Cation deficiency associated with the chemical exfoliation of lithium cobalt oxide

Compositional changes associated with the chemical exfoliation of lithium cobalt oxide, a layered transition metal oxide, are discussed. Starting from a layered bulk structure, lithium cobalt oxide can undergo chemical exfoliation through a two-step method: treatment with a protic acid, then treatment with tetramethylammonium hydroxide (this intercalates the layered structure and yields exfoliated nanosheets). This work provides an in-depth analysis of compositional and structural changes occurring to the powder upon the first step to exfoliation, treatment with acid, revealing variations in vacancies and valence changes depending on the conditions used. Through coupled analysis of X-ray photoelectron spectroscopy, X-ray diffraction, UV-Vis absorption spectroscopy, and inductively coupled plasma-optical emission spectroscopy data, we illustrate that both lithium and cobalt ions are diffusing out the structure along with the dissolution of full unit cells. As such, nanosheets accessed from the bulk by this exfoliation process should not be considered simply as divisions of the original unit cell. This work provides fundamental insights on the stability of LiCoO₂ and the exfoliation of layered transition metal oxides, beyond the access of individual nanosheets, and is vital to determining structure-property relationships of chemically exfoliated nanosheets (eg, changes in valency which dictate catalytic activity, magnetic susceptibility, etc).     

In situ X-ray diffraction of the early stages of the crystallization of Fe80B20

A new technique has been used for the early stages of crystallization of amorphous materials, like metallic alloys. In situ X-ray diffraction has been performed during the early stages of crystallization of Fe₈₀B₂₀. The samples are resistively heated to 600°C in a customized vacuum chamber. A programmable charge-coupled device detector records simultaneously the evolution of the three phases: -Fe, Fe₃B and Fe₂B in the minute scale. This is the first in situ X-ray diffraction study of this system in these temperature and time scales. Interesting behaviours have been seen: appearance and disappearance of phases, -Fe supersaturation solution in boron (found for the first time in this compound), and migration of B out of the -Fe matrix. The two-dimensional diffraction pictures show topography irregularities indicating crystallite inhomogeneties.     

Matrix-free algorithm for the optimization of multidisciplinary systems

Multidisciplinary engineering systems are usually modeled by coupling software components that were developed for each discipline independently. The use of disparate solvers complicates the optimization of multidisciplinary systems and has been a long-standing motivation for optimization architectures that support modularity. The individual discipline feasible (IDF) formulation is particularly attractive in this respect. IDF achieves modularity by introducing optimization variables and constraints that effectively decouple the disciplinary solvers during each optimization iteration. Unfortunately, the number of variables and constraints can be significant, and the IDF constraint Jacobian required by most conventional optimization algorithms is prohibitively expensive to compute. Furthermore, limited-memory quasi-Newton approximations, commonly used for large-scale problems, exhibit linear convergence rates that can struggle with the large number of design variables introduced by the IDF formulation. In this work, we show that these challenges can be overcome using a reduced-space inexact-Newton-Krylov algorithm. The proposed algorithm avoids the need for the explicit constraint Jacobian and Hessian by using a Krylov iterative method to solve the Newton steps. The Krylov method requires matrix-vector products, which can be evaluated in a matrix-free manner using second-order adjoints. The Krylov method also needs to be preconditioned, and a key contribution of this work is a novel and effective preconditioner that is based on approximating a monolithic solution of the (linearized) multidisciplinary system. We demonstrate the efficacy of the algorithm by comparing it with the popular multidisciplinary feasible formulation on two test problems.     

Adsorption of As(V) from Water Using Nanomagnetite

This paper describes a study of the removal of arsenate [As(V)] from aqueous solutions by adsorption on commercial nanomagnetite (NM). The influences of pH, initial arsenate [As(V)] concentration, and adsorbent concentration were investigated in multiple kinetic runs. The adsorption kinetics and isotherms were investigated in batch experiments. The experimental data were determined to be best described by the pseudosecond-order kinetic model. Langmuir and Freundlich isotherms were used to fit the adsorption data from equilibrium experiments. The findings have revealed that NM has high removal efficiency for arsenate, with its capacity to reduce an initial level of 300 to <5-μg/L As(V), i.e., below the limit (10-μg/L As) set for potable water by the World Health Organization.     

Changes in vibrational entropy during the early stages of chemical unmixing in fcc Cu–6% Fe

A nanocrystalline face-centered cubic (fcc) solid solution of 6% Fe in Cu was prepared by high-energy ball milling, and annealed at temperatures from 200 to 360 °C to induce chemical unmixing. The chemical state of the material was characterized by three-dimensional atom probe microscopy, Mössbauer spectrometry and X-ray powder diffractometry. The unmixing was heterogeneous, with iron atoms forming iron-rich zones that thicken with further annealing. The phonon partial density of states (pDOS) of ⁵⁷Fe was measured by nuclear resonant inelastic X-ray scattering, showing the pDOS of the as-prepared material to be that of an fcc crystal. The features of this pDOS became broader in the early stages of unmixing, but only small changes in average phonon frequencies occurred until the body-centered cubic (bcc) phase began to form. The vibrational entropy calculated from the pDOS underwent little change during the early stage of annealing, but decreased rapidly when the bcc phase formed in the material.     

