Computational modeling of electrochemical coupling: A novel finite element approach towards ionic models for cardiac electrophysiology

We propose a novel, efficient finite element solution technique to simulate the electrochemical response of excitable cardiac tissue. We apply a global–local split in which the membrane potential of the electrical problem is introduced globally as a nodal degree of freedom, while the state variables of the chemical problem are treated locally as internal variables on the integration point level. This particular discretization is efficient and highly modular since different cardiac cell models can be incorporated in a straightforward way through only minor local modifications on the constitutive level. Here, we derive the underlying algorithmic framework for a recently proposed ionic model for human ventricular cardiomyocytes, and demonstrate its integration into an existing nonlinear finite element infrastructure. To ensure unconditional algorithmic stability, we apply an implicit backward Euler scheme to discretize the evolution equations for both the electrical potential and the chemical state variables in time. To increase robustness and guarantee optimal quadratic convergence, we suggest an incremental iterative Newton–Raphson scheme and illustrate the consistent linearization of the weak form of the excitation problem. This particular solution strategy allows us to apply an adaptive time stepping scheme, which automatically generates small time steps during the rapid upstroke, and large time steps during the plateau, the repolarization, and the resting phases. We demonstrate that solving an entire cardiac cycle for a real patient-specific geometry characterized through a transmembrane potential, four ion concentrations, thirteen gating variables, and fifteen ionic currents requires computation times of less than ten minutes on a standard desktop computer.     

Quasi-solid-state dye-sensitized solar cells with cyanoacrylate as electrolyte matrix

A quasi-solid-state dye-sensitized solar cells (DSSCs) employing a commercial glue (“SuperGlue^®”) as electrolyte matrix was fabricated. The cyano groups of the cyanoacrylate can form a supramolecular complex with tetrapropylammonium cations. This immobilizes the cations and therefore might lead to a favored anionic charge transport necessary for a good performance of the iodide/triiodide electrolytic conductor. Obtaining energy conversion efficiencies of more than 4% under 100 mW/cm² of simulated A.M. 1.5 illumination, the cyanoacrylate quasi-solid-state electrolyte is an ordinary and low-cost compound which has fast drying property and offers significant advantages in the fabrication of solar cells and modules as it is in itself is a very good laminating agent. The influences of different porous layer thicknesses of titanium oxide and various kinds of cations on DSSC performance and long-term stability are presented.     

Internet-Based Design Catalogue for the Shaft and Bearing

The Internet and World Wide Web (WWW) are evolving as an important communication technology. This paper examines the development of an Internet-based online catalogue on the WWW. An interactive website is prepared that helps a remote designer to design shafts and bearings based on various input parameters provided. The web site also provides solid models of the shaft to perform CAD and FEM analysis. This permits the user to make further investigations, and helps to modify the design satisfactory.     

Effects of fineness of cement on polynaphthalene sulfonate based superplasticizer–cement interaction

The effects of fineness of portland cement procured from six different Turkish cement plants, on superplasticizer/cement interaction were investigated. CEM I 42.5 type portland cements (PC) were ground into different finenesses ranging from 280 to 550 m²/kg Blaine values. The effects of PC fineness on initial fluidity and fluidity loss of superplasticized cement paste were evaluated. It was found that increasing the Blaine fineness of incompatible cement up to a certain level reduced the viscosity of cement pastes but had no marked effect on the yield stress of the paste mixtures. Nevertheless, flow loss and also saturation point at 60 min increased with increasing the cement fineness. In other words, pastes with lower viscosity can be produced by using finer cement and more superplasticizer.     

30 years of contact lens prescribing for keratoconic patients in Turkey

Purpose

To assess retrospectively the course, the rate of bilateralness, prognosis, visual acuity with contact lenses, and corneal changes of a cohort with keratoconus.

Methods

Patients applying to Istanbul Faculty of Medicine, Department of Ophthalmology, Contact Lens Division during the period 1975-2005 with the diagnosis of keratoconus were recruited. The follow-up time ranged from 1.5 years to 25 years. This cohort consisted of 273 male, 245 female patients. The patients’ ages ranged from 12 years to 54 years (mean age 34.8 ± 10.1 years). 518 cases’ 1004 eyes were divided into four groups according to their mean keratometry values. The changes in visual acuity, keratometry values and the measurements of the used contact lenses were compared with each other, and statistical significance was sought.

Results

By self-report, the mean starting age of keratoconus was found to be 22.5 ± 7.6 years (range 7-35 years). 59 (11.4%) of 518 patients had unilateral keratoconus occurrence. The acute hydrops rate was found to be 0.3% (5 patients). In patients with advanced keratoconus, new contact lenses were applied with steeper radius of curvature. Penetrating keratoplasty was applied to 15 eyes (1.5%). Visual acuity examination on the patients’ last visit, when compared to previous examinations, was found to have decreased by 2-3 Snellen lines due to advancing keratoconus.

Conclusion

Keratoconus has shown to be a self-limited disease and in our study, with the use of contact lenses, successful outcomes which delayed the need for surgery were achieved in 98.9% of eyes (989/1004 eyes).     

Comparison of susceptibility of two stored-product insects, Ephestia kuehniella Zeller and Tribolium confusum du Val to gaseous ozone

In this study, the susceptibility of two stored-product insects, Ephestia kuehniella and Tribolium confusum, to gaseous ozone was investigated. Two ozone fumigation methods were used, an empty space fumigation with only one flush of ozone treatment held for 2 h, and a reflush ozone treatment at 30-min intervals for 5 h in the presence of 2 kg wheat, with an initial ozone concentration of 13.9 mg/L. Toxicity data for empty space ozone treatments indicated a remarkable difference in susceptibility between the life stages of E. kuehniella and T. confusum. For E. kuehniella, empty space ozone treatment resulted in complete mortality of adults, pupae and larvae, while only 62.5% of the eggs were killed. For T. confusum, ozone treatment resulted in very low mortality of adults, pupae and eggs, ranging from 4.2 to 14.1% while only larvae had a high mortality (74%). Generally T. confusum was more tolerant to ozone treatment than E. kuehniella. Ozone flush treatment at 30-min intervals for 5 h resulted in almost complete mortality of all life stages of E. kuehniella placed in the top position of 2 kg wheat, whereas eggs of E. kuehniella placed in the bottom position of 2 kg wheat were hard to kill. For T. confusum, larvae placed in the bottom position of 2 kg wheat were easily killed, whereas eggs, pupae and adults survived.     

Fuzzy Intellectual Capital Index for Construction Firms

Construction firms are now operating in a new era. Gaining and sustaining competitive advantage in this era primarily depends on effective and efficient management of knowledge assets. This paper proposes a performance evaluation model called fuzzy intellectual capital index (FICI) that can guide construction business executives to effectively and efficiently manage their knowledge assets. FICI incorporates an intellectual capital performance measurement model with fuzzy set theory to adequately handle imprecision, vagueness, and uncertainty that prevail in this process. FICI uses the fuzzy-weighted average algorithm to compute the intellectual capital performance of architectural/engineering/construction (A/E/C) firms. It is an internal reporting model that can guide executives of A/E/C firms to evaluate their firm’s ability to achieve their strategic objectives and to pinpoint their firm’s strengths and weaknesses in order to neutralize threats and to exploit opportunities presented by today’s construction business environment. A real-world case study is presented to illustrate the implementation and utility of the proposed model. Implications for practitioners and directions for future research are discussed.