111 research outputs found
Renewal, Modulation and Superstatistics
We consider two different proposals to generate a time series with the same
non-Poisson distribution of waiting times, to which we refer to as renewal and
modulation. We show that, in spite of the apparent statistical equivalence, the
two time series generate different physical effects. Renewal generates aging
and anomalous scaling, while modulation yields no aging and either ordinary or
anomalous diffusion, according to the prescription used for its generation. We
argue, in fact, that the physical realization of modulation involves critical
events, responsible for scaling. In conclusion, modulation rather than ruling
out the action of critical events, sets the challenge for their identification
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
EVALUATION OF FUGITIVE DUST FROM CONSTRUCTION SITES IN THE CITY OF SHANGHAI
Chinaâs cities are growing faster, more than in other countries. The presence of conspicuous number of construction
yards can affect seriously the air quality of the cities, moreover the PM10 emissions from these sources are still underestimate. A
monitoring campaign and model simulation results are presented in this paper. The aim of the project, conduct in the city of
Shanghai, was to evaluate a dust emission factor from the constructions sites. A first assessment activity was developed from
October to November 2006, in the Peng Xin Mansion construction site, where 8 PM10 sequential samplers and 2 meteorological
towers, were deployed. The data collected were used to improve a new simplify methodology, also a Gaussian plume model
AERMOD was rund. Results from the air dispersion model comes by different emission factors calculated from two procedures, one
from the AP-42 Environmental Protection Agency (EPA-USA) and the second from an empirical areal emission factor. The first
procedure assigns different sources depending on construction activities and in this case no good results were achieved. The reason
was identify in the lack of a knowledge regarding the source locations depending on schedule time, the specific employed
machinery and the detailed construction operations. The second procedure, based on the determination, from the measured data, of
an areal emission factor, gave, for 6 selected days, good results regarding the trends and the values obtained comparing with the
measured data. Considering the results obtained, we found for the construction site, one seasonal emission factor: the value is 1.8
g/(m2*sec) of PM10 emitted. At the end to better understand the role of the construction yards in the air quality budget in a city of
Shanghai we use the estimated emission factor as input in the AERMOD model
Aggregation-Induced Emission of Tetraphenylethylene in Styrene-Based Polymers
In the present work, the preparation of different styrene-based polymer films containing small amounts of TPE and the evaluation of their photoluminescent behaviour is reported. When TPE is dispersed in a poor solvent or in a glassy PS matrix, the arrested intramolecular rotations of its aryls favour the strong emission of light centred at about 455-460 nm. Conversely, TPE fluorescence significantly weakens to a faint signal when good solvents or viscous but not glassy polymer matrices are used. Near-field optical microscopy correlates the fluorescence behaviour with the different matrix morphologies. These results should be able to be used for developing a new tool for polymer traceability
Low-Energy Ions from Laser-Cooled Atoms
We report the features of an ion source based on two-color photoionization of a laser-cooled cesium beam outsourced from a pyramidal magneto-optical trap. The ion source operates in continuous or pulsed mode. At acceleration voltages below 300 V, it delivers some ten ions per bunch with a relative energy spread ÎUrms/Uâ0.032, as measured through the retarding field-energy-analyzer approach. Space-charge effects are negligible thanks to the low ion density attained in the interaction volume. The performances of the ion beam in a configuration using focused laser beams are extrapolated on the basis of the experimental results. Calculations demonstrate that our low-energy and low-current ion beam can be attractive for the development of emerging technologies requiring the delivery of a small amount of charge, down to the single-ion level and its eventual focusing in the 10-nm range
Processing and structural properties of random oriented lead lanthanum zirconate titanate thin films
Polycrystalline lead lanthanum zirconate titanate (PLZT) thin films have been prepared by a polymeric chemical route to understand the mechanisms of phase transformations and map the microstructure and elastic properties at the nanoscale in these films. X-ray diffraction, atomic force microscopy (AFM) and ultrasonic force microscopy (UFM) have been used as investigative tools. On one side, PLZT films with mixed-phase show that the pyrochlore phase crystallizes predominantly in the bottom film-electrode interface while a pure perovskite phase crystallizes in top film surface. On the contrary, pyrochlore-free PLZT films show a non-uniform microstrain and crystallite size along the film thickness with a heterogeneous complex grainy structure leading to different elastic properties at nanoscale
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Near-field surface plasmon field enhancement induced by rippled surfaces
The occurrence of plasmon resonances on metallic nanometer-scale structures is an intrinsically nanoscale phenomenon, given that the two resonance conditions (i.e., negative dielectric permittivity and large free-space wavelength in comparison with system dimensions) are realized at the same time on the nanoscale. Resonances on surface metallic nanostructures are often experimentally found by probing the structures under investigation with radiation of various frequencies following a trial-and-error method. A general technique for the tuning of these resonances is highly desirable. In this paper we address the issue of the role of local surface patterns in the tuning of these resonances as a function of wavelength and electric field polarization. The effect of nanoscale roughness on the surface plasmon polaritons of randomly patterned gold films is numerically investigated. The field enhancement and relation to specific roughness patterns is analyzed, producing many different realizations of rippled surfaces. We demonstrate that irregular patterns act as metalâdielectricâmetal local nanogaps (cavities) for the resonant plasmonic field. In turn, the numerical results are compared to experimental data obtained via aperture scanning near-field optical microscopy
Cytosolic 5'-Nucleotidase II Is a Sensor of Energy Charge and Oxidative Stress: A Possible Function as Metabolic Regulator
Cytosolic 5'-nucleotidase II (NT5C2) is a highly regulated enzyme involved in the maintenance of intracellular purine and the pyrimidine compound pool. It dephosphorylates mainly IMP and GMP but is also active on AMP. This enzyme is highly expressed in tumors, and its activity correlates with a high rate of proliferation. In this paper, we show that the recombinant purified NT5C2, in the presence of a physiological concentration of the inhibitor inorganic phosphate, is very sensitive to changes in the adenylate energy charge, especially from 0.4 to 0.9. The enzyme appears to be very sensitive to pro-oxidant conditions; in this regard, the possible involvement of a disulphide bridge (C175-C547) was investigated by using a C547A mutant NT5C2. Two cultured cell models were used to further assess the sensitivity of the enzyme to oxidative stress conditions. NT5C2, differently from other enzyme activities, was inactivated and not rescued by dithiothreitol in a astrocytoma cell line (ADF) incubated with hydrogen peroxide. The incubation of a human lung carcinoma cell line (A549) with 2-deoxyglucose lowered the cell energy charge and impaired the interaction of NT5C2 with the ice protease-activating factor (IPAF), a protein involved in innate immunity and inflammation
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