Symmetric hyperbolic systems for a large class of fields in arbitrary dimension

Symmetric hyperbolic systems of equations are explicitly constructed for a general class of tensor fields by considering their structure as r-fold forms. The hyperbolizations depend on 2r-1 arbitrary timelike vectors. The importance of the so-called "superenergy" tensors, which provide the necessary symmetric positive matrices, is emphasized and made explicit. Thereby, a unified treatment of many physical systems is achieved, as well as of the sometimes called "higher order" systems. The characteristics of these symmetric hyperbolic systems are always physical, and directly related to the null directions of the superenergy tensor, which are in particular principal null directions of the tensor field solutions. Generic energy estimates and inequalities are presented too.Comment: 24 pages, no figure

Atomistic Insight into Ion Transport and Conductivity in Ga/Al-Substituted Li7_7La3_3Zr2_2O12_{12} Solid Electrolytes

Garnet-structured Li$_{7}$La$_{3}$Zr$_{2}$O$_{12}$ is a promising solid electrolyte for next-generation solid-state Li batteries. However, sufficiently fast Li-ion mobility required for battery applications only emerges at high temperatures, upon a phase transition to cubic structure. A well-known strategy to stabilize the cubic phase at room temperature relies on aliovalent substitution; in particular, the substitution of Li$^{+}$ by Al$^{3+}$ and Ga$^{3+}$ ions. Yet, despite having the same formal charge, Ga$^{3+}$ substitution yields higher conductivities ($10^{-3}$~S/cm) than Al$^{3+}$ ($10^{-4}$~S/cm). The reason of such difference in ionic conductivity remains a mystery. Here we use molecular dynamic simulations and advanced sampling techniques to precisely unveil the atomistic origin of this phenomenon. Our results show that Li$^{+}$ vacancies generated by Al$^{3+}$ and Ga$^{3+}$ substitution remain adjacent to Ga$^{3+}$ and Al$^{3+}$ ions, without contributing to the promotion of Li$^{+}$ mobility. However, while Ga$^{3+}$ ions tend to allow limited Li$^{+}$ diffusion within their immediate surroundings, the less repulsive interactions associated with Al$^{3+}$ ions lead to a complete blockage of neighboring Li$^{+}$ diffusion paths. This effect is magnified at lower temperatures, and explains the higher conductivities observed for Ga-substituted systems. Overall this study provides a valuable insight into the fundamental ion transport mechanism in the bulk of Ga/Al-substituted Li$_{7}$La$_{3}$Zr$_{2}$O$_{12}$ and paves the way for rationalizing aliovalent substitution design strategies for enhancing ionic transport in these materials.ENE2016-81020-R (MINECO

PLA and PBAT-based electrospun fibers functionalized with antibacterial bio-based polymers

Antimicrobial fibers based on biodegradable polymers, poly(lactic acid) (PLA), and poly(butylene adipate-co-terephthalate) (PBAT) are prepared by electrospinning. For this purpose, a biodegradable/bio-based polyitaconate containing azoles groups (PTTI) is incorporated at 10 wt.% into the electrospinning formulations. The resulting fibers functionalized with azole moieties are uniform and free of beads. Then, the accessible azole groups are subjected to N-alkylation, treatment that provides cationic azolium groups with antibacterial activity at the surface of fibers. The positive charge density, roughness, and wettability of the cationic fibers are evaluated and compared with flat films. It is confirmed that these parameters exert an important effect on the antimicrobial properties, as well as the length of the alkylating agent and the hydrophobicity of the matrix. The quaternized PLA/PTTI fibers exhibit the highest efficiency against the tested bacteria, yielding a 4-Log reduction against S. aureus and 1.7-Log against MRSA. Then, biocompatibility and bioactivity of the fibers are evaluated in terms of adhesion, morphology and viability of fibroblasts. The results show no cytotoxic effect of the samples, however, a cytostatic effect is appreciated, which is ascribed to the strong electrostatic interactions between the positive charge at the fiber surface and the negative charge of the cell membranes

Biobased polymers derived from itaconic acid bearing clickable groups with potent antibacterial activity and negligible hemolytic activity.

Herein, we report, for the first time, the synthesis of clickable polymers derived from biobased itaconic acid, which was then used for the preparation of novel cationic polymers with antibacterial properties and low hemotoxicity via click chemistry. Itaconic acid (IA) was subjected to chemical modification by incorporating clickable alkyne groups on the carboxylic acids. The resulting monomer with pendant alkyne groups was easily polymerized and copolymerized with dimethyl itaconate (DMI) by radical polymerization. The feed molar ratio of comonomers was varied to precisely tune the content of alkyne groups in the copolymers and the amphiphilic balance. Subsequently, an azide with a thiazole group, which is a component of the vitamin thiamine (B1), was attached onto the polymers by copper-catalyzed azidealkyne cycloaddition (CuAAC) click chemistry leading to triazole linkages. N-Alkylation reactions of the thiazole and triazole groups with methyl and butyl iodides provide the corresponding itaconate derivatives with pendant azolium groups. The copolymers with variable cationic charge densities and hydrophobic/ hydrophilic balances, depending on the comonomer feed ratio, display potent antibacterial activity against Gram-positive bacteria, whereas the activity was almost null against Gram-negative bacteria. Hemotoxicity assays demonstrated that the copolymers exhibited negligible hemolysis and excellent selectivity, more than 1000-fold, for Gram-positive bacteria over human red blood cells.post-print1945 K

Effects of moderate static magnetic field on neural systems is a non-invasive mechanical stimulation of the brain possible theoretically?

