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1.
Sci Adv ; 5(6): eaat0122, 2019 06.
Artigo em Inglês | MEDLINE | ID: mdl-31249860

RESUMO

Fluctuations in biodiversity, large and small, pervade the fossil record, yet we do not understand the processes generating them. Here, we extend theory from nonequilibrium statistical physics to describe the fat-tailed form of fluctuations in Phanerozoic marine invertebrate richness. Using this theory, known as superstatistics, we show that heterogeneous rates of origination and extinction between clades and conserved rates within clades account for this fat-tailed form. We identify orders and families as the taxonomic levels at which clades experience interclade heterogeneity and within-clade homogeneity of rates, indicating that families are subsystems in local statistical equilibrium, while the entire system is not. The separation of timescales between within-clade background rates and the origin of major innovations producing new orders and families allows within-clade dynamics to reach equilibrium, while between-clade dynamics do not. The distribution of different dynamics across clades is consistent with niche conservatism and pulsed exploration of adaptive landscapes.

2.
Artigo em Inglês | MEDLINE | ID: mdl-27901630

RESUMO

Because of the intensive use of pharmaceutical substances in human life, studies on the detection of these chemical compounds and their metabolites as pollutants in water bodies are continuously reported. Some pharmaceutical agents are associated with adverse effects to aquatic life, even at very low concentrations (ng L-1 to µg L-1). For instance, the presence of antibiotics and hormones has been associated with increasing proliferation of antibiotic resistant pathogens and feminization and masculinization of some aquatic organisms. Currently, new attempts are being made to minimize or fully remove these types of pollutants from aquatic systems to protect the environment and human health. In this regard, physicochemical and biological treatments are among the most promising technologies for the treatment of wastewater containing pharmaceutical pollutants. These treatments are green alternatives for the degradation of hazardous organic compounds into nontoxic by-products. Here, we review some of the physicochemical and biological treatment methods used for the removal of the most extensively used antibiotics and hormones. Enzymatic oxidation, photocatalysis and electrochemical oxidation are described in terms of the aforementioned pharmaceutically active compounds (PhACs). The use of membrane technologies to separate different groups of antibiotics and hormones prior to biologic or physicochemical treatment methods is also addressed.


Assuntos
Antibacterianos/química , Preparações Farmacêuticas/química , Águas Residuárias , Poluentes Químicos da Água/química , Purificação da Água/métodos , Humanos , Oxirredução
3.
Artigo em Inglês | MEDLINE | ID: mdl-26565183

RESUMO

We describe the lifetimes associated with the stochastic evolution from an unstable uniform state to a patterned one when the time evolution of the field is controlled by a nonlocal Fisher equation. A small noise is added to the evolution equation to define the lifetimes and to calculate the mean first-passage time of the stochastic field through a given threshold value, before the patterned steady state is reached. In order to obtain analytical results we introduce a stochastic multiscale perturbation expansion. This multiscale expansion can also be used to tackle multiplicative stochastic partial differential equations. A critical slowing down is predicted for the marginal case when the Fourier phase of the unstable initial condition is null. We carry out Monte Carlo simulations to show the agreement with our theoretical predictions. Analytic results for the bifurcation point and asymptotic analysis of traveling wave-front solutions are included to get insight into the noise-induced transition phenomena mediated by invading fronts.

4.
Sensors (Basel) ; 15(10): 26929-39, 2015 Oct 23.
Artigo em Inglês | MEDLINE | ID: mdl-26512664

RESUMO

A novel fiber optic temperature sensor based on a liquid-core multimode interference device is demonstrated. The advantage of such structure is that the thermo-optic coefficient (TOC) of the liquid is at least one order of magnitude larger than that of silica and this, combined with the fact that the TOC of silica and the liquid have opposite signs, provides a liquid-core multimode fiber (MMF) highly sensitive to temperature. Since the refractive index of the liquid can be easily modified, this allows us to control the modal properties of the liquid-core MMF at will and the sensor sensitivity can be easily tuned by selecting the refractive index of the liquid in the core of the device. The maximum sensitivity measured in our experiments is 20 nm/°C in the low-temperature regime up to 60 °C. To the best of our knowledge, to date, this is the largest sensitivity reported for fiber-based MMI temperature sensors.


