Correlated ab-initio calculations for ground-state properties of II-VI semiconductors

Correlated ab-initio ground-state calculations, using relativistic energy-consistent pseudopotentials, are performed for six II-VI semiconductors. Valence ($ns,np$) correlations are evaluated using the coupled cluster approach with single and double excitations. An incremental scheme is applied based on correlation contributions of localized bond orbitals and of pairs and triples of such bonds. In view of the high polarity of the bonds in II-VI compounds, we examine both, ionic and covalent embedding schemes for the calculation of individual bond increments. Also, a partitioning of the correlation energy according to local ionic increments is tested. Core-valence ($nsp,(n-1)d$) correlation effects are taken into account via a core-polarization potential. Combining the results at the correlated level with corresponding Hartree-Fock data we recover about 94% of the experimental cohesive energies; lattice constants are accurate to \sim 1%; bulk moduli are on average 10% too large compared with experiment.Comment: 10 pages, twocolumn, RevTex, 3 figures, accepted Phys. Rev.

Influence of electron correlations on ground-state properties of III-V semiconductors

Lattice constants and bulk moduli of eleven cubic III-V semiconductors are calculated using an ab initio scheme. Correlation contributions of the valence electrons, in particular, are determined using increments for localized bonds and for pairs and triples of such bonds; individual increments, in turn, are evaluated using the coupled cluster approach with single and double excitations. Core-valence correlation is taken into account by means of a core polarization potential. Combining the results at the correlated level with corresponding Hartree-Fock data, we obtain lattice constants which agree with experiment within an average error of -0.2%; bulk moduli are accurate to +4%. We discuss in detail the influence of the various correlation contributions on lattice constants and bulk moduli.Comment: 4 pages, Latex, no figures, Phys. Rev. B, accepte

CEP-stable Tunable THz-Emission Originating from Laser-Waveform-Controlled Sub-Cycle Plasma-Electron Bursts

We study THz-emission from a plasma driven by an incommensurate-frequency two-colour laser field. A semi-classical transient electron current model is derived from a fully quantum-mechanical description of the emission process in terms of sub-cycle field-ionization followed by continuum-continuum electron transitions. For the experiment, a CEP-locked laser and a near-degenerate optical parametric amplifier are used to produce two-colour pulses that consist of the fundamental and its near-half frequency. By choosing two incommensurate frequencies, the frequency of the CEP-stable THz-emission can be continuously tuned into the mid-IR range. This measured frequency dependence of the THz-emission is found to be consistent with the semi-classical transient electron current model, similar to the Brunel mechanism of harmonic generation

OPTIMASI BIAYA DISTRIBUSI MATERIAL DENGAN METODE NWC (NORTH WEST CORNER) (STUDI KASUS : PEMBANGUNAN GEDUNG LABORATORIUM FAKULTAS TEKNIK UNIVERSITAS SAM RATULANGI)

Proses pendistribusian material merupakan salah satu aspek yang sangat penting untuk direncanakan, karena akan sangat berpengaruh terhadap efisiensi biaya proyek secara keseluruhan. Meningkatnya biaya proyek seringkali diakibatkan oleh proses pendistribusian material yang tidak optimal. Hal ini dapat terjadi terutama jika pekerjaan yang sedang ditangani terdiri dari beberapa proyek yang membutuhkan material dalam jumlah yang besar, dimana satu lokasi pengambilan material saja tidak akan mampu untuk mencukupi seluruh kebutuhan yang ada.Perbedaan jarak antara sejumlah sumber dengan lokasi-lokasi proyek yang ada ditambah perbedaan harga material di setiap sumber menyebabkan pihak pelaksana proyek harus menentukan suatu cara untuk mendapatkan material yang dibutuhkan dengan biaya distribusi minimum. Untuk itu diperlukan adanya metode yang dapat mengoptimalkan biaya distribusi material dari pemasalahan ini, seperti Metode North West Corner.Dari hasil pengolahan data menunjukkan bahwa dengan menggunakan Metode North West Corner, pada kasus yang ditinjau, didapatkan biaya distribusi bahan material untuk Semen sebesar Rp. 2.146.155.000,00; Pasir sebesar Rp. 123.331.214,20; dan Kerikil sebesar Rp. 698.879.141,20. Kata kunci: Optimasi, efisiensi, biaya, distribusi, material, proyek, Metode North West Corne

Cohesive energies of cubic III-V semiconductors

Cohesive energies for twelve cubic III-V semiconductors with zincblende structure have been determined using an ab-initio scheme. Correlation contributions, in particular, have been evaluated using the coupled-cluster approach with single and double excitations (CCSD). This was done by means of increments obtained for localized bond orbitals and for pairs and triples of such bonds. Combining these results with corresponding Hartree-Fock data, we recover about 92 \% of the experimental cohesive energies.Comment: 16 pages, 1 figure, late

Ground-state properties of rutile: electron-correlation effects

Electron-correlation effects on cohesive energy, lattice constant and bulk compressibility of rutile are calculated using an ab-initio scheme. A competition between the two groups of partially covalent Ti-O bonds is the reason that the correlation energy does not change linearly with deviations from the equilibrium geometry, but is dominated by quadratic terms instead. As a consequence, the Hartree-Fock lattice constants are close to the experimental ones, while the compressibility is strongly renormalized by electronic correlations.Comment: 1 figure to appear in Phys. Rev.

