Influence of Relativistic Effects on the Contact Formation of Transition Metals.

Our analysis of the contact formation processes undergone by Au, Ag, and Cu nanojunctions reveals that the distance at which the two closest atoms on a pair of opposing electrodes jump into contact is, on average, 2 times longer for Au than either Ag or Cu. This suggests the existence of a longer-range interaction between those two atoms in the case of Au, a result of the significant relativistic energy contributions to the electronic structure of this metal, as confirmed by ab initio calculations. Once in the contact regime, the differences between Au, Ag, and Cu are subtle, and the conductance of single-atom contacts for metals of similar chemical valence is mostly determined by geometry and coordination.

Topologically protected quantum transport in locally exfoliated bismuth at room temperature.

We report electrical conductance measurements of Bi nanocontacts created by repeated tip-surface indentation using a scanning tunneling microscope at temperatures of 4 and 300 K. As a function of the elongation of the nanocontact, we measure robust, tens of nanometers long plateaus of conductance G0 = 2e2/h at room temperature. This observation can be accounted for by the mechanical exfoliation of a Bi(111) bilayer, a predicted quantum spin Hall (QSH) insulator, in the retracing process following a tip-surface contact. The formation of the bilayer is further supported by the additional observation of conductance steps below G0 before breakup at both temperatures. Our finding provides the first experimental evidence of the possibility of mechanical exfoliation of Bi bilayers, the existence of the QSH phase in a two-dimensional crystal, and, most importantly, the observation of the QSH phase at room temperature.

A Group-Theoretic Approach to the Origin of Chirality-Induced Spin-Selectivity in Nonmagnetic Molecular Junctions.

Spin-orbit coupling gives rise to a range of spin-charge interconversion phenomena in nonmagnetic systems where certain spatial symmetries are reduced or absent. Chirality-induced spin-selectivity (CISS), a term that generically refers to a spin-dependent electron transfer in nonmagnetic chiral systems, is one such case, appearing in a variety of seemingly unrelated situations ranging from inorganic materials to molecular devices. In particular, the origin of CISS in molecular junctions is a matter of an intense current debate. Here, we derive a set of geometrical conditions for this effect to appear, hinting at the fundamental role of symmetries beyond otherwise relevant quantitative issues. Our approach, which draws on the use of point-group symmetries within the scattering formalism for transport, shows that electrode symmetries are as important as those of the molecule when it comes to the emergence of a spin-polarization and, by extension, to the possible appearance of CISS. It turns out that standalone metallic nanocontacts can exhibit spin-polarization when relative rotations which reduce the symmetry are introduced. As a corollary, molecular junctions with achiral molecules can also exhibit spin-polarization along the direction of transport, provided that the whole junction is chiral in a specific way. This formalism also allows the prediction of qualitative changes of the spin-polarization upon substitution of a chiral molecule in the junction with its enantiomeric partner. Quantum transport calculations based on density functional theory corroborate all of our predictions and provide further quantitative insight within the single-particle framework.

Unraveling the Interplay between Quantum Transport and Geometrical Conformations in Monocyclic Hydrocarbons' Molecular Junctions.

In the field of molecular electronics, especially in quantum transport experiments, determining the geometrical configurations of a single molecule trapped between two electrodes can be challenging. To address this challenge, we employed a combination of molecular dynamics (MD) simulations and electronic transport calculations based on density functional theory to determine the molecular orientation in our break-junction experiments under ambient conditions. The molecules used in this study are common solvents used in molecular electronics, such as benzene, toluene (aromatic), and cyclohexane (aliphatic). Furthermore, we introduced a novel criterion based on the normal vector of the surface formed by the cavity of these ring-shaped monocyclic hydrocarbon molecules to clearly define the orientation of the molecules with respect to the electrodes. By comparing the results obtained through MD simulations and density functional theory with experimental data, we observed that both are in good agreement. This agreement helps us to uncover the different geometrical configurations that these molecules adopt in break-junction experiments. This approach can significantly improve our understanding of molecular electronics, especially when using more complex cyclic hydrocarbons.

Mechanical annealing of metallic electrodes at the atomic scale.

