Anisotropic thermal expansion of bismuth from first principles

Some anisotropy in both mechanical and thermodynamical properties of bismuth is expected. A combination of density functional theory total energy calculations and density functional perturbation theory in the local density approximation is used to compute the elastic constants at 0 K using a finite strain approach and the thermal expansion tensor in the quasiharmonic approximation. The overall agreement with experiment is good. Furthermore, the anisotropy in the thermal expansion is found to arise from the anisotropy in both the directional compressibilities and the directional Gr\"uneisen functions.Comment: accepted for publication in PR

Research Performance of the ASEAN University Network Member Universities

The purpose of this research paper is to describe the research outputs of the member universities of the ASEAN University Network (AUN). The paper is an inductive type of research that used a variety of information from Scopus to determine what AUN member universities are actively writing about. The author captured data from 1997 to 2017 from scopus.com to analyze what the AUN member universities and their respective countries have been studying. Results show that almost 50% of the total research outputs of all the ASEAN nations are contributed by the AUN member Universities, with Singapore’s NUS and NUT contributing 76% of Singapore’s total research outputs, while the Philippines’ DLSU, ADMU, and UP contributes 50%. Wealthy nations such as Singapore and Malaysia have been focusing their researches on engineering and computer sciences while countries like the Philippines, Laos, and Cambodia have been researching about agriculture and biological sciences. Another study can be conducted to show research activities of the different universities all over Asia, including those that are not part of the ASEAN University Network

Destroying coherence in high temperature superconductors with current flow

The loss of single-particle coherence going from the superconducting state to the normal state in underdoped cuprates is a dramatic effect that has yet to be understood. Here, we address this issue by performing angle resolved photoemission spectroscopy (ARPES) measurements in the presence of a transport current. We find that the loss of coherence is associated with the development of an onset in the resistance, in that well before the midpoint of the transition is reached, the sharp peaks in the ARPES spectra are completely suppressed. Since the resistance onset is a signature of phase fluctuations, this implies that the loss of single-particle coherence is connected with the loss of long-range phase coherence.Comment: 7 pages, 7 figure

Efisiensi Produksi Padi di Kecamatan Kuala Kampar Kabupaten Pelalawan

Kecamatan Kuala Kampar sebagai daerah sentra produksi padi di kabupaten Pelalawan merupakan daerah yang diharapkan mampu menjaga stabilitas ketersediaan beras di Kabupaten Pelalawan. Tapi dalam Kenyataannya, produksi padi Kecamatan Kuala Kampar cendrung mengalami kenaikan namun juga mengalami penurunan. Produksi yang efisien akan menyebabkan penurunan biaya produksi yang selanjutnya akan menyebabkan peningkatan pendapatan petani. Secara umum penelitian ini bertujuan untuk menganalisis faktor produksi dan tingkat efisiensi penggunaan faktor produksi tanaman padi. Secara khusus tujuan penelitian adalah: (1) Mengetahui karakteristik petani padi sawah pasang surut, (2) Menganalisis faktor yang mempengaruhi produksi padi, (3) Menganalisis efisiensi teknis, alokatif dan ekonomi. Metode analisis yang digunakan adalah analisis deskriptif untuk menjawab tujuan pertama, analisis fungsi produksi Cobb-douglas untuk menjawab tujuan kedua, Data Envelopment Analysis (DEA) untuk tujuan ketiga. Hasil penelitian menunjukkan bahwa secara statistik variabel luas lahan, jumlah benih, pupuk KCl, pupuk SP36, pupuk NPK, tenaga kerja, dan dummy penggunaan bibit unggul berpengaruh nyata terhadap produksi padi. Umumnya petani responden telah efisien secara teknis namun belum efisien secara alokatif dan ekonomis

Protected nodes and the collapse of the Fermi arcs in high Tc cuprates

Angle resolved photoemission on underdoped Bi2Sr2CaCu2O8 reveals that the magnitude and d-wave anisotropy of the superconducting state energy gap are independent of temperature all the way up to Tc. This lack of T variation of the entire k-dependent gap is in marked contrast to mean field theory. At Tc the point nodes of the d-wave gap abruptly expand into finite length ``Fermi arcs''. This change occurs within the width of the resistive transition, and thus the Fermi arcs are not simply thermally broadened nodes but rather a unique signature of the pseudogap phase.Comment: Accepted by Phys. Rev. Let

Pairing in cuprates from high energy electronic states

The in-plane optical conductivity of Bi2Sr2CaCu2O8+d thin films with small carrier density (underdoped) up to large carrier density (overdoped) is analyzed with unprecedented accuracy. Integrating the conductivity up to increasingly higher energies points to the energy scale involved when the superfluid condensate builds up. In the underdoped sample, states extending up to 2 eV contribute to the superfluid. This anomalously large energy scale may be assigned to a change of in-plane kinetic energy at the superconducting transition, and is compatible with an electronic pairing mechanism.Comment: 11 pages, 3 figure

The change of Fermi surface topology in Bi2Sr2CaCu2O8 with doping

We report the observation of a change in Fermi surface topology of Bi2Sr2CaCu2O8 with doping. By collecting high statistics ARPES data from moderately and highly overdoped samples and dividing the data by the Fermi function, we answer a long standing question about the Fermi surface shape of Bi2Sr2CaCu2O8 close to the (pi,0) point. For moderately overdoped samples (Tc=80K) we find that both the bonding and antibonding sheets of the Fermi surface are hole-like. However for a doping level corresponding to Tc=55K we find that the antibonding sheet becomes electron-like. This change does not directly affect the critical temperature and therefore the superconductivity. However, since similar observations of the change of the topology of the Fermi surface were observed in LSCO and Bi2Sr2Cu2O6, it appears to be a generic feature of hole-doped superconductors. Because of bilayer splitting, though, this doping value is considerably lower than that for the single layer materials, which again argues that it is unrelated to Tc

Identifying the Background Signal in ARPES of High Temperature Superconductors

One of the interesting features of the photoemission spectra of the high temperature cuprate superconductors is the presence of a large signal (referred to as the "background'') in the unoccupied region of the Brillouin zone. Here we present data indicating that the origin of this signal is extrinsic and is most likely due to strong scattering of the photoelectrons. We also present an analytical method that can be used to subtract the background signal