Static magnetic fields have been shown to induce effects on the human brain. Different experiments seem to support the idea that moderate static magnetic field can exert some influence on the gating processes of the membrane channels. In this article we visit the order of magnitude of the energy magnetic terms associated with moderate applied field (between 10 and 200 milliteslas). It is shown that gradients of the Zeeman energy associated with the inhomogeneous applied fields can induce pressures of the order of 10^(-2)Pa. The surface tension generated by the magnetic pressure, on the surface delimiting the brain region subject to relevant field and gradients, is found to range between 10^(-1) and 1 mN.m^(-1). These pressures seem to be strong enough to interfere with the elastic and electrostatic energies involved in the channel activation-inactivation-deactivation mechanisms of biological membranes. It has been described that small mechanical force can activate voltage gated potassium channels. Moreover, stretch-activated ion channels are widely described in different biological tissues. Virtually, all these channels can modify their activity if stressed by a sufficient pressure delivered for enough time. We propose mechanical stimulation - possibly not exclusively - as a candidate mechanism how static magnetic field can produce effects in biological systems. It must be emphasized, that such field gradients were not previously proposed as a possible source of neural activity modification

Chaotic dynamics of electric-field domains in periodically driven superlattices

Self-sustained time-dependent current oscillations under dc voltage bias have been observed in recent experiments on n-doped semiconductor superlattices with sequential resonant tunneling. The current oscillations are caused by the motion and recycling of the domain wall separating low- and high-electric- field regions of the superlattice, as the analysis of a discrete drift model shows and experimental evidence supports. Numerical simulation shows that different nonlinear dynamical regimes of the domain wall appear when an external microwave signal is superimposed on the dc bias and its driving frequency and driving amplitude vary. On the frequency - amplitude parameter plane, there are regions of entrainment and quasiperiodicity forming Arnol'd tongues. Chaos is demonstrated to appear at the boundaries of the tongues and in the regions where they overlap. Coexistence of up to four electric-field domains randomly nucleated in space is detected under ac+dc driving.Comment: 9 pages, LaTex, RevTex. 12 uuencoded figures (1.8M) should be requested by e-mail from the autho

Adsorption of emerging pollutants on lignin-based activated carbon: Analysis of adsorption mechanism via characterization, kinetics and equilibrium studies

Lignin has been employed as a precursor to synthesize activated carbons with the aim of lignin-biomass revalorization. The properties of these activated carbons were compared, and the best adsorbent was employed to remove two emerging pollutants from water, acetaminophen and acetamiprid. The adsorption mechanisms of pharmaceutical and pesticide compounds were analyzed, modeled and interpreted via statistical physics models. In particular, adsorption kinetics and isotherms of acetaminophen and acetamiprid at temperatures between 20 and 60 ◦C were quantified experimentally. Equilibrium data were fitted to different statistical physics-based isotherm models to establish the corresponding adsorption mechanism. A double layer adsorption model with one type of functional group was the best to correlate and explain the removal of these organic molecules. Steric parameters for the adsorption of these organic compounds were also calculated thus determining that their adsorption was multi-molecular. At tested operating conditions, acetaminophen adsorption was endothermic, while acetamiprid removal was exothermic. Physical adsorption forces were expected to be responsible for the removal of both compounds. This study reports new insights on the adsorption mechanisms of relevant emerging pollutants commonly found in water worldwid

A randomized open-labeled study to examine the effects of creatine monohydrate and combined training on jump and scoring performance in young basketball players

BACKGROUND: Creatine monohydrate (CrM) supplementation has been shown to be an effective and safe nutritional supplement to improve performance; however, the impact of CrM supplementation in young basketball players is less clear. This study evaluated the effects of CrM supplementation during a strength and conditioning training (SCT) program on lower-limb strength parameters and performance in under-16 (U16) basketball players. METHODS: Twenty-three male U16 basketball players participated in this study (14.3 ± 0.4 years; BMI: 20.7 ± 2.2 kg∙m(−2)). The players were randomly assigned to either a CrM group (n = 12) that ingested 0.1 g·kg(−1)·day(−1) of CrM or to a non-supplemented control group (n = 11, CON). The athletes participated in an 8-week SCT program consisting of two lower-limb resistance-training sessions and two plyometric sessions per week. Squat jump (SJ), drop jump (DP), countermovement jump (CMJ), and Abalakov (ABK) jump power tests as well as basketball performance (points and minutes per game) were measured before, during and/or after the intervention. Data were analyzed using a general linear model with repeated measures with independent Student’s t-test pairwise comparisons. RESULTS: The results (95% confidence interval for mean change from baseline) show that there were significant differences for all variables for CrM and CON, respectively: SJ (cm): 2.6 – 6.4, P < 0.01 and 2.2–5.1 P < 0.01; DJ (cm): 2.5–5.6, P < 0.01, and 1.8–4.4, P < 0.01; CMJ (cm): 0.3–0.8, P < 0.01, and 0.2–0.5, P < 0.01; ABK (cm): 2.8–5.5, P < 0.01 and 0.7–2.6, P = 0.003. A significant group x time interaction (p = 0.003, η(p)(2) = 0.342) was observed in ABK performance. No significant group x time effects were seen in squat jump (p = 0.449, η(p)(2) = 0.028), drop jump (p = 0.143, η(p)(2) = 0.099), or counter movement jump (p = 0.304, η(p)(2) = 0.05). A significant interaction effect was also observed in points per game (p = 0.049, η(p)(2) = 0.149), while a non-significant but medium effect was seen in minutes per game (p = 0.166, η(p)(2) = 0.094). CONCLUSIONS: CrM supplementation in conjunction with resistance and plyometric training increased the lower-limb ABK power and scoring performance in U16 basketball players