Ultrafast Resonant Magnetic Responses of Non-magnetic 2D Semiconductors to Low-Frequency Optical Fields

Mahmut Sait Okyay,Bumseop Kim,Noejung Park 한국자기학회 2021 한국자기학회 학술연구발표회 논문개요집 Vol.31 No.2

All-optical helicity-dependent switching of magnetism has attracted broad attention from the perspective of non-magnetic fast control of spins. We examine ultrafast spin dynamics of two-dimensional non-magnetic semiconductors, particularly focusing on alteration of material’s time-reversal and valley symmetries driven by a circularly polarized light. Monolayer MoS₂ was selected as an exemplary system and the real-time time-dependent density functional theory (rt-TDDFT) calculations were carried out, together with a model Hamiltonian analysis. As a distinction from some of the previous reports, this study was circumscribed to the non-excitonic regime, i.e., an interval of frequency values below the band gap. 〈그림 본문참조〉 Our real-time ab initio calculations show that a circularly polarized light can induce a net magnetization in a non-magnetic two-dimensional material. We demonstrate that the magnetic responses are particularly amplified when the applied electric fields are in resonance with the spin-flipping band transition between valence and conduction bands through the second harmonic of the light. We forecast that a tunable spin dynamics can be achieved from these non-magnetic semiconductors when the light of the resonant frequency is combined with a proper setting of a few parameters such as field strength, pulse duration and the magnitude of spin-orbit coupling.

Cervical Cancer Screening in an Early Diagnosis and Screening Center in Mersin, Turkey

Nayir, Tufan,Okyay, Ramazan Azim,Nazlican, Ersin,Yesilyurt, Hakki,Akbaba, Muhsin,Ilhan, Berrin,Kemik, Aytekin Asian Pacific Journal of Cancer Prevention 2015 Asian Pacific journal of cancer prevention Vol.16 No.16

Cancer is a major public health problem due to the jeavy disease burden, fatality and tendency for increased incidence. Of all cancer types, cervical cancer is reported to be the fourth most common cancer in women, and the seventh overall, with an estimated 528,000 new cases worldwide in 2012. It features a long preclinical phase with slowly progressing precancerous lesions such as CIN 2 and 3 and adenocarcinoma in situ. Therefore, screening programs such as with Pap smear tests may play an important role in cervical cancer prevention. The purpose of this study was to present results of a Pap smear screening survey for cervical cancer targeting women living in an urban area in the province of Mersin, located in the Mediterranean region of Turkey. This community-based descriptive study included women living at Akdeniz county of Mersin province. A total of 1,032 screened women between 30 and 65 ages within the routine screening programme constituted the study population. The mean age of the participants was $43.8{\pm}8.6$ (min. 30, max. 65) years. The percentage of the participants who had previously undergone smears was 40.6%. Epithelial cell changes were found in 26 (2.5%) participants, with ASC-US in 18 (1.7%), ASC-H in 2 (0.2%), LSIL in 5 (0.5%) and HSIL in 1 (0.1%). The most common clinical presentation together with epithelial changes was abnormal vaginal discharge. Taking into account the presence of women who had never undergone Pap test; it should be offered at primary level of health care in the form of a community-based service to achieve reduced morbidity and mortality rates.

Time-dependent density functional theory calculations of spin-phonon dynamics and band topology of two-dimensional materials

Noejung Park,Mahmut Okyay,Bum Seop Kim 한국자기학회 2020 한국자기학회 학술연구발표회 논문개요집 Vol.30 No.2

Evaluation of Depression in Newly Diagnosed Breast Cancer Cases in Hatay Province of Turkey in 2011

Nazlican, Ersin,Akbaba, Muhsin,Okyay, R. Azim Asian Pacific Journal of Cancer Prevention 2012 Asian Pacific journal of cancer prevention Vol.13 No.6

Breast cancer is the most frequently diagnosed cancer and the leading cause of cancer death in females in Turkey. The main problems experienced by women with breast cancer are physical losses, emotional distress and degradation in family, work and social roles. The purpose of this cross-sectional retrospective study was to investigate the socio-demographical characteristics and depressive symptoms of 125 newly diagnosed cases with breast cancer reported to cancer control department of Hatay provincial health directorate in 2011. To evaluate the depressive symptoms the Beck Depression Inventory (BDI) was used. All 125 cases who participated in the study were female. The mean age was $49.2{\pm}11.9$. The mean BDI score of the cases was $17.5{\pm}10.6$. The number of cases whose BDI scores were 17 and above was 65 (52.0%), and the number of cases whose BDI scores were under 17 was 60 (48.0%). The most striking finding in our study was that only 4 of the cases were receiving psychological help and support. The rate of depression was found high in our study and psychological support is a must for patients with a life threatening disease such as cancer.

