1,887 research outputs found
Molecular dynamics of liquid acetone determined by Depolarized Rayleigh and low-frequency Raman scattering spectroscopy.
No full textMolecular dynamics of liquid acetone determined by Depolarized Rayleigh and low-frequency Raman scattering spectroscopy
M.G. Giorgini1, F. Palombo2, M. Paolantoni2, P. Sassi2 and A. Morresi2
1 Department of Physical and Inorganic Chemistry, University of Bologna, Viale del Risorgimento 4, I-40136 Bologna, Italy. Email: [email protected]
2 Department of Chemistry, University of Perugia, Via Elce di Sotto 8, I-06123 Perugia, Italy.
ABSTRACT
Depolarized Rayleigh and low-frequency Raman scattering (DRS-LFR) spectra of liquids such as polar solvents enable the slow to ultrafast molecular dynamics of the condensed phase to be assessed. Time correlation functions of the polarizability anisotropy can be extracted from the (DRS-LFR) spectra, and suitably compared with corresponding responses from OKE time-resolved experiments [1]. The application of such frequency-domain approach to the study of dynamics of the liquid acetone at different temperatures (T=5.8–44.3 °C) revealed the presence of ultra-fast, fast (sub-picoseconds) and slow (picoseconds) processes. The slow dynamical process, which is attributable to the collective orientational dynamics, shows an increasing rate with the temperature (1=1.45 ps, at T=5.8 °C, and 1.01 ps, at 44.3°C) and closely compares with the characteristic time obtained from the long-time Kerr transient decay (1,DRS=1.17 ps, at T=25.1 °C, and 1,OKE=1.09 ps, at 24.0°C) [2]. Being acetone an approximate oblate symmetric-top rotor,[3] a unique component of the anisotropy polarizability tensor (0) activates the DRS spectrum, whilst only the anisotropy polarizability derivative tensor (k0, where k indicates a totally symmetric normal mode) activates the anisotropic Raman spectrum. The reorientational motion of acetone proved to be better described by a model based on microviscosity rather than the Stokes-Einstein-Debye hydrodynamic theory. The fast process results largely temperature independent (2=0.42 ps, at T=5.8 °C, and 0.38 ps, at 44.3°C) and may be attributed to a structural relaxation of “solvent cages” around librating molecules in the liquid. Evidences of librational dynamics were obtained from the analysis of reduced susceptibility spectra, ”(̃). Information obtained from the spectra of neat liquid acetone will be applied to the study of complex systems such as ionic solutions of acetone, in a further development of this work.
REFERENCES
[1] McMorrow, D., Lotshaw, W. T., and Kenny-Wallace, G. A., “Femtosecond optical Kerr studies on the origin of the nonlinear responses in simple liquids” IEEE Journal of Quantum Electronics 24 (2), 443-454 (1988)
[2] Shirota, H., Fujisawa, T., Fukazawa, H., and Nishikawa, K., “Ultrafast dynamics in aprotic molecular liquids: a femtosecond Raman-induced Kerr effect spectroscopic study” Bulletin of the Chemical Society of Japan 82 (11), 1347-1366 (2009)
[3] Bródka, A., and Zerda, T. W., “Dynamics of liquid acetone: Computer simulation” Journal of Chemical Physics 104 (16), 6313-6318 (1996
Multifractality and heart rate variability
No full textIn this paper, we participate to the discussion set forth by the editor of Chaos for the controversy, “Is the normal heart rate chaotic?” Our objective was to debate the question, “Is there some more appropriate term to characterize the heart rate variability HRV fluctuations?” We focused on the 24 h RR series prepared for this topic and tried to verify with two different techniques, generalized structure functions and wavelet transform modulus maxima, if they might be described as being multifractal. For normal and congestive heart failure subjects, the hq exponents showed to be decreasing for increasing q with both methods, as it should be for multifractal signals. We then built 40 surrogate series to further verify such hypothesis. For most of the series 75%–80% of cases multifractality stood the test of the surrogate data employed. On the other hand, series coming from patients in atrial fibrillation showed a small, if any, degree of multifractality. The population analyzed is too small for definite conclusions, but the study supports the use of multifractal series to model HRV. Also it suggests that the regulatory action of autonomous nervous system might play a role in the observed multifractality
Regularity patterns in heart rate variability signal: the approximate entropy approach
No full textRecent approaches to the study of nonlinearity in biological systems ha ce found a powerful tool in the Approximate Entropy (ApEn) estimation. ApEn is a family of statistic indices that measures different degrees of regularity in time series without any a priori hypothesis about the system structure generating them. In this paper we analyze its ability to distinguish, in the short period, different physiological conditions in which the cardiovascular control system can influence the heart rate variability signal (HRV). In the same time we show results confirming a significant separation in myocardial infarction populations on the basis of the ApEn index. The experimental work also discusses the choice of parameters for a correct ApEn index estimation and its link with the neural mechanisms controlling HRV signal
Working on the Noltisalis Database: measurement of nonlinear properties in heart rate variability signals
No full textWe present results obtained from the analysis of 50 heart rate variability series (HRV) which have been extracted from Holter recordings in the 24-hours in normal subjects and pathological patients. Data have been collected inside a multicentric research program, which aimed at the nonlinear analysis of HRV series. Multifractal approaches such as generalized structure functions have been used to characterize the HRV signal. Moreover, classical parameters for the analysis of the HRV signal over long time scales have been considered to perform a proper comparison. We considered classical time-domain indexes, "monofractal" characteristics (1/fα spectrum; detrended fluctuation analysis) and a regularity statistic (approximate entropy). The hypothesis of nonlinearity for the HRV signal has been verified by computing the generalized structure function on a set of surrogate data (amplitude adjusted surrogate data). In most cases, the multifractal spectrum of the original HRV series significantly differs (t-test), from those obtained from surrogate signals. This result can be associated with the presence of nonlinear correlations in the HRV signal. Moreover, results show that nonlinear parameters can be used to separate normal subjects from patients suffering from cardiovascular diseases
