Dislocation screening in crystals with spherical topology

Whereas disclination defects are energetically prohibitive in two-dimensional flat crystals, their existence is necessary in crystals with spherical topology, such as viral capsids, colloidosomes or fullerenes. Such a geometrical frustration gives rise to large elastic stresses, which render the crystal unstable when its size is significantly larger than the typical lattice spacing. Depending on the compliance of the crystal with respect to stretching and bending deformations, these stresses are alleviated by either a local increase of the intrinsic curvature in proximity of the disclinations or by the proliferation of excess dislocations, often organized in the form of one-dimensional chains known as "scars". The associated strain field of the scars is such to counterbalance the one resulting from the isolated disclinations. Here, we develop a continuum theory of dislocation screening in two-dimensional closed crystals with genus one. Upon modeling the flux of scars emanating from a given disclination as an independent scalar field, we demonstrate that the elastic energy of closed two-dimensional crystals with various degrees of asphericity can be expressed as a simple quadratic function of the screened topological charge of the disclinations, both at zero and finite temperature. This allows us to predict the optimal density of the excess dislocations as well as the minimal stretching energy attained by the crystal

Sistem Pendukung Keputusan Penempatan Jabatan Menggunakan Metode Simple Additive Weighting (Saw) Berbasis Web (Studi Kasus : Smk PGRI Pekanbaru)

Dalam lingkungan Perusahaan atau organisasi, komputer merupakan alat bantu yang mutlak diperlukan sehingga penerapan sebuah sistem berbasis komputer menjadi kebutuhan pokok dan memberikan keunggulan kompetitif. Masalah yang terjadi dalam proses evaluasi (penilaian) kinerja guru diantaranya adalah terutama jika beberapa guru yang ada memiliki kemampuan yang tidak jauh berbeda. Proses evaluasi (penilaian) yang rumit terjadi sekarang umumnya adalah adanya guru yang menempati jabatan yang hanya melihat pada kriteria pertama saja, tetapi guru tersebut belum tentu unggul pada beberapa kriteria-kriteria yang lain. SMK PGRI pekanbaru merupakan salah satu sekolah swasta yang ada di pekanbaru. Dimana selama ini pada proses penempatan jabatan hanya dilihat dari hasil tes dan beberapa persyaratan dasar lainya. Sebagian besar guru mengalami kesulitan beradaptasi dengan tugas-tugas yang harus dilaksanakan karena tidak memiliki latar belakang pengetahuan yang sesuai dengan posisi yang yang ditempatinya. Jika dibiarkan terus-menerus, hal ini akan berdampak negatif pada kinerja yang diberikan dan menghambat kemajuan sekolah. Oleh karena itu, Pihak sekolah mencari solusi agar dapat meminimalisasi kesalahan yang diakibatkan oleh kinerja guru, yaitu dengan cara menempatkan guru pada posisi atau bidang yang sesuai dengan kemampuanya

Penggunaan Avogadro untuk Memperkenalkan Bentuk Molekul Sederhana pada SMP Negeri 27 Maluku Tengah

Kimia merupakan salah satu bagian dari pelajaran IPA di tingkat SMP yang mempelajari fenomena alam. Fenomena alam yang dibahas di tingkat SMP adalah Materi dan perubahannya. Di dalam materi dan perubahannya, ada bagian mengenai wujud zat. Untuk wujud zat hanya sebatas kasat mata, untuk bentuk molekul di dalam zat tersebut belum diperkenalkan. Perlu adanya pengenalan kepada para siswa SMP bagaimana bentuk molekul yang sebenarnya. Pengenalan bentuk molekul dapat dilakukan dengan melakukan dengan bantuan perangkat lunak seperti Avogadro. Avogadro dapat memberikan tampilan bentuk molekul sebenarnya dari suatu zat yang ada di lingkungan sekitar. Pelatihan penggunaan Avogadro dalam pengenalan bentuk molekul sederhana telah dilakukan pada SMP Negeri 27 Maluku tengah. Pelatihan ini bertujuan untuk memberikan gambaran mengenai bentuk molekul dari suatu zat yang ada di lingkungan sekitar, misalnya air, cuka, dan minyak. Pelatihan ini dilakukan dengan metode ceramah dan demonstrasi. Ceramah dilakukan oleh ketua tim dan dibantu oleh anggota tim. Ceramah dilakukan dengan pengantar pengenalan materi dan perubahannya diikuti dengan penjelasan tentang bentuk molekul dari zat yang ada dilingkungan sekitar. Demonstrasi dilakukan setelah ceramah dilakukan dengan menunjukkan cara mengunduh dan menginstal software avogadro serta cara menggambar molekul dengan software Avogadro. Hasil dari pelatihan ini diperoleh bahwa para peserta pelatihan (siswa-siswi SMP Negeri 27 Maluku Tengah) dapat mengerti tentang materi, atom, molekul dan bentuk molekul serta dapat menjalankan software Avogadro untuk menggambar bentuk molekul sederhana seperti air, cuka, dan minyak