The process of creating an atomically defined and robust metallic tip is described and quantified using measurements of contact conductance between gold electrodes and numerical simulations. Our experiments show how the same conductance behavior can be obtained for hundreds of cycles of formation and rupture of the nanocontact by limiting the indentation depth between the two electrodes up to a conductance value of approximately 5G0 in the case of gold. This phenomenon is rationalized using molecular dynamics simulations together with density functional theory transport calculations which show how, after repeated indentations (mechanical annealing), the two metallic electrodes are shaped into tips of reproducible structure. These results provide a crucial insight into fundamental aspects relevant to nanotribology or scanning probe microscopies.

Effect of glyphosate on growth of four freshwater species of phytoplankton: a microplate bioassay.

The acute toxicity of glyphosate herbicide was tested on the four species of freshwater phytoplankton, Scenedesmus acutus, Scenedesmus subspicatus, Chlorella vulgaris and Chlorella saccharophila. Herbicide concentrations eliciting a 50% growth reduction over 72 h (EC(50)) ranged from 24.5 to 41.7 mg L(-1), whilst a 10% growth inhibition is achieved by herbicide concentrations ranging from 1.6 to 3.0 mg L(-1), difficult to find neither in paddy fields (it is not used in rice) nor in the lake of the Albufera Natural Park. Chorella species are less sensitive to the herbicide than Scenedesmus species. It can be concluded that glyphosate has a low potential risk for the tested organisms.

A new methodology to assess the performance of AOPs in complex samples: Application to the degradation of phenolic compounds by O3 and O3/UV-A-Vis.

A methodology combining experimental design methodology, liquid chromatography, excitation emission matrixes (EEM) and bioassays has been applied to study the performance of O3 and O3/UVA-vis in the treatment of a mixture of eight phenolic pollutants. An experimental design methodology based on Doehlert matrixes was employed to determine the effect of pH (between 3 and 12), ozone dosage (02-1.0 g/h) and initial concentration of the pollutants (1-6 mg/L each). The following conclusions were obtained: a) acidic pH and low O3 dosage resulted in an inefficient process, b) increasing pH and O3 amount produced an enhancement of the reaction, and c) interaction of basic pH and high amounts of ozone decreased the efficiency of the process. The combination of O3/UVA-vis was able to enhance ozonation in those experimental regions were this reagent was less efficient, namely low pH and low ozone dosages. The application of EEM-PARAFAC showed four components, corresponding to the parent pollutants and three different groups of reaction product and its evolution with time. Bioassys indicated important detoxification (from 100% to less than 30% after 1 min of treatment with initial pollutant concentration of 6 mg/L, pH = 9 and ozone dosage of 0.8 g/h) according to the studied methods (D. magna and P. subcapitata). Also estrogenic activity and dioxin-like behavior were significantly decreased.

Impact of a shift work-like lighting schedule on the functioning of the circadian system in the short-lived fish Nothobranchius furzeri.

Adult Nothobranchius furzeri of the MZM-04/10 strain were individually kept and subjected to a "5 + 2" shifting lighting schedule (SHIFT) for 8 weeks in order to evaluate the desynchronizing effects of a simulated human-like shift-work schedule on the functioning of the circadian system (CS). With this aim, sixteen 21-week-old N. furzeri were placed into a Morning, Night and Evening schedule (lights on from 08:00 to 16:00, 00:00 to 08:00 and 16:00 to 00:00 h, respectively) and fed once a day in the middle of the corresponding photophase (12:00, 04:00 and 20:00 h, respectively). Then, in the weekends (2 days), fish were always returned to the Morning shift. As controls, 16 fish were maintained under a non-shifting LD cycle condition (CONTROL) throughout the whole experiment, with lights on from 08:00 to 16:00 h. Rest-activity rhythm (RAR) of fish subjected to SHIFT showed several symptoms of chronodisruption, such as a decrease in the percentage of diurnal activity and a reduction of the relative amplitude and the circadian function index with time. When a periodogram analysis was performed, RAR of N. furzeri under SHIFT conditions showed up to three separate circadian components: one longer than 24 h (26.5 h) that followed the weekly 8 h delays; a short-period component (~23 h) that was related to the weekend's phase advances, and finally, a 24 h component. The shifting LD schedule also affected fish CS at a molecular level, with several significant differences in the expression of core genes of the molecular clock (bmal1, clock, rorα, rev-erbα) between SHIFT and CONTROL animals. RAR impairment along with changes in clock gene expression could be associated with high stress and accelerated aging in these fish.