Nonlinear analysis of heart rate variability signal in heart transplanted subjects: bicaval vs standard orthotopic techniques
No full textTheoretical value of deceleration capacity points to deceleration reserve of fetal heart rate
No full textObjective: The interpretation of Average Acceleration and Deceleration Capacities (AC/DC), computed through Phase-Rectified Signal Averaging (PRSA), in intrapartum fetal heart rate (FHR) monitoring is still matter of investigation. We aimed to elucidate some behaviours of AC/DC. Methods: We derived the theoretical value of PRSA for stationary stochastic Gaussian processes and proved that for these time series AC and DC are necessarily identical in absolute value. The difference between DC and AC, termed Deceleration Reserve (DR), was introduced to detect signals' asymmetric trends. DR was tested on FHR signals from: near-term pregnant sheep model of labor consisting of chronically hypoxic and normoxic fetuses with both groups developing acidemia due to umbilical cord occlusions (UCO); and the CTU-UHB dataset containing fetal CTG recordings collected during labor of newborns that resulted acidotic and non-acidotic, respectively. DR was compared with AC and DC in terms of discriminatory power (AUC), between the groups, after correcting for signals' power or deceleration area, respectively. Results: DR displayed higher discriminatory power on the animal model during severe acidemia, with respect to AC/DC (p<0.05$ but also distinguished correctly all chronically hypoxic from normoxic fetuses at baseline prior to UCO. DR also outperformed AC/DC on the CTU-UHB dataset in distinguishing acidemic fetuses at birth (AUC: 0.65). Conclusion: Theoretical results motivated the introduction of DR, that proved to be superior than AC/DC for risk stratification during labor. Significance: DR, measured during labor, might permit to distinguish acidemic fetuses due to their different autonomic regulation, paving the way for new monitoring strategies
Multiscale entropy analysis of 24 hours heart rate variability time series
No full textWe assess the complexity of Heart Rate Variability (HRV) time series by computing Approximate Entropy (ApEn) and Sample Entropy (SampEn) on different time scales, according to a the Multiscale Entropy method (MSE) recently introduced. We find that considering multiple time scales enhances the ability to differentiate time series obtained from healthy and pathological subjects. Simulated signals such as white noise and 1/f^alpha noise have been analyzed to suggest possible reasons for these differences in HRV. Data belong to 10 Normal subjects, and patients who suffered from Myocardial Infarction (10), Congestive Heart Failure (10) and Heart transplant (10), all collected over 24 hours. Results show that the calculated parameters significantly separate the patient classes. The best performance is obtained for scale factors 3 to 8. We believe that the results could be exploited in order to reinforce indicators of risk prediction in cardiovascular pathologies
Multiparametric analysis of fetal heart rate: comparison of neural and statistical classifiers
No full textHeart Rate Variability analysis has demonstrated as a powerful diagnostic toot in many disease conditions which involve an alteration of the physiological control systems. In this paper we propose to classify Fetal Heart Rate signals through a set of indexes including time domain, frequency domain and other parameters related to signal morphology and regularity. This set is used as the input of an automatic system, whose goal is to detect the risk for the fetus to enter a pathological state. On a database of more than 400 recordings, we tested different classification methods to identify normals from potential pathological fetuses. A neural network approach was compared with classical statistical methods. The multilayer pereeptron, trained with the adaptive backpropagation algorithm, performed better than any tested statistical classifier
Dante poeta-profeta, pellegrino, autore : strutturazione espessiva della Commedia e visione escatologica dantesca
No full textLo studio del profetismo dantesco e del rapporto tra esso e la "lupa" (cioè la cupidigia-volontà di potenza, è condotto attraverso l'analisi dei momenti più intensamente profetici del poema: dagli aspetti escatologici, politici e sociali dell'antefatto, attraverso le intense reminiscenze da Ezechiele e da Apocalisse ricontestualizzate in Purg. XIX e XX, alle grandiose visioni escatologico-politiche di Purg. XXXII e XXXIII, alla sommessa e dolente speranza espressa negli ultimi canti di Beatrice.Il grido profetico di Dante è inseparabile dalle diverse immagini del poeta all'interno della Commedia: il poeta-pellegrino (l'agens); il poeta-scriba, addetto a riprodurre le esperienze vissute dal pellegrino; l'autore, cioè il poeta-profeta, il quale dice "io" anch'egli e intervienedal presente della scrittura per ammaestrare il lettore ed esecrare i vizi della cristianità sviata. Si esamina quindi la posizione di Dante tra i poeti-auctores antichi e l'auctoritas che spetta ai libri sacri di AT e di NT.The study of Dantean prophetism and of its relationship with the “she-wolf” (that is greed-lust for power), is carried out through the analysis of the most intensely prophetic moments of the poem: from the eschatological, political and social aspects of the background, through the intense reminiscences from Ezekiel and Apocalypse re-contextualized in Purgatory XIX and XX, to the great eschatological-political visions of Purgatory XXXII and XXXIII, to the quiet and sorrowful hope expressed in Beatrice's last cantos. Dante's prophetic cry is inseparable from the different images of the poet inside the Comedy : the pilgrim poet (the agens); the scribe poet, assigned to reproduce the experiences lived by the pilgrim; the author, that is the prophet poet, who also says “I” and intervenes from the present of the writing to teach the reader and execrate the vices of led astray Christianity. Then Dante's position is examined between the ancient auctores- poets and the auctoritas due to the holy books of the Old and New Testament
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