Assuntos
Tecnologia de Fibra Óptica/métodos , Desenho de Equipamento/métodos , Temperatura
5.
Opt Lett ; 39(2): 394-7, 2014 Jan 15.
Artigo em Inglês | MEDLINE | ID: mdl-24562155

RESUMO

We compare the performance of a self-mixing (SM) sensing system based on an uncooled monolithic array of 24×1 vertical-cavity surface-emitting lasers (VCSELs) in two modes of operation: single active channel and the concurrent multichannel operation. We find that the signal-to-noise ratio of individual SM sensors in a VCSEL array is markedly improved by multichannel operation, as a consequence of the increased operational temperature of the sensors. The performance improvement can be further increased by manufacturing VCSEL arrays with smaller pitch. This has the potential to produce an imaging system with high spatial and temporal resolutions that can be operated without temperature stabilization.

6.
Front Comput Neurosci ; 5: 167, 2014.
Artigo em Inglês | MEDLINE | ID: mdl-25566043

RESUMO

Learning under uncertainty is a common task that people face in their daily life. This process relies on the cognitive ability to adjust behavior to environmental demands. Although the biological underpinnings of those cognitive processes have been extensively studied, there has been little work in formal models seeking to capture the fundamental dynamic of learning under uncertainty. In the present work, we aimed to understand the basic cognitive mechanisms of outcome processing involved in decisions under uncertainty and to evaluate the relevance of previous experiences in enhancing learning processes within such uncertain context. We propose a formal model that emulates the behavior of people playing a well established paradigm (Iowa Gambling Task - IGT) and compare its outcome with a behavioral experiment. We further explored whether it was possible to emulate maladaptive behavior observed in clinical samples by modifying the model parameter which controls the update of expected outcomes distributions. Results showed that the performance of the model resembles the observed participant performance as well as IGT performance by healthy subjects described in the literature. Interestingly, the model converges faster than some subjects on the decks with higher net expected outcome. Furthermore, the modified version of the model replicated the trend observed in clinical samples performing the task. We argue that the basic cognitive component underlying learning under uncertainty can be represented as a differential equation that considers the outcomes of previous decisions for guiding the agent to an adaptive strategy.

7.
Bioprocess Biosyst Eng ; 36(12): 1947-56, 2013 Dec.
Artigo em Inglês | MEDLINE | ID: mdl-23708649

RESUMO

Cell culture on biopolymeric scaffolds has provided treatments for tissue engineering. Biopolymeric mixtures based on gelatin (Ge), chitosan (Ch) and hyaluronic acid (Ha) have been used to make scaffolds for wound healing. Thermal and physical properties of scaffolds prepared with Ge, Ch and Ha were characterized. Thermal characterization was made by using differential scanning calorimetry (DSC), and physical characterization by gas pycnometry and scanning electron microscopy. The effects of Ge content and cross-linking on thermophysical properties were evaluated by means of a factorial experiment design (central composite face centered). Gelatin content was the main factor that affects the thermophysical properties (microstructure and thermal transitions) of the scaffold. The effect of Ge content of the scaffolds for tissue engineering was studied by seeding skin cells on the biopolymers. The cell attachment was not significantly modified at different Ge contents; however, the cell growth rate increased linearly with the decrease of the Ge content. This relationship together with the thermophysical characterization may be used to design scaffolds for tissue engineering.


