188 research outputs found
Reversible and irreversible processes during cyclic voltammetry of an electrodeposited manganese oxide as catalyst for the oxygen evolution reaction
No full textAbstractManganese oxides have received much attention over the years among the wide range of electrocatalysts for the oxygen evolution reaction (OER) due to their low toxicity, high abundance and rich redox chemistry. While many previous studies focused on the activity of these materials, a better understanding of the material transformations relating to activation or degradation is highly desirable, both from a scientific perspective and for applications. We electrodeposited Na-containing MnOx without long-range order from an alkaline solution to investigate these aspects by cyclic voltammetry, scanning electron microscopy and x-ray absorption spectroscopy at the Mn-K and Mn-L edges. The pristine film was assigned to a layered edge-sharing Mn3+/4+ oxide with Mn-O bond lengths of mainly 1.87 Å and some at 2.30 Å as well as Mn-Mn bond lengths of 2.87 Å based on fits to the extended x-ray fine structure. The decrease of the currents at voltages before the onset of the OER followed power laws with three different exponents depending on the number of cycles and the Tafel slope decreases from 186 ± 48 to 114 ± 18 mV dec−1 after 100 cycles, which we interpret in the context of surface coverage with unreacted intermediates. Post-mortem microscopy and bulk spectroscopy at the Mn-K edge showed no change of the microstructure, bulk local structure or bulk Mn valence. Yet, the surface region of MnOx oxidized toward Mn4+, which explains the reduction of the currents in agreement with literature. Surprisingly, we find that MnOx reactivates after 30 min at open-circuit (OC), where the currents and also the Tafel slope increase. Reactivation processes during OC are crucial because OC is unavoidable when coupling the electrocatalysts to intermittent power sources such as solar energy for sustainable energy production.H2020 European Research Councilhttp://dx.doi.org/10.13039/10001066
Increases Overpotential of Electrocatalytic Water Oxidation in Lithium Hydroxide Electrolytes
No full textChemical and structural changes preceding electrocatalysis obfuscate the nature of the active state of electrocatalysts for the oxygen evolution reaction (OER), which calls for model systems to gain systematic insight. We investigated the effect of bulk oxidation on the overpotential of ink-casted LiMn2 O4 electrodes by a rotating ring-disk electrode (RRDE) setup and X-ray absorption spectroscopy (XAS) at the K shell core level of manganese ions (Mn-K edge). The cyclic voltammogram of the RRDE disk shows pronounced redox peaks in lithium hydroxide electrolytes with pH between 12 and 13.5, which we assign to bulk manganese redox based on XAS. The onset of the OER is pH-dependent on the scale of the reversible hydrogen electrode (RHE) with a Nernst slope of -40(4) mV/pH at -5 μA monitored at the RRDE ring. To connect this trend to catalyst changes, we develop a simple model for delithiation of LiMn2 O4 in LiOH electrolytes, which gives the same Nernst slope of delithiation as our experimental data, i. e., 116(25) mV/pH. From this data, we construct an ERHE -pH diagram that illustrates robustness of LiMn2 O4 against oxidation above pH 13.5 as also verified by XAS. We conclude that manganese oxidation is the origin of the increase of the OER overpotential at pH lower than 14 and also of the pH dependence on the RHE scale. Our work highlights that vulnerability to transition metal redox may lead to increased overpotentials, which is important for the design of stable electrocatalysts.collaborative research center (CRC)HZB http://dx.doi.org/10.13039/10001311
Formation of abiotic hydrocarbon from reduction of carbonate in subduction zones. Constraints from petrological observation and experimental simulation
No full textSubduction is a key process for linking the carbon cycle between the Earth's surface and its interior. Knowing the carbonation and decarbonation processes in the subduction zone is essential for understanding the global deep carbon cycle. In particular, the potential role of hydrocarbon fluids in subduction zones is not well understood and has long been debated. Here we report graphite and light hydrocarbon-bearing inclusions in the carbonated eclogite from the Southwest (S.W.) Tianshan subduction zone, which is estimated to have originated at a depth of at least 80 kilometers. The formation of graphite and light hydrocarbon likely results from the reduction of carbonate under low oxygen fugacity (∼FMQ - 2.5 log units). To better understand the origin of light hydrocarbons, we also investigated the reaction between iron-bearing carbonate and water under conditions relevant to subduction zone environments using large-volume high-pressure apparatus. Our high-pressure experiments provide additional constraints on the formation of abiotic hydrocarbons and graphite/diamond from carbonate-water reduction. In the experimental products, the speciation and concentration of the light hydrocarbons including methane (CH4), ethane (C2H6), and propane (C3H8) were unambiguously determined using gas chromatograph techniques. The formation of these hydrocarbons is accompanied by the formation of graphite and oxidized iron in the form of magnetite (Fe3O4). We observed the identical mineral assemblage (iron-bearing dolomite, magnetite, and graphite) associated with the formation of the hydrocarbons in both naturally carbonated eclogite and the experimental run products, pointing toward the same formation mechanism. The reduction of the carbonates under low oxygen fugacity is, thus, an important mechanism in forming abiotic hydrocarbons and graphite/diamond in the subduction zone settings
