Inducing a topological transition in graphene nanoribbon superlattices by external strain.

Armchair graphene nanoribbons, when forming a superlattice, can be classified into different topological phases, with or without edge states. By means of tight-binding and classical molecular dynamics (MD) simulations, we studied the electronic and mechanical properties of some of these superlattices. MD shows that fracture in modulated superlattices is brittle, as for unmodulated ribbons, and occurs at the thinner regions, with staggered superlattices achieving a larger fracture strain than inline superlattices. We found a general mechanism to induce a topological transition with strain, related to the electronic properties of each segment of the superlattice, and by studying the sublattice polarization we were able to characterize the transition and the response of these states to the strain. For the cases studied in detail here, the topological transition occurred at ∼3-5% strain, well below the fracture strain. The topological states of the superlattice - if present - are robust to strain even close to fracture. The topological transition was characterized by means of the sublattice polarization of the states.

Simulated mechanical properties of finite-size graphene nanoribbons.

There are many simulation studies of mechanical properties of graphene nanoribbons (GNR), but there is a lack of agreement regarding elastic and plastic behavior. In this paper we aim to analyze mechanical properties of finite-size GNR, including elastic modulus and fracture, as a function of ribbon size. We present classical molecular dynamics simulations for three different empirical potentials which are often used for graphene simulations: AIREBO, REBO-scr and REAXFF. Ribbons with and without H-passivation at the borders are considered, and the effects of strain rate and different boundaries are also explored. We focus on zig-zag GNR, but also include some armchair GNR examples. Results are strongly dependent on the empirical potential employed. Elastic modulus under uniaxial tension can depend on ribbon size, unlike predictions from continuum-scale models and from some atomistic simulations, and fracture strain and progress vary significantly amongst the simulated potentials. Because of that, we have also carried out quasi-static ab-initio simulations for a selected size, and find that the fracture process is not sudden, instead the wave function changes from Blöch states to a strong interaction between localized waves, which decreases continuously with distance. All potentials show good agreement with DFT in the linear elastic regime, but only the REBO-scr potential shows reasonable agreement with DFT both in the nonlinear elastic and fracture regimes. This would allow more reliable simulations of GNRs and GNR-based nanostructures, to help interpreting experimental results and for future technological applications.

Polycrystalline Ni nanotubes under compression: a molecular dynamics study.

Mechanical properties of nanomaterials, such as nanowires and nanotubes, are an important feature for the design of novel electromechanical nano-architectures. Since grain boundary structures and surface modifications can be used as a route to modify nanostructured materials, it is of interest to understand how they affect material strength and plasticity. We report large-scale atomistic simulations to determine the mechanical response of nickel nanowires and nanotubes subject to uniaxial compression. Our results suggest that the incorporation of nanocrystalline structure allows completely flexible deformation, in sharp contrast with single crystals. While crystalline structures at high compression are dominated by dislocation pinning and the multiplication of highly localized shear regions, in nanocrystalline systems the dislocation distribution is significantly more homogeneous. Therefore, for large compressions (large strains) coiling instead of bulging is the dominant deformation mode. Additionally, it is observed that nanotubes with only 70% of the nanowire mass but of the same diameter, exhibit similar mechanical behavior up to 0.3 strain. Our results are useful for the design of new flexible and light-weight metamaterials, when highly deformable struts are required.

Growth of Ni nanoclusters on irradiated graphene: a molecular dynamics study.

We studied the soft landing of Ni atoms on a previously damaged graphene sheet by means of molecular dynamics simulations. We found a monotonic decrease of the cluster frequency as a function of its size, but few big clusters comprise an appreciable fraction of the total number of Ni atoms. The aggregation of Ni atoms is also modeled by means of a simple phenomenological model. The results are in clear contrast with the case of hard or energetic landing of metal atoms, where there is a tendency to form mono-disperse metal clusters. This behavior is attributed to the high diffusion of unattached Ni atoms, together with vacancies acting as capture centers. The findings of this work show that a simple study of the energetics of the system is not enough in the soft landing regime, where it is unavoidable to also consider the growth process of metal clusters.

