The dynamics of cracks in torn thin sheets

Motivated by recent experiments, we present a study of the dynamics of cracks in thin sheets. While the equations of elasticity for thin plates are well known, there remains the question of path selection for a propagating crack. We invoke a generalization of the principle of local symmetry to provide a criterion for path selection and demonstrate qualitative agreement with the experimental findings. The nature of the singularity at the crack tip is studied with and without the interference of nonlinear terms.Comment: 7 pages, 11 figure

Exhaustion of Nucleation in a Closed System

We determine the distribution of cluster sizes that emerges from an initial phase of homogeneous aggregation with conserved total particle density. The physical ingredients behind the predictions are essentially classical: Super-critical nuclei are created at the Zeldovich rate, and before the depletion of monomers is significant, the characteristic cluster size is so large that the clusters undergo diffusion limited growth. Mathematically, the distribution of cluster sizes satisfies an advection PDE in "size-space". During this creation phase, clusters are nucleated and then grow to a size much larger than the critical size, so nucleation of super-critical clusters at the Zeldovich rate is represented by an effective boundary condition at zero size. The advection PDE subject to the effective boundary condition constitutes a "creation signaling problem" for the evolving distribution of cluster sizes during the creation era. Dominant balance arguments applied to the advection signaling problem show that the characteristic time and cluster size of the creation era are exponentially large in the initial free-energy barrier against nucleation, G_*. Specifically, the characteristic time is proportional to exp(2 G_*/ 5 k_B T) and the characteristic number of monomers in a cluster is proportional to exp(3G_*/5 k_B T). The exponentially large characteristic time and cluster size give a-posteriori validation of the mathematical signaling problem. In a short note, Marchenko obtained these exponentials and the numerical pre-factors, 2/5 and 3/5. Our work adds the actual solution of the kinetic model implied by these scalings, and the basis for connection to subsequent stages of the aggregation process after the creation era.Comment: Greatly shortened paper. Section on growth model removed. Added a section analyzing the error in the solution of the integral equation. Added reference

Kontribusi Pelestarian Hutan Mangrove terhadap Tingkat Pendapatan Anggota Kelompok Pengelola (Kpm) Belukap Desa Teluk Pambang Kecamatan Bantan Kabupaten Bengkalis Provinsi Riau

Mangrove forests are important life-supporting ecosistem in coastal areas. According to Macnae (1968), mangrove is defined as a group of vegetation that grow between the highest water level during high tide and the lowest water level during low tide. At Teluk Pambang village, an organization called Kelompok Pengelola Mangrove (KPM) Belukap was formed due to the anxiety of nearby people to further irresponsible demage of mangrove forests. After the co-fish project, a group was created to manage and project mangrove forests for fishery activities. This research aims to study the contribution of mangrove forest conservation to the income of KPM Belukap at Teluk Pambang village, Kecamatan Bantan, Kabupaten Bengkalis, Riau Province. Contribution of mangrove forest conservation and income data were collected, tabulated, analyzed. Income data were collected descriptively using survey papers. Analysis result show that the conservation of mangrove forests increase the income of KPM Belukap by 1,20% to 3,75%

Identifikasi Potensi Ekowisata Hutan Kota Pulau Bungin Kabupaten Kuantan Singingi

At this time the building of forest city pulau bungin still in step as the trees habitats in the middle of city that's why need the data about potency ecotourism of forest city pulau bungin located at kota taluk kuantan, kuantan singingi regency. This research doing at forest city pulau bungin, kuantan singingi regency, Riau province, helded at April-mei 2016. From the result of this reseach can conclude that the potency ecotourism of forest city located in forest city pulau bungin is pendopo, traditional track, jogging track, bridge, fruits forest, chair. The potency ecotourism of that very interesting in forest city pulau bungin is Fruits tree with precentage 48% and interesting category

Regulating the Energy Flow in a Cyanobacterial Light Harvesting Antenna Complex

Photosynthetic organisms harvest light energy, utilizing the absorption and energy transfer properties of protein-bound chromophores. Controlling the harvesting efficiency is critical for the optimal function of the photosynthetic apparatus. Here, we show that cyanobacterial light-harvesting antenna may be able to regulate the flow of energy in order to switch reversibly from efficient energy conversion to photo-protective quenching via a structural change. We isolated cyanobacterial light harvesting proteins, phycocyanin and allophycocyanin, and measured their optical properties in solution and in an aggregated-desiccated state. The results indicate that energy band structures are changed, generating a switch between two modes of operation: exciton transfer and quenching; achieved without dedicated carotenoid quenchers. This flexibility can contribute greatly to the large dynamic range of cyanobacterial light harvesting systems.Comment: Published at J. Phys. Chem.

Accounting for Memory Bank Contention and Delay in High-Bandwidth Multiprocessors

This paper considers issues of memory performance in shared memory multiprocessors that provide a high-bandwidth network and in which the memory banks are slower than the processors. We are concerned with the effects of memory bank contention, memory bank delay, and the bank expansion factor (the ratio of number of banks to number of processors) on performance, particularly for irregular memory access patterns. This work was motivated by observed discrepancies between predicted and actual performance in a number of irregular algorithms implemented for the cray C90 when the memory contention at a particular location is high. We develop a formal framework for studying memory bank contention and delay, and show several results, both experimental and theoretical. We first show experimentally that our framework is a good predictor of performance on the cray C90 and J90, providing a good accounting of bank contention and delay. Second, we show that it often improves performance to have addi..