4,808 research outputs found
Thermodynamics of the quantum spin-S XXZ chain
The thermodynamics of the spin- anisotropic quantum chain with
arbitrary value of and unitary norm, in the high-temperature regime, is
reported. The single-ion anisotropy term and the interaction with an external
magnetic field in the -direction are taken into account. We obtain, for
arbitrary value of , the -expansion of the Helmholtz free energy of
the model up to order and show that it actually depends on
. Its classical limit is obtained by simply taking . At and D=0, our high temperature expansion of the classical
model coincides with Joyce's exact solution\cite{joyce_prl}. We study, in the
high temperature region, some thermodynamic quantities such as the specific
heat and the magnetic susceptibility as functions of spin and verify for which
values of those thermodynamic functions behave classically. Their finite
temperature behavior is inferred from interpolation of their high- and
low-temperature behavior, and shown to be in good agreement with numerical
results. The finite temperature behavior is shown for higher values of spin.Comment: 18 pages, 14 figure
Exactly solvable mixed-spin Ising-Heisenberg diamond chain with the biquadratic interactions and single-ion anisotropy
An exactly solvable variant of mixed spin-(1/2,1) Ising-Heisenberg diamond
chain is considered. Vertical spin-1 dimers are taken as quantum ones with
Heisenberg bilinear and biquadratic interactions and with single-ion
anisotropy, while all interactions between spin-1 and spin-1/2 residing on the
intermediate sites are taken in the Ising form. The detailed analysis of the
ground state phase diagram is presented. The phase diagrams have shown to
be rather rich, demonstrating large variety of ground states: saturated one,
three ferrimagnetic with magnetization equal to 3/5 and another four
ferrimagnetic ground states with magnetization equal to 1/5. There are also two
frustrated macroscopically degenerated ground states which could exist at zero
magnetic filed.
Solving the model exactly within classical transfer-matrix formalism we
obtain an exact expressions for all thermodynamic function of the system. The
thermodynamic properties of the model have been described exactly by exact
calculation of partition function within the direct classical transfer-matrix
formalism, the entries of transfer matrix, in their turn, contain the
information about quantum states of vertical spin-1 XXZ dimer (eigenvalues of
local hamiltonian for vertical link).Comment: 14 pages, 9 figure
Physico-chemical properties of inorganic nps influence the absorption rate of aquatic mosses reducing cytotoxicity on intestinal epithelial barrier model
Noble metals nanoparticles (NPs) and metal oxide NPs are widely used in different fields of application and commercial products, exposing living organisms to their potential adverse effects. Recent evidences suggest their presence in the aquifers water and consequently in drinking water. In this work, we have carefully synthesized four types of NPs, namely, silver and gold NPs (Ag NPs and Au NPs) and silica and titanium dioxide NPs (SiO2 NPs and TiO2 NPs) having a similar size and negatively charged surfaces. The synthesis of Ag NPs and Au NPs was carried out by colloidal route using silver nitrate (AgNO3 ) and tetrachloroauric (III) acid (HAuCl4 ) while SiO2 NPs and TiO2 NPs were achieved by ternary microemulsion and sol-gel routes, respectively. Once the characterization of NPs was carried out in order to assess their physico-chemical properties, their impact on living cells was studied. We used the human colorectal adenocarcinoma cells (Caco-2), known as the best representative intestinal epithelial barrier model to understand the effects triggered by NPs through ingestion. Then, we moved to explore how water contamination caused by NPs can be lowered by the ability of three species of aquatic moss, namely, Leptodictyum riparium, Vesicularia ferriei, and Taxiphyllum barbieri, to absorb them. The experiments were conducted using two concentrations of NPs (100 ”M and 500 Mm as metal content) and two time points (24 h and 48 h), showing a capture rate dependent on the moss species and NPs type. Then, the selected moss species, able to actively capture NPs, appear as a powerful tool capable to purify water from nanostructured materials, and then, to reduce the toxicity associated to the ingestion of contaminated drinking water
Bioelectricity through microbial fuel cells using avocado waste
The dumping of organic waste in the areas surrounding food supply centers and the excessive use of fossil fuels for energy
generation have generated major pollution problems worldwide. One of the novel solutions is the use of organic waste for
electricity generation through the use of microbial fuel cell technology. In this research, low-cost, laboratory-scale, doublechamber microbial fuel cells were fabricated using zinc and copper as electrodes and avocado waste as fuel. Current and voltage
values of 3.7326 ± 0.05568 mA and 0.74 ± 0.02121 V were achieved on the seventh day, with an optimum operating pH of
5.98 ± 0.16 and a maximum electrical conductivity of 94.46 ± 5.12 mS/cm. The cells showed a very low operating resistance of
71.480 , indicating the good electrical conductivity of the electrodes. Likewise, a power density of 566.80 ± 13.48 mW/cm2
at a current density of 5.165 A/cm2 was generated. This research provides an eco-friendly solution to farmers and companies
dedicated to the export and import of this fruit because it shows the benefits of using their own waste for the generation of