The various power decays of the survival probability at long times for free quantum particle

The long time behaviour of the survival probability of initial state and its dependence on the initial states are considered, for the one dimensional free quantum particle. We derive the asymptotic expansion of the time evolution operator at long times, in terms of the integral operators. This enables us to obtain the asymptotic formula for the survival probability of the initial state $\psi (x)$, which is assumed to decrease sufficiently rapidly at large $|x|$. We then show that the behaviour of the survival probability at long times is determined by that of the initial state $\psi$ at zero momentum $k=0$. Indeed, it is proved that the survival probability can exhibit the various power-decays like $t^{-2m-1}$ for an arbitrary non-negative integers $m$ as $t \to \infty$, corresponding to the initial states with the condition $\hat{\psi} (k) = O(k^m)$ as $k\to 0$.Comment: 15 pages, to appear in J. Phys.

Irreversible Quantum Mechanics in the Neutral K-System

The neutral Kaon system is used to test the quantum theory of resonance scattering and decay phenomena. The two dimensional Lee-Oehme-Yang theory with complex Hamiltonian is obtained by truncating the complex basis vector expansion of the exact theory in Rigged Hilbert space. This can be done for K_1 and K_2 as well as for K_S and K_L, depending upon whether one chooses the (self-adjoint, semi-bounded) Hamiltonian as commuting or non-commuting with CP. As an unexpected curiosity one can show that the exact theory (without truncation) predicts long-time 2 pion decays of the neutral Kaon system even if the Hamiltonian conserves CP.Comment: 36 pages, 1 PostScript figure include

Analysis technique for exceptional points in open quantum systems and QPT analogy for the appearance of irreversibility

We propose an analysis technique for the exceptional points (EPs) occurring in the discrete spectrum of open quantum systems (OQS), using a semi-infinite chain coupled to an endpoint impurity as a prototype. We outline our method to locate the EPs in OQS, further obtaining an eigenvalue expansion in the vicinity of the EPs that gives rise to characteristic exponents. We also report the precise number of EPs occurring in an OQS with a continuum described by a quadratic dispersion curve. In particular, the number of EPs occurring in a bare discrete Hamiltonian of dimension $n_\textrm{D}$ is given by $n_\textrm{D} (n_\textrm{D} - 1)$; if this discrete Hamiltonian is then coupled to continuum (or continua) to form an OQS, the interaction with the continuum generally produces an enlarged discrete solution space that includes a greater number of EPs, specifically $2^{n_\textrm{C}} (n_\textrm{C} + n_\textrm{D}) [2^{n_\textrm{C}} (n_\textrm{C} + n_\textrm{D}) - 1]$, in which $n_\textrm{C}$ is the number of (non-degenerate) continua to which the discrete sector is attached. Finally, we offer a heuristic quantum phase transition analogy for the emergence of the resonance (giving rise to irreversibility via exponential decay) in which the decay width plays the role of the order parameter; the associated critical exponent is then determined by the above eigenvalue expansion.Comment: 16 pages, 7 figure

Climate Change and the Potential Spreading of Marine Mucilage and Microbial Pathogens in the Mediterranean Sea

Background: Marine snow (small amorphous aggregates with colloidal properties) is present in all oceans of the world. Surface water warming and the consequent increase of water column stability can favour the coalescence of marine snow into marine mucilage, large marine aggregates representing an ephemeral and extreme habitat. Marine mucilage characterize aquatic systems with altered environmental conditions. Methodology/Principal Findings: We investigated, by means of molecular techniques, viruses and prokaryotes within the mucilage and in surrounding seawater to examine the potential of mucilage to host new microbial diversity and/or spread marine diseases. We found that marine mucilage contained a large and unexpectedly exclusive microbial biodiversity and hosted pathogenic species that were absent in surrounding seawater. We also investigated the relationship between climate change and the frequency of mucilage in the Mediterranean Sea over the last 200 years and found that the number of mucilage outbreaks increased almost exponentially in the last 20 years. The increasing frequency of mucilage outbreaks is closely associated with the temperature anomalies. Conclusions/Significance: We conclude that the spreading of mucilage in the Mediterranean Sea is linked to climate-driven sea surface warming. The mucilage can act as a controlling factor of microbial diversity across wide oceanic regions and could have the potential to act as a carrier of specific microorganisms, thereby increasing the spread of pathogenic bacteria