STUDI PERUBAHAN FASE MODEL MAGNETIK SIMETRI POLIHEDRAL PADA KISI REGULER DAN KOMPLEKS

Studi perubahan fase (PF) merupakan salah satu kajian penting dalam fisika modern baik secara teoretik maupun eksperimen[1]. Hal ini disebabkan oleh kenyataan bahwa beberapa bahan memiliki sifat khusus dan bernilai tinggi jika berada dalam fase tertentu. Contoh paling lazim adalah bahan magnetik yang berada pada fase feromagnetik di bawah temperatur Curie. Fase magnetik adalah fase teratur yang merupakan realisasi dari gejala kerja-sama (cooperative phenomena) antara spin-spin (momen magnetik) yang sukses mengatasi fluktuasi termal[2]. Bahan magnet memiliki aplikasi sangat luas, dari storage, saklar, sensor, recorder magnetik, hingga komponen utama pembangkit listrik. \ud \ud Penemu-kenalan keberadaan PF dan sifat-sifatnya merupakan topik penting yang perlu dikaji. PF terjadi akibat adanya kompetisi antara sifat internal bahan (dinyatakan dalam tetapan gandeng) dan fluktuasi termal. Untuk bahan magnetik yang mengalami PF kontinu (orde kedua), karakteristik bahan di sekitar titik kritis ditentukan oleh sejumlah parameter kritis. Perolehan parameter kritis secara teoretik dan eksperimen sangat penting sebab memiliki sifat universalitas dimana sistem fisis berbeda dapat memiliki nilai kritis yang sama. Parameter kritis memuat informasi skenario kerusakan simetri dari sistem; dimana nilainya secara umum bergantung pada dimensi ruang, tetapan gandeng dan sifat simetri spin. Penemu-kenalan sifat kritis model-model magnetik berperan penting dalam pengembangan material baru dengan unjuk kerja (performance) handal

Canonical and Non-Canonical Ising Spin Glass on Randomly Rewired Regular Lattices

Submitted for International Conference: CCP2016 IUPAP Conference on Computational Physics, 10-14 July 2016 Pretoria, South AfricaSpin glass (SG) has been an active research field in theoretical and experimental condensed matter physics in the last four decades. It is a random magnetic system mainly characterized by a frozen spin orientation at low temperatures. Frustration and randomness are considered to be the key ingredients for a system to exhibit SG behavior. The so-called non-\ud canonical SG is a new type of SG???s where frustration and randomness are different from that of\ud the canonical one where both ferromagnetic (FM) and antiferromagnetic (AF) couplings exist.\ud It is a purely AF system on structures with random connectivity and topological frustration.\ud The existence of this new type of SGs on various structures, such as scale free network, rewired\ud lattices and regular graphs for models such as Ising and Heisenberg spins has been reported\ud by several previous studies. Further elaboration of this system is required, in particular for a\ud comparison to the canonical type of each corresponding model such as Ising and Heisenberg\ud model on the same irregular structure. Here we study the Ising models on rewired regular\ud lattices of both canonical and non-canonical SG model. We used Replica Exchange of Monte\ud Carlo method and calculate the SG order parameter to search for SG phase. We estimate the critical temperature and exponents of the SG phase observed

Diagram Fase Sistem Spin Ising Antiferomagnet Pada Jaringan Kompleks

Diagram fase dari sistem spin Ising antiferomagnet pada jaringan bebas skala yang rapat konektivitasnya bervariasi ditelaah dengan menggunakan metoda Monte Carlo algoritma pertukaran replika. Besaran fisis yang dihitung meliputi parameter pertindihan dan parameter Binder, keduanya bergantung pada temperatur. Jumlah simpul dalam jaringan bervariasi. Dengan menggunakan penyekalaan ukuran berhingga, temperatur peralihan fase untuk masing-masing rapat konektivitas dapat ditentukan, dan selanjutnya digambarkan diagram fasenya. Hasil yang diperoleh menunjukkan bahwa hingga rapat konektivitas tertentu, fase gelas spin kuat akan tetapi melemah pada keadaan konektivitas yang mendekati batas medan rerata, yaitu sistem kisi terkoneksi sempurna

Spin glass behavior of the antiferromagnetic Heisenberg model on scale free network

Hasanuddin UniversityThe study of spin glasses (SG???s) has been an active research field for the last three\ud decades. The importance of the systems lies in the fact that they have some significance not\ud only for other parts of physics, but also for such fields as computer science, mathematics and\ud biology, including many technological applications. They are a class of random magnets with\ud rich physical properties, such as infinite number of ground states, memory effect and aging\ud phenomena. Random frustration is considered to be the key ingredient for the existence of SG\ud behavior. It is realized by the presence of both ferromagnetic (FM) and antiferromagnetic\ud (AF) interactions in regular lattices. We previously observed spin glass behaviour of the\ud antiferromagnetic Ising model on scale free network (SFN)[1]. It is a new type of spin glass\ud systems, different from the canonical ones which requires random distribution of ferromagnetic\ud and antiferromagnetic interactions. Here we study spin glass behavior of Heisenberg spin models\ud with AF interaction on SFN. The canonical spin glass Heisenberg model is not observed in the d-\ud dimensional regular lattices for (d ?? 3)[2]. We can make an analogy for the connectivity density\ud C of SFN with the dimensionality of the regular lattice. It should be plausible to find the critical\ud value of C for the existence of SG behaviour, analogous to the lower critical dimension (dl) for\ud the canonical SG systems. We used Replica Exchange algorithm of Monte Carlo Method and\ud calculated the SG order parameter. We observed low temperature SG behavior and estimated\ud the critical temperature and exponents.\ud Reference

