The spin-1/2 square-lattice J_1-J_2 model: The spin-gap issue

We use the coupled cluster method to high orders of approximation in order to calculate the ground-state energy, the ground-state magnetic order parameter, and the spin gap of the spin-1/2 J_1-J_2 model on the square lattice. We obtain values for the transition points to the magnetically disordered quantum paramagnetic phase of J_2^{c1}=0.454J_1 and J_2^{c2}= 0.588 J_1. The spin gap is zero in the entire parameter region accessible by our approach, i.e. for J_2 \le 0.49J_1 and J_2 > 0.58J_1. This finding is in favor of a gapless spin-liquid ground state in this parameter regime.Comment: 10 pages, 3 figures, accepted versio

The magnetization process of the spin-one triangular-lattice Heisenberg antiferromagnet

We apply the coupled cluster method and exact diagonalzation to study the uniform susceptibility and the ground-state magnetization curve of the triangular-lattice spin-1 Heisenberg antiferromagnet. Comparing our theoretical data for the magnetization curve with recent measurements on the s=1 triangular lattice antiferromagnet Ba3NiSb2O9 we find a very good agreement.Comment: 2 pages, 3 figure

Geochemical Tracer in Coral as a Sea Surface Temperature Proxy: Records from Jukung Coral

Sr/Ca  has been analyzed from coral core from the Seribu Islands  reef complex  i.e  Jukung  Island.  SST  from  ERSST  dataset  and  air  temperature measured at Jakarta is used for Sr/Ca calibration. The results show that Jukung Island  coral  Sr/Ca  correlates  better  with  SST  than  with  air  temperature.  A comparison  between  the  Sr/Ca  records  with  the  Nino  3.4  index  shows  that Jukung  coral  sites  indicate  warming  sea  surface  temperatures  during  the beginning  of El Nino  events followed by cooling temperatures at the end of El Nino years

Geochemical Tracer in Coral as a Sea Surface Temperature Proxy: Records From Jukung Coral

Sr/Ca has been analyzed from coral core from the Seribu Islands reef complex i.e Jukung Island. SST from ERSST dataset and air temperature measured at Jakarta is used for Sr/Ca calibration. The results show that Jukung Island coral Sr/Ca correlates better with SST than with air temperature. A comparison between the Sr/Ca records with the Nino 3.4 index shows that Jukung coral sites indicate warming sea surface temperatures during the beginning of El Nino events followed by cooling temperatures at the end of El Nino years

Kinetic theory of cluster impingement in the framework of statistical mechanics of rigid disks

The paper centres on the evaluation of the function n(theta)=N(theta)/N0, that is the normalized number of islands as a function of coverage 0<theta<1, given N0 initial nucleation centres (dots) having any degree of spatial correlation. A mean field approach has been employed: the islands have the same size at any coverage. In particular, as far as the random distribution of dots is concerned, the problem has been solved by considering the contribution of binary collisions between islands only. With regard to correlated dots, we generalize a method previously applied to the random case only. In passing, we have made use of the exclusion probability reported in [S. Torquato, B. Lu, J. Rubinstein, Phys.Rev.A 41, 2059 (1990)], for determining the kinetics of surface coverage in the case of correlated dots, improving our previous calculation [M. Tomellini, M. Fanfoni, M. Volpe Phys. Rev.B 62, 11300, (2000)].Comment: 10 pages, 3 figure

Facies and faunal assemblage changes in response to the Holocene transgression in the Lagoon of Mayotte (Comoro Archipelago, SW Indian Ocean)

This paper documents the facies change in response to the Holocene transgression within five sediment cores taken in the lagoon of Mayotte, which contain a Type-1 depositional sequence (lowstand, transgressive and highstand deposits underlain by an erosive sequence boundary). Quantitative compositional analysis and visual examination of the bioclasts were used to document the facies changes. The distribution of the skeletal and non-skeletal grains in the lagoon of Mayotte is clearly controlled by (1) the rate and amplitude of the Holocene sea-level rise, (2) the pre-Holocene basement topography and (3) the growth-potential of the barrier reef during sea-level rise, and the changes in bathymetry and continuity during this period. The sequence boundary consists of the glacial karst surface. The change-over from the glacial lowstand is marked by the occurrence of mangrove deposits. Terrigenous and/or mixed terrigenous-carbonate muds to sandy muds with a mollusc or mollusc-ostracod assemblage dominate the transgressive deposits. Mixed carbonate-siliciclastic or carbonate sand to gravel with a mollusc-foraminifer or mollusc-coral-foraminifer assemblage characterize the early highstand deposits on the inner lagoonal plains. The early highstand deposits in the outer lagoonal plains consist of carbonate muds with a mollusc-foraminifer assemblage. Late highstand deposits consist of terrigenous muds in the nearshore bays, mixed terrigenous-carbonate sandy muds to sands with a mollusc-foraminifer assemblage on the inner lagoonal plains and mixed muds with a mollusc-foraminifer assemblage on the outer deep lagoonal plains. The present development stage of the individual lagoons comprises semi-enclosed to open lagoons with fair or good water exchange with the open ocean