Reduction of thermal conductivity in ferroelectric SrTiO3 thin films

Bulk SrTiO3 is a quantum paraelectric in which an antiferrodistortive distortion below approximate to 105 K and quantum fluctuations at low temperature preclude the stabilization of a long-range ferroelectric state. However, biaxial mechanical stress, impurity doping, and Sr nonstoichiometry, among other mechanisms, are able to stabilize a ferroelectric or relaxor ferroelectric state at room temperature, which develops into a longer-range ferroelectric state below 250 K. In this paper, we show that epitaxial SrTiO3 thin films grown under tensile strain on DyScO3 exhibit a large reduction of thermal conductivity, approximate to 60% of at room temperature, with respect to identical strain-free or compressed films. The thermal conductivity shows a further reduction below 250 K, a temperature concurrent with the peak in the dielectric constant [J. H. Haeni et al., Nature (London) 430, 758 (2004)]. These results suggest that strain gradients in the relaxor and ferroelectric phase of SrTiO3 are very effective phonon scatterers, limiting the thermal transport in this material

Sleep hygiene impacts on episodic memories in young and older adults during quarantine by Covid-19: preliminary results

Sleep benefits off-line memory consolidation. Due to quarantine by Covid-19, sleep routines and sleep quality were affected. Preliminary results from our Lab showed that episodic memory formation is impaired by emotional variables, such as anxiety and depression. We hypothesize that sleep hygiene during quarantine positively impacts memory processes and emotional variables. To test this, we perform a 21-day study. Young and older participants were trained on the episodic memory task (video of neutral content). On day 7 they were tested and half of them began a sleep hygiene program. On day 14, participants were trained in a new episodic task and were tested on day 21. We found that young and older adults that received the sleep hygiene treatment had a positive impact on memory performance. Furthermore, older adults had better performance in memory recognition than young adults independently of the hygiene treatment. Moreover, older adults that received the sleep hygiene treatment showed a positive correlation between the total amount of sleep hygiene activities and the amount of correct recognition as well as a negative correlation with false recognition. We did not found a significant effect on emotional variables. These results demonstrate that sleep hygiene can be an effective tool for young and older adults to improve memory, however one-week treatment is not enough to induce emotional improvements.Fil: Tassone, Leonela Magali. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Instituto Tecnológico de Buenos Aires; ArgentinaFil: Moyano, Malen Daiana. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Instituto Tecnológico de Buenos Aires; ArgentinaFil: Solferino, C.. Instituto Tecnológico de Buenos Aires; ArgentinaFil: Feldberg, Carolina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Instituto de Neurociencias Buenos Aires S. A.; ArgentinaFil: Tartaglini, Maria Florencia. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Instituto de Neurociencias Buenos Aires S. A.; ArgentinaFil: Brusco, I.. Centro de Neuropsiquiatría y Neurología de la Conducta; ArgentinaFil: Forcato, Cecilia. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Instituto Tecnológico de Buenos Aires; ArgentinaXXXV Annual Meeting of the Argentinian Society for Neuroscience ResearchCiudad Autónoma de Buenos AiresArgentinaSociedad Argentina de Investigación en Neurociencia

Efficiency of Energy Conversion in Thermoelectric Nanojunctions

Using first-principles approaches, this study investigated the efficiency of energy conversion in nanojunctions, described by the thermoelectric figure of merit $ZT$. We obtained the qualitative and quantitative descriptions for the dependence of $ZT$ on temperatures and lengths. A characteristic temperature: $T_{0}= \sqrt{\beta/\gamma(l)}$ was observed. When $T\ll T_{0}$, $ZT\propto T^{2}$. When $T\gg T_{0}$, $ZT$ tends to a saturation value. The dependence of $ZT$ on the wire length for the metallic atomic chains is opposite to that for the insulating molecules: for aluminum atomic (conducting) wires, the saturation value of $ZT$ increases as the length increases; while for alkanethiol (insulating) chains, the saturation value of $ZT$ decreases as the length increases. $ZT$ can also be enhanced by choosing low-elasticity bridging materials or creating poor thermal contacts in nanojunctions. The results of this study may be of interest to research attempting to increase the efficiency of energy conversion in nano thermoelectric devices.Comment: 2 figure

Effect of Thermoelectric Cooling in Nanoscale Junctions

We propose a thermoelectric cooling device based on an atomic-sized junction. Using first-principles approaches, we investigate the working conditions and the coefficient of performance (COP) of an atomic-scale electronic refrigerator where the effects of phonon's thermal current and local heating are included. It is observed that the functioning of the thermoelectric nano-refrigerator is restricted to a narrow range of driving voltages. Compared with the bulk thermoelectric system with the overwhelmingly irreversible Joule heating, the 4-Al atomic refrigerator has a higher efficiency than a bulk thermoelectric refrigerator with the same $ZT$ due to suppressed local heating via the quasi-ballistic electron transport and small driving voltages. Quantum nature due to the size minimization offered by atomic-level control of properties facilitates electron cooling beyond the expectation of the conventional thermoelectric device theory.Comment: 8 figure

