Synthesis and defect characterization of hybrid ceria nanostructures as a possible novel therapeutic material towards COVID-19 mitigation.

This study reports the synthesis of hybrid nanostructures composed of cerium dioxide and microcrystalline cellulose prepared by the microwave-assisted hydrothermal route under distinct temperature and pH values. Their structural, morphological and spectroscopic behaviors were investigated by X-Rays Diffraction, Field Emission Gun Scanning Electron Microscopy, High-Resolution Transmission Electron Microscopy, and Fourier-Transform Infrared, Ultraviolet-Visible, Raman and Positron Annihilation Lifetime spectroscopies to evaluate the presence of structural defects and their correlation with the underlying mechanism regarding the biocide activity of the studied material. The samples showed mean crystallite sizes around 10 nm, characterizing the formation of quantum dots unevenly distributed along the cellulose surface with a certain agglomeration degree. The samples presented the characteristic Ce-O vibration close to 450 cm-1 and a second-order mode around 1050 cm-1, which is indicative of distribution of localized energetic levels originated from defective species, essential in the scavenging of reactive oxygen species. Positron spectroscopic studies showed first and second lifetime components ranging between 202-223 ps and 360-373 ps, respectively, revealing the presence of two distinct defective oxygen species, in addition to an increment in the concentration of Ce3+-oxygen vacancy associates as a function of temperature. Therefore, we have successfully synthesized hybrid nanoceria structures with potential multifunctional therapeutic properties to be further evaluated against the COVID-19.

Overactivated transport in the localized phase of the superconductor-insulator transition.

Beyond a critical disorder, two-dimensional (2D) superconductors become insulating. In this Superconductor-Insulator Transition (SIT), the nature of the insulator is still controversial. Here, we present an extensive experimental study on insulating NbxSi1-x close to the SIT, as well as corresponding numerical simulations of the electrical conductivity. At low temperatures, we show that electronic transport is activated and dominated by charging energies. The sample thickness variation results in a large spread of activation temperatures, fine-tuned via disorder. We show numerically and experimentally that this originates from the localization length varying exponentially with thickness. At the lowest temperatures, there is an increase in activation energy related to the temperature at which this overactivated regime is observed. This relation, observed in many 2D systems shows that conduction is dominated by single charges that have to overcome the gap when entering superconducting grains.

Multicolor Quantum Control for Suppressing Ground State Coherences in Two-Dimensional Electronic Spectroscopy.

The measured multidimensional spectral response of different light harvesting complexes exhibits oscillatory features which suggest an underlying coherent energy transfer. However, making this inference rigorous is challenging due to the difficulty of isolating excited state coherences in highly congested spectra. In this work, we provide a coherent control scheme that suppresses ground state coherences, thus making rephasing spectra dominated by excited state coherences. We provide a benchmark for the scheme using a model dimeric system and numerically exact methods to analyze the spectral response. We argue that combining temporal and spectral control methods can facilitate a second generation of experiments that are tailored to extract desired information and thus significantly advance our understanding of complex open many-body structure and dynamics.

Charge distribution from SKPM images.

Inferring the surface charge distribution from experimental Kelvin probe microscopy measurements is usually a hard task. Although several approximations have been proposed in order to estimate the effect of these charges, the real inverse problem has not been addressed so far. In this paper, we propose a fast and intuitive method based on Fast Fourier Transform algorithms that allows the surface charge distribution to be obtained directly from the experimental Kelvin voltage measurements. With this method, quantitative physical information such as the total charge and charge position is accessible even in complex charge distributions such as highly insulating polymer surfaces. Moreover, one of the strongest points is that sub-tip resolution is achieved, and therefore the usually unknown charge size can be estimated.

Localized charge imaging with scanning Kelvin probe microscopy.

