Random barrier double-well model for resistive switching in tunnel barriers

The resistive switching phenomenon in MgO-based tunnel junctions is attributed to the effect of charged defects inside the barrier. The presence of electron traps in the MgO barrier, that can be filled and emptied, locally modifies the conductance of the barrier and leads to the resistive switching effects. A double-well model for trapped electrons in MgO is introduced to theoretically describe this phenomenon. Including the statistical distribution of potential barrier heights for these traps leads to a power-law dependence of the resistance as a function of time, under a constant bias voltage. This model also predicts a power-law relation of the hysteresis as a function of the voltage sweep frequency. Experimental transport results strongly support this model and in particular confirm the expected power laws dependencies of resistance. They moreover indicate that the exponent of these power laws varies with temperature as theoretically predicted.Comment: 18 pages, 5 figures, final versio

Neurocognitive profile of the post-COVID condition in adults in Catalonia. A mixed method prospective cohort and nested case-control study: Study Protocol

The diagnosis of the post-COVID condition is usually achieved by excluding other diseases; however, cognitive changes are often found in the post-COVID disorder. Therefore, monitoring and treating the recovery from the post-COVID condition is necessary to establish biomarkers to guide the diagnosis of symptoms, including cognitive impairment. Our study employs a prospected cohort and nested case-control design with mixed methods, including statistical analyses, interviews, and focus groups. Our main aim is to identify biomarkers (functional and structural neural changes, inflammatory and immune status, vascular and vestibular signs and symptoms) easily applied in primary care to detect cognitive changes in post-COVID cases. The results will open up a new line of research to inform diagnostic and therapeutic decisions with special considerations for cognitive impairment in the post-COVID condition

Neurocognitive Profile of the Post-COVID Condition in Adults in Catalonia-A Mixed Method Prospective Cohort and Nested Case-Control Study : Study Protocol

Altres ajuts: This study is also supported in part by grants from the CIBER-Consorcio Centro de Investigación Biomédica en Red-(CB 2021), Ministerio de Ciencia e Innovación and Unión Europea, NextGenerationEU.The diagnosis of the post-COVID condition is usually achieved by excluding other diseases; however, cognitive changes are often found in the post-COVID disorder. Therefore, monitoring and treating the recovery from the post-COVID condition is necessary to establish biomarkers to guide the diagnosis of symptoms, including cognitive impairment. Our study employs a prospected cohort and nested case-control design with mixed methods, including statistical analyses, interviews, and focus groups. Our main aim is to identify biomarkers (functional and structural neural changes, inflammatory and immune status, vascular and vestibular signs and symptoms) easily applied in primary care to detect cognitive changes in post-COVID cases. The results will open up a new line of research to inform diagnostic and therapeutic decisions with special considerations for cognitive impairment in the post-COVID condition

Mitochondria Express α7 Nicotinic Acetylcholine Receptors to Regulate Ca2+ Accumulation and Cytochrome c Release: Study on Isolated Mitochondria

Nicotinic acetylcholine receptors (nAChRs) are ligand-gated ion channels that mediate synaptic transmission in the muscle and autonomic ganglia and regulate transmitter release in the brain. The nAChRs composed of α7 subunits are also expressed in non-excitable cells to regulate cell survival and proliferation. Up to now, functional α7 nAChRs were found exclusively on the cell plasma membrane. Here we show that they are expressed in mitochondria and regulate early pro-apoptotic events like cytochrome c release. The binding of α7-specific antibody with mouse liver mitochondria was revealed by electron microscopy. Outer membranes of mitochondria from the wild-type and β2−/− but not α7−/− mice bound α7 nAChR-specific antibody and toxins: FITC-labeled α-cobratoxin or Alexa 555-labeled α-bungarotoxin. α7 nAChR agonists (1 µM acetylcholine, 10 µM choline or 30 nM PNU-282987) impaired intramitochondrial Ca2+ accumulation and significantly decreased cytochrome c release stimulated with either 90 µM CaCl2 or 0.5 mM H2O2. α7-specific antagonist methyllicaconitine (50 nM) did not affect Ca2+ accumulation in mitochondria but attenuated the effects of agonists on cytochrome c release. Inhibitor of voltage-dependent anion channel (VDAC) 4,4′-diisothio-cyano-2,2′-stilbene disulfonic acid (0.5 µM) decreased cytochrome c release stimulated with apoptogens similarly to α7 nAChR agonists, and VDAC was co-captured with the α7 nAChR from mitochondria outer membrane preparation in both direct and reverse sandwich ELISA. It is concluded that α7 nAChRs are expressed in mitochondria outer membrane to regulate the VDAC-mediated Ca2+ transport and mitochondrial permeability transition

Mixed Dentition Analysis among a Nigerian Population

Mixed dentition space analysis forms an important aspect of orthodontic diagnosis and treatment planning. A commonly used method involves the use of regression equations to predict the sizes of the unerupted canines and premolars. The objective of this study was therefore to evaluate the accuracy of the Tanaka and Johnston tooth size prediction equations in a Nigerian population. Methodology Mesiodistal tooth widths of teeth from 150 pairs of dental casts, obtained from junior secondary school children (88 females, 62 males) aged between 12 and 16 years old were measured with a digital caliper. The mean sum of the four mandibular incisors was then used to predict the sum of the canines and premolars in one quadrant, using the Tanaka and Johnston equations. These predicted values were then compared statistically with their respective actual measurements from the casts. Results. Results indicated that statistically significant differences (p˂0.05) exist between the actual measurements (Σ 345) and their predicted sizes using the Tanaka Johnston tooth size prediction equations. New prediction equations were therefore formulated for use on Nigerians. Conclusion. The Tanaka and Johnston tooth size prediction equation cannot be used for Nigerians

