Purely Magnetic Spacetimes

Purely magnetic spacetimes, in which the Riemann tensor satisfies $R_{abcd}u^bu^d=0$ for some unit timelike vector $u^a$, are studied. The algebraic consequences for the Weyl and Ricci tensors are examined in detail and consideration given to the uniqueness of $u^a$. Some remarks concerning the nature of the congruence associated with $u^a$ are made.Comment: 12 pages, standard latex. Submitted to Classical and Quantum Gravity

Peningkatan Kemampuan Menulis Pengumuman Melalui Metode Latihan Siswa Kelas IV SD Inpres 2 Gio Kecamatan Moutong

Permasalahan penelitian ini adalah apakah dengan menggunakan metode latihan dapat meningkatkan kemampuan menulis pengumuman siswa kelas IV SD Inpres 2 Gio Kecamatan Moutong? Tujuan penelitian ini untuk meningkatkan kemampuan menulis pengumuman melalui metode latihan siswa kelas IV SD Inpres 2 Gio Kecamatan Moutong. Sumber data siswa dan guru (peneliti). Jenis data adalah data kuantitatif berupa hasil evaluasi pada siklus I dan siklus II dan data kualitatif beupa hasil observasi aktivitas guru dan siswa. Subjek penelitian adalah siswa kelas IV berjumlah 27 siswa terdiri dari 12 laki-laki dan 15 perempuan. Proses penelitian tindakan kelas ini dilaksanakan dua siklus meliputi: (1) perncanaan, (2) pelaksanaan tindakan, (3) Observasi, (4) Refleksi. Hasil evaluasi siswa siklus I rata-rata daya serap 71,07 % dengan presentase ketuntasan klasikal 63 % siklus II nilai rata-rata daya serap meningkat menjadi 79,88 dengan ketuntasan klasikal 93%. Hasil observasi guru siklus I sebesar 75% kategori cukup siklus II sebesar 82% kategori baik. Hasil observasi siswa siklus I sebesar 77,5% kategori cukup siklus II sebesar 82,50% kategori baik. Berdasarkan data tersebut, menunjukan bahwa metode latihan dapat meningkatkan kemampuan menulis pengumuman siswa kelas IV SD Inpres 2 Gio Kecamatan Moutong

Evaluation of greenwaste mulch to control runoff quality from landfill sites during frequent storms

This paper describes a preliminary evaluation of two types of greenwaste (fresh and aged) used as a mulch layer to control runoff from disturbed landfill areas. Fresh greenwaste refers to woody and herbaceous garden waste that has been recently collected, chopped and shredded. Aged greenwaste is greenwaste which has been stockpiled for 18 months. We used rainfall simulator tests to investigate two aspects: (1) the performance of greenwaste mulch in reducing runoff during designed storm events with a high frequency of occurrence and (2) the release of pollutants via runoff as total suspended solids (TSS) and total organic carbon (TOC) during rain. Rainfall of <5-year average recurrence interval (ARI) was generally applied, consistent with stormwater compliance requirements for many Australian landfills. TOC released from fresh greenwaste material was higher in concentration than from aged greenwaste. However when used as a 10cm-deep mulch layer, fresh greenwaste was able to completely prevent runoff, even when tested under rainfalls up to 50 year ARI duration. An equivalent mulch layer of aged greenwaste was also effective in reducing runoff volume and TSS concentration compared with the bare soil during a 3.5-year ARI rainfall, but mean TOC concentration was higher. Based on these preliminary results, fresh greenwaste mulching of bare soils is an attractive option to control runoff and erosion from areas subject to intermittent landfill operations and worthy of further investigations

Length and time scale divergences at the magnetization-reversal transition in the Ising model

The divergences of both the length and time scales, at the magnetization- reversal transition in Ising model under a pulsed field, have been studied in the linearized limit of the mean field theory. Both length and time scales are shown to diverge at the transition point and it has been checked that the nature of the time scale divergence agrees well with the result obtained from the numerical solution of the mean field equation of motion. Similar growths in length and time scales are also observed, as one approaches the transition point, using Monte Carlo simulations. However, these are not of the same nature as the mean field case. Nucleation theory provides a qualitative argument which explains the nature of the time scale growth. To study the nature of growth of the characteristic length scale, we have looked at the cluster size distribution of the reversed spin domains and defined a pseudo-correlation length which has been observed to grow at the phase boundary of the transition.Comment: 9 pages Latex, 3 postscript figure

Dynamic Magnetization-Reversal Transition in the Ising Model

We report the results of mean field and the Monte Carlo study of the dynamic magnetization-reversal transition in the Ising model, brought about by the application of an external field pulse applied in opposition to the existing order before the application of the pulse. The transition occurs at a temperature T below the static critical temperature T_c without any external field. The transition occurs when the system, perturbed by the external field pulse competing with the existing order, jumps from one minimum of free energy to the other after the withdrawal of the pulse. The parameters controlling the transition are the strength h_p and the duration Delta t of the pulse. In the mean field case, approximate analytical expression is obtained for the phase boundary which agrees well with that obtained numerically in the small Delta t and large T limit. The order parameter of the transition has been identified and is observed to vary continuously near the transition. The order parameter exponent beta was estimated both for the mean field (beta =1) and the Monte Carlo beta = 0.90 \pm 0.02 in two dimension) cases. The transition shows a "critical slowing-down" type behaviour near the phase boundary with diverging relaxation time. The divergence was found to be logarithmic in the mean field case and exponential in the Monte Carlo case. The finite size scaling technique was employed to estimate the correlation length exponent nu (= 1.5 \pm 0.3 in two dimension) in the Monte Carlo case.Comment: 13 pages, latex, 8 figure

Gluon Condensates, Chiral Symmetry Breaking and Pion Wave Function

We consider here chiral symmetry breaking in quantum chromodynamics arising from gluon condensates in vacuum. Through coherent states of gluons simulating a mean field type of approximation, we show that the off-shell gluon condensates of vacuum generate a mass-like contribution for the quarks, giving rise to chiral symmetry breaking. We next note that spontaneous breaking of global chiral symmetry links the four component quark field operator to the pion wave function. This in turn yields many hadronic properties in the light quark sector in agreement with experiments, leading to the conclusion that low energy hadron properties are primarily driven by the vacuum structure of quantum chromodynamics.Comment: 25 pages, IP/BBSR/92-76, revte