748 research outputs found
Synchronised firing patterns in a random network of adaptive exponential integrate-and-fire neuron model
Acknowledgements This study was possible by partial financial support from the following Brazilian government agencies: CNPq, CAPES, and FAPESP (2011/19296-1 and 2015/07311-7). We also wish thank Newton Fund and COFAP.Peer reviewedPostprin
Statistics of finite-time Lyapunov exponents in the Ulam map
The statistical properties of finite-time Lyapunov exponents at the Ulam
point of the logistic map are investigated. The exact analytical expression for
the autocorrelation function of one-step Lyapunov exponents is obtained,
allowing the calculation of the variance of exponents computed over time
intervals of length . The variance anomalously decays as . The
probability density of finite-time exponents noticeably deviates from the
Gaussian shape, decaying with exponential tails and presenting spikes
that narrow and accumulate close to the mean value with increasing . The
asymptotic expression for this probability distribution function is derived. It
provides an adequate smooth approximation to describe numerical histograms
built for not too small , where the finiteness of bin size trimmes the sharp
peaks.Comment: 6 pages, 4 figures, to appear in Phys. Rev.
Conformational study and reassessment of the vibrational assignments for Norspermidine
The present study presents and discusses the conformational preferences of Norspermidine (NSpd). The effects of varying the dielectric constant on the conformational preferences are discussed, with a view to infer which conformation will correspond to the most stable in the pure condensed liquid phase. Within the same context, a set of NSpd-NH3 molecular adducts were simulated in order to determine the relevance of intermolecular hydrogen bonding on the overall stability and relative positioning of the respective vibrational frequencies. The calculations presently performed allowed a reassessment of the vibrational assignments for NSpd. A full assignment of the NSpd vibrational spectra is presented, with special emphasis being given to the vibrational modes that proved to be most affected by hydrogen bonding. The various inconsistencies of a prior study found in the literature were identified and rectified
Accessing gelling ability of vegetable proteins using rheological and fluorescence techniques
This work aims to present a comprehensive study about the macroscopic characteristics of globular vegetable proteins, in terms of their
gelling ability, by understanding their molecular behaviour, when submitted to a thermal gelling process. The gels of soy, pea and lupin
proteins were characterized by rheological techniques. Gelation kinetics, mechanical spectra, as well as the texture of these gels were
analyzed and compared. Additionally, capillary viscometry, steady-state fluorescence and fluorescence anisotropy were used to monitor the
structural changes induced by the thermal denaturation, which constitutes the main condition for the formation of a gel structure. Based on
these techniques it was possible to establish a relationship between the gelling ability of each protein isolate and their structural resistance to
thermal unfolding, enabling us to explain the weakest and the strongest gelling ability observed for lupin and soy proteins isolates, respectivel
Efficiency of free energy calculations of spin lattices by spectral quantum algorithms
Quantum algorithms are well-suited to calculate estimates of the energy
spectra for spin lattice systems. These algorithms are based on the efficient
calculation of the discrete Fourier components of the density of states. The
efficiency of these algorithms in calculating the free energy per spin of
general spin lattices to bounded error is examined. We find that the number of
Fourier components required to bound the error in the free energy due to the
broadening of the density of states scales polynomially with the number of
spins in the lattice. However, the precision with which the Fourier components
must be calculated is found to be an exponential function of the system size.Comment: 9 pages, 4 figures; corrected typographical and minor mathematical
error
Model for tumour growth with treatment by continuous and pulsed chemotherapy
Peer reviewedPreprin
Sunscreen Effects In Skin Analyzed By Photoacoustic Spectroscopy