Scale-free networks in complex systems

In the past few years, several studies have explored the topology of interactions in different complex systems. Areas of investigation span from biology to engineering, physics and the social sciences. Although having different microscopic dynamics, the results demonstrate that most systems under consideration tend to self-organize into structures that share common features. In particular, the networks of interaction are characterized by a power law distribution, $P(k)\sim k^{-\alpha}$, in the number of connections per node, $k$, over several orders of magnitude. Networks that fulfill this propriety of scale-invariance are referred to as ``scale-free''. In the present work we explore the implication of scale-free topologies in the antiferromagnetic (AF) Ising model and in a stochastic model of opinion formation. In the first case we show that the implicit disorder and frustration lead to a spin-glass phase transition not observed for the AF Ising model on standard lattices. We further illustrate that the opinion formation model produces a coherent, turbulent-like dynamics for a certain range of parameters. The influence, of random or targeted exclusion of nodes is studied.Comment: 9 pages, 4 figures. Proceeding to "SPIE International Symposium Microelectronics, MEMS, and Nanotechnology", 11-15 December 2005, Brisbane, Australi

TRUST DAN JOB SATISFACTION SEBAGAI MEDIASI VIRTUAL LEADERSHIP TERHADAP TASK PERFORMANCE

Penelitian ini bertujuan untuk menganalisis penyebab rendahnya task performance staf PPIC di PT. Charon Pokphand Indonesia, Tbk (CPI), yang sejak April 2020 mengalami perubahan pola kerja dari tradisional menjadi virtual. Berdasarkan kajian teori dibangun model hipotesis yang menduga bahwa trust dan job jatisfaction berperan sebagai mediasi pengaruh virtual leadership terhadap task performance. Untuk membuktikan model tersebut, penelitian ini menggunakan Structural Equation Modeling (SEM) Amos yang menganalisis data yang diperoleh dari 434 staf PPIC yang telah bekerja virtual lebih dari 1 tahun. Hasil analisis membuktikan bahwa trust hanya sebagai mediasi parsial yang lebih kecil peranannya daripada pengaruh virtual leadership secara langsung terhadap task performance. Secara deskriptif diperoleh faktor gender sebagai penyebab peranan mediasi trust yang lebih kecil. Responden perempuan lebih rendah tingkat trust ketika bekerja secara virtual daripada laki-laki. Temuan lain membuktikan bahwa job satisfaction tidak signifikan sebagai mediasi. Secara deskriptif terlihat bahwa minimnya pengalaman bekerja virtual karyawan sebagai penyebab rendahnya job satisfaction ketika bekerja secara virtual. Seiring dengan meningkatnya frekuensi pengalaman karyawan bekerja virtual menunjukkan trend peningkatan job satisfaction. Penelitian ini merekomendasikan bagi manajemen CPI untuk mengakomodir hasil kajian dan temuan penelitian ini sebagai dasar penyusunan standard operational procedure karyawan bekerja virtual dalam upaya meningkatkan task performance. Penelitian ini juga merekomendasikan bagi peneliti selanjutnya untuk menyempurnakan hasil penelitian ini dengan menambah variabel gender dan frekuensi pengalaman kerja virtual dan dapat pula menggunakan metode penelitian kualitatif untuk menambah wawasan yang luas dan mendalam tentang bidang penelitian ini. This study aims to analyze the causes of the low performance of PPIC staff at PT. Charon Pokphand Indonesia, Tbk (CPI), which since April 2020 has experienced a change in work patterns from traditional to virtual. Based on the theoretical review, a hypothetical model was developed which assumes that trust and job satisfaction play the role of mediating the effect of virtual leadership on task performance. To prove this model, this study uses Amos' Structural Equation Modeling (SEM) which analyzes data obtained from 434 PPIC staff who have worked virtually for more than 1 year. The results of the analysis prove that trust is only a partial mediation that has a smaller role than the direct influence of virtual leadership on task performance. Descriptively, it shows a smaller factor that causes the role of mediating beliefs, namely the gender factor. Female respondents have a lower level of trust when working virtually than men. Other findings prove that job satisfaction is not significant as a mediation. Descriptively, the lack of employee virtual work experience is the cause of low job satisfaction when working virtually. With increasing frequency of virtual work experiences, employees show a tendency to increase job satisfaction. This study recommends that CPI management accommodate research results and research findings as a basis for preparing SOPs for employees to work virtually to improve task performance. These results can be refined by adding gender and frequency variables to virtual work experience. Future studies can also use qualitative research methods to provide a broad and deep insight into this field