1000 resultados para Kohan, Martín
Resumo:
Generally, medicine books are concentrated almost exclusively in explaining methodology that analyzes fixed measures, measures done in a certain moment, nevertheless the evolution of the measurement and correct interpretation of the missed values are very important and sometimes can give the key information of the results obtained. Thus, the analysis of the temporary series and spectral analysis or analysis of the time series in the dominion of frequencies can be regarded as an appropriate tool for this kind of studies.In this work the frequency of the pulsating secretion of luteinizing hormone LH (thatregulates the fertile life of women) were analyzed in order to determine the existence of the significant frequencies obtained by analysis of Fourier. Detection of the frequencies, with which the pulsating secretion of the LH takes place, is a quite difficult question due topresence of the random errors in measures and samplings, i.e. that pulsating secretions of small amplitude are not detected and disregarded. In physiology it is accepted that cyclical patterns in the secretion of the LH exist and in the results of this research confirm this pattern and determine its frequency presented in the corresponded periodograms to each of studied cycle. The obtained results can be used as key pattern for future sampling frequencies in order to ¿catch¿ the significant picks of the luteinizing hormone and reflect on time forproductivity treatment of women.
Resumo:
Palaeobotany applied to freshwater plants is an emerging field of palaeontology. Hydrophytic plants reveal evolutionary trends of their own, clearly distinct from those of the terrestrial and marine flora. During the Precambrian, two groups stand out in the fossil record of freshwater plants: the Cyanobacteria (stromatolites) in benthic environments and the prasinophytes (leiosphaeridian acritarchs) in transitional planktonic environments. During the Palaeozoic, green algae (Chlorococcales, Zygnematales, charophytes and some extinct groups) radiated and developed the widest range of morphostructural patterns known for these groups. Between the Permian and Early Cretaceous, charophytes dominated macrophytic associations, with the consequence that over tens of millions of years, freshwater flora bypassed the dominance of vascular plants on land. During the Early Cretaceous, global extension of the freshwater environments is associated with diversification of the flora, including new charophyte families and the appearance of aquatic angiosperms and ferns for the first time. Mesozoic planktonic assemblages retained their ancestral composition that was dominated by coenobial Chlorococcales, until the appearance of freshwater dinoflagellates in the Early Cretaceous. In the Late Cretaceous, freshwater angiosperms dominated almost all macrophytic communities worldwide. The Tertiary was characterised by the diversification of additional angiosperm and aquatic fern lineages, which resulted in the first differentiation of aquatic plant biogeoprovinces. Phytoplankton also diversified during the Eocene with the development of freshwater diatoms and chrysophytes. Diatoms, which were exclusively marine during tens of millions of years, were dominant over the Chlorococcales during Neogene and in later assemblages. During the Quaternary, aquatic plant communities suffered from the effects of eutrophication, paludification and acidification, which were the result of the combined impact of glaciation and anthropogenic disturbance.
Resumo:
Fossil charophytes were recorded in two different stratigraphic units from the non-marine Palaeogene of the Balearic Islands. In the Peguera Limestone Fm. of Mallorca the charophyte flora is characterised by two assemblages. The first contains Raskyella peckii subsp. meridionale, Harrisichara caeciliana and Maedleriella mangenoti, from the Bartonian and Lutetian; whilst the second is characterised by Harrisichara vasiformistuberculata and Nitellopsis (Tectochara) aemula, Middle Priabonian in age. The Cala Blanca Detrital Fm. has yielded Lychnothamnus stockmansii and Sphaerochara inconspicua in Menorca whilst in Mallorca it contains Lychnothamnus praelangeri, L. langeri and Sphaerochara hirmeri. This flora is Late Priabonian and Oligocene in age. These results suggest that the beginning of Paleogene non-marine deposition was diachronic in Mallorca. In terms of biogeography, the Eocene charophytes of Mallorca show affinity with North-African floras. The presence of the Eocene African subspecies Raskyella peckii meridionale in Mallorca enables the biogeographic boundary between this form and the European subspecies R. peckii peckii to be drawn at about 32º N latitude in the Iberian Plate.
Resumo:
We apply majorization theory to study the quantum algorithms known so far and find that there is a majorization principle underlying the way they operate. Grover's algorithm is a neat instance of this principle where majorization works step by step until the optimal target state is found. Extensions of this situation are also found in algorithms based in quantum adiabatic evolution and the family of quantum phase-estimation algorithms, including Shor's algorithm. We state that in quantum algorithms the time arrow is a majorization arrow.
