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2.
Sensors (Basel) ; 21(6)2021 Mar 19.
Artículo en Inglés | MEDLINE | ID: mdl-33808821

RESUMEN

Dermal water content is an important biophysical parameter in preserving skin integrity and preventing skin damage. Traditional electrical-based and open-chamber evaporimeters have several well-known limitations. In particular, such devices are costly, sizeable, and only provide arbitrary outputs. They also do not permit continuous and non-invasive monitoring of dermal water content, which can be beneficial for various consumer, clinical, and cosmetic purposes. We report here on the design and development of a digital multi-wavelength optical sensor that performs continuous and non-invasive measurement of dermal water content. In silico investigation on porcine skin was carried out using the Monte Carlo modeling strategy to evaluate the feasibility and characterize the sensor. Subsequently, an in vitro experiment was carried out to evaluate the performance of the sensor and benchmark its accuracy against a high-end, broad band spectrophotometer. Reference measurements were made against gravimetric analysis. The results demonstrate that the developed sensor can deliver accurate, continuous, and non-invasive measurement of skin hydration through measurement of dermal water content. Remarkably, the novel design of the sensor exceeded the performance of the high-end spectrophotometer due to the important denoising effects of temporal averaging. The authors believe, in addition to wellbeing and skin health monitoring, the designed sensor can particularly facilitate disease management in patients presenting diabetes mellitus, hypothyroidism, malnutrition, and atopic dermatitis.


Asunto(s)
Piel , Agua , Animales , Biofisica , Simulación por Computador , Humanos , Método de Montecarlo , Porcinos
3.
J Environ Manage ; 289: 112513, 2021 Jul 01.
Artículo en Inglés | MEDLINE | ID: mdl-33823416

RESUMEN

Effects of external disturbances such as the population change on dynamics of water supply, power generation and environmental (WPE) systems have seldom been investigated. Following the WPE nexus profiled in the study of Feng et al. (2016), this study incorporated stochasticity of population, water supply and power generation into the modeling of the dynamical system in the Hehuang region of China, and further quantified resilience measures to understand the system's ability to withstand stochastic disturbances. First, the stochastic differential equations were used to improve the simulation of stochasticity in the WPE nexus. Next, the transient probability distribution functions (pdfs) of system variables, obtained by Monte Carlo simulation, were used to describe the evolutionary process of the system. Finally, the stationary pdfs of variables which reflect stable states of the system were derived to calculate four resilience measures. It is shown that: (1) The system approached a stable state after Year 2400 by calculating the L2 norm of the difference between transient and stationary pdfs. (2) The environmental system was identified as the most vulnerable subsystem because of its long convergence time. (3) The water supply system did not change greatly and it would remain stable at its current low level, i.e., water consumption per capita would be less than 80m3. The method adopted in this study is conducive to avoiding risk and the results provide valuable insights for regional management of a WPE nexus.


Asunto(s)
Abastecimiento de Agua , Agua , China , Simulación por Computador , Método de Montecarlo
5.
An Acad Bras Cienc ; 93(1): e20190406, 2021.
Artículo en Inglés | MEDLINE | ID: mdl-33909817

RESUMEN

Besides increasing the amount of data that can be used in a fitting process, the Regional Frequency Analysis (RFA) also assesses the quality of weather station networks. This technique assumes that it is possible to form homogeneous groups of meteorological series presenting independent and identically distributed data. Based on the hypothesis that such homogeneous groups can be formed under tropical-subtropical conditions, this study applied the RFA to assess the probability of one-day annual maximum rainfall in the State of São Paulo, Brazil. Critical limits used in previous studies to declare a region/group as 'acceptable homogeneous' (H≤1.00) or to select a distribution (|Z|≤1.64) were evaluated through Monte Carlo simulations. While the limit H≤1 is appropriate, the limit |Z|≤1.64 may lead to unacceptably high rates of rejecting a true null hypothesis. This statement is particularly true for the general logistic distribution. A computational algorithm allowing the selection of critical limits corresponding to pre-specified probabilities of rejecting a true null hypothesis is provided. Considering the new critical limits, data from one of the largest weather station networks of the State have been pooled into four homogeneous groups. Both generalized logistic and extreme value distributions are recommended for the probabilistic assessment of such groups.