In this work, we propose an intuitive and easily implementable approach to model and interpret scanning Kelvin probe microscopy images of insulating samples with localized charges. The method, based on the image charges method, has been validated by a systematic comparison of its predictions with experimental measurements performed on charge domains of different sizes, injected in polymethyl methacrylate discontinuous films. The agreement between predictions and experimental lateral profiles, as well as with spectroscopy tip-sample distance curves, supports its consistency. The proposed procedure allows obtaining quantitative information such as total charge and the size of a charge domain and allows estimating the most adequate measurement parameters.

Green functions of interacting systems in the strongly localized regime.

We have developed an approach to calculate the single-particle Green function of a one-dimensional many-body system in the strongly localized limit at zero temperature. Our approach sums the contributions of all possible forward scattering paths in configuration space. We demonstrate that for fermions and nearest neighbors interactions the Green function factorizes at every link connecting two sites with the same occupation. As a consequence, the conductance distribution function for interacting systems is log-normal, in the same universality class as non-interacting systems. We have developed a numerical procedure to calculate the ground state and the Green function, generating all possible paths in configuration space. Our results agree with results obtained by exact diagonalization of small systems in the limit of large disorder.

Electronic transport in two-dimensional high dielectric constant nanosystems.

There has been remarkable recent progress in engineering high-dielectric constant two dimensional (2D) materials, which are being actively pursued for applications in nanoelectronics in capacitor and memory devices, energy storage, and high-frequency modulation in communication devices. Yet many of the unique properties of these systems are poorly understood and remain unexplored. Here we report a numerical study of hopping conductivity of the lateral network of capacitors, which models two-dimensional insulators, and demonstrate that 2D long-range Coulomb interactions lead to peculiar size effects. We find that the characteristic energy governing electronic transport scales logarithmically with either system size or electrostatic screening length depending on which one is shorter. Our results are relevant well beyond their immediate context, explaining, for example, recent experimental observations of logarithmic size dependence of electric conductivity of thin superconducting films in the critical vicinity of superconductor-insulator transition where a giant dielectric constant develops. Our findings mark a radical departure from the orthodox view of conductivity in 2D systems as a local characteristic of materials and establish its macroscopic global character as a generic property of high-dielectric constant 2D nanomaterials.

Emergent SO(5) Symmetry at the Néel to Valence-Bond-Solid Transition.

We show numerically that the "deconfined" quantum critical point between the Néel antiferromagnet and the columnar valence-bond solid, for a square lattice of spin 1/2, has an emergent SO(5) symmetry. This symmetry allows the Néel vector and the valence-bond solid order parameter to be rotated into each other. It is a remarkable (2+1)-dimensional analogue of the SO(4)=[SU(2)×SU(2)]/Z(2) symmetry that appears in the scaling limit for the spin-1/2 Heisenberg chain. The emergent SO(5) symmetry is strong evidence that the phase transition in the (2+1)-dimensional system is truly continuous, despite the violations of finite-size scaling observed previously in this problem. It also implies surprising relations between correlation functions at the transition. The symmetry enhancement is expected to apply generally to the critical two-component Abelian Higgs model (noncompact CP(1) model). The result indicates that in three dimensions there is an SO(5)-symmetric conformal field theory that has no relevant singlet operators, so is radically different from conventional Wilson-Fisher-type conformal field theories.

Length distributions in loop soups.

Statistical lattice ensembles of loops in three or more dimensions typically have phases in which the longest loops fill a finite fraction of the system. In such phases it is natural to ask about the distribution of loop lengths. We show how to calculate moments of these distributions using CP(n-1) or RP(n-1) and O(n) σ models together with replica techniques. The resulting joint length distribution for macroscopic loops is Poisson-Dirichlet with a parameter θ fixed by the loop fugacity and by symmetries of the ensemble. We also discuss features of the length distribution for shorter loops, and use numerical simulations to test and illustrate our conclusions.

3D loop models and the CP(n-1) sigma model.

