Ahmet Nihat Berker

Berker, Ahmet Nihat

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https://hdl.handle.net/20.500.12469/6148

Name Variants

Nihat Berker A.
BERKER, Ahmet Nihat
Ahmet Nihat, Berker
Berker,Ahmet Nihat
Berker, AHMET NIHAT
A. Berker
B.,Ahmet Nihat
Berker,A.N.
Berker, A.
Berker, Ahmet Nihat
Berker N.
Ahmet Nihat Berker
Ahmet Nihat BERKER
Berker, A. N.
B., Ahmet Nihat
AHMET NIHAT BERKER
A. N. Berker
BERKER, AHMET NIHAT
Berker A.
Berker, A. Nihat

Job Title

Prof. Dr.

Email Address

[email protected]

Main Affiliation

Electrical-Electronics Engineering

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Current Staff

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Documents

159

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6781

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42

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Documents

135

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6618

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Scholarly Output

31

Articles

31

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173/3100

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0

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WoS Citation Count

120

Scopus Citation Count

126

WoS h-index

7

Scopus h-index

7

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0

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WoS Citations per Publication

3.87

Scopus Citations per Publication

4.06

Open Access Source

24

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0

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Journal	Count
Physical Review E	17
Physica A: Statistical Mechanics and its Applications	4
Physica A-Statistical Mechanics and Its Applications	3
Chaos Solitons & Fractals	2
Chaos, Solitons & Fractals	1