Asunto(s)
Tiempo (Meteorología) , Brasil , Método de Montecarlo , Probabilidad
6.
Water Sci Technol ; 83(5): 1085-1102, 2021 Mar.
Artículo en Inglés | MEDLINE | ID: mdl-33724938

RESUMEN

A new parameter optimization and uncertainty assessment procedure using the Bayesian inference with an adaptive Metropolis-Hastings (AM-H) algorithm is presented for extreme rainfall frequency modeling. An efficient Markov chain Monte Carlo sampler is adopted to explore the posterior distribution of parameters and calculate their uncertainty intervals associated with the magnitude of estimated rainfall depth quantiles. Also, the efficiency of AM-H and conventional maximum likelihood estimation (MLE) in parameter estimation and uncertainty quantification are compared. And the procedure was implemented and discussed for the case of Chaohu city, China. Results of our work reveal that: (i) the adaptive Bayesian method, especially for return level associated to large return period, shows better estimated effect when compared with MLE; it should be noted that the implementation of MLE often produces overy optimistic results in the case of Chaohu city; (ii) AM-H algorithm is more reliable than MLE in terms of uncertainty quantification, and yields relatively narrow credible intervals for the quantile estimates to be instrumental in risk assessment of urban storm drainage planning.


Asunto(s)
Algoritmos , Teorema de Bayes , China , Ciudades , Simulación por Computador , Cadenas de Markov , Método de Montecarlo , Incertidumbre
7.
Math Biosci Eng ; 18(2): 1833-1844, 2021 02 22.
Artículo en Inglés | MEDLINE | ID: mdl-33757213

RESUMEN

In this paper, we present an SEIIaHR epidemic model to study the influence of recessive infection and isolation in the spread of COVID-19. We first prove that the infection-free equilibrium is globally asymptotically stable with condition R0<1 and the positive equilibrium is uniformly persistent when the condition R0>1. By using the COVID-19 data in India, we then give numerical simulations to illustrate our results and carry out some sensitivity analysis. We know that asymptomatic infections will affect the spread of the disease when the quarantine rate is within the range of [0.3519, 0.5411]. Furthermore, isolating people with symptoms is important to control and eliminate the disease.


Asunto(s)
/epidemiología , Epidemias , Modelos Biológicos , Infecciones Asintomáticas/epidemiología , Número Básico de Reproducción/estadística & datos numéricos , /transmisión , Simulación por Computador , Epidemias/prevención & control , Epidemias/estadística & datos numéricos , Humanos , India/epidemiología , Cadenas de Markov , Conceptos Matemáticos , Método de Montecarlo , Pandemias/prevención & control , Pandemias/estadística & datos numéricos , Cuarentena/estadística & datos numéricos
8.
PLoS One ; 16(3): e0238800, 2021.
Artículo en Inglés | MEDLINE | ID: mdl-33760817

RESUMEN

New Zealand had 1499 cases of COVID-19 before eliminating transmission of the virus. Extensive contract tracing during the outbreak has resulted in a dataset of epidemiologically linked cases. This data contains useful information about the transmission dynamics of the virus, its dependence on factors such as age, and its response to different control measures. We use Monte-Carlo network construction techniques to provide an estimate of the number of secondary cases for every individual infected during the outbreak. We then apply standard statistical techniques to quantify differences between groups of individuals. Children under 10 years old are significantly under-represented in the case data. Children infected fewer people on average and had a lower probability of transmitting the disease in comparison to adults and the elderly. Imported cases infected fewer people on average and also had a lower probability of transmitting than domestically acquired cases. Superspreading is a significant contributor to the epidemic dynamics, with 20% of cases among adults responsible for 65-85% of transmission. Subclinical cases infected fewer individuals than clinical cases. After controlling for outliers serial intervals were approximated with a normal distribution (µ = 4.4 days, σ = 4.7 days). Border controls and strong social distancing measures, particularly when targeted at superspreading, play a significant role in reducing the spread of COVID-19.


