Estimates of air–sea feedbacks on sea surface temperature anomalies in the southern ocean

Sea surface temperature (SST) air–sea feedback strengths and associated decay time scales in the Southern Ocean (SO) are estimated from observations and reanalysis datasets of SST, air–sea heat fluxes, and ocean mixed layer depths. The spatial, seasonal, and scale dependence of the air–sea heat flux feedbacks is mapped in circumpolar bands and implications for SST persistence times are explored. It is found that the damping effect of turbulent heat fluxes dominates over that due to radiative heat fluxes. The turbulent heat flux feedback acts to damp SSTs in all bands and spatial scales and in all seasons, at rates varying between 5 and 25 W m⁻² K⁻¹, while the radiative heat flux feedback has a more uniform spatial distribution with a magnitude rarely exceeding 5 W m⁻² K⁻¹. In particular, the implied net air–sea feedback (turbulent + radiative) on SST south of the polar front, and in the region of seasonal sea ice, is as weak as 5–10 W m⁻² K⁻¹ in the summertime on large spatial scales. Air–sea interaction alone thus allows SST signals induced around Antarctica in the summertime to persist for several seasons. The damping effect of mixed layer entrainment on SST anomalies averages to approximately 20 W m⁻² K⁻¹ across the ACC bands in the summer-to-winter entraining season and thereby reduces summertime SST persistence to less than half of that predicted by air–sea interaction alone (i.e., 3–6 months).National Science Foundation (U.S.). Frontiers in Earth System Dynamic

Dense Ionized and Neutral Gas Surrounding Sgr A*

We present high resolution H41a hydrogen recombination line observations of the 1.2' (3 pc) region surrounding Sgr A* at 92 GHz using the OVRO Millimeter Array with an angular resolution of 7" x 3" and velocity resolution of 13 km/s. New observations of H31a, H35a, H41a, and H44a lines were obtained using the NRAO 12-m telescope, and their relative line strengths are interpreted in terms of various emission mechanisms. These are the most extensive and most sensitive observations of recombination line to date. Observations of HCO+ (1 - 0) transition at 89 GHz are also obtained simultaneously with a 40% improved angular resolution and 4-15 times improved sensitivity over previous observations, and the distribution and kinematics of the dense molecular gas in the circumnuclear disk (CND) are mapped and compared with those of the ionized gas. The line brightness ratios of the hydrogen recombination lines are consistent with purely spontaneous emission from 7000 K gas with n_e = 20,000 cm$^{-3}$ near LTE condition. A virial analysis suggests that the most prominent molecular gas clumps in the CND have mean densities of 10^7 cm^{-3}, sufficient to withstand the tidal shear in the Galactic Center region. Therefore, these clumps may survive over several dynamical times, and the CND may be a dynamically stable structure. We estimate a total gas mass of 3 x 10^5 solar mass for the CND. \Comment: 34 pages including 11 figures (4 jpgs), Latex, uses aastex. The full pdf format file including high resolution figures is available at http://www.astro.umass.edu/~myun/papers/SgrA.pdf . To appear in the 20 November 2004 (V616) issue of the Astrophysical Journa

EUVE J0425.6-5714: A Newly Discovered AM Herculis Star

We detected a new AM Her star serendipitously in a 25 day observation with the EUVE satellite. A coherent period of 85.82 min is present in the EUVE Deep Survey imager light curve of this source. A spectroscopic identification is made with a 19th magnitude blue star that has H and He emission lines, and broad cyclotron humps typical of a magnetic cataclysmic variable. A lower limit to the polar magnetic field of 46 MG is estimated from the spacing of the cyclotron harmonics. EUVE J0425.6-5714 is also detected in archival ROSAT HRI observations spanning two months, and its stable and highly structured light curve permits us to fit a coherent ephemeris linking the ROSAT and EUVE data over a 1.3 yr gap. The derived period is 85.82107 +/- 0.00020 min, and the ephemeris should be accurate to 0.1 cycles until the year 2005. A narrow but partial X-ray eclipse suggests that this object belongs to the group of Am Her stars whose viewing geometry is such that the accretion stream periodically occults the soft X-ray emitting accretion spot on the surface of the white dwarf. A non-detection of hard X-rays from ASCA observations that are contemporaneous with the ROSAT HRI shows that the soft X-rays must dominate by at least an order of magnitude, which is consistent with a known trend among AM Her stars with large magnetic field. This object should not be confused with the Seyfert galaxy 1H 0419-577 (= LB 1727), another X-ray/EUV source which lies only 4' away, and was the principal target of these monitoring observations.Comment: 13 pages, 5 figures, to appear in PASP, Dec. 1998 issu

Numerical and approximate analytical results for the frustrated spin-1/2 quantum spin chain

We study the $T=0$ frustrated phase of the $1D$ quantum spin-$\frac 12$ system with nearest-neighbour and next-nearest-neighbour isotropic exchange known as the Majumdar-Ghosh Hamiltonian. We first apply the coupled-cluster method of quantum many-body theory based on a spiral model state to obtain the ground state energy and the pitch angle. These results are compared with accurate numerical results using the density matrix renormalisation group method, which also gives the correlation functions. We also investigate the periodicity of the phase using the Marshall sign criterion. We discuss particularly the behaviour close to the phase transitions at each end of the frustrated phase.Comment: 17 pages, Standard Latex File + 7 PostScript figures in separate file. Figures also can also be requested from [email protected]