Modifications induced by atherogenic diet in the capacity of the arterial wall in rats to respond to surgical insult.

A study was made of events occurring in the arterial wall of the rat after administration of an atherogenic calcification-inducing diet and of vascular response in a model of combined metabolic aggression (atherogenic, calcification-inducing diet) and surgical aggression (adventitial resection). Female Sprague-Dawley rats were fed an atherogenic, calcification-inducing diet for 24 consecutive days, after which half the rats returned to standard diet (group I, n = 12) and the other half (group II) underwent resection of the adventitia on a segment of common iliac artery on day 25 before returning to standard diet. Normolipemic rats and rats that underwent adventitial resection without the atherogenic, calcification-inducing diet were used as the control groups. The rats were killed at 10 min, 1 and 24 h, 5, 14, 21, 30, 50, 70, 120 and 180 days. Morphologic studies were made with light microscopy and electron microscopy (scanning and transmission), as well as biochemical studies. Monocyte adherence and infiltration of the arterial intima, thickening of the subintimal space, the presence of monocyte-macrophages, calcification in the medial layer, intense adventitial fibrosis, and vacuolization of the endothelial cells of the adventitial microvessels were common findings in the two groups receiving the atherogenic, calcification-inducing diet. However, these groups differed in the intensity of calcification: the deep part of the medial layer did not become calcified when the adventitia was resected. Moreover, adventitial regeneration was delayed in group II with respect to the animals that underwent adventitial resection without atherogenic, calcification-inducing diet. We conclude that this diet induced atherosclerotic lesions in the vessel wall and inhibited adventitial regeneration in the rats that underwent resection.

Effects of metabolic control on vitamin E nutritional status in children with type 1 diabetes mellitus.

OBJECTIVE: To evaluate the effects of the metabolic control of the insulin-dependent diabetes mellitus (IDDM) on the nutritional status of vitamin E. METHODS: A total of 47 children with IDDM and a mean age of 11.91+/-1.60 (mean+/-SD) years were studied, matched for age and sex with 16 healthy children (11.75+/-1.83 years). Following the American and British Associations for IDDM, we used a classification of "good", "moderate" or "poor" control of the illness: (a) good control [glycosilated haemoglobin (HbAlc) < or =7%]; (b) moderate control (7%< HbAlc < or =8%); and (c) poor control (HbAlc>8%). Serum concentrations of total cholesterol (CHOL), triglycerides (TG), high-density lipoproteins-cholesterol (HDLc), very low- and low-density lipoproteins cholesterol (VLDLc and LDLc), plasma and erythrocyte vitamin E (Vit Ep and Vit Ee) and plasma vitamin A (Vit Ap) were measured in all children. RESULTS: The children with "poor" metabolic control of the illness presented significantly higher plasma concentrations of CHOL, LDLc, VLDLc, LDLc/HDLc, (VLDL+LDL)c/HDLc, TG and Vit Ep; higher indices Vit Ep/Vit Ee and Vit Ep/Vit Ap relative to those with a "good" control of the illness. Direct-linear correlations were found between Vit Ep and the percentage of HbAlc and with the markers of atherogenic risk in the IDDM children. CONCLUSION: There is a significant rise in Vit Ep concentrations as metabolic control of the illness worsens, whereas Vit Ee remained unchanged. These results suggest that vitamin E maintains its nutritional status despite a poor control of the IDDM during childhood.

Molinate decontamination processes in effluent water from rice fields.

The performance of aeration, photodecomposition and biological degradation processes as methods to reduce molinate contamination levels in effluent water from rice fields was studied. Aeration produced a molinate dissipation of 84%, as against 22% without aeration. Application of UV-light to clean water solutions achieved a molinate photodecomposition of 96% in 24 h. Maximal degradation obtained in algal cultures was 55% in 20 days and 78% in 40 days. In micro-organism cultures, kept in darkness and with a continuous flow of aqueous solution of molinate and inorganic salts, a degradation of 97% was achieved.