Asunto(s)
/epidemiología , Brotes de Enfermedades/prevención & control , /prevención & control , Trazado de Contacto/métodos , Trazado de Contacto/estadística & datos numéricos , Epidemias/prevención & control , Humanos , Método de Montecarlo , Nueva Zelanda/epidemiología , /patogenicidad
9.
Water Res ; 194: 116953, 2021 Apr 15.
Artículo en Inglés | MEDLINE | ID: mdl-33657494

RESUMEN

The quasi-Monte Carlo (QMC) method was enhanced to solve the population balance model (PBM) including aggregation and fragmentation processes for simulating the temporal evolutions of characteristic sizes and floc size distributions (FSDs) of cohesive sediments. Ideal cases with analytical solutions were firstly adopted to validate this QMC model to illustrate selected pure aggregation, pure fragmentation, and combined aggregation and fragmentation systems. Two available laboratory data sets, one with suspended kaolinite and the other with a mixture of kaolinite and montmorillonite, were further used to monitor the FSDs of cohesive sediments in controlled shear conditions. The model results show reasonable agreements with both analytical solutions and laboratory experiments. Moreover, different QMC schemes were tested and compared with the standard Monte Carlo scheme and a Latin Hypercube Sampling scheme to optimize the model performance. It shows that all QMC schemes perform better in both accuracy and time consumption than standard Monte Carlo scheme. In particular, compared with other schemes, the QMC scheme using Halton sequence requires the least particle numbers in the simulated system to reach reasonable accuracy. In the sensitivity tests, we also show that the fractal dimension and the fragmentation distribution function have large impacts on the predicted FSDs. This study indicates a great advance in employing QMC schemes to solve PBM for simulating the flocculation of cohesive sediments.


Asunto(s)
Fractales , Sedimentos Geológicos , Floculación , Caolín , Método de Montecarlo
10.
BMC Infect Dis ; 21(1): 307, 2021 Mar 26.
Artículo en Inglés | MEDLINE | ID: mdl-33771113

RESUMEN

BACKGROUND: Limited clinical studies describe the pharmacodynamics of fosfomycin (FOS), tigecycline (TGC) and colistin methanesulfonate (CMS) in combination against KPC-producing Klebsiella pneumoniae (KPC-Kp). Population pharmacokinetic models were used in our study. Monte Carlo simulation was conducted to calculate probability of target attainment (PTA) and cumulative fraction of response (CFR) of each agent alone and in combination against KPC-Kp in patients with normal or decreased renal function. RESULTS: The simulated regimen of FOS 6 g q8h reached ≥90% PTA against a MIC of 64 mg/L in patients with normal renal function. For patients with renal impairment, FOS 4 g q8h could provide sufficient antimicrobial coverage against a MIC of 128 mg/L. And increasing the daily dose could result to the cut-off value to 256 mg/L in decreased renal function. For TGC, conventional dosing regimens failed to reach 90% PTA against a MIC of 2 mg/L. Higher loading and daily doses (TGC 200/400 mg loading doses followed by 100 mg q12h/200 mg q24h) were needed. For CMS, none achieved 90% PTA against a MIC of 2 mg/L in normal renal function. Against KPC-Kp, the regimens of 200/400 mg loading dose followed by 100 q12h /200 mg q24h achieved > 80% CFRs regardless of renal function, followed by CMS 9 million IU loading dose followed by 4.5/3 million IU q12h in combination with FOS 8 g q8h (CFR 75-91%). CONCLUSIONS: The use of a loading dose and high daily dose of TGC and CMS in combination with FOS can provide sufficient antimicrobial coverage against critically ill patients infected with KPC-Kp.


