On a Kelvin-Voigt Viscoelastic Wave Equation with Strong Delay

An initial-boundary value problem for a viscoelastic wave equation subject to a strong time-localized delay in a Kelvin & Voigt-type material law is considered. Transforming the equation to an abstract Cauchy problem on the extended phase space, a global well-posedness theory is established using the operator semigroup theory both in Sobolev-valued $C^{0}$- and BV-spaces. Under appropriate assumptions on the coefficients, a global exponential decay rate is obtained and the stability region in the parameter space is further explored using the Lyapunov's indirect method. The singular limit $\tau \to 0$ is further studied with the aid of the energy method. Finally, a numerical example from a real-world application in biomechanics is presented.Comment: 34 pages, 4 figures, 1 set of Matlab code

Service evaluation to establish the sensitivity, specificity and additional value of broad-range 16S rDNA PCR for the diagnosis of infective endocarditis from resected endocardial material in patients from eight UK and Ireland hospitals

Infective endocarditis (IE) can be diagnosed in the clinical microbiology laboratory by culturing explanted heart valve material. We present a service evaluation that examines the sensitivity and specificity of a broad-range 16S rDNA polymerase chain reaction (PCR) assay for the detection of the causative microbe in culture-proven and culture-negative cases of IE. A clinical case-note review was performed for 151 patients, from eight UK and Ireland hospitals, whose endocardial specimens were referred to the Microbiology Laboratory at Great Ormond Street Hospital (GOSH) for broad-range 16S rDNA PCR over a 12-year period. PCR detects the causative microbe in 35/47 cases of culture-proven IE and provides an aetiological agent in 43/69 cases of culture-negative IE. The sensitivity, specificity, positive predictive value (PPV) and negative predictive value (NPV) of the 16S rDNA PCR assay were calculated for this series of selected samples using the clinical diagnosis of IE as the reference standard. The values obtained are as follows: sensitivity = 67 %, specificity = 91 %, PPV = 96 % and NPV = 46 %. A wide range of organisms are detected by PCR, with Streptococcus spp. detected most frequently and a relatively large number of cases of Bartonella spp. and Tropheryma whipplei IE. PCR testing of explanted heart valves is recommended in addition to culture techniques to increase diagnostic yield. The data describing the aetiological agents in a large UK and Ireland series of culture-negative IE will allow future development of the diagnostic algorithm to include real-time PCR assays targeted at specific organisms

A new look at the modified Coulomb potential in a strong magnetic field

The static Coulomb potential of Quantum Electrodynamics (QED) is calculated in the presence of a strong magnetic field in the lowest Landau level (LLL) approximation using two different methods. First, the vacuum expectation value of the corresponding Wilson loop is calculated perturbatively in two different regimes of dynamical mass $m_{dyn.}$, {\it i.e.}, $|{\mathbf{q}}_{\|}^{2}|\ll m_{dyn.}^{2}\ll |eB|$ and $m_{dyn.}^{2}\ll |\mathbf{q}_{\|}^{2}|\ll|eB|$, where $\mathbf{q}_{\|}$ is the longitudinal components of the momentum relative to the external magnetic field $B$. The result is then compared with the static potential arising from Born approximation. Both results coincide. Although the arising potentials show different behavior in the aforementioned regimes, a novel dependence on the angle $\theta$ between the particle-antiparticle's axis and the direction of the magnetic field is observed. In the regime $|{\mathbf{q}}_{\|}^{2}|\ll m_{dyn.}^{2}\ll |eB|$, for strong enough magnetic field and depending on the angle $\theta$, a qualitative change occurs in the Coulomb-like potential; Whereas for $\theta=0,\pi$ the potential is repulsive, it exhibits a minimum for angles $\theta\in]0,\pi[$.Comment: V1: 26 pages, 8 figures, latex format, V2: Accepted for publication in PRD (2007

Optimization and validation of a method for extraction and quantification of ochratoxin A in black pepper

Abstract The extraction method for the determination of ochratoxin A (OTA) in black pepper was optimized. The influence of three variables, i.e., type of solvent, solvent-volume-to-samplesize ratio (v/w) and amount of sodium chloride (NaCl) (g), on OTA recovery was evaluated. Analysis of variance was used to compare recovery values obtained from different solvents, and response surface methodology (RSM) was used to determine the optimum amount of NaCl and the solvent-volume-to-sample-size ratio. The concentration of OTA was determined by high-performance liquid chromatography with fluorescence detection. The highest recovery (95.2 %) was obtained when methanol/water (80:20, v/v) was used as the solvent. The RSM results showed that the experimental data could be adequately fitted to a second-order polynomial model with multiple regression coefficients (R 2 ) of 0.962. The optimum amount of NaCl was determined to be 3 g, whereas the optimum solvent-volume-to-sample-size ratio (v/w) was found to be 4. The proposed method was applied to 20 samples, and the presence of OTA was found in 8 (40%) samples ranging from 0.11 to 3.16 ng g -1