Assuntos
Biopolímeros/química , Quitosana/química , Gelatina/química , Ácido Hialurônico/química , Engenharia Tecidual , Animais , Varredura Diferencial de Calorimetria , Adesão Celular , Divisão Celular , Células Cultivadas , Microscopia Eletrônica de Varredura , Ratos , Temperatura , Tecidos Suporte
8.
Electron. j. biotechnol ; 13(5): 20-21, Sept. 2010. ilus, tab
Artigo em Inglês | LILACS | ID: lil-591902

RESUMO

Gelatin, chitosan and hyaluronic acid are natural components used to prepare polymeric scaffold in tissue engineering. The physical properties of these materials confer an appropriate microenvironment for cells, which can be used as a regeneration system for skin and cartilage. In this work, we prepared and characterized a Gelatin/Chitosan/Hyaluronan lyophilized-polymer. Physical properties of lyophilized-polymer changed slightly with moisture, but when polymer was totally hydrated the elasticity changed significantly. Thermophysical characterisation indicated that temperatures higher than 30ºC could modify irreversibly the polymeric matrix probably due to protein denaturation. Besides, we used the polymer as scaffold to prepare a biosynthetic-skin, reporting biological behaviour and its mechanical properties.


Assuntos
Ácido Hialurônico/química , Gelatina/química , Quitosana/química , Varredura Diferencial de Calorimetria , Imuno-Histoquímica , Microscopia Eletrônica de Varredura , Materiais Biocompatíveis/química , Polímeros , Pele Artificial
9.
J Transl Med ; 8: 59, 2010 Jun 17.
Artigo em Inglês | MEDLINE | ID: mdl-20565787

RESUMO

BACKGROUND: This manuscript reports the production and preclinical studies to examine the tolerance and efficacy of an autologous cellular gel-matrix integrated implant system (IIS) aimed to treat full-thickness skin lesions. METHODS: The best concentration of fibrinogen and thrombin was experimentally determined by employing 28 formula ratios of thrombin and fibrinogen and checking clot formation and apparent stability. IIS was formed by integrating skin cells by means of the in situ gelification of fibrin into a porous crosslinked scaffold composed of chitosan, gelatin and hyaluronic acid. The in vitro cell proliferation within the IIS was examined by the MTT assay and PCNA expression. An experimental rabbit model consisting of six circular lesions was utilized to test each of the components of the IIS. Then, the IIS was utilized in an animal model to cover a 35% body surface full thickness lesion. RESULTS: The preclinical assays in rabbits demonstrated that the IIS was well tolerated and also that IIS-treated rabbit with lesions of 35% of their body surface, exhibited a better survival rate (p = 0,06). CONCLUSION: IIS should be further studied as a new wound dressing which shows promising properties, being the most remarkable its good biological tolerance and cell growth promotion properties.


Assuntos
Géis/farmacologia , Implantes Experimentais , Cicatrização/efeitos dos fármacos , Animais , Bioensaio , Coagulação Sanguínea/efeitos dos fármacos , Proliferação de Células/efeitos dos fármacos , Sobrevivência Celular/efeitos dos fármacos , Fibrinogênio/metabolismo , Imuno-Histoquímica , Antígeno Nuclear de Célula em Proliferação/metabolismo , Coelhos , Pele/efeitos dos fármacos , Pele/patologia , Trombina/metabolismo , Resultado do Tratamento
10.
J Theor Biol ; 265(1): 18-26, 2010 Jul 07.
Artigo em Inglês | MEDLINE | ID: mdl-20417646

RESUMO

Vegetation pattern formation is a striking characteristic of several water-limited ecosystems around the world. Typically, they have been described on runoff-based ecosystems emphasizing local interactions between water, biomass interception, growth and dispersal. Here, we show that this situation is by no means general, as banded patterns in vegetation can emerge in areas without rainfall and in plants without functional root (the Bromeliad Tillandsia landbeckii) and where fog is the principal source of moisture. We show that a simple model based on the advection of fog-water by wind and its interception by the vegetation can reproduce banded patterns which agree with empirical patterns observed in the Coastal Atacama Desert. Our model predicts how the parameters may affect the conditions to form the banded pattern, showing a transition from a uniform vegetated state, at high water input or terrain slope to a desert state throughout intermediate banded states. Moreover, the model predicts that the pattern wavelength is a decreasing non-linear function of fog-water input and slope, and an increasing function of plant loss and fog-water flow speed. Finally, we show that the vegetation density is increased by the formation of the regular pattern compared to the density expected by the spatially homogeneous model emphasizing the importance of self-organization in arid ecosystems.


