FINITE TIME BLOW UP OF SOLUTIONS FOR A STRONGLY DAMPED NONLINEAR KLEIN-GORDON EQUATION WITH VARIABLE EXPONENTS

Piskin, Erhan The Honam Mathematical Society 2018 호남수학학술지 Vol.40 No.4

This paper, we investigate a strongly damped nonlinear Klein-Gordon equation with nonlinearities of variable exponent type $$u_{tt}-{\Delta}u-{\Delta}u_t+m^2u+{\mid}u_t{\mid}^{p(x)-2}u_t={\mid}u{\mid}^{q(x)-2}u$$ associated with initial and Dirichlet boundary conditions in a bounded domain. We obtain a nonexistence of solutions if variable exponents p (.), q (.) and initial data satisfy some conditions.

Annealing of Co-Cr dental alloy: effects on nanostructure and Rockwell hardness

Bulent Piskin,Hasan Suat Gokce,Cumhur Sipahi,Selim Kılıc,Semra İde,Elif Hilal Soylu,Simel Ayyıldız 대한치과보철학회 2013 The Journal of Advanced Prosthodontics Vol.5 No.4

PURPOSE The aim of the study was to evaluate the effect of annealing on the nanostructure and hardness of Co-Cr metal ceramic samples that were fabricated with a direct metal laser sintering (DMLS) technique. MATERIALS AND METHODS Five groups of Co-Cr dental alloy samples were manufactured in a rectangular form measuring 4 × 2 × 2 mm. Samples fabricated by a conventional casting technique (Group I) and prefabricated milling blanks (Group II) were examined as conventional technique groups. The DMLS samples were randomly divided into three groups as not annealed (Group III), annealed in argon atmosphere (Group IV), or annealed in oxygen atmosphere (Group V). The nanostructure was examined with the small-angle X-ray scattering method. The Rockwell hardness test was used to measure the hardness changes in each group, and the means and standard deviations were statistically analyzed by one-way ANOVA for comparison of continuous variables and Tukey's HSD test was used for post hoc analysis. P values of <.05 were accepted as statistically significant. RESULTS The general nanostructures of the samples were composed of small spherical entities stacked atop one another in dendritic form. All groups also displayed different hardness values depending on the manufacturing technique. The annealing procedure and environment directly affected both the nanostructure and hardness of the Co-Cr alloy. Group III exhibited a non-homogeneous structure and increased hardness (48.16 ± 3.02 HRC) because the annealing process was incomplete and the inner stress was not relieved. Annealing in argon atmosphere of Group IV not only relieved the inner stresses but also decreased the hardness (27.40 ± 3.98 HRC). The results of fitting function presented that Group IV was the most homogeneous product as the minimum bilayer thickness was measured (7.11 Å). CONCLUSION After the manufacturing with DMLS technique, annealing in argon atmosphere is an essential process for Co-Cr metal ceramic substructures. The dentists should be familiar with the materials that are used in clinic for prosthodontics treatments.

Coexistence of Darier's Disease and Acrokeratosis Verruciformis of Hopf

Suleyman Piskin,Aslihan Saygin,Latife Doganay,Deniz Kircuval,Eylem Gurkan 연세대학교의과대학 2004 Yonsei medical journal Vol.45 No.5

Darier's disease and acrokeratosis verruciformis are inherited with the same pattern and they share similar clinical properties. We present a patient with both Darier's disease and acrokeratosis verruciformis. The patient had had brownish and skin-colored papules, initially on her face and neck, since the age of 25. Similar lesions had gradually spread to various parts of her body and lastly the dorsal aspect of her feet. On dermatological examination, brownish and skin-colored, 2 to 5mm, keratotic papules were observed on her face, neck, both axillae, inframammary regions, and dorsa of the hands and feet. The nail examination revealed “V” shaped notches and longitudinal ridges on the fingers of both hands. The biopsy taken from the neck showed typical findings for Darier's disease. The biopsy from the dorsa of the left foot revealed the distinctive structures of acrokeratosis verruciformis. In this article the clinical and histopathological findings of these diseases are reviewed based on our patient.