Development of a protocol to study the bactericidal activity of metal anatase (TiO 2 )

Metal anatase (TiO 2 ) is an industrially important compound, currently used in a variety of applications as a white pigment. Anatase has also been shown to kill bacteria in the presence of blue light. This property has been exploited in the purification of water. However, the basis of cell killing has not been confirmed and remains under investigation. To study the proposed model of killing by reactive oxygen species, a suitable protocol must be designed. Sample volume, culture concentration, method of anatase plate sterilization, and light intensity are important variables that influence the degree of killing. Previous experiments focused on small volume sizes, however in this study larger sample volumes were used to investigate the feasibility of large scale sterilization procedures. Due to difficulties in development of a functional protocol, killing in large volume samples could not be assessed, yet remains a future pursuit. Killing in a 150µl bubble was enhanced when anatase plates were sterilized by boiling in water compared to sterilization with acetone. Killing was also enhanced when light intensity was increased. Although these modifications resulted in enhanced cell killing, it was still substantially less than previously reported. As the activity of these anatase plates was greater in experiments conducted five years ago, the effect of plate age and storage on the long-term activity of anatase should be investigated. The metal anatase (TiO 2 ) is currently used in interior paints, plastic filling, paper filling and highway marking paints as a white pigment. Interestingly, it may also play a role as a disinfectant. The first report of photocatalytic disinfection was the work of Matsunaga and coworkers in 1985 (3). Over the last 25 years, its usefulness in the removal of organic matter from air and water has been explored (1, 2, 4). However, the basis of cell killing has not been confirmed and remains under investigation. Anatase has photocatalytic activity that through a series of chemical steps produces reactive oxygen species (including the hydroxyl radical) that can cause fatal damage to microorganisms. Light is required to initiate this process by the following reaction: TiO 2 + Blue Light → TiO 2 -+ OH • (1). Initially, this study was most interested in investigating the relationship between reactive oxygen species and cell death, a relationship that has yet to be confirmed and characterized. It was thought that a correlation between the concentration of reactive oxygen species and the amount of cell death might be observed and lend support to this model of cell killing. However, in preparation for this proposed experiment, the authors found that the set-up and design required multiple tests and modifications, and thus the study became one of experimental design. The effects of volume, concentration of bacterial sample, method of sterilization of the anatase plates, and the effect of light intensity were explored. MATERIALS AND METHODS E. coli B23 was grown overnight in M9 medium + 0.4% (w/v) glycerol. The culture was diluted to a concentration of 10 5 cells/ml. Anatase plates were sterilized in acetone, dried, and activated under fluorescent light for 5 minutes. Fluorescent light was used as it contains the desired spectrum of light (blue light ~400nm). Samples of different volumes were placed on anatase plates at an equal distance (5.8cm) from the fluorescent light In subsequent experimentation several modifications to the initial protocol were made. Firstly, smaller sample sizes of 150µl, 300µl, 450µl, and 750µl, each in the form of a bubble on the surface of the anatase plates, were tested. The 150 µl sample was placed on the smaller sized plate while the 300µl, 450µl, and 750µl samples were placed on the larger sized plates. These four plates were used for the remainder of the experiment. Cell concentration was also decreased 10-fold to 10 4 cells/ml and all other conditions were held constant. Secondly, the time course 17

Carbon isotope fluctuations in Precambrian carbonate sequences of several localities in Brazil

Carbon isotope fluctuations in Precambrian sedimentary carbonates between 2.8 Ga and 0.60 Ga in Brazil are examined in this study. The carbonate facies of the BIF of the 2.8 Ga-old Carajás Formation, state of Pará in northern Brazil, has rather homogeneous delta13C (-5 o/ooPDB), compatible with carbonatization of a silicate protolith by a CO2-rich fluid from mantle degassing. The Paleoproterozoic Gandarela Formation, state of Minas Gerais, displays a narrow delta13C variation (-1.5 to +0.5 o/oo) compatible with carbon isotope signatures of carbonates deposited around 2.4 Ga worldwide. The Fecho do Funil Formation has probably recorded the Lomagundi delta13C positive anomaly (+6.4 to +7.1 o/ooPDB). The magnesite-bearing carbonates of the Orós mobile belt, state of Ceará, exhibit carbon isotope fluctuation within the range for carbonates deposited at 1.8 Ga. The C-isotope record of the Frecheirinha Formation, northwestern state of Ceará, shows negative delta13C values in its lower portion (-2 o/oo) and positive values up section (+1 to +3 o/oo), which suggests this sequence is a cap carbonate deposited after a glacial event around 0.95 Ga. The Jacoca and Acauã sedimentary carbonate Formations, state of Sergipe, NE Brazil, show carbon isotope fluctuations very similar to each other (average around -5 o/oo), compatible with a deposition around 0.76 Ga. The younger Olho D'Água carbonate Formation, however, also in the state of Sergipe, displays negative delta13C values at the lower portion of the Formation, changing dramatically up section to positive values as high as +10 o/oo, a characteristic compatible with a Sturtian cap carbonate deposited around 0.69 Ga. On the light of the C isotope data discussed in this study, it seems that delta13C fluctuations in Paleoproterozoic carbonates in Brazil are within the range found globally for metasedimentary carbonates of this age. Carbon isotope data proved to be very useful in establishing relative chronology of Neoproterozoic carbonate formations for which precise radiometric ages are not available