Preliminary evidence for human fecal contamination in corals of the Florida Keys,USA

Corals and reef environments are under increased stress from anthropogenic activities, particularly those in the vicinity of heavily populated areas such as the Florida Keys. The potential adverse impacts of wastewater can affect both the environment and human health; however, because of the high decay rate of bacterial indicators in coral reef waters it has been difficult to document the presence of microbial contaminants and to assign risks in these environments. Here we show initial evidence that microorganisms associated with human feces are concentrated along the surface of coral heads relative to the overlying water column in the Florida Keys. Bacterial indicators (fecal coliform bacteria, enterococci or Clostridium perfringens) were detected in 66.7% of the coral surface microlayer (CSM) samples at levels between five and 1000 CFU/100 ml, but were found infrequently and at low numbers in the overlying water column ( < or = 2.5 CFU/100 ml). Similarly, enterovirus nucleic acid sequences, an indicator of human-specific waste, were detected in 93.3% of the CSM samples and only once in the water column by cell culture. Results show that coral mucus may accumulate enteric microorganisms in reef environments, and may indicate a risk to public and environmental health despite low indicator levels in the surrounding water.     

Comparison of Transient Network Brightenings and Explosive Events in the Solar Transition Region

I analyze the properties of the pulsed emission from the accreting millisecond pulsar SAX J1808.4-3658 in observations of its 1998 April outburst by the Rossi X-Ray Timing Explorer. Pulse phase spectroscopy shows that the emission evolves from a hard spectrum (power law with photon index of 2.39+/-0.06) to a soft spectrum (index of 3.39+/-0.24). This softening is also observable as a phase lag in the fundamental of low-energy photons with respect to high-energy photons. I show that this lag is roughly constant over 10 days of the outburst. I fit these data with a model in which the pulse emission is from a hot spot on the rotating neutron star and the flux as a function of phase is determined in a calculation which includes the effects of general relativity. The energy-dependent lags are very well described by this model. The harder spectra at earlier phases (i.e., as the spot approaches) are the result of larger Doppler-boosting factors that are important for this fast pulsar. Since this model is sensitive to the equatorial speed as an independent parameter and since the spin frequency is known, this offers us a new means of measuring the neutron star radius, which is notoriously difficult to determine.     

L1551NE-Discovery of a Binary Companion

L1551NE is a very young (class 0 or I) low-mass protostar located close to the well-studied L1551 IRS 5. Here we present evidence, from 1.3 mm continuum interferometric observations at approximately 1&arcsec; resolution, for a binary companion to L1551NE. The companion, whose 1.3 mm flux density is approximately 13 that of the primary component, is located 1&farcs;43 ( approximately 230 AU at 160 pc) to the southeast. The millimeter-wave emission from the primary component may have been just barely resolved, with a deconvolved size of approximately 0&farcm;82x0&farcm;70 ( approximately 131x112 AU). The companion emission was unresolved (<100 AU). The pair is embedded within a flattened circumbinary envelope of size approximately 5&farcm;4x2&farcm;3 ( approximately 860x370 AU). The masses of the three components (i.e., from the circumstellar material of the primary star and its companion and the envelope) are approximately 0.044, 0.014, and 0.023 M middle dot in circle, respectively.     

ASCA Observation of the Quiescent X-Ray Counterpart to SGR 1627-41

We present a 2-10 keV ASCA observation of the field around the soft gamma repeater SGR 1627-41. A quiescent X-ray source, whose position is consistent both with that of a recently discovered BeppoSAX X-ray source and with the Interplanetary Network localization for this soft gamma repeater, was detected in this observation. In 2-10 keV X-rays, the spectrum of the X-ray source may be fit equally well by a power-law, blackbody, or bremsstrahlung function, with unabsorbed flux approximately 5x10-12 ergs cm-2 s-1. We do not confirm a continuation of a fading trend in the flux, and we find no evidence for periodicity, both of which were noted in the earlier BeppoSAX observations.     

