¿Cuán abundantes son los conjuntos de números? Estudiantes comparando infinitos

Estudiamos las concepciones sobre la cardinalidad infinita de conjuntos numéricos, de estudiantes con distinta formación matemática. Se analizó una tarea de comparación de conjuntos infinitos de números, resuelta por estudiantes de educación secundaria y estudiantes universitarios con distinto grado de formación matemática. Se clasificó a los estudiantes según sus ideas sobre el infinito y se realizó un Análisis Factorial de Correspondencia relacionando éstas clases con el nivel de estudios de los estudiantes. Encontramos un gradiente de profundidad de estas ideas que comienzan desde de lo que hemos denominado horror infiniti, con las variantes de evitar el infinito o considerarlo como indefinido, presente principalmente en los estudiantes con menor nivel de estudios de matemática. En una zona intermedia se ubica la concepción más frecuente, la concepción finitista, ya sea tácita, explícita, o se base en los enteros como modelo de inclusión. La concepción más compleja, la infinitista, sólo fue explicitada por estudiantes universitarios, según dos enfoques: pensar la cardinalidad de los conjuntos infinitos como una única cantidad infinita, o concebir distintos cardinales infinitos, este último expresado sólo por estudiantes avanzados de matemática

Long-term effectiveness of cinacalcet in non-dialysis patients with chronic kidney disease and seconday hyperparathyroidism

Background: secondary hyperparathyroidism (SHPT) is a common complication of chronic kidney disease (CKD). Cinacalcet use is controversial in non-dialysis patients. Methods: this retrospective observational study recruited patients receiving cinacalcet (off-label use) in 2010 and 2011. Patients were followed for three years from the beginning of treatment using an intention-to-treat approach. Results: forty-one patients were studied: 14 CKD stage 3 (34.1%), 21 CKD stage 4 (51.2%), and 6 CKD stage 5 (14.6%). Median baseline parathyroid hormone (PTH) was 396 (101-1,300) pg/mL. Upon cinacalcet treatment (22 ± 12 months), PTH levels decreased by ≥ 30% in 73.2% of patients (P < 0.001; 95% confidence interval [CI], 59-87%), with a mean time for response of 18.7 months (95% CI, 15.4-22.1). Sixteen patients were followed for 36 months and treated for 32 ± 9 months. Mean reduction in their PTH levels was 50.1% (P < 0.001; 95% CI, 33.8-66.4%) at 36 months, with 62.5% of patients (P < 0.001; 95% CI, 35.9-89.1%) presenting reductions of ≥ 30%. Serum calcium levels decreased from 9.95 ± 0.62 mg/dL to 9.21 ± 0.83 and 9.12 ± 0.78 mg/dL at 12 and 36 months, respectively (P < 0.001). Serum phosphorus levels increased from 3.59 ± 0.43 to 3.82 ± 0.84 at 12 months (P = 0.180), remaining so at 36 months (P = 0.324). At 12 and 36 months, 2 (12.5%) patients experienced hypocalcemia. Meanwhile, 1 (6.3%) and 4 (25.0%) patients reported hyperphosphatemia at 12 and 36 months, respectively. Conclusion: Cinacalcet remained effective for at least 36 months in non-dialysis patients with SHPT. Electrolytic disturbances were managed with concurrent use of vitamin D and its analogs or phosphate binders

Toxic gas removal – metal–organic frameworks for the capture and degradation of toxic gases and vapours

The release of anthropogenic toxic pollutants into the atmosphere is a worldwide threat of growing concern. In this regard, it is possible to take advantage of the high versatility of MOFs materials in order to develop new technologies for environmental remediation purposes. Consequently, one of the main scientific challenges to be achieved in the field of MOF research should be to maximize the performance of these solids towards the sensing, capture and catalytic degradation of harmful gases and vapors by means of a rational control of size and reactivity of the pore walls that are directly accessible to guest molecules.The authors are grateful for the generous support by the Spanish Ministries of Economy (project: CTQ2011-22787) and Defense (COINCIDENTE Program) as well as Junta de Andalucia (P09-FQM-4981)

Battery Health Quantification for TDRS Spacecraft by Using Signature Discriminability Measurement

The NASA/GSFC Space Network Project Office (SN) currently operates a constellation of ten geosynchronous TDRS spacecraft launched over the past 30 years. The SN project collects up to 16.5 Gigabytes of telemetry every month. Generally, the spacecraft health and functionality are obtained by the use of real-time telemetry data for the multiple spacecraft subsystems, which are transmitted to the main ground station at the White Sands Complex in Las Cruces, NM. Recently, the SN has instituted a program of Big Data to analyze the large amounts of data using a variety of tools including Machine Learning, Artificial Intelligence, development of training sets, and a variety of mathematical modeling tools. The goal is to improve spacecraft management and obtain a more accurate prediction of the spacecraft end of life. The combination of these efforts with those of the Aerospace Corporation, which has a contract with the SN to produce yearly reliability estimates for the TDRS fleet, will be performed. This paper presents a new concept called telemetry quality quantification (TQQ) and discusses the progress that has been made in battery performance estimation for the second-generation TDRS spacecraft using a signature discriminability measures (SDM) algorithm combined with the Aerospace Corp. battery life estimation models. This activity is important because many of the TDRS fleet of spacecraft have exceeded their on-orbit design lifetime and, therefore, NASA must carefully manage the spacecraft to continue operations while avoiding an end-of-mission scenario that leaves a non-functioning spacecraft in geosynchronous orbit