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Now showing 1 - 10 of 31

Spin-Glass Phases and Multichaos in the Ashkin–Teller Model
(Elsevier Ltd, 2026) Saray, A.; Berker, A.N.
The global phase diagram of the Ashkin–Teller spin glass is calculated in d=3 spatial dimensions by renormalization-group theory. Depending on the value of the positive or negative four-spin interaction, qualitatively different topologies are found for the spin-glass phase diagram in the usual variables of temperature and fraction of antiferromagnetic nearest-neighbor interactions. Two different spin-glass phases occur. Both spin-glass phases are chaotic. One spin-glass exhibits phase reentrance that is reverse from the reentrances seen in previous spin-glass phase diagrams. Seven different phases: Ferromagnetic and antiferromagnetic, entropic ferromagnetic and entropic antiferromagnetic, spin-glass and entropic spin-glass, and disordered phases occur. The entropic ferromagnetic phase unusually but understandably occurs at temperatures above one spin-glass phase. A random disorder line is identified and no phase transition occurs on this line. Our calculation is exact on the d = 3 hierarchical lattice and Migdal–Kadanoff approximate on the cubic lattice. © 2025 Elsevier Ltd.
Multiplicity of Algebraic Order From Fixed Lines of Potential Surfaces: X-Y-Ashkin in Spatial Dimension D=2
(Amer Physical Soc, 2025) Artun, E.C.; Berker, A.N.
A position-space renormalization-group study is done for the Ashkin-Tellerized XY model, as an exact solution on the d=2 hierarchical lattice and an approximate solution on the square lattice. A multiplicity of algebraic order is found in the phase diagram, in the form of renormalization-group fixed lines composed of a continuous sequence of interaction potential surfaces. In the Ashkin-Tellerized XY model, each site has two continuously varying spins, each spin being an XY spin, that is, having orientation continuously varying in 2π radians. Nearest-neighbor sites are coupled by two-spin and four-spin interactions. The phase diagram has algebraically ordered phases that are ferromagnetic and antiferromagnetic in each of the spins, and algebraically ordered phases that are ferromagnetic and antiferromagnetic in the combined spin variable. These phases are subtended by fixed lines of potential surfaces that are multiplicatively different Berezinskii-Kosterlitz-Thouless fixed potentials. The evolution of continuously varying criticality is traced within each of the four phases. The renormalization-group flows, the fixed lines, and the interaction surfaces are in terms of the doubly composite Fourier coefficients of the exponentiated energy of the four nearest-neighbor spins. The disordered phase is maintained along two semi-infinite a priori quasi-disorder lines. This record is sourced from MEDLINE/PubMed, a database of the U.S. National Library of Medicine
Citation - WoS: 1
Citation - Scopus: 1
Fractal Measures of Sea, Lake, Strait, and Dam-Reserve Shores: Calculation, Differentiation, and Interpretation
(ELSEVIER, 2021) Yılmazer, Dilara; Berker, A. Nihat; Yılmaz, Yücel
The fractal dimensions d(f) of the shore lines of the Mediterranean, the Aegean, the Black Sea, the Bosphorus Straits (on both the Asian and European sides), the Van Lake, and the lake formed by the Ataturk Dam have been calculated. Important distinctions have been found and explained. (C) 2021 Elsevier B.V. All rights reserved.
Citation - WoS: 5
Citation - Scopus: 5
Asymmetric Phase Diagrams, Algebraically Ordered Berezinskii-Kosterlitz Phase, and Peninsular Potts Flow Structure in Long-Range Spin Glasses
(Amer Physical Soc, 2022) Gurleyen, S. Efe; Berker, A. Nihat
The Ising spin-glass model on the three-dimensional (d = 3) hierarchical lattice with long-range ferromagnetic or spin-glass interactions is studied by the exact renormalization-group solution of the hierarchical lattice. The chaotic characteristics of the spin-glass phases are extracted in the form of our calculated, in this case continuously varying, Lyapunov exponents. Ferromagnetic long-range interactions break the usual symmetry of the spin-glass phase diagram. This phase-diagram symmetry breaking is dramatic, as it is underpinned by renormalization-group peninsular flows of the Potts multicritical type. A Berezinskii-Kosterlitz-Thouless (BKT) phase with algebraic order and a BKT-spin-glass phase transition with continuously varying critical exponents are seen. Similarly, for spin-glass long-range interactions, the Potts mechanism is also seen, by the mutual annihilation of stable and unstable fixed distributions causing the abrupt change of the phase diagram. On one side of this abrupt change, two distinct spin-glass phases, with finite (chaotic) and infinite (chaotic) coupling asymptotic behaviors are seen with a spin-glass to spin-glass phase transition.
Citation - WoS: 1
Citation - Scopus: 1
Covid-19 Modeling Based on Real Geographic and Population Data
(Tubitak Scientific & Technological Research Council Turkey, 2023) Baysazan, Emir; Berker, A. Nihat; Mandal, Hasan; Kaygusuz, Hakan
Background/aim: Intercity travel is one of the most important parameters for combating a pandemic. The ongoing COVID-19 pandemic has resulted in different computational studies involving intercity connections. In this study, the effects of intercity connections during an epidemic such as COVID-19 are evaluated using a new network model. Materials and methods: This model considers the actual geographic neighborhood and population density data. This new model is applied to actual Turkish data by means of provincial connections and populations. A Monte Carlo algorithm with a hybrid lattice model is applied to a lattice with 8802 data points. Results: Around Monte Carlo step 70, the number of active cases in Turkiye reaches up to 8.0% of the total population, which is followed by a second wave at around Monte Carlo step 100. The number of active cases vanishes around Monte Carlo step 160. Starting with Istanbul, the epidemic quickly expands between steps 60 and 100. Simulation results fit the actual mortality data in Turkiye. Conclusion: This model is quantitatively very efficient in modeling real-world COVID-19 epidemic data based on populations and geographical intercity connections, by means of estimating the number of deaths, disease spread, and epidemic termination.
