Search results for " magnitude"
showing 10 items of 407 documents
On the Schwarzschild Effect in 3D Two‐Photon Laser Lithography
2019
International audience; The two‐photon Schwarzschild effect in photoresists suitable for 3D laser lithography is revisited. The study ranges over seven orders of magnitude in exposure time (from 1 µs to 10 s) and investigates a wide variety of different photoresist compositions. For short exposure times (“regime I”), the laser power at the polymerization threshold can scale with the inverse square root of the exposure time, as naively to be expected for two‐photon absorption. Substantial deviations occur, however, for low photoinitiator concentrations. For intermediate exposure times (“regime II”), a Schwarzschild‐type of behavior is found, as discussed previously. For very long exposure ti…
Root topology and allocation patterns of Atriplex patula supplied with different nutrient concentrations
2007
To test whether sub-optimal available nutrient concentrations would result in a more herringbone root branching pattern, in lower root diameters, and in greater resource allocation to root growth than to above-ground portions, seedlings of Atriplex patula were grown under optimal (full), intermediate (1/3 full), and low (1/6 full) nutrient treatments. No significant differences were found between the full and 1/3 nutrient treatments for any of the parameters tested. Root topologies did not show conclusive responses to nutrient availability, however roots treated with 1/6 nutrient concentration showed the tendency to grow in a more herringbone pattern. Total dry weights and shoot dry weights…
Evaluation of yogurt and various beverages as carriers of lactic acid bacteria producing 2-branched (1,3)-β-D-glucan
2011
8 páginas, 2 figuras, 2 tablas -- PAGS nros. 3271-3278
Fluorescence and amplified spontaneous emission of glass forming compounds containing styryl-4H-pyran-4-ylidene fragment
2012
Potential of glassy films of newly synthesised low molecular weight organic molecules for light amplification and lasing applications has been investigated by analysing fluorescence, transient differential absorption and amplified spontaneous emission properties. These non-symmetric and symmetric molecules contain styryl-4H-pyran-4-ylidene fragment with three different electron acceptor groups: dicyanomethylene, barbituric acid, indene-1,3-dione. Fluorescence quantum yields of the investigated compounds in solutions are between 0.32 and 0.54, while they drop down by an order of magnitude in thin solid films. Incorporation of bulky side groups reduced excitonic interactions enabling manifest…
Polyelectrolytes: Intrinsic Viscosities in the Absence and in the Presence of Salt
2008
Intrinsic viscosities were determined at 25 °C for 10 samples of narrowly distributed sodium polystyrene sulfonate (the molecular weights M ranging from 0.9 to 1000 kg/mol) in pure water and in aqueous solutions containing 0.9 wt % NaCl from the slope of ln ηrel versus polymer concentration. In the middle range of M, the [η] values are in the former case almost 2 orders of magnitude larger than in the latter case. In the absence of salt, the plot of log [η] as a function of log M exhibits a sigmoidal shape, which can be approximated within the interval 3 < M (in kg mol-1) < 30 by log[η] = −0.17 + 2.1 log M. In the presence of salt, the following relation holds true in the entire regime: lo…
Precipitation chromatography. III. Optimization of the experimental conditions and determination of the polydispersity of fractions
1974
The influence of the solvent–nonsolvent gradient and the temperature gradient on the efficiency of the precipitation chromatography is investigated with radically and anionically prepared polystyrene samples. Only a combination of both gradients gives optimal effectiveness of the column. The separating power of the column was determined by using mixtures of well defined samples. From the elution curves of the mixtures the nonuniformity Ufr of fractions can be estimated. For fractions of anionically prepared polystyrenes Ufr is on the average 0.001; this value is of the same order of magnitude as the statistical error. These results show that with this chromatographic method it is possible t…
Enhanced thermoelectric performance of PEDOT with different counter-ions optimized by chemical reduction
2014
This work reports on the synthesis of the intrinsically conducting polymer poly(3,4-ethylenedioxythiophene) (PEDOT) doped with several counter-ions, ClO4, PF6 and bis(trifluoromethylsulfonyl)imide (BTFMSI), by electro-polymerization and its thermoelectric properties. We show that, depending on the counter-ion size, the thermoelectric efficiency of PEDOT can be increased up to two orders of magnitude. A further chemical reduction with hydrazine optimizes the power factor (PF). By changing the counter-ions, we were able to increase the electrical conductivity (σ) of PEDOT by a factor of three, while the Seebeck coefficient remains at the same order of magnitude in the three polymers. The best…
Association of model peptides and dehydropeptides: N-acetyl-L-butyrine and (Z)-dehydrobutyrine N',N'-dimethylamides.
2006
These comparative studies on the aggregation behaviour of Ac-(Z)-DeltaAbu-NMe(2) and Ac-L-Abu-NMe(2) in carbon tetrachloride were performed by the analysis of their FTIR spectra and by theoretical calculations. The percentage of the monomeric form (alpha) decreased as concentration increased and this occurred to a higher degree for the (Z)-DeltaAbu derivative than for its saturated analogue. The dimerization constant K(D), calculated on the basis of the intensity of the monomer and associate bands in the nu(s)(N-H) vibration region, is by three orders of magnitude larger for Ac-(Z)-DeltaAbu-NMe(2) than for Ac-L-Abu-NMe(2). The obtained dimer geometries of the dehydro- compound were calculat…
Topology-Sensitive Microfluidic Filter for Polymers of Varying Stiffness
2017
The separation of polymers based on their size, rigidity, and topology is an essential but also highly challenging task for nanoscience and engineering. Using hybrid molecular dynamics simulations that correctly take into account hydrodynamics, we have designed microfluidic channels for separating linear from ring polymers in dilute solutions. We establish that the transport velocity of the polymers is independent of their topology and rigidity when the channel walls are smooth and repulsive. However, when the walls are decorated with attractive spots arranged on lines parallel to the flow, ring polymers exhibit an order of magnitude higher transport velocity compared to linear chains. The …
Intrinsic viscosities of polyelectrolytes in the absence and in the presence of extra salt: Consequences of the stepwise conversion of dextran into a…
2011
Abstract Viscosities of dilute polymer solutions were measured in capillary viscometers for samples varying in their fraction f of charged units from 0.00 to 0.90. The dependence of the logarithm of the relative viscosity on polymer concentration c is in all cases reproduced quantitatively by three characteristic parameters: [ η ], the intrinsic viscosity; B , a viscometric interaction parameter (related to the Huggins constant); [ η ] , a parameter required only for polyelectrolytes at low concentrations of extra salt. In pure water [ η ] increases more than 80 times as the fraction f rises from zero to 0.90 and [ η ] starts from zero and goes up to ≈71 mL/g. Upon the addition of NaCl [ η …