3,309 research outputs found
Superconductivity Phase Diagram of Na(x)CoO(2).1.3H(2)O
Although the microscopic origin of the superconductivity in high Tc copper
oxides remains the subject of active inquiry, several of their electronic
characteristics are well established as universal to all the known materials,
forming the experimental foundation that all theories must address. The most
fundamental of those characteristics is the dependence of the superconducting
transition temperature on the degree of electronic band filling. Since the
discovery of cuprate superconductivity in 1986 (1), the search for other
families of superconductors that might help shed light on the superconducting
mechanism of the cuprates has been of great interest. The recent report of
superconductivity near 4K in the triangular lattice, layered sodium cobalt
oxyhydrate, Na0.35CoO2.1.3H2O, is the best indication that superconductors
related to the cuprates may be found (2). Here we show that the superconducting
transition temperature of this compound displays the same kind of band-filling
behavior that is observed in the cuprates. Specifically, that the optimal
superconducting Tc occurs in a narrow range of band filling, and decreases for
both underdoped and overdoped materials, in dramatic analogy to the phase
diagram of the cuprate superconductors. Our results suggest that
characterization of the detailed electronic and magnetic behavior of these new
materials may help establish which of the many special characteristics of the
cuprates is fundamental to their high Tc superconductivity.Comment: revised, publication information adde
Retrofit of water network with regeneration using water pinch analysis
This paper presents the development of a new systematic technique for the retrofit of water network with regeneration based on water pinch analysis. The procedure consists of two parts: retrofit targeting and design for a water network with regeneration unit(s). In the targeting stage, retrofit targets (utility savings and capital investment) were determined for a range of process parameters (total flowrate and/or outlet concentration of the regeneration unit) to obtain a savings versus investment curve. Next, the existing water network was re-designed to meet the chosen targets. A case study on paper making process was used to demonstrate the new methodology
A novel route to phase formation of cobalt oxyhydrates using KMnO4 as an oxidizing agent
We have first succeefully synthesized the sodium cobalt oxyhydrate
superconductors using KMnO4 as a de-intercalating and oxidizing agent. It is a
novel route to form the superconductive phase of NaxCoO2.yH2O without resorting
to the commonly used Br2/CH3CN solution. The role of the KMnO4 is to
de-intercalate the Na+ from the parent compound Na0.7CoO2 and oxidize the Co
ion as a result. The higher molar ratio of KMnO4 relative to the sodium content
tends to remove more Na+ from the parent compound and results in a slight
expansion of the c-axis in the unit cell. The superconducting transition
temperature is 4.6-3.8 K for samples treated by the aqueous KMnO4 solution with
the molar ratio of KMnO4 relative to the sodium content in the range of 0.3 and
2.29.Comment: 10 pages, 3 figure
Process modelling of a PVC production plant
This paper presents the modelling of a Polyvinyl Chloride (PVC) resins manufacturing process with batch process simulator, SuperPro Designer V6.0. The simulation model has been developed based on the operating condition of a local PVC manufacturing plant. As the polymerisation process is carried out in batch operation mode, efforts have been made to document the scheduling details of each unit operation and results are presented in the Gantt chart. Cycle time for a complete polymerisation process is determined to be 14.28 hours. The model also reveals that approximately 17 batches of polymerisation reaction can be processed per day, which tallies the real operation of the PVC manufacturing plant
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Patient-Related Barriers to Timely Dialysis Access Preparation: A Qualitative Study of the Perspectives of Patients, Family Members, and Health Care Providers
Rational & Objective
A key aspect of smooth transition to dialysis is the timely creation of a permanent access. Despite early referral to kidney care, initiation onto dialysis is still suboptimal for many patients, which has clinical and cost implications. This study aimed to explore perspectives of various stakeholders on barriers to timely access creation.
Study Design
Qualitative study.
Setting & Participants
Semi-structured interviews with 96 participants (response rate, 67%), including patients with stage 4 chronic kidney disease (n = 30), new hemodialysis patients with (n = 18) and without (n = 20) permanent access (arteriovenous fistula), family members (n = 19), and kidney health care providers (n = 9).
Analytical Approach
Thematic analysis.