Association of rs10757274 and rs2383206 Polymorphisms on 9p21 locus with Coronary Artery Disease in Turkish Population

Çağrı Yayla,Kaan Okyay,Asife Şahinarslan,Akın Yılmaz,Atiye Seda Yar Sağlam,Azmi Eyiol,Hasan Ata Bolayır,Burak Sezenöz,Sevda Menevşe,Atiye Çengel 대한심장학회 2016 Korean Circulation Journal Vol.46 No.5

Background and Objectives: Genetic predisposition is an important risk factor for coronary artery disease (CAD). In this study, we aimed to evaluate the impact of rs10757274 and rs2383206 polymorphisms in chromosome 9p21 on presence and severity of CAD in a Turkish population. Subjects and Methods: A total of 646 patients who underwent coronary angiography were included in this study. Coronary vessel score and Gensini score were calculated to assess the angiographic severity of CAD. Alleles of AA, AG, and GG were determined for rs10757274 (polymorphism-1) and rs2383206 (polymorphism-2) polymorphisms located in chromosome 9p21 from the blood samples. Results: There was a significant difference between the alleles in polymorphism-1 in the presence of coronary artery disease (38.9% in AA, 48.0% in GG and 56.4% in AG, p=0.017). However, there was no difference between the alleles in polymorphism-2. According to vessel scores, there was a significant difference between the alleles in polymorphism-1 (AA 0.71±1.04, GG 0.88±1.07, AG 1.06±1.12, p=0.018). In polymorphism-2, vessel scores did not show a difference between the alleles. In polymorphism-1, there was a significant difference in Gensini score (p=0.041). Gensini scores did not differ between the alleles in polymorphism-2 (p>0.05 for all). In multivariate analyses, none of the alleles was an independent factor for presence of CAD. Conclusion: The presence of rs10757274 polymorphism including AG allele in chromosome 9p21 was related to CAD. However, this relationship was not independent of other cardiovascular risk factors.

All-optical fast control of band topology by exploiting the correlation between Berry curvature and magnetic anisotropy

Bumseop Kim,Mahmut Sait Okyay,Noejung Park 한국자기학회 2021 한국자기학회 학술연구발표회 논문개요집 Vol.31 No.1

The effect of light pulse on magnetic materials have attracted broad interest in the perspective of laser-induced demagnetization and ultrafast controls of spin [1-3]. Here we focus on the fact that, beyond such passive roles, appropriately selected light conditions can result in more active effect in terms of magnetization density and magnetization direction. We selected a few examples of two-dimensional ferromagnetic insulators, and performed real-time time-dependent density functional theory by implementing the external light field in terms of vector potential. We find that asymmetric single-cycle light pulses can rotate the anisotropic local magnetization direction smoothly as shown in Fig 1. We discuss the effect of this optical reorientation of local moment, in the context of Mermin-Wagner’s theorem, on the long-range order of two-dimensional magnet. Our first-principles computations of real materials expect that this optical control of magnetization direction can adjust the Berry curvature distribution over the Brillouin zone, which eventually can switch the topological nature of quantum anomalous Hall state of ferromagnetic insulators.

Bifunctional sulfur-doped cobalt phosphide electrocatalyst outperforms all-noble-metal electrocatalysts in alkaline electrolyzer for overall water splitting

Anjum, Mohsin Ali Raza,Okyay, Mahmut Sait,Kim, Minkyung,Lee, Min Hee,Park, Noejung,Lee, Jae Sung Elsevier 2018 Nano energy Vol.53 No.-

<P><B>Abstract</B></P> <P>Sulfur-doped CoP (S:CoP) nanoparticles are synthesized as a noble metal-free electrocatalyst <I>via</I> a novel and eco-friendly thiourea-phosphate-assisted solvothermal route. When used as a bifunctional electrocatalyst for the hydrogen and oxygen evolution reactions from water splitting in an alkaline solution, the electrode exhibits excellent activity and stability outperforming noble mental-based Pt/C, IrO<SUB>2</SUB>, and reported non-noble metal-based electrocatalysts. Density functional theory calculations indicate that the excellent performance is attributable to the improved charge-transfer characteristics of the S:CoP nanoparticles owing to their modified electronic structure. It also increases the number of exposed active sites especially on the conductive substrates. A bifunctional S:CoP catalyst-based alkaline electrolyzer for overall water splitting exhibits a stable current density of 100 mA/cm<SUP>2</SUP> at an overvoltage of 0.55 V during a long-term operation; this performance is superior to that obtained from all-noble metal electrolyzer with a Pt/C cathode and an IrO<SUB>2</SUB> anode.</P> <P><B>Highlights</B></P> <P> <UL> <LI> S:CoP is synthesized by eco-friendly thiourea-phosphate-assisted solvothermal route. </LI> <LI> S:CoP/NF becomes an active and stable bifunctional water splitting electrocatalyst. </LI> <LI> S-doping improves charge transfer and increases density of active sites. </LI> <LI> An alkaline electrolyzer with bifunctional S:CoP outperforms all-noble-metal electrolyzer. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>The electronic properties of CoP are modulated by doping S into its structure through an environment-friendly thiourea-phosphate route, and produced S:CoP electrocatalysts efficiently catalyze both HER and OER in alkaline media.</P> <P>[DISPLAY OMISSION]</P>