Effects of bensulfuron-methyl and cinosulfuron on growth of four freshwater species of phytoplankton.

The acute toxicity of sulfonylurea herbicides bensulfuron-methyl and cinosulfuron was tested on the five species of freshwater phytoplankton: Scenedesmus acutus, Scenedesmus subspicatus, Chlorella vulgaris and Chlorella saccharophila. Herbicide concentrations eliciting a 50% growth reduction over 96 h (EC50) ranged from 8 to 104 mg/l for cinosulfuron and from 0.015 to 6.2 mg/l for bensulfuron-methyl. The pesticides bensulfuron-methyl, atrazine and benthiocarb were more toxic than cinosulfuron, chlorsulfuron, molinate, fenitrothion and pyridaphenthion in a toxicity study with the same algal species. The transformation of effective concentrations of bensulfuron-methyl and cinosulfuron and other pesticides, obtained from toxicity measurements, into percent of the saturation level in water is used as a first evaluation of potential hazard to aquatic systems. The herbicides cinosulfuron, methyl-bensulfuron, atrazine and chlorsulfuron were more dangerous than the herbicides benthiocarb and molinate and than the insecticides fenitrothion and pyridaphenthion, in a study of hazard evaluation. The two species of Chlorella were more tolerant to both herbicides than the two species of Scenedesmus. A potential environmental hazard of sulfonylurea herbicides to aquatic systems has to be expected even at low environmental concentrations.

Effects of pyridaphenthion on growth of five freshwater species of phytoplankton. A laboratory study.

The acute toxicity of the insecticide and acaricide pyridaphenthion to five species of freshwater phytoplankton, Scenedesmus acutus, Scenedesmus subspicatus, Chlorella vulgaris, Chlorella saccharophila and Pseudanabaena galeata was determined. Insecticide concentrations eliciting a 50% growth reduction over 96 h (EC50) ranged from 2.2 to 30.9 mg/l. The two species of Chlorella and the cyanobacteria P. galeata were more tolerant than the two species of Scenedesmus. Concentrations of pyridaphenthion detected in some natural waters were less than the toxic threshold for these species.

Effects of propanil, tebufenozide and mefenacet on growth of four freshwater species of phytoplankton: a microplate bioassay.

The Albufera Natural Park situated in Valencia (Spain), with a very rich flora and fauna is surrounded by rice fields in which pesticide spraying is a regular practice. With this in mind, the sensitivity of four algal species, Scenedesmus acutus, Scenedesmus subspicatus, Chlorella vulgaris and Chlorella saccharophila to pesticides propanil, tebufenozide and mefenacet was studied using single species toxicity tests. Organisms were exposed to different concentrations of these herbicides and the algal growth was measured in a microplate reader at 410 nm, at 0, 24, 48 and 72 h. Tebufenozide appeared to be the most inhibitory to Scenedesmus and Chlorella species growth. 72 h EC50 of propanil, tebufenozide and mefenacet ranged from 0.29 to 5.98 mg/l, 0.12 to 0.15 mg/l and from 0.25 to 0.67 mg/l, respectively for the four algal species. The two species of Chlorella were more tolerant than the two species of Scenedesmus.

Bioconcentration of the insecticide pyridaphenthion by the green algae Chlorella saccharophila.

A study was undertaken to examine the uptake of the organophosphate insecticide pyridaphenthion in the chlorophyta Chlorella saccharophila. Algae cultures were exposed to the initial nominal concentration 10.0 mg l(-1) pyridaphention during seven days. The insecticide bioconcentrates in the biomass to the highest level of 441.5 +/- 25.9 mg kg(-1) on the fifth day of exposure and was followed by a decrease to 76.6 +/- 5.1 mg kg(-1) on the seventh day. A model was constructed to describe the dynamic process, which estimated a bioconcentration factor (BCF) equal to 28. The study demonstrates the potential of accumulation of pyridaphenthion in aquatic organisms and helps to expand the pyridaphenthion toxicity database. The replacement of fenitrothion by pyridaphenthion concerning their use in rice flooded cultures is discussed.