Results
Patients reported differential levels of behavioral activation toward access creation: avoidance/denial, wait and see, or active intention. 6 core themes were identified: (1) lack of symptoms, (2) dialysis fear and practical concerns (exaggerated fear, pain, cost, lifestyle disruptions, work-related concerns, burdening their families), (3) evaluating value against costs/risks of access creation (benefits, threat of operation, viability, prompt for early initiation), (4) preference for alternatives, (5) social influences (hearsay, family involvement, experiences of others), and (6) health care provider interactions (mistrust, interpersonal tension, lack of clarity on information). Themes were common to all groups, whereas nuanced perspectives of family members and health care providers were noted in some subthemes.
Limitations
Response bias.
Conclusions
Individual, interpersonal, and psychosocial factors compromise dialysis preparation and contribute to suboptimal dialysis initiation. Our findings support the need for interventions to improve patient and family engagement and address emotional concerns and misperceptions about preparing for dialysis
IL-33 ameliorates Alzheimerās disease-like pathology and cognitive decline
Alzheimerās disease (AD) is a devastating condition with no known effective treatment. AD is characterized by memory loss as well as impaired locomotor ability, reasoning, and judgment. Emerging evidence suggests that the innate immune response plays a major role in the pathogenesis of AD. In AD, the accumulation of Ī²-amyloid (AĪ²) in the brain perturbs physiological functions of the brain, including synaptic and neuronal dysfunction, microglial activation, and neuronal loss. Serum levels of soluble ST2 (sST2), a decoy receptor for interleukin (IL)-33, increase in patients with mild cognitive impairment, suggesting that impaired IL-33/ST2 signaling may contribute to the pathogenesis of AD. Therefore, we investigated the potential therapeutic role of IL-33 in AD, using transgenic mouse models. Here we report that IL-33 administration reverses synaptic plasticity impairment and memory deficits in APP/PS1 mice. IL-33 administration reduces soluble AĪ² levels and amyloid plaque deposition by promoting the recruitment and AĪ² phagocytic activity of microglia; this is mediated by ST2/p38 signaling activation. Furthermore, IL-33 injection modulates the innate immune response by polarizing microglia/macrophages toward an antiinflammatory phenotype and reducing the expression of proinflammatory genes, including IL-1Ī², IL-6, and NLRP3, in the cortices of APP/PS1 mice. Collectively, our results demonstrate a potential therapeutic role for IL-33 in AD
Magnetic and Metal-Insulator Transitions in beta-Na0.5CoO2 and gamma-K0.5CoO2 -NMR and Neutron Diffraction Studies-
Co-oxides beta-Na0.5CoO2 and gamma-K0.5CoO2 have been prepared by the Na
de-intercalation from alpha-NaCoO2 and by the floating-zone method,
respectively. It has been found that successive phase transitions take place at
temperatures Tc1 and Tc2 in both systems. The appearance of the internal
magnetic field at Tc1 with decreasing temperature T indicates that the
antiferromagnetic order exists at T < Tc1, as in gamma-Na0.5CoO2. For
beta-Na0.5CoO2, the transition temperatures and the NMR parameters determined
from the data taken for magnetically ordered state are similar to those of
gamma-Na0.5CoO2, indicating that the difference of the stacking ways of the
CoO2 layers between these systems do not significantly affect their physical
properties. For gamma-K0.5CoO2, the quantitative difference of the physical
quantities are found from those of beta- and gamma-Na0.5CoO2. The difference
between the values of Tci (i = 1 and 2) of these systems might be explained by
considering the distance between CoO2 layers.Comment: 8 pages, 14 figures, 1 Tabl
23Na NMR study of non-superconducting double-layer hydrate NaxCoO2.yH2O
We report 23Na NMR studies of the polycrystalline samples of double-layer
hydrated cobalt oxides NaxCoO2.yH2O (x ~ 0.35 and y ~ 1.3) with the
superconducting transition temperatures Tc < 1.8K and ~4.5K, and the dehydrated
NaxCoO2 (x ~ 0.35). The hyperfine field and the electric field gradient at the
Na sites in the non-hydrated Na0.7CoO2 and the dehydrated Na0.35CoO2 are found
to be significantly reduced by the hydration, which indicates a strong
shielding effect of the intercalated water molecules on the Na sites. The
temperature dependence of 23 Na nuclear spin-lattice relaxation rate 1/23T1 of
the non-superconducting double-layer hydrate NaxCoO2.yH2O is found to be
similar to that of the non-hydrated Na0.7CoO2, whose spin dynamics is
understood by A-type (intra-layer ferromagnetic and inter-layer
antiferromagnetic) spin fluctuations. The superconducting phase is located
close to the quantum critical point with the A-type magnetic instability.Comment: 4 pages, 4 figure
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