Repeated administration of mazindol reduces spontaneous pain-related behaviors without modifying bone density and microarchitecture in a mouse model of complete Freund's adjuvant-induced knee arthritis.

BACKGROUND: The role of dopaminergic system in the development of rheumatoid arthritis-related pain, a major symptom in this disease, has not been explored. Therefore, the anti-nociceptive effect of mazindol, a dopamine uptake inhibitor, was evaluated in a model of complete Freund's adjuvant (CFA)-induced arthritis. Furthermore, as studies have shown that the dopaminergic system regulates bone metabolism, the effect of mazindol on bone mass and microarchitecture was determined. METHODS: Adult ICR male mice received intra-articular injections of either CFA or saline into the right knee joint every week. Spontaneous pain-like behaviors (flinching and guarding) and locomotor activity were assessed at day 26 post-first CFA, following which, a single intraperitoneally (i.p.) administered dose of mazindol was given (1, 3 and 10 mg/kg). Then, the antinociceptive effect of a repeated administration of 3 mg/kg mazindol (daily, i.p.; day 15-day 26) was evaluated. Additionally, at day 26, the participation of D1-like, D2-like or opioid receptors in the antinociceptive effect of mazindol was evaluated. The effect of mazindol on bone density and microarchitecture was evaluated by micro-computed tomography. RESULTS: Acute administration of mazindol decreased the spontaneous pain-like behaviors in a dose-dependent manner without reducing the knee edema. However, mazindol at 10 mg/kg significantly increased the locomotor activity; therefore, 3 mg/kg mazindol was used for further studies. Repeated administration of 3 mg/kg mazindol significantly decreased the pain-like behaviors without modifying locomotor activity. The antinociceptive effect of mazindol was blocked by administration of a D2-like receptor antagonist (haloperidol), but not by administration of D1-like receptor antagonist (SCH 23390) or an opioid receptor antagonist (naloxone). Repeated administration of mazindol did not significantly modify the density and microarchitecture of periarticular bone of the arthritic and nonarthritic knee joints. CONCLUSION: Results suggest that mazindol via D2-like receptors has an antinociceptive role in mice with CFA-induced knee arthritis without modifying the bone health negatively.

Biogas production in an anaerobic sequencing batch reactor by using tequila vinasses: effect of pH and temperature.

In recent years, anaerobic digestion has been recognized as a suitable alternative for tequila vinasses treatment due to its high energy recovery and chemical oxygen demand (COD) removal efficiency. However, key factors such as the lack of suitable monitoring schemes and the presence of load disturbances, which may induce unstable operating conditions in continuous systems, have limited its application at full scale. Therefore, the aim of this work was to evaluate the anaerobic sequencing batch reactor (AnSBR) configuration in order to provide a low cost and easy operation alternative for the treatment of these complex effluents. In particular, the AnSBR was evaluated under different pH-temperature combinations: 7 and 32 °C; 7 and 38 °C; 8 and 32 °C and 8 and 38 °C. Results showed that the AnSBR configuration was able to achieve high COD removal efficiencies (around 85%) for all the tested conditions, while the highest methane yield was obtained at pH 7 and 38 °C (0.29 L/g COD added). Furthermore, high robustness was found in all the AnSBR experiments. Therefore, the full-scale application of the AnSBR technology for the treatment of tequila vinasses is quite encouraging, in particular for small and medium size tequila industries that operate under seasonal conditions.

Production of fructanase by a wild strain of Saccharomyces cerevisiae on tequila agave fructan.

A new wild strain of Saccharomyces cerevisiae (CF3) isolated from tequila must was evaluated for production of fructanase on Agave tequilana Weber fructan (FT). Fructanase activity (F) was assessed by a 3(3) factorial design (substrate, temperature and pH). High enzymatic activity (31.1 U/ml) was found at 30 °C, pH 5, using FT (10 g/l) as substrate. The effect of initial substrate concentration on F (FT0, 5.7-66 g/l) was studied and it was found that F was highest (44.8 U/ml) at FT0 25 g/l. A 2(2) factorial experimental design with five central points was utilized to study the effect of stirring and aeration on fructanase activity; stirring exhibited a stronger effect on F. The ratio fructanase to invertase (F/S) was 0.57, which confirms that the enzymes are fructanase. Crude fructanase reached high substrate hydrolysis (48 wt%) in 10 h. It is shown that S. cerevisiae CF3 was able to produce large amounts of fructanase by growing it on fructan from A. tequilana.