Neuro-adaptive sliding-mode tracking control of robot manipulators

Topalov, Andon V.,Kaynak, Okyay,Aydin, Gokhan John Wiley Sons, Ltd. 2007 International journal of adaptive control and sign Vol.21 No.8

<P>In this work, a new dynamical on-line learning algorithm for robust model-free neuro-adaptive control of a class of nonlinear systems with uncertain dynamics is proposed and experimentally tested in order to evaluate its performance and practical feasibility in industrial settings. The control application studied is the trajectory tracking control task for the first three joints of an open architecture articulated robot manipulator. The control scheme makes use of variable structure systems theory and the feedback-error-learning concept. An inner sliding motion is established in terms of the neurocontroller parameters, aiming to lead the error in its control signal towards zero. The outer sliding motion bears on the system under control, the state tracking error vector of which is simultaneously driven towards the origin of the phase space. The existing relation between the two sliding motions is shown. Experimental results illustrate that the proposed neural-network-based controller possesses a remarkable learning capability to control complex dynamical systems, virtually without requiring a priori knowledge of the plant dynamics and laborious start-up procedures. Copyright © 2007 John Wiley & Sons, Ltd.</P>

Experimental and theoretical investigation of phosphorus in-situ doping of germanium epitaxial layers

Yu, H.Y.,Battal, E.,Okyay, A.K.,Shim, J.,Park, J.H.,Baek, J.W.,Saraswat, K.C. Elsevier 2013 Current Applied Physics Vol.13 No.6

We investigate phosphorus in-situ doping characteristics in germanium (Ge) during epitaxial growth by spreading resistance profiling analysis. In addition, we present an accurate model for the kinetics of the diffusion in the in-situ process, modeling combined growth and diffusion events. The activation energy and pre-exponential factor for phosphorus (P) diffusion are determined to be 1.91 eV and 3.75 x 10<SUP>-5</SUP> cm<SUP>2</SUP>/s. These results show that P in-situ doping diffusivity is low enough to form shallow junctions for high performance Ge devices.

An efficient and pH-universal ruthenium-based catalyst for the hydrogen evolution reaction

Mahmood, Javeed,Li, Feng,Jung, Sun-Min,Okyay, Mahmut Sait,Ahmad, Ishfaq,Kim, Seok-Jin,Park, Noejung,Jeong, Hu Young,Baek, Jong-Beom Nature Publishing Group, a division of Macmillan P 2017 Nature nanotechnology Vol.12 No.5

<P>The hydrogen evolution reaction (HER) is a crucial step in electro-chemical water splitting and demands an efficient, durable and cheap catalyst if it is to succeed in real applications(1-3). For an energy-efficient HER, a catalyst must be able to trigger proton reduction with minimal overpotential(4) and have fast kinetics(5-9). The most efficient catalysts in acidic media are platinum-based, as the strength of the Pt-H bond(10) is associated with the fastest reaction rate for the HER11,12. The use of platinum, however, raises issues linked to cost and stability in non-acidic media. Recently, non-precious-metal-based catalysts have been reported, but these are susceptible to acid corrosion and are typically much inferior to Pt-based catalysts, exhibiting higher overpotentials and lower stability(13-15). As a cheaper alternative to platinum, ruthenium possesses a similar bond strength with hydrogen (similar to 65 kcal mol(-1))(16), but has never been studied as a viable alternative for a HER catalyst. Here, we report a Ru-based catalyst for the HER that can operate both in acidic and alkaline media. Our catalyst is made of Ru nanoparticles dispersed within a nitrogenated holey two-dimensional carbon structure (Ru@C2N). The Ru@C2N electrocatalyst exhibits high turnover frequencies at 25 mV (0.67 H-2 s(-1) in 0.5 M H2SO4 solution; 0.75 H-2 s(-1) in 1.0 M KOH solution) and small overpotentials at 10 mA cm(-2) (13.5 mV in 0.5 M H2SO4 solution; 17.0 mV in 1.0 M KOH solution) as well as superior stability in both acidic and alkaline media. These performances are comparable to, or even better than, the Pt/C catalyst for the HER.</P>