IMECE2008-68886 EXPERIMENTAL NONLINEAR VIBRATION ANALYSIS OF PIEZOELECTRICALLY ACTUATED MICROCANTILEVERS

ABSTRACT With daily growth of using microcantilevers in microelectromechanical systems, comprehensive analysis on their dynamical behavior is necessary since they are mostly utilized as the main sensing device. In this paper, the out-ofplane vibrations of the piezoelectrically actuated microcantilever are experimentally investigated. The microcantilever is covered with a piezoelectric layer on its top surface through which it can be excited by applying the voltage to the piezoelectric actuator. The nonlinear frequency response of the microcantilever is studied and shift in natural frequency due to nonlinearity is examined. By observing the subharmonics of the fundamental frequencies at 2X and 3X, it is experimentally shown that there exist cubic and quadratic nonlinearities in the microcantilever. A mathematical model based on these experimental tests is then proposed and verified. The out-of-plane measurements provide the ability to observe both transversal and torsional modes. In addition, the modes in which the microcantilever acts like a plate are observed. INTRODUCTION Microcantilevers find many applications in nanomechanical sensors/actuators and especially piezoelectrically-actuated microcantilevers have recently received considerable attention since they are capable of better actuation. The sensing/actuating operation is based on static and dynamic deflections of the microcantilevers. However, measurement of the dynamic vibrations of the microcantilever is the base sensing strategy. Therefore, a nonlinear comprehensive experimental study on the frequency response of these microcantilevers seems to be essential since in such small scale even very small excitations can provide large amplitude and consequently nonlinear vibration

Comparison of Propolis and Calcium Hydroxide in terms of Mineralization and Cytotoxicity Using Dental Pulp Stem Cells

Objectives: This study aimed to compare the in vitro cytotoxic activity of propolis, a bioactive material made by the honeybee, and calcium hydroxide (CH) and their effect on formation of mineralized nodules by human dental pulp stem cells (HDPSCs).Methods: In this in vitro study, HDPSCs were obtained from the Cellular and Molecular Oral Biology Laboratory of School of Dentistry, Shahid Beheshti University of Medical Sciences. In order to evaluate the proliferative effect of propolis and CH, HDPSCs were incubated with different concentrations of propolis (0-32mg/mL) and CH (0-4.8 mg/mL). Twenty-four and 48 hours later, the methylthiazolyl diphenyl-tetrazolium bromide (MTT) assay was carried out to evaluate the proliferation potential and viability of HDPSCs treated with propolis and CH. The effect of propolis and CH on mineralization of HDPSCs was assessed by alizarin red staining.Results: The MTT assay revealed that propolis at its highest concentration caused the greatest proliferation after 24 and 48 hours. Alizarin test showed that the lowest concentrations of CH and propolis at 14 days induced the formation of calcium nodules but at 21 days, propolis was deposited on the cells and calcification was not well recognizable.Conclusion: Propolis led to higher cell vitality at all concentrations in comparison to CH. However, due to its deposition on the cells, its effects on mineralization at 48 hours could not be determined

Obstacles and Challenges in the Use of Probiotics

BACKGROUND AND OBJECTIVE: Probiotics are living microorganisms whose adequate intake has shown healthful effects in the host body and have been suggested to have beneficial effects in the prevention and treatment of many diseases. This study was conducted to investigate the obstacles and challenges of probiotic products in the production process and their effects on human health. METHODS: For data collection in this review article, articles containing one of the terms “probiotic”, “lactobacillus”, “bifidobacterium”, “biogenic amine” and “antibiotic resistance” from 1990 to 2017 were searched and reviewed at Thomson Reuters, Pubmed, Scopus, Science Direct and Islamic World Science Citation Center(ISC). FINDING: Research has shown that systematic infections and chronic diseases, over-stimulation of the immune system, transfer of antibiotic resistance genes, production of biogenic amines and D-lactic acidosis, lack of survival and sustainability of microorganisms and ultimately the change in the taste and flavor of probiotic products are among the obstacles and challenges facing the production of probiotics. The use of bifidobacterium to transfer antibiotic resistance genes is safer than other microorganisms for the production of probiotic products. CONCLUSION: Based on the results of this study, probiotics are only safe in healthy people, although they are very useful for human health, but their use in children, pregnant women and people with a weakened immune system causes infection