Intra-articular administration of an antibody against CSF-1 receptor reduces pain-related behaviors and inflammation in CFA-induced knee arthritis.

Several studies have shown that blockade of colony stimulating factor-1 (CSF-1) or its receptor (CSF-1R) inhibits disease progression in rodent models of rheumatoid arthritis (RA); however, the role of the CSF-1/CSF-1R pathway in RA-induced pain and functional deficits has not been studied. Thus, we examined the effect of chronic intra-articular administration of a monoclonal anti-CSF-1R antibody (AFS98) on spontaneous pain, knee edema and functional disabilities in mice with arthritis. Unilateral arthritis was produced by multiple injections of complete Freund's adjuvant (CFA) into the right knee joint of adult male ICR mice. CFA-injected mice were then treated twice weekly from day 10 until day 25 with anti-CSF-1R antibody (3 and 10 µg/5 µL per joint), isotype control (rat IgG 10 µg/5 µL per joint) or PBS (5 µl/joint). Knee edema, spontaneous flinching, vertical rearing and horizontal exploratory activity were assessed at different days. Additionally, counts of peripheral leukocytes and body weight were measured to evaluate general health status. Intra-articular treatment with anti-CSF-1R antibody significantly increased horizontal exploratory activity and vertical rearing as well as reduced spontaneous flinching behavior and knee edema as compared to CFA-induced arthritis mice treated with PBS. Treatment with this antibody neither significantly affect mouse body weight nor the number of peripheral leukocytes. These results suggest that blockade of CSF-1R at the initial injury site (joint) could represent a therapeutic alternative for improving the functional disabilities and attenuating pain and inflammation in patients with RA.

Hardware de un impresor térmico para electrocardiógrafos

Los impresores térmicos son periféricos necesarios para el desarrollo de electrocardiógrafos. El costo elevado y algunos otros inconvenientes hacen reflexionar sobre la factibilidad de un desarrollo propio a la medida de las necesidades. Son analizadas las propiedades y requistos de los elementos componentes de un impresor térmico; por lo que derivado de este trabajo se propone la adquisición de un módulo mecánico y el desarrollo de una tarjeta de control electrónico para su manipulación desde un nivel superior por un procesador. Se exponen a manera de conclusión las comprobaciones funcionales realizadas(AU)

Effects of chlorophyllin on acetaldehyde: lack of modulation of the rate of sister-chromatid exchanges in mouse bone marrow, and of complex formation in aqueous solution.

Acetaldehyde (Ace) is a reactive compound widely found in natural and industrialized products. On the other hand, chlorophyllin (Chl) is a chloropyll derivative which has shown DNA modulatory effects in several models. The first aim of the present study was to determine the capacity of Ace to increase the rate of sister-chromatid exchanges (SCEs) in mouse bone marrow cells in vivo, as well as to determine its capacity to modify the mitotic index (MI) and the average generation time (AGT). For this experiment we tested four dosages of Ace by the i.p. route (0.4, 4.0, 40.0 and 400 mg/kg), and found a genotoxic effect with the two highest dosages (more than double the basal level was observed with 400 mg/kg). We also found that none of the doses tested modified the MI or the AGT. A second objective was to explore the potential of Chl to modulate the genotoxicity of Ace in the same model. We evaluated whether an oral administration of Chl (2.0, 6.0 and 10.0 mg/kg), given 1 h before an i.p. administration of Ace (100 mg/kg), could modulate the SCEs produced by the mutagen. The result showed a similar SCE rate in both, the Ace-treated mice and those administered with the two chemicals, indicating that Chl was not a modulatory chemical on the genotoxicity of Ace. No modifications were observed concerning the MI or the AGT either. A third objective was to determine whether the two compounds (Ace and Chl) may form a molecular complex in aqueous solution. In agreement with the lack of modulatory effect by Chl, a reversed HPLC and a spectrophotometric analysis showed that the two compounds were unable to form a complex. This report confirms the importance of the specificity concerning the interaction mutagen/antimutagen.