External and internal interface controlled trimetallic PtCuNi nanoframes with high defect density for enhanced electrooxidation of liquid fuels
Full text linkSelectively exposing active surfaces of Pt based nanoframes NFs can promote electrocatalysis of small organic molecules, especially regarding improved diffusion and anti poisoning properties. However, the systematic investigation on the synthesis, as well as structure property relationship, of Pt based NFs with tunable external and internal surface structures is still at its early stage. Herein, we report a facile, environmental and one pot approach to fabricate PtCuNi NFs with tunable external and internal surface structures by flexibly adjusting coordination and reducing agents. Interestingly, electrocatalytic results reveal that the PtCuNi NFs with variable external structures possess higher performance activity and anti CO poisoning capability than those with tunable internal structures as well as commercial Pt C. Especially, the PtCuNi eb NFs external branch NFs exhibit the excellent specific activities of methanol and formic acid oxidation reactions MOR and FAOR , 10.7 and 7.9 times higher than those of commercial Pt C, respectively. The PtCuNi eb NFs also possess a superior diffusion ability for methanol electrooxidation 0.0276 and formic acid electrooxidation 0.0153 compared to other PtCuNi NFs with plentiful internal surface. The enhanced MOR and FAOR activities of PtCuNi eb NFs are ascribed to its abundant external surface area and high defect density e.g. vacancy, subtle lattice distortion and high index facets , which results in an optimal anti CO poisoning capability due to the diffusion and ligand effects. This work opens up a new pathway for enhancing the electrooxidation performance anti poisoning property and diffusion rate of liquid fuels by tuning the surface structures of nanoframe catalyst
High-pressure experimental verification of rutile-ilmenite oxybarometer: Implications for the redox state of the subduction zone
No full textThe more oxidized mantle peridotites above subducting slabs than stable continental areas have been attributed to the
infiltration of some oxidizing fluids released from the subducting slabs. However, knowledge for the redox states of the slabs
itself is very limited. Until now, few oxybarometers can be directly used to constrain the redox states of the subducting slabs.
The rutile-ilmenite oxybarometer was proposed and successfully applied to constrain the oxygen fugacity of mantle assemblages.
However, its application to rocks equilibrated at crustal P-T conditions has been hampered by some uncertainties in an early solid
solution model of ilmenite. With a newly-released solid solution model for the ilmenite, we have conducted high-P experiments
(at 3 and 5 GPa, and 900–1300°C) to test the accuracy of this oxybarometer. The experiments were performed with their oxygen
fugacities controlled by the CCO buffer (i.e., C+O2=CO2). We demonstrated that the oxygen fugacities calculated for our high-P
experimental products by using the rutile-ilmenite oxybarometer were in excellent agreement with the fO2 dictated by the CCO
buffer, suggesting a wide applicability of this oxybarometer to crust rocks. As examples, the rutile-ilmenite oxybarometer has been
used to constrain the oxygen fugacities of some metamorphic rocks such as eclogite, granulite and amphibolite usually observed
from the subduction zone
1.23 Ga mafic dykes in the North China Craton and their implications for the reconstruction of the Columbia supercontinent
No full textAbstract not availableWei Wang, Shuwen Liu, M. Santosh, Lifei Zhang, Xiang Bai, Yue Zhao, Shuanhong Zhang, Rongrong Gu
[[alternative]]A Study on a Psychotherapist’s Countertransference during the Process of Psychotherapy
No full text[[abstract]]A Study on a Psychotherapist’s Countertransference during the Process of Psychotherapy
Pey-Ling Shieh
Abstract
The purpose of this study is to explore the countertransference during an ongoing process of psychotherapy. The study is conducted by the phenomenology approach. As a ten-session psychotherapy progressed, the psychotherapist was interviewed within 30 hours after each session. The data were analyzed by a framework retrieved from the data itself. The contextual factors, natures and transformation of the countertransference were all described.
The result yielded 22 units of countertransference experience. When compared with contextual factors, the psychotherapist’s countertransference to the specific client was found to have dual implications and to be more various than her original definition of and previous experiences of countertransference. The related factors of countertransference consisted of the fixed background of the therapist as well as the unique portion of the therapist-client interaction. The four domains of countertransference were classified as ‘feelings or cognitions toward the client’, ‘the role and position of the therapist and psychotherapy’, ’relationship and therapy maintenance’ and ‘distraction with associations’.