Assuntos
Ecossistema , Modelos Biológicos , Tillandsia/crescimento & desenvolvimento , Tempo (Meteorologia) , Chile , Análise Numérica Assistida por Computador
11.
PLoS One ; 4(12): e8243, 2009 Dec 23.
Artigo em Inglês | MEDLINE | ID: mdl-20041178

RESUMO

Many studies assume stock prices follow a random process known as geometric Brownian motion. Although approximately correct, this model fails to explain the frequent occurrence of extreme price movements, such as stock market crashes. Using a large collection of data from three different stock markets, we present evidence that a modification to the random model--adding a slow, but significant, fluctuation to the standard deviation of the process--accurately explains the probability of different-sized price changes, including the relative high frequency of extreme movements. Furthermore, we show that this process is similar across stocks so that their price fluctuations can be characterized by a single curve. Because the behavior of price fluctuations is rooted in the characteristics of volatility, we expect our results to bring increased interest to stochastic volatility models, and especially to those that can produce the properties of volatility reported here.


Assuntos
Comércio/economia , Investimentos em Saúde/economia , Marketing/economia
12.
Phys Rev E Stat Nonlin Soft Matter Phys ; 80(6 Pt 2): 065102, 2009 Dec.
Artigo em Inglês | MEDLINE | ID: mdl-20365214

RESUMO

Stock prices are known to exhibit non-Gaussian dynamics, and there is much interest in understanding the origin of this behavior. Here, we present a model that explains the shape and scaling of the distribution of intraday stock price fluctuations (called intraday returns) and verify the model using a large database for several stocks traded on the London Stock Exchange. We provide evidence that the return distribution for these stocks is non-Gaussian and similar in shape and that the distribution appears stable over intraday time scales. We explain these results by assuming the volatility of returns is constant intraday but varies over longer periods such that its inverse square follows a gamma distribution. This produces returns that are Student distributed for intraday time scales. The predicted results show excellent agreement with the data for all stocks in our study and over all regions of the return distribution.

13.
J Theor Biol ; 254(2): 408-16, 2008 Sep 21.
Artigo em Inglês | MEDLINE | ID: mdl-18602649

RESUMO

During the course of development cells undergo division producing a variety of cell types. Proliferation and differentiation are dependent on both genetic programs, encoded by the cellular genome, and environmental cues produced by the local cellular environment imposing local selection pressures on cells. We explore the role that cellular signals play over a large range of potential parameter regimes, in minimizing developmental error: errors in differentiation where an inappropriate proportion of differentiated daughter cells are generated. We find that trophic factors produced by the population of dividing cells can compensate for increased error rates when signals act through a form of positive feedback--survival signals. We operationalize these signals as the somatic niche and refer to their production as somatic niche construction. We find that tissue development switches to an autonomous state, independent of cellular signals, when errors are unmanageably high or density regulation is very strong. A signal-selective regime--strong niche dependence--is favored at low to intermediate error, assuming compartmentalized density dependence.


Assuntos
Linhagem da Célula/fisiologia , Desenvolvimento Embrionário/fisiologia , Células-Tronco Embrionárias/citologia , Meio Ambiente , Regulação da Expressão Gênica no Desenvolvimento , Transdução de Sinais/fisiologia , Animais , Diferenciação Celular/fisiologia , Divisão Celular/fisiologia , Modelos Biológicos , Linfócitos T/fisiologia
14.
IEEE Trans Biomed Eng ; 55(4): 1355-64, 2008 Apr.
Artigo em Inglês | MEDLINE | ID: mdl-18390326