Thermal Conductivity of Carbon Nanotubes and their Polymer Nanocomposites: A Review

Thermally conductive polymer composites offer new possibilities for replacing metal parts in several applications, including power electronics, electric motors and generators, heat exchangers, etc., thanks to the polymer advantages such as light weight, corrosion resistance and ease of processing. Current interest to improve the thermal conductivity of polymers is focused on the selective addition of nanofillers with high thermal conductivity. Unusually high thermal conductivity makes carbon nanotube (CNT) the best promising candidate material for thermally conductive composites. However, the thermal conductivities of polymer/CNT nanocomposites are relatively low compared with expectations from the intrinsic thermal conductivity of CNTs. The challenge primarily comes from the large interfacial thermal resistance between the CNT and the surrounding polymer matrix, which hinders the transfer of phonon dominating heat conduction in polymer and CNT. This article reviews the status of worldwide research in the thermal conductivity of CNTs and their polymer nanocomposites. The dependence of thermal conductivity of nanotubes on the atomic structure, the tube size, the morphology, the defect and the purification is reviewed. The roles of particle/polymer and particle/particle interfaces on the thermal conductivity of polymer/CNT nanocomposites are discussed in detail, as well as the relationship between the thermal conductivity and the micro- and nano-structure of the composite

Evaluación de los aprendizajes a las asignaturas de practicas externas del grado de ciencia y tecnología de los alimentos y del máster de desarrollo e innovación de alimentos

Memòria final del projecte d'innovació docent 2019pid-ub/008 del Grup d’innovació docent consolidat NUTRICIOPRACTICA-RiDoR (GINDO-UB/167)El objetivo principal de este proyecto de innovación docente ha sido diseñar instrumentos para evaluar el aprendizaje durante la formación práctica de los estudiantes de Prácticas Externas del grado de Ciencia y Tecnología de los Alimentos (CTA) y del Máster de Desarrollo e Innovación De Alimentos (DIA)

Neurotrophin-3 Is Involved in the Formation of Apical Dendritic Bundles in Cortical Layer 2 of the Rat

Apical dendritic bundles from pyramidal neurons are a prominent feature of cortical neuropil but with significant area specializations. Here, we investigate mechanisms of bundle formation, focusing on layer (L) 2 bundles in rat granular retrosplenial cortex (GRS), a limbic area implicated in spatial memory. By using microarrays, we first searched for genes highly and specifically expressed in GRS L2 at postnatal day (P) 3 versus GRS L2 at P12 (respectively, before and after bundle formation), versus GRS L5 (at P3), and versus L2 in barrel field cortex (BF) (at P3). Several genes, including neurotrophin-3 (NT-3), were identified as transiently and specifically expressed in GRS L2. Three of these were cloned and confirmed by in situ hybridization. To test that NT-3–mediated events are causally involved in bundle formation, we used in utero electroporation to overexpress NT-3 in other cortical areas. This produced prominent bundles of dendrites originating from L2 neurons in BF, where L2 bundles are normally absent. Intracellular biocytin fills, after physiological recording in vitro, revealed increased dendritic branching in L1 of BF. The controlled ectopic induction of dendritic bundles identifies a new role for NT-3 and a new in vivo model for investigating dendritic bundles and their formation

Electrostatic free energy landscapes for nucleic acid helix assembly

Metal ions are crucial for nucleic acid folding. From the free energy landscapes, we investigate the detailed mechanism for ion-induced collapse for a paradigm system: loop-tethered short DNA helices. We find that Na(+) and Mg(2+) play distinctive roles in helix–helix assembly. High [Na(+)] (>0.3 M) causes a reduced helix–helix electrostatic repulsion and a subsequent disordered packing of helices. In contrast, Mg(2+) of concentration >1 mM is predicted to induce helix–helix attraction and results in a more compact and ordered helix–helix packing. Mg(2+) is much more efficient in causing nucleic acid compaction. In addition, the free energy landscape shows that the tethering loops between the helices also play a significant role. A flexible loop, such as a neutral loop or a polynucleotide loop in high salt concentration, enhances the close approach of the helices in order to gain the loop entropy. On the other hand, a rigid loop, such as a polynucleotide loop in low salt concentration, tends to de-compact the helices. Therefore, a polynucleotide loop significantly enhances the sharpness of the ion-induced compaction transition. Moreover, we find that a larger number of helices in the system or a smaller radius of the divalent ions can cause a more abrupt compaction transition and a more compact state at high ion concentration, and the ion size effect becomes more pronounced as the number of helices is increased