Most units of countertransference fall into the category of ‘Feelings or cognitions toward the client’. The therapist had various feelings toward the client and some of those feeling led to cognitions about the client. ‘Role and position of the therapist and psychotherapy’ is the second most frequent category of the countertransference, which happened when the therapist wondered about ‘what is the role of a therapist’ and ’what is the position of psychotherapy’. The feeling of being used and of not being respected would contribute to the discontinuity of therapy. As for the countertransference of ’relationship and therapy maintenance’, therapist’s assessment of the relationship was directly related to the maintenance of therapy. On ‘distraction with associations’, the therapist experienced various association and identification.
During the process of the psychotherapy, the familiarity of the therapist with the client increased. The global trend of understanding moved from stereotype-based and experience-based toward specific issues of the client. The focus of hypotheses-testing moved from ‘content consistency between client’s story and therapist’s experience’ toward ’internal consistency within client’s aspects of story’ or ’consistency between client’s story and hypotheses’. The transformation between sessions fluctuated and was recurrent. All four domains occurred at the initial stage and were intertwined with each other throughout the psychotherapy. process.
Given the findings that the countertransference displayed various natures and was formed by multiple factors, the author suggests some directions about future training and research.
Keywords: countertransference, process of psychotherapy, phenomenology
Shape-controlled synthesis and application of one-dimensional cadmium chalcogenide nanocrystals
No full textIn recent years, the synthesis of one-dimensional (1D) nanocrystals has attracted considerable interest. The morphologies of the 1D nanocrystals studied include rods, wires, belts and tubes whose lateral dimensions fall within the 1 to 100 nm range. Their potential applications are related to their size- and shape-dependent physicochemical and optoelectronic properties. 1D cadmium chalcogenide nanocrystals have become important potential building blocks for new electronic and optical nanodevices. As the electronic and optical properties are dependent on the crystal dimensions, the issue of how to control the growth of 1D cadmium chalcogenide nanocrystals is of prime importance and this issue remains one of the most challenging issues to address in both chemistry and materials science. This is one of the motivations behind this study. In this work, three catalyst-free and solution-based methods were used for the synthesis of 1D cadmium chalcogenide nanocrystals. These methods are the reverse micelle method, the hydrothermal method and the hot coordinating solvents method. Using both the reverse micelle method and the hydrothermal method, we have successfully synthesized CdSe nanorods. We found that the reverse micelle method has better morphological control than the hydrothermal method, but the latter has both the higher crystallinity and yield. Using the hot coordinating solvents method, good size distribution, controllable growth and an aspect ratio as high as 170 has been achieved. This is significant because in the past fifteen years, this method has only been able to generate low aspect ratio nanorods (less than 20). Contrary to the existing mechanisms, an oriented attachment mechanism was observed and proposed in this study. We also attempted to synthesiz CdSe nanowires using the same method. Although this method has been successful in producing cadmium selenide (CdSe) nanodots, nanorods and tetrapods, it remains a challenge to obtain nanowires. After systematically varying the parameters, we were able to gain some understanding in the growth of anisotropic nanocrystals. CdSe nanowires with a length of 220 nm and a diameter of 8 nm were successfully synthesized.DOCTOR OF PHILOSOPHY (MSE
疏肝理肺方防治應激條件下大鼠哮喘的作用機制研究
No full textOBJECTIVE: To explore the influence of psychological factor on asthma, the protective and therapeutic effects of Shugan Lifei Recipe on rats with asthma under stress and the mechanisms. METHODS: Allergy and stress-induced asthma models were established in rats by giving ovalbumin and restraining stress. Radioimmunoassay, enzyme linked immunosorbent assay, in situ hybridization and immunohistochemical method were used to detect plasma corticosterone, IL-4, IFN-gamma, expression of glucocorticoid receptor (GR) mRNA in hippocampus and adrenocorticotropic hormone corticoliberin (CRH) positive neuron in hypothalamus. Optical and electron microscopes were used to observe the morphological changes of pulmonary hilar and hippocampal tissues. RESULTS: Shugan Lifei Recipe (SGLFR) could reduce plasma corticosterone, decrease CRH positive neurons in paraventricular nucleus of hypothalamus, up-regulate the expression of GR mRNA in hippocampus and reduce the injury of hippocampal neuron. SGLFR had certain inhibitive effect on hyperfunction of hypothalamo-pituitary-adrenal cortex (HPA) axis in rats with asthma under stress and could also relieve the pathological changes of the pulmonary hilar tissue. The level of plasma IFN-gamma was increased while the level of plasma IL-4 was decreased in SGLFR-treated group. CONCLUSION: The mechanism of SGLFR in treating the rats with asthma under stress is probably to regulate the hyperfunction of HPA axis and the disorder of immuo-system.link_to_subscribed_fulltex
Dante\u27s Virgils
No full textThe questions brought to a text define the reading of it, questions both invited by the author and assumed by the reader. Dante\u27s Divine Comedy opens with a remarkable ambiguity that calls for an investigation of the questions being brought to the poem:
Midway along the journey of our lifeI woke to find myself in a dark wood,For I had wandered off from the straight path. (Inf 1.1-3)
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