Thermal degradation characteristic of Tetra Pak panel boards under inert atmosphere

Sabriye Piskin,Aysel Kantürk Figen,Evren Terzi,Nural Yilgör,Saip Nami Kartal 한국화학공학회 2013 Korean Journal of Chemical Engineering Vol.30 No.4

Thermal degradation characteristics of Tetra Pak panel boards (TPPB) can be useful to improve usage of such panels as an alternative to wood-based products such as plywood, fiberboard, and particleboard. In the study, samples from the TPBBs manufactured from waste Tetra Pak packages (WTPP) were heated in a nitrogen atmosphere at different heating rates (10, 15 and 20 oC/min) using a thermal analysis system. The Coats-Redfern kinetic model was applied to calculate kinetic parameters. The degradation rate equations were then established. In addition, the kinetic compensation effect (KCE) was used to correlate the pre-exponential factor (ko) with activation energy (Ea) and the existence of the KCE was accepted. TG-FT/IR analyses were applied to the TPPB degradation and then the FT-IR stack plot was used to analyze gas products (CO2, CH4, HCOOH, and CH3OH). Infrared vibrational frequencies and the micro,crystal structure of the TPPBs were investigated by Fourier transform infrared spectroscopy (FT-IR), Scanning electron microscope (SEM) and X-Ray diffraction analysis (XRD), respectively.

Synthesis, crystal structure and dehydration kinetics of NaB(OH)4·2H2O

Sabriye Piskin,Aysel Kanturk,Muge Sari 한국화학공학회 2008 Korean Journal of Chemical Engineering Vol.25 No.6

Sodium metaborate tetrahydrate (NaB(OH)4·2H2O) was synthesized by reaction of anhydrous borax (Na2O· 2B2O3) with sodium hydroxide (NaOH) under conditions at 90 oC for 150 min. The structure was characterized by Xray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), Scanning electron microscope (SEM) and Thermogravimetric (TG) analyses. Moreover, dehydration kinetics of NaB(OH)4·2H2O was carried out under non-isothermal conditions and the Coats-Redfern method was applied to analyze the TG data for calculation of activation energies (Ea) and pre-exponential factors (ko) for different heating rates. It was determined that dehydration of sodium metaborate tetrahydrate occurred in five steps. According to the Coats-Redfern non-isothermal model, Ea and ko were calculated as 50.89 kJ/mol and 26×104 min−1 for region I, 18.51 kJ/mol and 0.87×103 min−1 for region II, 15.72 kJ/mol and 0.52× 103 min−1 for region III, 4.37 kJ/mol and 0.04×103 min−1 for region IV and 37.42 kJ/mol and 8.56×103 min−1 for region V, respectively.

Blow up of solutions for a Petrovsky type equation with logarithmic nonlinearity

Jorge Ferreira,Nazli Irkil,Erhan Piskin,Carlos Raposo,Mohammad Shahrouzi 대한수학회 2022 대한수학회보 Vol.59 No.6

This paper aims to investigate the initial boundary value problem of the nonlinear viscoelastic Petrovsky type equation with nonlinear damping and logarithmic source term. We derive the blow-up results by the combination of the perturbation energy method, concavity method, and differential-integral inequality technique.

Covalent Modification of Cellulosic-based Textiles: A New Strategy to Obtain Antimicrobial Properties

Frederico Nogueira,Joana Vaz,Claudia Mouro,Erhan Piskin,Isabel Gouveia 한국생물공학회 2014 Biotechnology and Bioprocess Engineering Vol.19 No.3

In the past years the textile industry haswitnessed new advances in the area of textile fiber chainsengineering, which allow the modification of the structureof such chains so as to produce polymers responsive tochanges in the environment, thus capable of attaching tocells and bioactive molecules. On the other hand, followingour society's trend towards higher hygiene standards, theresearch and development of antimicrobial textiles hasshown a remarkable increase. Applications of such textilescan nowadays be found in underwear, sportswear, homefurnishing, protective clothing, wound-dressings and inmicrobial infection high risk settings, such as health careinstitutions. The present research aims at the developmentof a strong, durable and washable antimicrobial L-Cysteine(L-Cys)-functionalized cotton by means of a covalentmechanism. The covalent binding of L-Cys onto cellulosicfibers was assessed by Scanning Electron Microscopy-Energy Dispersive X-ray Spectroscopy (SEM-EDS) andFourier Transform Infrared Spectroscopy (FTIR) analysis. Antimicrobial assays showed that the functionalized cottonyielded strong microbial killing rates, exhibiting inhibitionratios of 89 and 83% against K. pneumoniae and S. aureus,respectively. These results demonstrate the effectiveness ofthe covalent modification of cotton fabrics with L-Cysadding antimicrobial properties to cotton fibers and thusopen the door to a world of applications in the area ofincreased risk microbial infections.