electricity, reducing costs
Cell wall composition and biomass digestibility diversity in Mexican maize (Zea mays L) landraces and CIMMYT inbred lines
Maize is one of the most important crops worldwide. Historically, breeding efforts in this crop have been primarily focused on the improvement of grain yield and stability and just recently also on the potential utility of maize stover (above ground biomass excluding the grain) as a source of biomass for the production of feed, fiber and cellulosic ethanol. The International Maize and Wheat Improvement Center (CIMMYT) holds one of the largest maize germplasm collections in the world and therefore is an important source of phenotypic and genetic diversity for many traits. Our objectives were to assess the phenotypic diversity for cell wall composition and biomass digestibility in Mexican tropical, subtropical and highland maize landraces and elite maize lines (CMLs) in the CIMMYT germplasm collection, as well as to evaluate the relationship between place of origin of these materials and phenotypic expression of biomass compositional traits. The range of variation for neutral detergent fiber for three groups of landraces was from 47 to 73%. Slightly larger levels of phenotypic variation were observed for this trait in the set of CMLs evaluated (42 to 78%). Some of the inbred lines, such as CML 507, presented superior characteristics in terms of cell wall composition and digestibility. The Tuxpeño tropical-subtropical race, widely used in CIMMYT breeding programs, formed a cluster characterized by high cell wall content and low biomass digestibility. The CIMMYT germplasm collection appears to be a vast source of untapped genetic and phenotypic variation for the improvement of maize biomass composition
Post-synthesis incorporation of Al into germanosilicate ITH zeolites: the influence of treatment conditions on the acidic properties and catalytic behavior in tetrahydropyranylation
Post-synthesis alumination of germanosilicate medium-pore ITH zeolites was shown to be an effective procedure for tuning their acidity. Treatment of ITH zeolites synthesized with different chemical compositions (i.e. Si/Ge = 2.5, 4.4 and 5.8) with aqueous Al(NO3)(3) solution led to the formation of strong Bronsted and Lewis acid sites and an increasing fraction of ultramicro- and meso-pores in Ge-rich ITH samples (Si/Ge = 2.5 and 4.4). The concentration of Al incorporated into the framework increases with decreasing Si/Ge ratio of the parent ITH. The increasing temperature of alumination from 80 to 175 degrees C (HT conditions) resulted in (1) a 1.5-2-fold increase in the concentration of Bronsted acid sites formed and (2) a decreasing fraction of framework Al atoms detectable with base probe molecules (i.e. pyridine, 2,6-di-tert-butylpyridine), i.e. an increased concentration of the "inner" acid sites. The activity of prepared Al-substituted ITH zeolites in tetrahydropyranylation of alcohols is enhanced with increasing amount of accessible acid sites in bulky crystals (e.g. alumination at lower temperature) or with increasing total concentration of acid centres within tiny ITH crystals (e.g. alumination under HT conditions). This trend became more prominent with increasing kinetic diameter of the substrate molecules under investigation (methanol < 1-propanol < 1-hexanol).Post-synthesis alumination of germanosilicate medium-pore ITH zeolites was shown to be an effective procedure for tuning their acidity. Treatment of ITH zeolites synthesized with different chemical compositions (i.e.Si/Ge = 2.5, 4.4 and 5.8) with aqueous5529732984Czech Science Foundation [14-30898P, 13-17593P
"Detection of Helicobacter pylori in faeces of children of rural human settlements: An exploratory study in Peru"
"Introduction: Helicobacter pylori is one of the major infectious agents in low-income countries, and its clinical
characteristics are unknown in many populations. Children are a susceptible population and can contract these
pathogens through contaminated food and water.
Objectives: To determine the presence of Helicobacter pylori in children under eight years of age of rural human
settlements in Peru.
Methods: This exploratory study was conducted with 25 child volunteers authorized by the parents for their
evaluation, without precedent of any apparent clinical manifestation. Antigen detection of H. pylori in faeces by a
rapid assay onsite H. pylori Ag. Rapid test according to the manufacturerâs requirements. Has been evaluated the
social determinants related to possible infection.
Results: The average age (2±1.8 years) of 14 girls was different from the average age (2.7±2.2 years) of 11 boys
included in the study (p=0.010). Of the total we determinate nine (36%) positive tests, which mainly affected boys
(five patients 20%) under two years of age (six patients, 24%). In general, ~90% wash their hands with soap and
water and ~70% wash fruits and vegetables with water before eating. In addition, >50% ate foods outside of home
and ~24% was asymptomatic and did not have a specific meal schedule.
Conclusions: Among rural children, Helicobacter pylori antibody was detected in 36% of the participants,
unaffected by gender, and presenting specific dietary patterns.
New prenylated quinones from Peperomia galioides
Two new prenylated quinones, piperogalone and galopiperone, and a new prenylated dihydroquinone, hydropiperone, were isolated from #Peperomia galioides H.B.K (#Piperaceae). Hydropiperone exhibited potent antiparasitic activity against three species of #Leishmania$. (Résumé d'auteur
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