Asunto(s)
Antibacterianos/farmacocinética , Riñón/fisiopatología , Infecciones por Klebsiella/tratamiento farmacológico , Anciano , Anciano de 80 o más Años , Antibacterianos/uso terapéutico , Enterobacteriaceae Resistentes a los Carbapenémicos/efectos de los fármacos , Colistina/farmacocinética , Colistina/uso terapéutico , Enfermedad Crítica , Femenino , Fosfomicina/farmacocinética , Fosfomicina/uso terapéutico , Humanos , Pruebas de Función Renal , Klebsiella pneumoniae/efectos de los fármacos , Masculino , Pruebas de Sensibilidad Microbiana , Persona de Mediana Edad , Método de Montecarlo , Tigeciclina/farmacocinética , Tigeciclina/uso terapéutico
11.
J Environ Radioact ; 232: 106573, 2021 Jun.
Artículo en Inglés | MEDLINE | ID: mdl-33751985

RESUMEN

A new measurement model composed of High Purity Germanium detector HPGe including Lead Shield with a mixed source of Am-241, Cd-109, …in a soil matrix packed in a cylindrical container was developed by Monte Carlo N-Particles code MCNP5. The Monte Carlo models being largely used for efficiencies calculations in routine environmental radioactivity measurements of high volume soil samples. In order to validate the simulation, a multi-radionuclides soil matrix source in a cylindrical container is prepared. Comparing the simulated results to the experimental ones, allows us to correct coincidence summing in the soil standard and study its effect in activity measurements where a good agreement is found between corrected activities and results found by another geometry and show how uncorrected efficiency curves lead to erroneous activity calculation. Finally, the developed model is applied to study the distribution of natural and artificial radioactivity in a forest site in Bainem, northern of Algeria, these results are invested for radiological impact and soil erosion studies in the study Area.


Asunto(s)
Monitoreo de Radiación , Espectrometría gamma , Simulación por Computador , Método de Montecarlo , Radioisótopos/análisis
12.
PLoS One ; 16(3): e0245728, 2021.
Artículo en Inglés | MEDLINE | ID: mdl-33735225

RESUMEN

At the beginning of 2020, the COVID-19 pandemic was able to spread quickly in Wuhan and in the province of Hubei due to a lack of experience with this novel virus. Additionally, authories had no proven experience with applying insufficient medical, communication and crisis management tools. For a considerable period of time, the actual number of people infected was unknown. There were great uncertainties regarding the dynamics and spread of the Covid-19 virus infection. In this paper, we develop a system dynamics model for the three connected regions (Wuhan, Hubei excl. Wuhan, China excl. Hubei) to understand the infection and spread dynamics of the virus and provide a more accurate estimate of the number of infected people in Wuhan and discuss the necessity and effectivity of protective measures against this epidemic, such as the quarantines imposed throughout China. We use the statistics of confirmed cases of China excl. Hubei. Also the daily data on travel activity within China was utilized, in order to determine the actual numerical development of the infected people in Wuhan City and Hubei Province. We used a multivariate Monte Carlo optimization to parameterize the model to match the official statistics. In particular, we used the model to calculate the infections, which had already broken out, but were not diagnosed for various reasons.


Asunto(s)
/epidemiología , Algoritmos , /transmisión , China/epidemiología , Humanos , Modelos Estadísticos , Método de Montecarlo , Pandemias , Cuarentena , Viaje
13.
J Med Internet Res ; 23(3): e26516, 2021 03 03.
Artículo en Inglés | MEDLINE | ID: mdl-33656440

RESUMEN

BACKGROUND: The COVID-19 pandemic has caused patients to avoid seeking medical care. Provision of telemonitoring programs in addition to usual care has demonstrated improved effectiveness in managing patients with heart failure (HF). OBJECTIVE: We aimed to examine the potential clinical and health economic outcomes of a telemonitoring program for management of patients with HF during the COVID-19 pandemic from the perspective of health care providers in Hong Kong. METHODS: A Markov model was designed to compare the outcomes of a care under COVID-19 (CUC) group and a telemonitoring plus CUC group (telemonitoring group) in a hypothetical cohort of older patients with HF in Hong Kong. The model outcome measures were direct medical cost, quality-adjusted life-years (QALYs), and incremental cost-effectiveness ratio. Sensitivity analyses were performed to examine the model assumptions and the robustness of the base-case results. RESULTS: In the base-case analysis, the telemonitoring group showed a higher QALY gain (1.9007) at a higher cost (US $15,888) compared to the CUC group (1.8345 QALYs at US $15,603). Adopting US $48,937/QALY (1 × the gross domestic product per capita of Hong Kong) as the willingness-to-pay threshold, telemonitoring was accepted as a highly cost-effective strategy, with an incremental cost-effective ratio of US $4292/QALY. No threshold value was identified in the deterministic sensitivity analysis. In the probabilistic sensitivity analysis, telemonitoring was accepted as cost-effective in 99.22% of 10,000 Monte Carlo simulations. CONCLUSIONS: Compared to the current outpatient care alone under the COVID-19 pandemic, the addition of telemonitoring-mediated management to the current care for patients with HF appears to be a highly cost-effective strategy from the perspective of health care providers in Hong Kong.