Aberrant redox regulation in human metastatic melanoma cells compared to normal melanocytes.

Melanocytes and melanoma cells contain melanin, a complex polymer that modulates redox changes in these cells. Relative intracellular hydrogen peroxide levels measured by dichlorodihydrofluorescein are similar in the two cell types, but the levels of superoxide anion measured by dihydroethidium were markedly increased in melanoma cells. Chelator-induced oxidative stress is efficiently suppressed by melanocytes without substantial recruitment of the transcription factors NF-kappaB and AP-1 as measured by electrophoretic mobility shift assay and quantitated by densitometry or by a change in frequency of apoptosis as determined by annexin V binding. In contrast, NF-kappaB in melanoma cells is strongly recruited by changes in redox status and exhibits a correlative relationship to intracellular hydrogen peroxide (but not superoxide anion). However, the response of the NF-kappaB pathway to intracellular hydrogen peroxide is anomalous, including downregulation of p65 and IkappaBalpha RNA expression (Northern blot). Additionally, recruitment of AP-1 binding in melanoma cells was directly correlated with intracellular levels of superoxide anion (but not hydrogen peroxide). Neither the degree of NF-kappaB nor AP-1 binding in melanoma cells was related to the frequency of apoptosis. The responsiveness of NF-kappaB and AP-1 recruitment to intracellular levels of hydrogen peroxide and superoxide anion without concomitant control of apoptosis provides a general mechanism by which these cells can escape noxious injury (e.g., chemotherapy). The marked enhancement of apoptosis in melanoma cells by chelators indicates, however, that this alteration can be circumvented and offers a unique therapeutic window to explore.

Public policy and older women's health.

This article provides an overview of the aging of our population and its implications for women and the nursing profession in general. A brief history of women's role in the legislative and policy arena is provided along with a brief synopsis of legislative initiatives introduced in the 105th and 106th Congress and suggestions for nursing intervention.

Dupuytren's disease.

Dupuytren's disease is an extremely common malady, affecting as many as 3% of the general population. Presenting features are variable and include simple asymptomatic palmar nodules or refractory contractures of the interphalangeal joints. Substantial associations with knuckle pads, plantar nodules, and Peyronie's disease are noteworthy. Although a strong familial tendency is present, the precise pathologic mechanism is unknown. Treatment is frequently unnecessary, but when indicated it includes a variety of surgical alternatives. An appropriately timed referral to a surgical specialist before irreversible contracture of the interphalangeal joints can prevent a permanent loss of function. When surgical intervention is not elected, careful and regular follow-up is necessary to detect early joint contracture.

The use of skin grafts in the treatment of Dupuytren's contracture.

Digital contractures caused by Dupuytren's disease can best be treated by open fasciotomy plus excision of all overlying involved skin and replacement by full-thickness skin grafts. Such a procedure results in minimal operative morbidity, early recovery of function, and low incidence of recurrent contractures.

Dupuytren's contracture of the fingers: a simplified approach to the surgical treatment.

Hematoma formation, delay in healing, pain, stiffened finger joints are complications that sometimes follow classical surgical approaches to Dupuytren's contracture. A new surgical approach to the disease that can correct the contractures without the attendant morbidity is urgently needed. By treating Dupuytren's as any other scar contracture (division of the contracting soft tissue at its point of maximal tension and interposing normal free full-thickness skin) postoperative morbidity can be greatly decreased. Full return of function was achieved within 21 days following operation in 85 percent of the cases in which finger contractures were present before operation. Contracture release of 100 joints was done by this means, with loss of only one graft and without recurrence of the disease. This technique offers simple surgical control of progressive and recurrent Dupuytren's contracture of the fingers with minimal postoperative morbidity.