoA gene. The results of this study indicate that the perturbation of an acute glyphosate exposure in a soil with long-history of this herbicide does not have a conditioning effect on the response to a subsequent dry-rewetting disturbance according to a physiological indicator or the quantified bacterial/archaeal genes. This is particularly relevant for the sustainability of soils in rainfed agriculture, where frequent exposure to GBHs along with intensification of hydrological cycles are expected to occur. Further studies considering multiple dry-rewetting disturbances and in different soil types should be conducted to simulate those conditions and to validate our results.Fil: Allegrini, Marco. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Rosario. Instituto de Investigaciones en Ciencias Agrarias de Rosario. Universidad Nacional de Rosario. Facultad de Ciencias Agrarias. Instituto de Investigaciones en Ciencias Agrarias de Rosario; ArgentinaFil: Gomez, Elena del Valle. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Rosario. Instituto de Investigaciones en Ciencias Agrarias de Rosario. Universidad Nacional de Rosario. Facultad de Ciencias Agrarias. Instituto de Investigaciones en Ciencias Agrarias de Rosario; ArgentinaFil: Zabaloy, Maria Celina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Centro de Recursos Naturales Renovables de la Zona Semiárida. Universidad Nacional del Sur. Centro de Recursos Naturales Renovables de la Zona Semiárida; Argentin

Photoionization spectroscopy of excited states of cold cesium dimers

Photoionization spectroscopy of cold cesium dimers obtained by photoassociation of cold atoms in a magneto-optical trap is reported here. In particular, we report on the observation and on the spectroscopic analysis of all the excited states that have actually been used for efficient detection of cold molecules stabilized in the triplet a^3Sigma_u^+ ground state. They are: the (1)^3Sigma_g^+ state connected to the 6s+6p asymptote, the (2)^3Sigma_g^+ and (2)^3Pi_g states connected to the 6s+5d asymptote and finally the (3)^3Sigma_g^+ state connected to the 6s + 7s asymptote. The detection through these states spans a wide range of laser energies, from 8000 to 16500 cm-1, obtained with different laser dyes and techniques. Information on the initial distribution of cold molecules among the different vibrational levels of the a^3Sigma_u^+ ground state is also provided. This spectroscopic knowledge is important when conceiving schemes for quantum manipulation, population transfer and optical detection of cold cesium molecules.Comment: 24 pages, 11 figures. Note: tables are available separately. Accepted in Molecular Physic

Suppression treatment differentially influences the microbial community and the occurrence of broad host range plasmids in the rhizosphere of the model cover crop Avena sativa L.

Cover crop suppression with glyphosate-based herbicides (GBHs) represents a common agricultural practice. The objective of this study was to compare rhizospheric microbial communities of A. sativa plants treated with a GBH relative to the mechanical suppression (mowing) in order to assess their differences and the potential implications for soil processes. Samples were obtained at 4, 10, 17 and 26 days post-suppression. Soil catabolic profiling and DNA-based methods were applied. At 26 days, higher respiration responses and functional diversity indices (Shannon index and catabolic evenness) were observed under glyphosate suppression and a neat separation of catabolic profiles was detected in multivariate analysis. Sarcosine and Tween 20 showed the highest contribution to this separation. Metabarcoding revealed a non-significant effect of suppression method on either alpha-diversity metrics or beta-diversity. Conversely, differences were detected in the relative abundance of specific bacterial taxa. Mesorhizobium sequences were detected in higher relative abundance in glyphosate-treated plants at the end of the experiment while the opposite trend was observed for Gaiella. Quantitative PCR of amoA gene from ammonia-oxidizing archaea showed a lower abundance under GBH suppression again at 26 days, while ammonia-oxidizing bacteria remained lower at all sampling times. Broad host range plasmids IncP-1β and IncP-1ε were exclusively detected in the rhizosphere of glyphosate-treated plants at 10 days and at 26 days, respectively. Overall, our study demonstrates differential effects of suppression methods on the abundance of specific bacterial taxa, on the physiology and mobile genetic elements of microbial communities while no differences were detected in taxonomic diversity.Fil: Allegrini, Marco. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Rosario. Instituto de Investigaciones en Ciencias Agrarias de Rosario. Universidad Nacional de Rosario. Facultad de Ciencias Agrarias. Instituto de Investigaciones en Ciencias Agrarias de Rosario; ArgentinaFil: Gomez, Elena del Valle. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Rosario. Instituto de Investigaciones en Ciencias Agrarias de Rosario. Universidad Nacional de Rosario. Facultad de Ciencias Agrarias. Instituto de Investigaciones en Ciencias Agrarias de Rosario; ArgentinaFil: Smalla, Kornelia. Julius Kühn-institut; AlemaniaFil: Zabaloy, Maria Celina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Centro de Recursos Naturales Renovables de la Zona Semiárida. Universidad Nacional del Sur. Centro de Recursos Naturales Renovables de la Zona Semiárida; Argentin