Citation - WoS: 2
Citation - Scopus: 2
Spin-S Spin-Glass Phases in the D=3 Ising Model
(Amer Physical Soc, 2021) Artun, E. Can; Berker, A. Nihat
All higher-spin (s >= 1/2) Ising spin glasses are studied by renormalization-group theory in spatial dimension d = 3, exactly on a d = 3 hierarchical model and, simultaneously, by the Migdal-Kadanoff approximation on the cubic lattice. The s-sequence of global phase diagrams, the chaos Lyapunov exponent, and the spin-glass runaway exponent are calculated. It is found that, in d = 3, a finite-temperature spin-glass phase occurs for all spin values, including the continuum limit of s -> infinity. The phase diagrams, with increasing spin s, saturate to a limit value. The spin-glass phase, for all s, exhibits chaotic behavior under rescalings, with the calculated Lyapunov exponent of lambda = 1.93 and runaway exponent of y(R) = 0.24, showing simultaneous strong-chaos and strong-coupling behavior. The ferromagnetic-spin-glass and spin-glass-antiferromagnetic phase transitions occurring, along their whole length, respectively at p(t) = 0.37 and 0.63 are unaffected by s, confirming the percolative nature of this phase transition.
Citation - WoS: 2
Citation - Scopus: 2
Maximally Random Discrete-Spin Systems With Symmetric and Asymmetric Interactions and Maximally Degenerate Ordering
(Amer Physical Soc., 2018) Atalay, Bora; Berker, A. Nihat
Discrete-spin systems with maximally random nearest-neighbor interactions that can be symmetric or asymmetric ferromagnetic or antiferromagnetic including off-diagonal disorder are studied for the number of states q = 34 in d dimensions. We use renormalization-group theory that is exact for hierarchical lattices and approximate (Migdal-Kadanoff) for hypercubic lattices. For all d > 1 and all nonmfimte temperatures the system eventually renormalizes to a random single state thus signaling q x q degenerate ordering. Note that this is the maximally degenerate ordering. For high-temperature initial conditions the system crosses over to this highly degenerate ordering only after spending many renormalization-group iterations near the disordered (infinite-temperature) fixed point. Thus a temperature range of short-range disorder in the presence of long-range order is identified as previously seen in underfrustrated Ising spin-glass systems. The entropy is calculated for all temperatures behaves similarly for ferromagnetic and antiferromagnetic interactions and shows a derivative maximum at the short-range disordering temperature. With a sharp immediate contrast of infinitesimally higher dimension 1 + epsilon the system is as expected disordered at all temperatures for d = 1.
Metastable Potts droplets
(AMER PHYSICAL SOC, 2021) Artun, E. Can; Berker, A. Nihat
The existence and limits of metastable droplets have been calculated using finite-system renormalization-group theory, for q-state Potts models in spatial dimension d = 3. The dependence of the droplet critical sizes on magnetic field, temperature, and number of Potts states q has been calculated. The same method has also been used for the calculation of hysteresis loops across first-order phase transitions in these systems. The hysteresis loop sizes and shapes have been deduced as a function of magnetic field, temperature, and number of Potts states q. The uneven appearance of asymmetry in the hysteresis loop branches has been noted. The method can be extended to criticality and phase transitions in metastable phases, such as in surface-adsorbed systems and water.
Merged Potts-Clock Model: Algebraic and Conventional Multistructured Multicritical Orderings in Two and Three Dimensions
(Amer Physical Soc, 2023) Artun, E. Can; Berker, A. Nihat
A spin system is studied with simultaneous permutation-symmetric Potts and spin-rotation-symmetric clock interactions in spatial dimensions d = 2 and 3. The global phase diagram is calculated from the renormalization-group solution with the recently improved (spontaneous first-order detecting) Migdal-Kadanoff approximation or, equivalently, with hierarchical lattices with the inclusion of effective vacancies. Five different ordered phases are found: Conventionally ordered ferromagnetic, quadrupolar, antiferromagnetic phases and algebraically ordered antiferromagnetic, antiquadrupolar phases. These five different ordered phases and the disordered phase are mutually bounded by first-and second-order phase transitions, themselves delimited by multicritical points: Inverted bicritical, zero-temperature bicritical, tricritical, second-order bifurcation, and zero-temperature highly degenerate multicritical points. One rich phase diagram topology exhibits all of these phenomena.
Citation - WoS: 14
Citation - Scopus: 14
Lower Lower-Critical Spin-Glass Dimension From Quenched Mixed-Spatial Spin Glasses
(Amer Physical Soc., 2018) Atalay, Bora; Berker, A. Nihat
By quenched-randomly mixing local units of different spatial dimensionalities we have studied Ising spin-glass systems on hierarchical lattices continuously in dimensionalities 1 <= d <= 3. The global phase diagram in temperature antiferromagnetic bond concentration and spatial dimensionality is calculated. We find that as dimension is lowered the spin-glass phase disappears to zero temperature at the lower-critical dimension d(c) = 2.431. Our system being a physically realizable system this sets an upper limit to the lower-critical dimension in general for the Ising spin-glass phase. As dimension is lowered towards d(c) the spin-glass critical temperature continuously goes to zero but the spin-glass chaos fully subsists to the brink of the disappearance of the spin-glass phase. The Lyapunov exponent measuring the strength of chaos is thus largely unaffected by the approach to d and shows a discontinuity to zero at d(c.)

Berker, Ahmet Nihat

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LIFE ON LAND

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PEACE, JUSTICE AND STRONG INSTITUTIONS

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ZERO HUNGER

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INDUSTRY, INNOVATION AND INFRASTRUCTURE

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