What triggers a microcrack in printed engineering parts produced by selective laser sintering on the first place?

The proximity of un-melted particles within Selective Laser Sintered (SLS) printed engineering parts made of Nylon-12 is found as a major triggering effect for cracking and ultimately failure. The numerical investigation, by means of the eXtended Finite Element Method (XFEM), was performed over samples with different arrangements of un-melted particles obtained experimentally. The onset and propagation of microcracks was simulated. This included inherently how the degree of particle melt (DPM) in SLS parts affects and controls both crack initiation and propagation. The results evidenced that a microcrack started invariably between the two closest un-melted particles in all numerical tests performed considering different arrangements of un-melted particles

Ultrasonic inline inspection of a cement-based drinking water pipeline

The integrity of the drinking water infrastructure deteriorates with time. Monitoring the condition of the drinking water mains can enhance the remaining operational lifetime assessment of the network. In this research a method to translate ultrasonic signals to degradation levels from an inline inspection in a cement-based drinking water pipeline is proposed. The data was obtained from an inspection performed in a Dutch drinking main section. The data is processed in two major steps. Firstly, the parameters that provide the condition of the cement are extracted. Secondly, images of the degradation within the pipes of the inspected trajectory were generated. The main contributions in this paper are (i) the estimation of relative degradation levels of a cement-based pipeline based on the ultrasonic pulse-echo technique and (ii) the upscaling of the processing method in an automated manner for visualization of the degraded condition. Lastly, a sensitivity study of the parameters relevant to the determination of the degraded depth has been performed. The speed of sound in cement is the most relevant parameter to consider. Estimating absolute degradation levels needs further study.</p

An approach to the reconfiguration of the space and the tourist consumption in Coyoacán

Con la incorporación de la economía de libre mercado, en la realidad urbana se desencadenaron profundas modificaciones, que orientaron hacia la producción de espacios estratégicos para la acumulación del capital, tomando en consideración que este, se apropia de las condiciones preexistentes que le favorecen para su reproducción. Por lo tanto, el objetivo del artículo es analizar la reconfiguración del espacio urbano para la comprensión de la elitización de la vida a través del consumo turístico, en la experiencia del Centro Histórico de Coyoacán, México. En donde se da cuenta, del vínculo concreto entre el consumo turístico y la complejidad de los procesos urbanos como consecuencias que amenazan la reproducción de los espacios de vida

Experimental Validation of Non-Collinear Wave Mixing Model in a PVC Specimen

A scattering wave generated from the interaction of two incident acoustic waves contains information on the third order elastic constants of a solid material. The scattering amplitude is known to be dependent on the interaction angle between the two incident waves. However, the realization of experimental tests is hampered due to the geometry and accessibility to the surfaces. In this research, the amplitude of the scattering wave is investigated as a function of the excitation frequency of the incident waves, while the interaction angle is kept constant. The amplitude coefficient and scattering amplitude were solved analytically for two interaction processes. The analytical solutions were validated with experiments. The model qualitatively agrees with the experiments. The two main results are stressed: the angle of the scattering wave is controlled by the frequency ratio of the two interaction waves, rather than by the angle between these waves. The second advantage is the possibility to use a wider range of excitation frequencies of the incident waves. This is a great advantage in applications where, for example, there is only access to one surface of a flat specime

ARQUITECTURA COMPUTACIONAL

GUÍA PEDAGÓGIC

Zerovalent bismuth nanoparticles inhibit Streptococcus mutans growth and formation of biofilm

Background and methods: Despite continuous efforts, the increasing prevalence of resistance among pathogenic bacteria to common antibiotics has become one of the most significant concerns in modern medicine. Nanostructured materials are used in many fields, including biological sciences and medicine. While some bismuth derivatives has been used in medicine to treat vomiting, nausea, diarrhea, and stomach pain, the biocidal activity of zerovalent bismuth nanoparticles has not yet been studied. The objective of this investigation was to analyze the antimicrobial activity of bismuth nanoparticles against oral bacteria and their antibiofilm capabilities. Results: Our results showed that stable colloidal bismuth nanoparticles had 69% antimicrobial activity against Streptococcus mutans growth and achieved complete inhibition of biofilm formation. These results are similar to those obtained with chlorhexidine, the most commonly used oral antiseptic agent. The minimal inhibitory concentration of bismuth nanoparticles that interfered with S. mutans growth was 0.5 mM. Conclusion: These results suggest that zerovalent bismuth nanoparticles could be an interesting antimicrobial agent to be incorporated into an oral antiseptic preparation

Abordaje diagnóstico del gato con enfermedad del tracto urinario

ABORDAJE DIAGNÓSTICO DEL GATO CON ENFERMEDAD DEL TRACTO URINARIOLas enfermedades del tracto urinario caudal de los gatos (ETUCG) son un grupo de patologías que afectan a la vejiga y/o uretra, manifestándose por la presencia de signos clínicos del tracto urinario caudal; estas se pueden mostrar con cuadros obstructivos o no obstructivos. Su abordaje diagnóstico implica un proceso sistemático basado en los hallazgos de los estudios epidemiológicos

Effect of Lipophilic Bismuth Nanoparticles on Erythrocytes

Lipophilic bismuth dimercaptopropanol nanoparticles (BisBAL NPs) have a very important antimicrobial activity; however their effect on human cells or tissues has not been completely studied. Undesirable effects of bismuth include anemia which could result from suicidal erythrocyte death or eryptosis. The objective of this research was to determine the effect of bismuth dimercaptopropanol nanoparticles on blood cells. The nanoparticles are composed of 53 nm crystallites on average and have a spherical structure, agglomerating into clusters of small nanoparticles. Based on cell viability assays and optical microscopy, cytotoxicity on erythrocytes was observed after growing with 500 and 1000 µM of BisBAL NPs for 24 h. AM Calcein was retained inside erythrocytes when they were exposed to 100 µM (or lower concentrations) of BisBAL NPs for 24 h, suggesting the absence of damage in plasmatic membrane. Genotoxic assays revealed no damage to genomic DNA of blood cells after 24 h of exposition to BisBAL NPs. Finally, 100–1000 µM of bismuth nanoparticles promotes apoptosis between blood cells after 24 h of incubation. Hence BisBAL NPs at concentrations lower than 100 µM do not cause damage on blood cells; they could potentially be used by humans without affecting erythrocytes and leukocytes