Excretion of Vancomycin-Resistant Enterococci by Wild Mammals

A survey of fecal samples found enterococcal excretion in 82% of 388 bank voles (Clethrionomys glareolus), 92% of 131 woodmice (Apodemus sylvaticus), and 75% of 165 badgers (Meles meles). Vancomycin-resistant enterococci, all Enterococcus faecium of vanA genotype, were excreted by 4.6% of the woodmice and 1.2% of the badgers, but by none of the bank voles

Observation of reduced thermal conductivity in a metal-organic framework due to the presence of adsorbates

Whether the presence of adsorbates increases or decreases thermal conductivity in metal-organic frameworks (MOFs) has been an open question. Here we report observations of thermal transport in the metal-organic framework HKUST-1 in the presence of various liquid adsorbates: water, methanol, and ethanol. Experimental thermoreflectance measurements were performed on single crystals and thin films, and theoretical predictions were made using molecular dynamics simulations. We find that the thermal conductivity of HKUST-1 decreases by 40 – 80% depending on the adsorbate, a result that cannot be explained by effective medium approximations. Our findings demonstrate that adsorbates introduce additional phonon scattering in HKUST-1, which particularly shortens the lifetimes of low-frequency phonon modes. As a result, the system thermal conductivity is lowered to a greater extent than the increase expected by the creation of additional heat transfer channels. Finally, we show that thermal diffusivity is even more greatly reduced than thermal conductivity by adsorption

TARTESSUS: A customized electrospun drug delivery system loaded with Irinotecan for Local and sustained chemotherapy release in pancreatic cancer

Post-surgical chemotherapy in pancreatic cancer has notorious side effects due to the high dose required. Multiple devices have been designed to tackle this aspect and achieve a delayed drug release. This study aimed to explore the controlled and sustained local delivery of a reduced drug dose from an irinotecan-loaded electrospun nanofiber membrane (named TARTESSUS) that can be placed on the patients' tissue after tumor resection surgery. The drug delivery system formulation was made of polycaprolactone (PCL). The mechanical properties and the release kinetics of the drug were adjusted by the electrospinning parameters and by the polymer ratio between 10 w.t.% and 14 w.t.% of PCL in formic acid:acetic acid:chloroform (47.5:47.5:5). The irinotecan release analysis was performed and three different release periods were obtained, depending on the concentration of the polymer in the dissolution. The TARTESSUS device was tested in 2D and 3D cell cultures and it demonstrated a decrease in cell viability in 2D culture between 72 h and day 7 from the start of treatment. In 3D culture, a decrease in viability was seen between 72 h, day 7 (p < 0.001), day 10 (p < 0.001), 14 (p < 0.001), and day 17 (p = 0.003) as well as a decrease in proliferation between 72 h and day 10 (p = 0.030) and a reduction in spheroid size during days 10 (p = 0.001), 14 (p < 0.001), and 17 (p < 0.001). In conclusion, TARTESSUS showed a successful encapsulation of a chemotherapeutic drug and a sustained and delayed release with an adjustable releasing period to optimize the therapeutic effect in pancreatic cancer treatment

Methanol Steam Reformer on a Silicon Wafer

A study of the reforming rates, heat transfer and flow through a methanol reforming catalytic microreactor fabricated on a silicon wafer are presented. Comparison of computed and measured conversion efficiencies are shown to be favorable. Concepts for insulating the reactor while maintaining small overall size and starting operation from ambient temperature are analyzed

Application of GFAT as a Novel Selection Marker to Mediate Gene Expression

The enzyme glutamine: fructose-6-phosphate aminotransferase (GFAT), also known as glucosamine synthase (GlmS), catalyzes the formation of glucosamine-6-phosphate from fructose-6-phosphate and is the first and rate-limiting enzyme of the hexosamine biosynthetic pathway. For the first time, the GFAT gene was proven to possess a function as an effective selection marker for genetically modified (GM) microorganisms. This was shown by construction and analysis of two GFAT deficient strains, E. coli ΔglmS and S. pombe Δgfa1, and the ability of the GFAT encoding gene to mediate plasmid selection. The gfa1 gene of the fission yeast Schizosaccharomyces pombe was deleted by KanMX6-mediated gene disruption and the Cre-loxP marker removal system, and the glmS gene of Escherichia coli was deleted by using λ-Red mediated recombinase system. Both E. coli ΔglmS and S. pombe Δgfa1 could not grow normally in the media without addition of glucosamine. However, the deficiency was complemented by transforming the plasmids that expressed GFAT genes. The xylanase encoding gene, xynA2 from Thermomyces lanuginosus was successfully expressed and secreted by using GFAT as selection marker in S. pombe. Optimal glucosamine concentration for E. coli ΔglmS and S. pombe Δgfa1 growth was determined respectively. These findings provide an effective technique for the construction of GM bacteria without an antibiotic resistant marker, and the construction of GM yeasts to be applied to complex media