Asunto(s)
Atención Ambulatoria , Análisis de Datos , Insuficiencia Cardíaca/epidemiología , Método de Montecarlo , Telemedicina/economía , Telemedicina/métodos , Atención Ambulatoria/economía , Atención Ambulatoria/métodos , Estudios de Cohortes , Análisis Costo-Beneficio , Hong Kong/epidemiología , Humanos , Cadenas de Markov , Pandemias , Años de Vida Ajustados por Calidad de Vida
14.
Nat Commun ; 12(1): 1904, 2021 03 26.
Artículo en Inglés | MEDLINE | ID: mdl-33771988

RESUMEN

The spread of Coronavirus disease 19 (COVID-19) has led to many healthcare systems being overwhelmed by the rapid emergence of new cases. Here, we study the ramifications of hospital load due to COVID-19 morbidity on in-hospital mortality of patients with COVID-19 by analyzing records of all 22,636 COVID-19 patients hospitalized in Israel from mid-July 2020 to mid-January 2021. We show that even under moderately heavy patient load (>500 countrywide hospitalized severely-ill patients; the Israeli Ministry of Health defined 800 severely-ill patients as the maximum capacity allowing adequate treatment), in-hospital mortality rate of patients with COVID-19 significantly increased compared to periods of lower patient load (250-500 severely-ill patients): 14-day mortality rates were 22.1% (Standard Error 3.1%) higher (mid-September to mid-October) and 27.2% (Standard Error 3.3%) higher (mid-December to mid-January). We further show this higher mortality rate cannot be attributed to changes in the patient population during periods of heavier load.


Asunto(s)
/prevención & control , Mortalidad Hospitalaria/tendencias , Hospitales/estadística & datos numéricos , /aislamiento & purificación , Adulto , Anciano , Anciano de 80 o más Años , /virología , Epidemias , Femenino , Hospitalización/estadística & datos numéricos , Humanos , Israel/epidemiología , Masculino , Persona de Mediana Edad , Método de Montecarlo , /fisiología
15.
Int J Mol Sci ; 22(5)2021 Feb 26.
Artículo en Inglés | MEDLINE | ID: mdl-33652934

RESUMEN

Biological membranes are composed of isotropic and anisotropic curved nanodomains. Anisotropic membrane components, such as Bin/Amphiphysin/Rvs (BAR) superfamily protein domains, could trigger/facilitate the growth of membrane tubular protrusions, while isotropic curved nanodomains may induce undulated (necklace-like) membrane protrusions. We review the role of isotropic and anisotropic membrane nanodomains in stability of tubular and undulated membrane structures generated or stabilized by cyto- or membrane-skeleton. We also describe the theory of spontaneous self-assembly of isotropic curved membrane nanodomains and derive the critical concentration above which the spontaneous necklace-like membrane protrusion growth is favorable. We show that the actin cytoskeleton growth inside the vesicle or cell can change its equilibrium shape, induce higher degree of segregation of membrane nanodomains or even alter the average orientation angle of anisotropic nanodomains such as BAR domains. These effects may indicate whether the actin cytoskeleton role is only to stabilize membrane protrusions or to generate them by stretching the vesicle membrane. Furthermore, we demonstrate that by taking into account the in-plane orientational ordering of anisotropic membrane nanodomains, direct interactions between them and the extrinsic (deviatoric) curvature elasticity, it is possible to explain the experimentally observed stability of oblate (discocyte) shapes of red blood cells in a broad interval of cell reduced volume. Finally, we present results of numerical calculations and Monte-Carlo simulations which indicate that the active forces of membrane skeleton and cytoskeleton applied to plasma membrane may considerably influence cell shape and membrane budding.