Exciton decay dynamics in individual carbon nanotubes at room temperature

We studied the exciton decay dynamics of individual semiconducting single-walled carbon nanotubes at room temperature using time-resolved photoluminescence spectroscopy. The photoluminescence decay from nanotubes of the same (n,m) type follows a single exponential decay function, however, with lifetimes varying between about 1 and 40 ps from nanotube to nanotube. A correlation between broad photoluminescence spectra and short lifetimes was found and explained by defects promoting both nonradiative decay and vibronic dephasing

High-Resolution Indicators of Soil Microbial Responses to N Fertilization and Cover Cropping in Corn Monoculture

Cover cropping (CC) is the most promising in-field practice to improve soil health and mitigate N losses from fertilizer use. Although the soil microbiota play essential roles in soil health, their response to CC has not been well characterized by bioindicators of high taxonomic resolution within typical agricultural systems. Our objective was to fill this knowledge gap with genus-level indicators for corn [Zea mays L.] monocultures with three N fertilizer rates (N0, N202, N269; kg N ha−1), after introducing a CC mixture of cereal rye [Secale cereale L.] and hairy vetch [Vicia villosa Roth.], using winter fallows (BF) as controls. A 3 × 2 split-plot arrangement of N rates and CC treatments was studied in a randomized complete block design with three replicates over two years. Bacterial and archaeal 16S rRNA and fungal ITS regions were sequenced with Illumina MiSeq system. Overall, our high-resolution bioindicators were able to represent specific functional or ecological shifts within the microbial community. The abundances of indicators representing acidophiles, nitrifiers, and denitrifiers increased with N fertilization, while those of heterotrophic nitrifiers, nitrite oxidizers, and complete denitrifiers increased with N0. Introducing CC decreased soil nitrate levels by up to 50% across N rates, and CC biomass increased by 73% with N fertilization. CC promoted indicators of diverse functions and niches, including N-fixers, nitrite reducers, and mycorrhizae, while only two N-cycling genera were associated with BF. Thus, CC can enhance the soil biodiversity of simplified cropping systems and reduce nitrate leaching, but might increase the risk of nitrous oxide emission without proper nutrient management. This primary information is the first of its kind in this system and provided valuable insights into the limits and potential of CC as a strategy to improve soil health.Fil: Kim, Nakian. University of Illinois at Urbana; Estados UnidosFil: Riggins, Chance W.. University of Illinois at Urbana; Estados UnidosFil: Zabaloy, Maria Celina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Centro de Recursos Naturales Renovables de la Zona Semiárida. Universidad Nacional del Sur. Centro de Recursos Naturales Renovables de la Zona Semiárida; Argentina. Universidad Nacional del Sur. Departamento de Agronomía; ArgentinaFil: Allegrini, Marco. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Rosario. Instituto de Investigaciones en Ciencias Agrarias de Rosario. Universidad Nacional de Rosario. Facultad de Ciencias Agrarias. Instituto de Investigaciones en Ciencias Agrarias de Rosario; ArgentinaFil: Rodriguez Zas, Sandra L.. University of Illinois at Urbana; Estados UnidosFil: Villamil, Maria Bonita. University of Illinois at Urbana; Estados Unido