Resumo:
This volume reflects a variegated and fruitful dialogue between classical and medieval philologists and historians of science, philosophy, literature and language as well as of medicine - the diverse range of interests that the history of medicine in the Graeco-Roman world and the medieval West continues to stimulate and draw on. A recurrent theme is the transformation of medical knowledge in different languages, literary forms and cultural milieux. Several papers concern editorial work in progress on unpublished texts, available only in manuscript or early printed editions. Ce recueil met en dialogue des spécialistes des textes médicaux latins de l'Antiquité et du Moyen Âge. Certaines analyses adoptent une approche sociolinguistique, d'autres s'intéressent à des questions de transmission et de réception, d'autres enfin livrent des études sur le lexique médical. Mais toutes concourent à éclairer une histoire culturelle de la médecine qui s'inscrit dans un monde en mutation. With a preface by D. R. Langslow, and contributions by M. Baldin, J. P. Barragán Nieto, P. P. Conde Parrado, D. Crismani, M. Cronier, C. de la Rosa Cubo, A. Ferraces Rodríguez, K.-D. Fischer, P. Gaillard-Seux, A. García González, V. Gitton-Ripoll, G. Haverling, F. Le Blay, B. Maire, G. Marasco, A. I. Martín Ferreira, I. Mazzini, F. Messina, Ph. Mudry, V. Nutton, M. Pardon-Labonnelie, R. Passarella, M. J. Pérez Ibáñez, S. Sconocchia, A. M. Urso, M. E. Vázquez Buján, and H. von Staden.
Resumo:
Coherence resonance occurring in semiconductor lasers with optical feedback is studied via the Lang-Kobayashi model with external nonwhite noise in the pumping current. The temporal correlation and the amplitude of the noise have a highly relevant influence in the system, leading to an optimal coherent response for suitable values of both the noise amplitude and correlation time. This phenomenon is quantitatively characterized by means of several statistical measures.
Resumo:
We show that time-dependent couplings may lead to nontrivial scaling properties of the surface fluctuations of the asymptotic regime in nonequilibrium kinetic roughening models. Three typical situations are studied. In the case of a crossover between two different rough regimes, the time-dependent coupling may result in anomalous scaling for scales above the crossover length. In a different setting, for a crossover from a rough to either a flat or damping regime, the time-dependent crossover length may conspire to produce a rough surface, although the most relevant term tends to flatten the surface. In addition, our analysis sheds light into an existing debate in the problem of spontaneous imbibition, where time-dependent couplings naturally arise in theoretical models and experiments.
Resumo:
We propose a method to obtain a single centered correlation with use of a joint transform correlator. We analyze the required setup to carry out the whole process optically, and we also present experimental results.
Resumo:
The development of liquid-crystal panels for use in commercial equipment has been aimed at improving the pixel resolution and the display efficiency. These improvements have led to a reduction in the thickness of such devices, among other outcomes, that involves a loss in phase modulation. We propose a modification of the classical phase-only filter to permit displays in VGA liquid-crystal panels with a constant amplitude modulation and less than a 2¿(PI) phase modulation. The method was tested experimentally in an optical setup.
Resumo:
We propose a method to display full complex Fresnel holograms by adding the information displayed on two analogue ferroelectric liquid crystal spatial light modulators. One of them works in real-only configuration and the other in imaginary-only mode. The Fresnel holograms are computed by backpropagating an object at a selected distance with the Fresnel transform. Then, displaying the real and imaginary parts on each panel, the object is reconstructed at that distance from the modulators by simple propagation of light. We present simulation results taking into account the specifications of the modulators as well as optical results. We have also studied the quality of reconstructions using only real, imaginary, amplitude or phase information. Although the real and imaginary reconstructions look acceptable for certain distances, full complex reconstruction is always better and is required when arbitrary distances are used.
Resumo:
The use of different kinds of nonlinear filtering in a joint transform correlator are studied and compared. The study is divided into two parts, one corresponding to object space and the second to the Fourier domain of the joint power spectrum. In the first part, phase and inverse filters are computed; their inverse Fourier transforms are also computed, thereby becoming the reference in the object space. In the Fourier space, the binarization of the power spectrum is realized and compared with a new procedure for removing the spatial envelope. All cases are simulated and experimentally implemented by a compact joint transform correlator.
Resumo:
Optical aberration due to the nonflatness of spatial light modulators used in holographic optical tweezers significantly deteriorates the quality of the trap and may easily prevent stable trapping of particles. We use a Shack-Hartmann sensor to measure the distorted wavefront at the modulator plane; the conjugate of this wavefront is then added to the holograms written into the display to counteract its own curvature and thus compensate the optical aberration of the system. For a Holoeye LC-R 2500 reflective device, flatness is improved from 0.8¿ to ¿/16 (¿=532 nm), leading to a diffraction-limited spot at the focal plane of the microscope objective, which makes stable trapping possible. This process could be fully automated in a closed-loop configuration and would eventually allow other sources of aberration in the optical setup to be corrected for.
Resumo:
In this study, we present a method designed to generate dynamic holograms in holographic optical tweezers. The approach combines our random mask encoding method with iterative high-efficiency algorithms. This hybrid method can be used to dynamically modify precalculated holograms, giving them new functionalities¿temporarily or permanently¿with a low computational cost. This allows the easy addition or removal of a single trap or the independent control of groups of traps for manipulating a variety of rigid structures in real time.
Resumo:
En este trabajo se presentan distintas alternativas para obtener la modulación compleja completa de frentes de onda mediante la suma de la modulación introducida por dos pantallas de cristal líquido. Para los distintos métodos se presentan resultados simulados de reconstrucciones de hologramas de Fresnel digitales.