RESUMO

There are concerns about workers repeatedly exposed to magnetic fields exceeding regulatory limits with respect to modern magnetic resonance imaging (MRI). As a result, there is need for an ambulatory magnetic field dosimeter capable of measuring these fields in and around an MRI scanner in order to evaluate the regulatory guidelines and determine any underlying exposure risks. This study presents results of tri-axial measurements using an ambulatory magnetic field dosimeter worn by workers during normal working shifts. We recorded and analyzed magnetic field exposures in and around 1.5 T, 2 T, and 4 T magnets during routine patient procedures. The data was integrated and averaged over time and evaluated against the latest exposure standards. Time-varying magnetic fields occur when individuals move through spatially non-uniform static magnetic fields or during gradient-pulsed magnetic fields or a combination of both. Our previous numerical analysis shows that at certain positions surrounding the MRI scanner ends, such fields may induce current densities and electric fields that may exceed the relevant EU, ICNIRP, and IEEE standards. A high-speed acquisition version of the dosimeter measured gradient- pulsed fields at positions accessible by MRI workers near the scanner ends, and the results were evaluated and compared against the numerical simulations and the standards. Our measurements confirm that workers can be exposed to magnetic fields exceeding the guidelines at positions near the gradient coil ends during clinical imaging and a high degree of correlation exists with the numerical results. While the time-weighted average magnetic field exposures in 1.5 T, 2 T, and 4 T were all within the regulatory limits during static magnetic field measurements, the peak limits for the head can be exceeded in some circumstances. This study presents a small number of routine shifts of data that provide indicative results of magnetic field exposure in real situations.


Assuntos
Carga Corporal (Radioterapia) , Campos Eletromagnéticos , Imagem por Ressonância Magnética , Corpo Clínico , Exposição Ocupacional/análise , Monitoramento de Radiação/métodos , Proteção Radiológica/métodos , Austrália , Humanos , Concentração Máxima Permitida , Doses de Radiação , Eficiência Biológica Relativa , Reprodutibilidade dos Testes , Sensibilidade e Especificidade
15.
J R Soc Interface ; 5(19): 237-45, 2008 Feb 06.
Artigo em Inglês | MEDLINE | ID: mdl-17594963

RESUMO

Of considerable interest are the evolutionary and developmental origins of complex, adaptive structures and the mechanisms that stabilize these structures. We consider the relationship between the evolutionary process of gene duplication and deletion and the stability of morphogenetic patterns produced by interacting activators and inhibitors. We compare the relative stability of patterns with a single activator and inhibitor (two-dimensional system) against a 'redundant' system with two activators or two inhibitors (three-dimensional system). We find that duplication events can both expand and contract the space of patterns. We study developmental robustness in terms of stochastic escape times from this space, also known as a 'canalization potential'. We embed the output of pattern formation into an explicit evolutionary model of gene duplication, gene loss and variation in the steepness of the canalization potential. We find that under all constant conditions, the system evolves towards a preference for steep potentials associated with low phenotypic variability and longer lifespans. This preference leads to an overall decrease in the density of redundant genotypes as developmental robustness neutralizes the advantages of genetic robustness.


Assuntos
Evolução Biológica , Padronização Corporal/genética , Duplicação Gênica , Modelos Genéticos , Simulação por Computador , Deleção de Genes
16.
Chem Commun (Camb) ; (7): 898-900, 2005 Feb 21.
Artigo em Inglês | MEDLINE | ID: mdl-15700074

RESUMO

Gold electrodes, previously prepared with surface anchored PAMAM dendrimers, were further modified with a Ni-containing tetraazamacrocycle resulting in a novel electrocatalytic material which proved to be particularly efficient for the electrochemical oxidation of methanol in basic aqueous medium.


Assuntos
Dendrímeros/química , Membranas Artificiais , Metanol/química , Níquel/química , Compostos Organometálicos/química , Poliaminas/química , Catálise , Eletroquímica , Estrutura Molecular , Oxirredução , Propriedades de Superfície , Água/química
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