Asunto(s)
Forma de la Célula , Citoesqueleto/metabolismo , Eritrocitos/citología , Microdominios de Membrana/metabolismo , Simulación por Computador , Elasticidad , Membrana Eritrocítica/metabolismo , Eritrocitos/metabolismo , Humanos , Modelos Biológicos , Modelos Moleculares , Método de Montecarlo
16.
Environ Pollut ; 278: 116823, 2021 Jun 01.
Artículo en Inglés | MEDLINE | ID: mdl-33735793

RESUMEN

Chinese children have been exposed to high level of lead due to polluted air, dust, contaminated foods and water, etc. In this research, we investigated published blood lead levels (BLLs) reflecting 1,057,832 Chinese children aged at 0-12 and teenagers aged at 13-18 in the past 30 years (1991-2020). The data mining and estimation were performed innovatively by Monte Carlo simulation to remedy the skewed distribution-induced bias. The temporal trend of Chinese children's BLLs showed an obvious decrease in the past decades from 88.74 µg/L (Geometric SD = 4.09) during 1991-1995 to 27.32 µg/L (Geometric SD = 4.18) during 2016-2020. This study also indicated that children's BLLs of Yunnan, Guizhou, Shanxi were at relatively high levels and most provinces showed a downward trend. Chinese boys aged at 1-18 years old had higher BLLs (GM: 44.03 µg/L) compared to girls (GM: 41.32 µg/L) (p < 0.001). At different age groups, Chinese children's BLLs were 42.04 µg/L (1-3 years old), 52.88 µg/L (4-6 years old), 50.49 µg/L (7 and above years old), respectively. Although the BLLs of Chinese children exhibited a continuous declined trend in the past 30 years, it was still higher than that in developed countries, which indicated that more efforts are needed in children's BLLs control.


Asunto(s)
Intoxicación por Plomo , Plomo , Adolescente , Niño , Preescolar , China , Exposición a Riesgos Ambientales , Femenino , Humanos , Lactante , Recién Nacido , Masculino , Método de Montecarlo
17.
Value Health ; 24(3): 369-376, 2021 03.
Artículo en Inglés | MEDLINE | ID: mdl-33641771

RESUMEN

OBJECTIVES: To investigate the safety and cost-effectiveness of lengthening the time between surveillance ultrasound scans in the UK Abdominal Aortic Aneurysm (AAA) Screening Programme. METHODS: A discrete event simulation model was used to evaluate the cost-effectiveness of AAA screening for men aged 65, comparing current surveillance intervals to 6 alternative surveillance interval strategies that lengthened the time between surveillance scans for 1 or more AAA size categories. The model considered clinical events and costs incurred over a 30-year time horizon and the cost per quality-adjusted life year (QALY). The model adopted the National Health Service perspective and discounted future costs and benefits at 3.5%. RESULTS: Compared with current practice, alternative surveillance strategies resulted in up to a 4% reduction in the number of elective AAA repairs but with an increase of up to 1.6% in the number of AAA ruptures and AAA-related deaths. Alternative strategies resulted in a small reduction in QALYs compared to current practice but with reduced costs. Two strategies that lengthened surveillance intervals in only very small AAAs (3.0-3.9 cm) provided, at a cost-effectiveness threshold of £20 000 per QALY, the highest positive incremental net benefit. There was negligible chance that current practice is the most cost-effective strategy at any threshold below £40 000 per QALY. CONCLUSIONS: Lengthening surveillance intervals in the UK Abdominal Aortic Aneurysm Screening Programme, especially for small AAA, can marginally reduce the incremental cost per QALY of the program. Nevertheless, whether the cost savings from refining surveillance strategies justifies a change in clinical practice is unclear.


