On the definition of matter collineations

It is shown that when the stress-energy tensor of a spacetime is diagonal and is written in the mixed form, its collineations admit infinite dimensional Lie algebras except possibly in the case when the tensor depends on all the spacetime coordinates. The result can be extended for more general second rank tensors

Greybody factor of scalar fields from black strings

The greybody factor of massless, uncharged scalar fields is studied in the background of cylindrically symmetric spacetimes, in the low-energy approximation. We discuss two cases. In the first case we derive analytical expression for the absorption probability when the spacetime is kinetically coupled with the Einstein tensor. In the second case we do the analysis in the absence of the coupling constant. For this purpose we analyze the wave equation which is obtained from Klein-Gordon equation. The radial part of the wave equation is solved in the form of the hypergeometric function in the near horizon region, whereas in the far region the solution is of the form of Bessel's function. Finally, considering continuity of the wave function we smoothly match the two solutions in the low energy approximation to get the formula for the absorption probability

Classification of spacetimes according to conformal Killing vectors

Conformal Killing vectors (CKVs) preserve the spacetime metric up to a factor. Homothetic vectors and Killing vectors are special cases of CKVs. Classification of some classes of spacetimes on the basis of CKVs give interesting results showing how homothetic and Killing vectors which form subsets of the set of CKVs can be recovered as a result of the above classification.Comment: 4 page

KERAGAMAN PARASITOID SEBAGAI MUSUH ALAMI HAMA PADA PADI SAWAH DI KABUPATEN ACEH BESAR

ABSTRAKEksplorasi Parasitoid Sebagai Musuh Alami Hama Pada Padi Sawah di Kabupaten Aceh BesarSaifullah 1), Jauharlina2), Husni2)1Program Studi Agroteknologi, Fakultas Pertanian, Universitas Syiah Kuala 2Program Studi Proteksi Tanaman, Fakultas Pertanian, Universitas Syiah Kuala Abstrak. Dalam ekosistem sawah serangga parasitoid merupakan salah satu musuh alami yang banyak memberikan keuntungan karena selain aman terhadap lingkungan juga dapat berkembang secara alami. Penelitian ini bertujuan untuk mengetahui keragaman dan kelimpahan parasitoid yang terdapat pada tanaman padi sawah di Kabupaten Aceh Besar. Penelitian dilakukan dengan cara pengambilan sampel di Kabupaten Aceh Besar dari dua Kecamatan yaitu Kecamatan Blang Bintang dan Kecamatan Lembah Seulawah. Pengambilan sampel dilakukan dua kali yaitu masa vegetatif (35 HST) dan generatif (55 HST). Pengambilan sampel dilakukan dengan menggumpulkan kelompok telur, larva dan pupa secara kumulatif. Hasil penelitian menunjukkan bahwa Jenis- jenis musuh alami parasitoid yang berhasil ditemukan pada tanaman padi sawah di Kabupaten Aceh Besar terdiri dari 2 Ordo, 7 Family dan 13 Spesies. Kelimpahan musuh alami tertinggi yaitu spesies Tetrastichus schoenobii (Hymenoptera : Eulophidae) dan Apanteles sp. (Hymenoptera : Braconidae) dan nilai indeks keanekaragaman di Kabupaten Aceh Besar memiliki nilai dengan kategori buruk dan dengan kondisi struktur komunitas tidak stabil.Kata kunci : Pengendalian hayati, Populasi parasitoid, Keanekaragama