Many statistical mechanics problems can be framed in terms of random curves; we consider a class of three-dimensional loop models that are prototypes for such ensembles. The models show transitions between phases with infinite loops and short-loop phases. We map them to CP(n-1) sigma models, where n is the loop fugacity. Using Monte Carlo simulations, we find continuous transitions for n=1, 2, 3, and first order transitions for n≥5. The results are relevant to line defects in random media, as well as to Anderson localization and (2+1)-dimensional quantum magnets.

Temperature dependence on free volume in cured natural rubber and styrene-butadiene rubber blends.

A systematic study on the evolution of free volume as a function of the temperature in vulcanized at 433 K natural rubber (NR) and styrene butadiene rubber (SBR) in 25-75, 50-50, 75-25 NR-SBR (percent content of pure NR and SBR, respectively) blends was studied by positron annihilation lifetime spectroscopy. All samples were prepared with sulfur and TBBS (n-t-butyl-2-benzothiazole sulfenamide) as accelerator. The glass transition temperatures of the samples studied were determined by differential scanning calorimetry (DSC) and from lifetime data. In general, a sigmoidal-like complex behavior of the long-lived lifetime component, linked to the nanohole free volume, as a function of the temperature was found. For SBR, the slope of the ortho-positronium lifetime against temperature curves could be well-fitted using a linear function. For blends and also for NR, two different linear functions were necessary. This last behavior is explained in terms of the supercooled process involving a reconfiguration of the elastomeric chains. In the case of blends, the state of cure of NR and SBR in each NR-SBR sample was also taken into account in the discussion of the results obtained. Besides, thermal expansion coefficients of the free volumes in the transition and glassy region of all compounds were estimated. The differences observed in the values of this parameter are discussed by taking into account the morphology and formulation of each blend, the crosslink densities, and the role of the interphases formed between both NR and SBR elastomers.

Receptor for advanced glycation end-products expression in subcutaneous adipose tissue is related to coronary artery disease.

OBJECTIVE: Obesity, a risk factor for coronary artery disease (CAD), is associated with inflammation and reactive oxygen species (ROS) production, while advanced glycation end-products, through their receptor (AGER or RAGE), play an important role on these processes. The aim of this study was to analyze the expression levels of RAGE, NADPH oxidase subunits, and catalase in adipose tissue in relation with CAD. DESIGN AND METHODS: Patients undergoing heart surgery were included in two groups: with and without CAD. Epicardial adipose tissue (EAT) and subcutaneous adipose tissue (SAT) biopsies were analyzed for gene expression by RT-quantitative PCR, immunohistochemistry, or western blot. RESULTS: RAGE mRNA and protein expression in SAT from patients with CAD was lower than in patients without CAD. However, there was no change in EAT from patients with or without CAD. P22-PHOX and RAGE gene expression were higher in EAT than in SAT, whereas catalase mRNA levels were lower. NADPH oxidase subunits and catalase mRNA expression were not influenced by CAD. Whereas NADPH oxidase-dependent oxidative response of SAT and EAT to lipid circulating levels could be different; glycemic levels were not related with the analyzed genes expression. CONCLUSIONS: This study demonstrates that RAGE expression in SAT, but not in EAT, is down-regulated in patients with CAD with respect to those without CAD. Although changes were not observed for NADPH oxidase subunits or catalase expression between CAD and non-CAD patients, a possible relationship between ROS production and RAGE expression in adipose tissues cannot be ruled out.

Lower epicardial adipose tissue adiponectin in patients with metabolic syndrome.