Asunto(s)
Aneurisma de la Aorta Abdominal/diagnóstico , Tamizaje Masivo/economía , Anciano , Anciano de 80 o más Años , Análisis Costo-Beneficio , Femenino , Humanos , Masculino , Modelos Económicos , Método de Montecarlo , Medicina Estatal , Factores de Tiempo , Ultrasonografía , Reino Unido
18.
Sci Total Environ ; 772: 145532, 2021 Jun 10.
Artículo en Inglés | MEDLINE | ID: mdl-33578164

RESUMEN

The application of nanomaterials is expanding. Therefore, it is necessary to investigate the relationship between the structure and toxicity of different nanomaterials. Quasi-SMILES is a line of symbols which are codes of corresponding conditions of experiments aimed to estimate the toxicity of ZnO nanoparticles towards the rat via intraperitoneal injections. By means of the Monte Carlo method, the so-called correlation weights for fragments of quasi-SMILES can be calculated. Having the numerical data on the correlation weights one can build up a one-variable model for the toxicity. The checking up of the approach with five random splits of all available data on results of thirty-six experiments into a sub-system of training and sub-system of validation has confirmed the significance of the statistical quality of models obtained with the above approach. The average determination coefficient equal to 0.957 (dispersion 0.010) and average root mean square error equal to 7.25 [mg/kg] (dispersion 0.59 [mg/kg]).


Asunto(s)
Nanopartículas , Óxido de Zinc , Animales , Método de Montecarlo , Nanopartículas/toxicidad , Relación Estructura-Actividad Cuantitativa , Ratas , Programas Informáticos , Óxido de Zinc/toxicidad
19.
Nucleic Acids Res ; 49(5): 2537-2551, 2021 03 18.
Artículo en Inglés | MEDLINE | ID: mdl-33589918

RESUMEN

Nucleosome-nucleosome interactions drive the folding of nucleosomal arrays into dense chromatin fibers. A better physical account of the folding of chromatin fibers is necessary to understand the role of chromatin in regulating DNA transactions. Here, we studied the unfolding pathway of regular chromatin fibers as a function of single base pair increments in linker length, using both rigid base-pair Monte Carlo simulations and single-molecule force spectroscopy. Both computational and experimental results reveal a periodic variation of the folding energies due to the limited flexibility of the linker DNA. We show that twist is more restrictive for nucleosome stacking than bend, and find the most stable stacking interactions for linker lengths of multiples of 10 bp. We analyzed nucleosomes stacking in both 1- and 2-start topologies and show that stacking preferences are determined by the length of the linker DNA. Moreover, we present evidence that the sequence of the linker DNA also modulates nucleosome stacking and that the effect of the deletion of the H4 tail depends on the linker length. Importantly, these results imply that nucleosome positioning in vivo not only affects the phasing of nucleosomes relative to DNA but also directs the higher-order structure of chromatin.


Asunto(s)
Cromatina/química , ADN/química , Nucleosomas/química , Histonas/genética , Modelos Moleculares , Método de Montecarlo , Conformación de Ácido Nucleico
20.
Epidemics ; 34: 100439, 2021 03.
Artículo en Inglés | MEDLINE | ID: mdl-33556763

RESUMEN

Epidemiological models are widely used to analyze the spread of diseases such as the global COVID-19 pandemic caused by SARS-CoV-2. However, all models are based on simplifying assumptions and often on sparse data. This limits the reliability of parameter estimates and predictions. In this manuscript, we demonstrate the relevance of these limitations and the pitfalls associated with the use of overly simplistic models. We considered the data for the early phase of the COVID-19 outbreak in Wuhan, China, as an example, and perform parameter estimation, uncertainty analysis and model selection for a range of established epidemiological models. Amongst others, we employ Markov chain Monte Carlo sampling, parameter and prediction profile calculation algorithms. Our results show that parameter estimates and predictions obtained for several established models on the basis of reported case numbers can be subject to substantial uncertainty. More importantly, estimates were often unrealistic and the confidence/credibility intervals did not cover plausible values of critical parameters obtained using different approaches. These findings suggest, amongst others, that standard compartmental models can be overly simplistic and that the reported case numbers provide often insufficient information for obtaining reliable and realistic parameter values, and for forecasting the evolution of epidemics.


Asunto(s)
/epidemiología , Modelos Estadísticos , Pandemias , Algoritmos , China/epidemiología , Predicción , Humanos , Cadenas de Markov , Método de Montecarlo , Reproducibilidad de los Resultados , Incertidumbre
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