Harmonic Generation from Relativistic Plasma Surfaces in Ultra-Steep Plasma Density Gradients

Harmonic generation in the limit of ultra-steep density gradients is studied experimentally. Observations demonstrate that while the efficient generation of high order harmonics from relativistic surfaces requires steep plasma density scale-lengths ($L_p/\lambda < 1$) the absolute efficiency of the harmonics declines for the steepest plasma density scale-length $L_p \to 0$, thus demonstrating that near-steplike density gradients can be achieved for interactions using high-contrast high-intensity laser pulses. Absolute photon yields are obtained using a calibrated detection system. The efficiency of harmonics reflected from the laser driven plasma surface via the Relativistic Oscillating Mirror (ROM) was estimated to be in the range of 10^{-4} - 10^{-6} of the laser pulse energy for photon energies ranging from 20-40 eV, with the best results being obtained for an intermediate density scale-length

TRANSPLANTASI KARANG BATU BERCABANG DI PERAIRAN TANJUNG PAPUTUNGAN

The formation of coral reefs is a long and complex process. The process of forming coral reefs begins with the attachment of various lime-producing biota on a hard substrate. Coral reefs take quite a long time to recover and are highly dependent on water conditions. Until now, pressures caused by human activities such as pollution from land and destructive fisheries practices have been considered a major threat to coral reefs. Efforts to overcome damage to coral reef ecosystems can be done by developing coral transplantation techniques. In response to this, the research wiil apply the method of artificial reefs from concrete blocks as a container for the installation of colonies of Acropora formosa spesies and Porites cylindrica spesies. A total of 75 branched coral colonies were transplanted in the waters of 75 branched coral colonies were transplanted in the waters of the Paputungan cape 39 colonies of branched growth forms of Acropora form and 36 colonies of branched grotwth forms of Porites cylindrica spesies were transplanted in artificial reef units. Data collection in the field in the form colonies that were successfully transplanted into artificial reef units totaling 6 units will be documented using cameras from each block taken perpendicular pictures and photographing colonies from earch artificial reef unit. The results of the shoot were then analyzed using software of the Image-J application. At the end of the observation process, it was found that the highest resistence of transplane colonies was 97.2 % where there were 35 surviving colonies and 1 dead colony out of a total of 36 colonies transplanted by Porites cylindrica spesies. Meanwhile, observations found that the lowest resistnce of transplant colonies that survived and 13 colonies that died out of a total of 39 colonies transplanted by acropora formosa spesies. Acropora formosa has a relatively fast increase compared to Porites cylindrica spesies. The highest accretion was dominated by the 18.05 mm fragment-size Acropora formosa spesies at the end of the sixth lunar observation.Keywords: Restoration, transplantation, Branching Coral, Tanjung Paputungan, North Minahasa ABSTRAKTerbentuknya terumbu karang merupakan suatu proses yang lama dan kompleks. Proses terbentuknya terumbu karang dimulai dengan penempelan berbagai biota penghasil kapur pada substrat yang keras. Terumbu karang membutuhkan waktu yang cukup lama untuk pulih kembali dan sangat tergantung dari kondisi perairan. Hingga kini, tekanan yang disebabkan oleh kegiatan manusia seperti pencemaran dari daratan dan praktek perikanan yang merusak telah dianggap sebagai ancaman utama untuk terumbu karang. Upaya penanggulangan kerusakan ekosistem terumbu karang dapat dilakukan dengan menggembangkan teknik transplantasi karang (coral transplantation). Menanggapi hal tersebut, maka dalam penelitian kali akan menerapkan metode terumbu buatan dari blok beton sebagai wadah untuk pemasangan koloni spesies Acropora formosa dan spesies Porites cylindrica. Sebanyak 75 koloni karang bercabang yang di transplantasi di perairan tanjung Paputungan 39 koloni bentuk pertumbuhan bercabang spesies Acropora formosa dan 36 koloni bentuk pertumbuhan bercabang spesies Porites cylindrica ditransplantasikan pada unit terumbu buatan. Pengambilan data dilapangan berupa Koloni yang berhasil di transplantasi ke unit terumbu buatan berjumlah 6 unit akan didokumentasikan menggunakan kamera dari tiap-tiap blok di ambil gambar tegak lurus dan memotret koloni dari masing-masing unit terumbu buatan. Hasil pemotretan tersebut selanjutnya dianalisa menggunakan sofware atau aplikasi Image-J. Akhir proses pengamatan ditemukan bahwa ketahanan koloni transplan tertinggi yaitu 97,2 % dimana terdapat 35 koloni yang bertahan hidup dan 1 koloni yang mati dari total 36 koloni yang di transplantasi spesies Porites cylindrica. Sedangkan pengamatan ditemukan bahwa ketahanan koloni transplan terendah yaitu 66,6 % dimana terdapat 26 koloni yang bertahan hidup dan 13 koloni yang mati dari total 39 koloni yang di transplantasi spesies Acropora formosa. Acropora formosa mempunyai pertambahan relatif cepat di bandingkan janis Porites cylindrica. Pertambahan paling tinggi didominasi oleh spesies Acropora formosa ukuran fragmen 18,05 mm di akhir pengamatan bulan keenam.Kata Kunci: Restorasi, Transplantasi, Karang bercabang, Tanjung Paputungan, Minahasa Utar