BACKGROUND: Adiponectin is an anti-atherogenic insulin-sensitizer hormone whose plasma concentration is lower in patients with metabolic syndrome (MS). Visceral adiposity, including epicardial adipose tissue (EAT), is closely related to the development of MS and coronary artery disease (CAD). We sought to study whether EAT and subcutaneous adipose tissue (SAT) adiponectin mRNA levels are similar in patients with and without MS. METHODS: EAT, SAT and blood samples were collected from patients undergoing elective cardiac surgery, for revascularization (n=19) or other procedures (n=27). Plasma adiponectin was measured using ELISA. mRNA was purified and adiponectin mRNA quantified by real time RT-PCR. RESULTS: Mean (SD) age was 71.6 (9.6) years. Patients who met Adult Treatment Panel III MS criteria (n=29) presented lower plasma adiponectin concentrations (11.2 (7.4) vs. 19.6 (8.4) mg/l, P=0.004), lower EAT adiponectin mRNA (12.7 (3.0) vs. 15.1 (3.7) a.u., P=0.029) and similar SAT adiponectin mRNA levels (13.7 (4.2) vs. 15.6 (5.7) a.u., P=0.25) than those without MS. After adjusting for age, sex, CAD and heart failure, the association with MS remained statistically significant for plasma adiponectin (OR 0.862 (0.762-0.974)), was of borderline significance for EAT adiponectin mRNA (OR 0.796 (0.630-1.005)) and not significant for SAT adiponectin mRNA (OR 0.958 (0.818-1.122)). Patients in the lower quartiles of EAT adiponectin mRNA and plasma adiponectin presented a higher mean of components of the MS. CONCLUSIONS: Subjects with MS present lower EAT adiponectin mRNA levels than those without MS, whereas SAT adiponectin mRNA levels do not seem to differ between both groups. EAT might be the link between MS and its atherothrombotic cardiac complications.

Diabetic and nondiabetic patients express similar adipose tissue adiponectin and leptin levels.

OBJECTIVE: Epicardial adipose tissue (EAT) is an interesting visceral fat pad with a particular location. EAT and subcutaneous adipose tissue (SAT) produce a wide range of adipokines. Some of them, including adiponectin and leptin, can influence the risk of development of diabetes and other associated metabolic and cardiovascular conditions. We sought to assess whether EAT and SAT adiponectin and leptin expression levels are different in diabetic patients with respect to nondiabetic subjects. SUBJECTS AND METHODS: We collected samples of EAT from 120 patients and samples of SAT from 88 of the same group of patients undergoing elective cardiac surgery for coronary artery bypass grafting (n=69) or other procedures (n=51). After RNA isolation, adiponectin and leptin expression levels were analyzed by real-time reverse transcriptase PCR. Plasma levels were determined in small subsamples of subjects. Baseline clinical and treatment data were obtained from medical records. RESULTS: A total of 45 diabetic and 75 nondiabetic subjects were included in the study. Mean (s.d.) age was 70.1 (7.8) years and there were 32% women. EAT and SAT adiponectin and leptin mRNA expression levels were similar in the diabetic and the nondiabetic groups (EAT adiponectin 14.4 (4.3) vs 14.6 (3.4) arbitrary units (a.u.), P=0.79; SAT adiponectin 15.6 (4.7) vs 15.1 (3.9), P=0.54; EAT leptin 9.3 (interquartile range 2.5) vs 9.5 (1.9) a.u., P=0.72; SAT leptin 9.9 (3.6) vs 10.0 (2.5) a.u., P=0.96). These findings persisted after stratification for sex and coronary artery disease. Logistic regression models including possible confounders and a combination of diabetes and impaired fasting glucose as a dependent variable led to similar results. Plasma adiponectin levels were lower in diabetic patients, whereas leptin levels showed a nonsignificant trend. CONCLUSION: Diabetic and nondiabetic subjects express similar EAT and SAT adiponectin and leptin levels. Counter-regulatory mechanisms of adiponectin and leptin expression in patients with established diabetes might partly account for these findings.

Random walks and Anderson localization in a three-dimensional class C network model.

We study the disorder-induced localization transition in a three-dimensional network model that belongs to symmetry class C. The model represents quasiparticle dynamics in a gapless spin-singlet superconductor without time-reversal invariance. It is a special feature of network models with this symmetry that the conductance and density of states can be expressed as averages in a classical system of dense, interacting random walks. Using this mapping, we present a more precise numerical study of critical behavior at an Anderson transition than has been possible previously in any context.