Assessment of operational and environmental performance of the thermal power plants in Turkey by using data envelopment analysis

In this study, efficiency analyses of the eleven lignite-fired, one hard coal-fired and three natural gas-fired state-owned thermal power plants used for electricity generation were conducted through data envelopment analysis (DEA). Two efficiency indexes, operational and environmental performance, were defined and pursued. In the calculation of the operational performance, main production indicators were used as input, and fuel cost per actual production (Y) was used as output (Model 1). On the other hand, in the calculation of the environmental performance, gases emitted to the environment were used as output (Model 2). Data envelopment analysis (DEA) is the main instrument for the measurement of relative performances of the decision making units with multiple inputs and outputs. Constant returns to scale (CRS or CCR) and variable returns to scale (VRS or BCC) type DEA models were used in the analyses. The relationship between efficiency scores and input/output factors was investigated. Employing the obtained results, the power plants were evaluated with respect to both the cost of electricity generation and the environmental effects.     

Effectiveness of combined sewer overflow treatment for dissolved oxygen improvement in the Chicago waterways.

An Use Attainability Analysis (UAA) has been initiated to evaluate what water-quality standards can be achieved in the Chicago Waterway System (CWS). There are nearly 200 combined sewer overflow (CSO) locations discharging to the CWS by gravity. Three CSO pumping stations also drain approximately 140 km2. Because of the dynamic nature of the CWS the DUFLOW model that is capable of simulating hydraulics and water-quality processes under unsteady-flow conditions was used to evaluate the effectiveness of water-quality improvement techniques identified by the UAA including CSO treatment. Several CSO treatment levels were applied at gravity flow CSOs to evaluate improvement in dissolved oxygen (DO). The results show that pollutant removal at CSOs improves DO to a certain degree, but it still was not sufficient to bring DO concentrations to 5 mg/L or higher for 90% of the time during wet weather at most locations on the CWS. Flow from the pumping stations results in substantial stress on DO since a huge amount of un-treated water with a high pollution load is discharged into the CWS in a short period of time at a certain location. The simulation results indicate that CSO treatment does not effectively improve DO during wet-weather periods on the CWS.     

Renovation of a Safety-Inspection Methodology for River Bridges

River bridges and related infrastructural elements need to be monitored and inspected periodically for deterioration and loss of function due to aging, adverse hydraulic conditions, and chemical attacks. Necessary protective works and related actions should then be implemented to increase safety. Types of items to be inspected would be categorized as structural, geotechnical, hydraulic, and structural material conditions. Requirements for periodic inspections and the ways of handling these activities were discussed within the framework of the aforementioned aspects. Since each bridge authority has its own inspection grading system according to variations in local conditions and the socioeconomic status of the country, a common core methodology should be implemented such that comparisons with different case studies are meaningful. The aim of this study is the renovation of the current inspection system in Turkey, in order to implement it primarily for saving human life, as well as promoting Turkey’s economy, labor, and manpower. An algorithm, based on evaluating components of the main body, earth-retaining facilities, and serviceability, as well as hydraulic aspects, is proposed. This renovation enables the identification of rank-based prioritization of events. The evaluation and interpretation steps were displayed with the help of a case study.     

Long‐term effects of daily hemodialysis on vascular access outcomes: A prospective controlled study

Daily hemodialysis has been associated with surrogate markers of improved survival among hemodialysis patients. A potential disadvantage of daily hemodialysis is that frequent vascular access cannulations may affect long‐term vascular access patency. The study design was a 4‐year, nonrandomized, contemporary control, prospective study of 77 subjects in either 3‐h daily hemodialysis (six 3‐h dialysis treatments weekly; n = 26) or conventional dialysis (three 4‐h dialysis treatments weekly; n = 51). Outcomes of interest were vascular access procedures (fistulagram, thrombectomy and access revision). Total access procedures (fistulagram, thrombectomy and access revision) were 543.2 (95% confidence interval [CI]: 432.9, 673.0) per 1000 person‐years in the conventional dialysis group vs. 400.8 (95% CI: 270.2, 572.4) per 1000 person‐years in the daily hemodialysis dialysis group (incidence rate ratio = 0.74 with 95% CI: from 0.40 to 1.36, P = 0.33), after adjusting for age, gender, diabetes status, serum phosphorus, hemoglobin level and erythropoietin dose, there was no significant differences in incidence rate of total access procedures (P‐value > 0.05). There was no difference in time to first access revision between the daily dialysis and the conventional dialysis groups after adjustment for covariates (hazard ratio = 0.99 95% CI: 0.42, 2.36, P = 0.96). Daily hemodialysis is not associated with increased vascular access complications, or increased vascular access failure rates.