Annealing of Co-Cr dental alloy: effects on nanostructure and Rockwell hardness

Ayyildiz, Simel,Soylu, Elif Hilal,ide, Semra,Kilic, Selim,Sipahi, Cumhur,Piskin, Bulent,Gokce, Hasan Suat The Korean Academy of Prosthodonitics 2013 The Journal of Advanced Prosthodontics Vol.5 No.4

PURPOSE. The aim of the study was to evaluate the effect of annealing on the nanostructure and hardness of Co-Cr metal ceramic samples that were fabricated with a direct metal laser sintering (DMLS) technique. MATERIALS AND METHODS. Five groups of Co-Cr dental alloy samples were manufactured in a rectangular form measuring $4{\times}2{\times}2$ mm. Samples fabricated by a conventional casting technique (Group I) and prefabricated milling blanks (Group II) were examined as conventional technique groups. The DMLS samples were randomly divided into three groups as not annealed (Group III), annealed in argon atmosphere (Group IV), or annealed in oxygen atmosphere (Group V). The nanostructure was examined with the small-angle X-ray scattering method. The Rockwell hardness test was used to measure the hardness changes in each group, and the means and standard deviations were statistically analyzed by one-way ANOVA for comparison of continuous variables and Tukey's HSD test was used for post hoc analysis. P values of <.05 were accepted as statistically significant. RESULTS. The general nanostructures of the samples were composed of small spherical entities stacked atop one another in dendritic form. All groups also displayed different hardness values depending on the manufacturing technique. The annealing procedure and environment directly affected both the nanostructure and hardness of the Co-Cr alloy. Group III exhibited a non-homogeneous structure and increased hardness ($48.16{\pm}3.02$ HRC) because the annealing process was incomplete and the inner stress was not relieved. Annealing in argon atmosphere of Group IV not only relieved the inner stresses but also decreased the hardness ($27.40{\pm}3.98$ HRC). The results of fitting function presented that Group IV was the most homogeneous product as the minimum bilayer thickness was measured (7.11 ${\AA}$). CONCLUSION. After the manufacturing with DMLS technique, annealing in argon atmosphere is an essential process for Co-Cr metal ceramic substructures. The dentists should be familiar with the materials that are used in clinic for prosthodontics treatments.

Controlled release of doxorubicin from polyethylene glycol functionalized melanin nanoparticles for breast cancer therapy: Part I. Production and drug release performance of the melanin nanoparticles

Ozlu, Busra,Kabay, Gozde,Bocek, Ilyas,Yilmaz, Merve,Piskin, Ayse Kevser,Shim, Bong Sup,Mutlu, Mehmet Elsevier 2019 International Journal of Pharmaceutics Vol.570 No.-

<P><B>Abstract</B></P> <P>In this study, polyethylene glycol (PEG) conjugated melanin nanoparticles (MNPs) were prepared (PEG-MNPs). A model chemotherapy drug, doxorubicin (DOX), was loaded into the PEG-MNPs with varied concentrations (0.125, 0.250, 0.500 mg/mL). TEM images showed that, DOX-PEG-MNPs are spherical-shaped and 15 ± 2.2 nm in diameter. FTIR spectroscopy analysis demonstrated that MNPs were successfully modified with PEG. The UV–Vis spectroscopy results showed that the drug loading capacity of MNPs was 0.7 mg/ml of DOX in 2 mg/ml of PEG-MNPs. The time course data showed that, the release behavior of DOX from MNPs was primarily diffusion controlled. In vitro cytotoxicity assays demonstrated that MNP and PEG-MNP did not show any toxic effect on mouse fibroblast cells while DOX-PEG-MNP was able to inhibit the proliferation of human breast cancer cells. The results confirm that the application area of MNPs in controlled and prolonged drug release could be extended to the different types of cancer therapeutics.</P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

Plasmon e plasmon interaction effect on effective medium electrical conductivity (an effective agent for photothermal therapy)

A. SalmanOgli,B. Nasseri,M. Yazdani Kohneh shahri,E. Piskin 한국물리학회 2016 Current Applied Physics Vol.16 No.11

This article presents an investigative study of the photothermal effect of various compound nanoparticles (attaching the several small nanoparticles to a large nanoparticle by linkers). Initially, some compound nanoparticles such as Au-Au nanoparticles were fabricated and the effective medium electrical conductivities, found to vary greatly in gradient with variations in temperature, were analyzed using a nanolens e based approach. A nano-lens forms when Au-Au nanoparticles interact with electromagnetic waves. More precisely, the interaction of larger nanoparticles with an incident light generates a high intensity plasmonic field around it, and the dramatic effect of this near-field on small nanoparticles leads to the creation of a nano-lens. The modeled and experimental results obtained in this study showed that the Plasmon-plasmon interaction, which leads to the formation of a nano-lens with Au-Au nanoparticles, strongly influenced the medium electrical conductivity which is a vital key for detection of cancer cells. The gradient of electrical conductivity correlated directly with the amount of localized heat generation by Au-Au nanoparticles, offering means by which the temperature could be inferred. The amount of heat generated depended on both the number of nanoparticles present and the effectiveness with which they interacted, particularly in such a high intensity nano-lens.