Conducta asertiva y autoeficacia para la prevención de ETS en jóvenes estudiantes de la ciudad de Asunción / Assertive behavior and self-efficacy for the prevention of STDs in young students in the city of Asuncion

Se presenta un estudio correlacional entre la conducta asertiva y la autoeficacia para la prevención de Enfermedades de Transmisión Sexual (ETS), en estudiantes de educación media. Para cumplir con los objetivos de la investigación se midieron y correlacionaron las variables; asertividad y autoeficacia para la prevención de ETS con la Escala validada de Autoeficacia para la prevención del SIDA en adolescentes (SEA – 27) de López-Rosales, F. (2001) y el Cuestionario de Asertividad de De Gambrill, E.D. y Richey, C.A (1975). Los datos fueron procesados con el paquete estadístico SPSS. Se concluye que no existe correlación significativa en cuanto a la hipótesis especifica, al nivel de p<0.05, entre las variables de estudio, aceptando la hipótesis nula planteada.

Effective temperature in relaxation of Coulomb glasses.

We study relaxation in two-dimensional Coulomb glasses up to macroscopic times. We use a kinetic Monte Carlo algorithm especially designed to escape efficiently from deep valleys around metastable states. We find that, during the relaxation process, the site occupancy follows a Fermi-Dirac distribution with an effective temperature much higher than the real temperature T. Long electron-hole excitations are characterized by T(eff), while short ones are thermalized at T. We argue that the density of states at the Fermi level is proportional to T(eff) and is a good thermometer to measure it. T(eff) decreases extremely slowly, roughly as the inverse of the logarithm of time, and it should affect hopping conductance in many experimental circumstances.

Universal distribution functions in two-dimensional localized systems.

We find the conductance distribution function of the two-dimensional Anderson model in the strongly localized limit. The fluctuations of lng grow with lateral size as L1/3 and follow a universal distribution that depends on the type of leads. For narrow leads, it is the Tracy-Widom distribution, which appears in the problem of the largest eigenvalue of random matrices from the Gaussian unitary ensemble and in many other problems like the longest increasing subsequence of a permutation, directed polymers, or polynuclear growth. We also show that for wide leads the conductance follows a related, but different, distribution.

Characterization of free volume during vulcanization of styrene butadiene rubber by means of positron annihilation lifetime spectroscopy and dynamic mechanical test.

An experimental investigation was performed to study the effect on the free volume of the advance of the cross-linking reaction in a copolymer of styrene butadiene rubber by sulfur vulcanization. The dynamic modulus and loss tangent were evaluated over samples cured for different times at 433 K by dynamic mechanical tests over a range of frequencies between 5 and 80 Hz at temperatures between 200 and 300 K. Using the William-Landel-Ferry relationship, master curves were obtained at a reference temperature of 298 K and the coefficients c(0)(1) and c(0)(2) were evaluated. From these parameters the dependence of the free volume on the cure time is obtained. Positron annihilation lifetime spectroscopy was also used to estimate the size and number density of free volume sites in the material. The spectra were analyzed in terms of continuous distributions of free volume size. The results suggest an increase of the lower free volume size when cross linking takes place. Both techniques give similar results for the dependence of free volume on the time of cure of the polymer.

Nonerasing dose readout in lithium fluoride crystals by positron lifetime spectroscopy.

The measurement of the mean lifetime of the positron (tau) in a lithium fluoride (LiF) chip which had been irradiated with up to 40 Gy from a 60Co gamma-ray source demonstrates a correlation between the positron mean lifetime and the dose which has been delivered to the crystal. This result points out the possibility of performing the readout of gamma-irradiated LiF thermoluminescent dosimeters by positron lifetime spectroscopy without changing the information stored in the chip significantly.