In the photoacoustic technique, the signal is proportional to the heat produced in a sample as a consequence of modulated light absorption. This technique allows the spectroscopic characterization of multilayer systems: as the thermal diffusion length varies with the light modulation frequency, one can obtain the depth profile of the sample by analyzing the frequency-dependence of the signal. As the photoacoustic signal depends on thermal and optical properties of the sample, structural changes in the system under analysis account for signal variations in time. In this work, photoacoustic spectroscopy was used to characterize samples of sunscreen and the system formed by sunscreen plus skin. Measurements used a 1000W Xe arc lamp as light source, for wavelengths between 240nm and 400nm. This range corresponds to most of the UV radiation that reaches Earth. Skin samples were disks of about 0,5cm diameter. The absorption spectrum of sunscreen was obtained. Finally, photoacoustics was employed to monitor the absorption kinetics of the sunscreen applied to skin samples. This was done by applying sunscreen in a skin sample and recording the photoacoustic spectra in regular time intervals, up to 90 minutes after application. According to measurements, light absorption by the sunscreen plus skin system stabilizes between 25 and 45 minutes after sunscreen application. Results show that this technique can be utilized to monitor drug delivery and farmacokinetics in skin samples.5325143149Barja, P.R., (1996) Estudo da Indução Fotossintética Através da Técnica Fotoacústica: Efeitos de Saturação e Fotoinibição, , (master thesis), IFGW, UNICAMPRosencwaig, A., (1980) Photoacoustics and Photoacoustic Spectroscopy, pp. 219-231. , New York, John Wiley & SonsPucceti, G., Leblanc, R.M., A comparative study on chromophore diffusion inside porous filters by pulsed photoacoustic spectroscopy (1996) Journal of Membrane Science, 119, pp. 213-228Gutiérrez-Juárez, G., Vargas-Luna, M., Córdova, T., In vivo measurement of the human skin absorption of topically applied substances by photoacoustic technique (2002) Physiological Measurement, 23, pp. 1-12Bernengo, J.C., Photoacoustics as a tool for cutaneous permeation studies (1998) High Temperatures-high Pressures, 30, pp. 619-624Azevedo, J.S., UVA/UVB sunscreen determination by second-order derivative ultraviolet spectrophotometry (1999) II Farmaco, 54, pp. 573-578Rettberg, P., Horneck, G., Biologically weighted measurement of UV radiation in space on Earth with the biofilm technique (2000) Advanced Space Research, 26, pp. 2005-2014Van Der Leun, J.C., UV radiation from sunlight: Summary, conclusions and recommendations (1996) Journal of Photochemistry and Photobiology B: Biology, 35, pp. 237-2441Wolf, R., Sunscreens (2001) Clinics in Dermatology, 19, pp. 452-45
Anomalous synchronization threshold in coupled logistic maps
We consider regular lattices of coupled chaotic maps. Depending on lattice
size, there may exist a window in parameter space where complete
synchronization is eventually attained after a transient regime. Close outside
this window, an intermittent transition to synchronization occurs. While
asymptotic transversal Lyapunov exponents allow to determine the
synchronization threshold, the distribution of finite-time Lyapunov exponents,
in the vicinity of the critical frontier, is expected to provide relevant
information on phenomena such as intermittency. In this work we scrutinize the
distribution of finite-time exponents when the local dynamics is ruled by the
logistic map . We obtain a theoretical estimate for the
distribution of finite-time exponents, that is markedly non-Gaussian. The
existence of correlations, that spoil the central limit approximation, is shown
to modify the typical intermittent bursting behavior. The present scenario
could apply to a wider class of systems with different local dynamics and
coupling schemes.Comment: 6 pages, 6 figure
Validity of numerical trajectories in the synchronization transition of complex systems
We investigate the relationship between the loss of synchronization and the
onset of shadowing breakdown {\it via} unstable dimension variability in
complex systems. In the neighborhood of the critical transition to strongly
non-hyperbolic behavior, the system undergoes on-off intermittency with respect
to the synchronization state. There are potentially severe consequences of
these facts on the validity of the computer-generated trajectories obtained
from dynamical systems whose synchronization manifolds share the same
non-hyperbolic properties.Comment: 4 pages, 4 figure
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