Cooperation and defection in ghetto

We consider ghetto as a community of people ruled against their will by an external power. Members of the community feel that their laws are broken. However, attempts to leave ghetto makes their situation worse. We discuss the relation of the ghetto inhabitants to the ruling power in context of their needs, organized according to the Maslow hierarchy. Decisions how to satisfy successive needs are undertaken in cooperation with or defection the ruling power. This issue allows to construct the tree of decisions and to adopt the pruning technique from the game theory. Dynamics of decisions can be described within the formalism of fundamental equations. The result is that the strategy of defection is stabilized by the estimated payoff.Comment: 12 pages, 2 figure

Modeling the Ecological and Phenological Predictors of Fruit Consumption by Gibbons (Hylobates albibarbis)

Understanding the ecological interactions between plant reproductive strategies and frugivore feeding behavior can offer insight into the maintenance of tropical forest biodiversity. We examined the role of plant ecological and phenological characteristics in influencing fruit consumption by the White‐bearded gibbon (Hylobates albibarbis) in Gunung Palung National Park, Indonesian Borneo. Gibbons are widespread across Borneo, highly frugivorous and perform important seed dispersal services. We compare multiple models using information criteria to identify the ecological and phenological predictors that most strongly influence gibbon fruit use of 154 plant genera. The most important predictors of resource use were the overall abundance of a genus and the consistency of fruit availability. Plant genera can maintain constant fruit availability as a result of (1) individual stems fruiting often or (2) stems fruiting out of synchrony with each other (asynchrony). Our results demonstrate that gibbons prefer to feed on plant genera that provide consistent fruit availability due to fruiting asynchrony. Because gibbons feed more often on genera that fruit asynchronously, gibbons are more likely to disperse seeds of plant genera with this reproductive strategy. Research on other frugivorous species is needed to determine whether the results for gibbons are generalizable more broadly. Finally, these results suggest that asynchronously fruiting plant genera may be particularly important for habitat restoration in tropical forests designed for frugivore conservation.RingkasanPemahaman mengenai hubungan interaksi ekologi antara strategi reproduksi tumbuhan dan perilaku makan satwa frugivore (pemakan buah) dapat memberikan pengetahuan lebih mendalam untuk pelestarian keanekargaman hayati hutan tropis. Di dalam studi ini, kami meneliti bagaimana peran karakteristik ekologi dan fenologi pada tumbuhan dapat memengaruhi konsumsi buah oleh Kelampiau berjanggut putih (Hylobates albibarbis) di Taman Nasional Gunung Palung, Kalimantan Barat, Indonesia. Kelampiau tersebar luas di seluruh Kalimantan, satwa yang sangat “frugivorous” dan memiliki peran penting dalam penyebaran biji. Kami membandingkan beberapa model dengan menggunakan kriteria informasi untuk mengidentifikasikan beberapa prediksi ekologi dan fenologi yang paling kuat dalam memengaruhi makanan buah Kelampiau dengan menggunakan 154 jenis tumbuhan. Sumber prediksi yang paling penting digunakan yaitu pada saat melimpahnya ketersediaan buah yang terjadi secara menyeluruh dan konsisten. Jenis tumbuhan dapat mempertahankan ketersediaan buahnya secara konstan sebagai hasil dari 1) individu yang sering berbuah atau 2) batang pada individu yang berbuah diwaktu yang berbeda dengan individu lain dari jenis yang sama (asynchrony). Hasil kami menunjukkan bahwa Kelampiau lebih memilih makan dari jenis tumbuhan yang menyediakan buah secara konsisten, karena adanya asynchrony antar individu di dalam jenisnya. Dikarenakan Kelampiau lebih sering makan dari jenis buah dengan karakteristik asynchrony, maka Kelampiau lebih memungkinkan melakukan penyebaran biji dengan strategi reproduksi tersebut. Penelitian pada spesies frugivorous lainnya diperlukan untuk dapat menentukan apakah hasil dari Kelampiau dapat digeneralisasikan lebih luas lagi. Pada akhirnya, hasil penelitian ini dapat menunjukkan bahwa jenis tumbuhan dengan karakteristik asynchrony mungkin sangat penting untuk pemulihan habitat di hutan tropis yang dikelola untuk konservasi frugivore.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/110616/1/btp12176.pd

Sign Rules for Anisotropic Quantum Spin Systems

We present new and exact ``sign rules'' for various spin-s anisotropic spin-lattice models. It is shown that, after a simple transformation which utilizes these sign rules, the ground-state wave function of the transformed Hamiltonian is positive-definite. Using these results exact statements for various expectation values of off-diagonal operators are presented, and transitions in the behavior of these expectation values are observed at particular values of the anisotropy. Furthermore, the effects of sign rules in variational calculations and quantum Monte Carlo calculations are considered. They are illustrated by a simple variational treatment of a one-dimensional anisotropic spin model.Comment: 4 pages, 1 ps-figur