A Measurement of Omega from the North American Test Flight of Boomerang

We use the angular power spectrum of the cosmic microwave background, measured during the North American test flight of the Boomerang experiment, to constrain the geometry of the universe. Within the class of cold dark matter models, we find that the overall fractional energy density of the universe Omega is constrained to be 0.85相似文献   

Supernova Sources and the 92Nb-92Zr p-Process Chronometer

We report new Zr isotope evidence for live (92)Nb (mean life: tau&d1;92Nb=52 Myr) within the early solar system resulting in &parl0;92Nb&solm0;93Nb&parr0;initial approximately 10-3. The meteoritic minerals rutile and zircon have, respectively, very high and very low Nb/Zr ratios and are ideal for exploring the (92)Nb-(92)Zr chronometer. Rutiles exhibit high positive straightepsilon92Zr ( approximately 14-36) while a zircon has a negative straightepsilon92Zr ( approximately -4), as would be expected if (92)Nb was live in the early solar system. The meteoritic rutiles appear to be young, with apparent times of formation of approximately 80-220 Myr subsequent to the origin of the solar system. The initial (92)Nb/(92)Mo for the solar system is broadly compatible with a model of uniform production if the (92)Nb/(92)Mo production ratio for Type II supernova (SNII) sources with neutrino-driven winds is used. Data for all the now extinct p-process nuclides ((92)Nb, (97)Tc, and (146)Sm) are consistent with these isotopes being derived by uniform production from SNII sources and a free decay interval of approximately 10 Myr. Consideration of a range of models indicates that the average p-process production ratio of (92)Nb/(92)Mo needs to be at least in the range of 0.06-0.25.     

Discovery of High Proper-Motion Ancient White Dwarfs: Nearby Massive Compact Halo Objects?

We present the discovery and spectroscopic identification of two very high proper-motion ancient white dwarf stars, found in a systematic proper-motion survey. Their kinematics and apparent magnitude clearly indicate that they are halo members, while their optical spectra are almost identical to the recently identified cool halo white dwarf WD 0346+246. Canonical stellar halo models predict a white dwarf volume density that is 2 orders of magnitude less than the rho approximately 7x10-4 M middle dot in circle pc-3 inferred from this survey. With the caveat that the sample size is very small, it appears that a significant fraction, approximately 10%, of the local dark matter halo is in the form of very old, cool, white dwarfs.     

New Non-Gaussian Feature in COBE-DMR 4 Year Maps

Recent determinations of the abundance of the light-element Li in very metal-poor stars show that its intrinsic dispersion is essentially zero and that the random error in the estimated mean Li abundance is negligible. However, a decreasing trend in the Li abundance toward lower metallicity indicates that the primordial abundance of Li can be inferred only after allowing for nucleosynthesis processes that must have been in operation in the early history of the Galaxy. We show that the observed Li versus Fe trend provides a strong discriminant between alternative models for Galactic chemical evolution of the light elements at early epochs. We critically assess current systematic uncertainties and determine the primordial Li abundance within new, much tighter limits: &parl0;Li&solm0;H&parr0;p=1.23+0.68-0.32x10-10. We show that the Li constraint on OmegaB is now limited as much by uncertainties in the nuclear cross sections used in big bang nucleosynthesis (BBN) calculations as by the observed abundance itself. A clearer understanding of systematics allows us to sharpen the comparison with 4He and deuterium and the resulting test of BBN.     

LiBr溶液从低浓度到高浓度的分子动力学模拟

在 L i Br与水的物质量比分别为 1∶ 64、1∶ 32、1∶ 16、1∶ 8、1∶ 4和 1∶ 3的情况下 ,对 L i Br溶液从低温到高温的分子动力学模拟进行了研究。随浓度增加 ,锂离子的水合数量呈减少趋势但同时又从 L i+- Br-接触离子对的数量增加中得到补偿 ,而 L i离子的第一配位壳层的配位数量保持不变。在高浓度 Li Br溶液中 ,Br- O之间的距离有所增加 ,Br-- O的径向分布的形状更趋于非对称 ,从而很好地确定了 Br离子水合壳层 L i+- Br-接触离子对可以在更稀的溶液中产生 ,但随浓度增加而增加。L i+- Br-距离明显短于溶液中 Li离子与 Br离子的离子半径之和 ,也短于 L i Br晶体中两者离子半径之和。高浓度溶液中水分子的结构几乎被破坏 ,水分子间的氢键明显增加 ,但没有消失。对 L i+、Br-和水的扩数系数计算值与实验值进行了比较     

The Kyonggi Shear Zone of the Central Korean Peninsula: Late Orogenic Imprint of the North and South China Collision

The crustal-scale Kyonggi shear zone of central Korea has been identified as a major boundary between the Precambrian Kyonggi massif in the south and the Imjingang belt in the north. The latter is an eastward extension of the Qinling-Dabie-Sulu collisional belt of China. Field observations and microstructural analysis indicate that the extensional shear zone evolved from a deep crustal ductile regime to a shallow crustal brittle regime, associated with a rapid uplift of the Kyonggi massif following the Late Permian-Early Triassic collision between the Sino-Korean and Yangtze cratons. A Rb-Sr muscovite age (226+/-1.2 Ma) of the mylonite suggests that the extensional ductile shearing occurred during the Late Triassic.