Surgery of the innominate artery.

The authors describe their experience with the surgical treatment of 28 patients with obliteration or stenosis of the innominate artery. In 18 (64.3%) patients an intrathoracic operation was done and in three of these a multiple bypass from the aorta to the affected trunks was carried out. In the remaining 10 patients (35.7%) extrathoracic operations were carried out. Immediate results were good in 24 (85.7%) of cases. Thrombosis occurred in 3 during the first 30 days after operation. One patient suffered thrombosis of the bypass and following removal of this became comatose and subsequently died. Long term results were good inasmuch as at 5 years 94.8% of patients survived with a patent reconstruction. The clinical procedures reviewed as is the topography of associated lesions of the other supra-aortic trunks together with the different techniques employed and their indications. The authors express their preference for the technique of an end to side graft in the aorta and end to end in the innominate artery, when the distal portion of this artery is patent and the age and general state of the patient permits a thoracic approach. This technique assures revascularization of the right carotid and vertebral areas, apart from complying with optimal hemodynamic conditions.

[Surgical treatment of the pathology of the descending aorta. Aneurysm and dissection]. / Tratamiento quirúrgico de la patología de la aorta descendente. Aneurisma y disección.

Aortic aneurysm and dissection of descending aorta have to be rapidly diagnosed and treated. The treatment frequently includes surgery. The natural history, indications of surgical treatment and surgical technique are reviewed.

[Long-term effectiveness of an intervention to discontinue chronic benzodiazepine use]. / Eficacia a largo plazo de una intervención para la deshabituación del consumo crónico de benzodiazepinas.

INTRODUCTION: We establish the long-term effectiveness of a brief intervention to withdraw from chronic benzodiazepine use. METHODS: Follow-up after a randomized clinical trial. SETTING: Three health care centers covering 82,000 inhabitants. SUBJECTS: 135 patients who completed the previous clinical trial (66 from the intervention group, 63 from the control group, 6 had died). Intervention-measurements: the previous clinical trial compared an intervention consisting of standardized advice and a dose tapering schedule against a control group followed by usual care. Results were evaluated at 12 months. main outcome: benzodiazepine use three years after the end of the clinical trial, type of drug and the reason for prescription. RESULTS: After 3 years of follow up, 25/66 (37.9%) subjects from the intervention group and 14/63 (22.2%) from the control group were benzodiazepine free. The probability of withdrawal from benzodiazepine between patients in the intervention group was 41% higher than in the control group. Relative risk: 1.41 (95% confidence interval: 0.98-1.66). In the intervention group, 16 from 31 (51.6%) patients who had withdrawn at 12 months were benzodiazepine free after 3 years. The most prescribed benzodiazepine is lorazepam (27.9%), followed by alprazolam (12.4%) and the main reason for prescription is anxiety (16.3%) followed by anxious-depressive disorder (10.9%). CONCLUSIONS: Even though there is a substantial relapse rate, the intervention to reduce chronic benzodiazepine use remains effective in the long-term.

Effects of the organophosphorus insecticide fenitrothion on growth in five freshwater species of phytoplankton.

The acute toxicity of the insecticide fenitrothion was measured using four freshwater algae (Chlorella saccharophila, Chlorella vulgaris, Scenedesmus acutus, and Scenedesmus subspicatus) and one cyanobacteria (Pseudanabaena galeata). Insecticide concentrations eliciting 50% growth reduction over 96 hr (EC50) ranged from 0.84 to 11.9 mg/L. Fenitrothion was more toxic than other pesticides studied with the same algal species such as chlorsulfuron, molinate, and pyridaphenthion. The transformation of effective concentrations of fenitrothion and other pesticides obtained from toxicity measurements into percent of the saturation level in water is used as a first evaluation of potential hazard to aquatic systems. The insecticides fenitrothion and pyridaphenthion were less hazardous than the herbicides atrazine, benthiocarb, cinosulfuron, chlorsulfuron, methyl-bensulfuron, and molinate. The two species of Chlorella and the cyanobacterium Pseudanabaena were more tolerant to fenitrothion than the two species of Scenedesmus.