简并度对引力不稳定性的影响

本文讨论了无碰撞粒子系统中简并度对引力不稳定性的影响,计算了塌缩时间的Ｌａｎｄａｕ阻尼时间．在研究费密型暗物质占主导地位的宇宙中星系形成的理论时,系统分布函数的简并度对引力不稳定性的影响有重要意义．     

Photoacclimation of the invasive alga Caulerpa racemosa var. cylindracea to depth and daylight patterns and a putative new role for siphonaxanthin

The introduced green alga Caulerpa racemosa var. cylindracea grows along a broad depth range (from very shallow to 60 m depth) in the Mediterranean basin. In the present work, the photoacclimation capacity of this invasive variety was investigated in summer, the season of its maximum spread. Natural populations from the Gulf of Naples (Italy) were analyzed for photoresponse on two scales of light variability: a spatial scale (at three stations along a depth gradient, from 0.3 to 20 m depth) and a temporal scale (on the shallowest meadow, from sunrise to sunset). These responses were studied through pigment analysis (with HPLC), and in situ measurements of photosynthetic parameters (with a Diving‐PAM fluorometer). Electron transport rate (ETR)–irradiance curve parameters showed acclimation along environmental gradients dominated by variation in irradiance. In the shallowest plants, the lack of a midday depression in both the maximum relative ETRs and the photosynthetic efficiency at sub‐saturating irradiance (α) pointed to a maintenance of energy conversion levels despite the protective lowering of light‐harvesting efficiency revealed by the trend in F_v/F_m. On the other side, variation of photosynthetic efficiency occurred with depth and buffered the effect of decreasing light on maximum photosynthetic rates. A previously undescribed xanthophyll cycle centred on lutein‐siphonaxanthin interconversion appeared to operate in the shallowest populations in addition to the violaxanthin/antheraxanthin/zeaxanthin cycle commonly occurring in Chlorophyta; this would further enhance phototolerance of the alga. A further role of siphonaxanthin is in the acclimation to low light of deep environments as indicated by its stronger increase from the surface to the deepest station with respect to siphonein and chlorophyll b.     

Morphologic features of juvenile pyroclasts from magmatic and phreatomagmatic deposits of Vesuvius

Three eruptive sequences of historical and recent activity of Vesuvius were carefully studied using scanning electron microscopy analysis techniques. The aim of this study was to characterize and distinguish deposits from magmatic and phreatomagmatic eruption phases.The sample pretreatment methods from previous authors were reviewed and a washing technique was checked, making it possible to obtain easily examinable samples without modifying their morphologic features.In each stratigraphic sequence the single samples were examined and their shape, type of vesiculation, and state of glass (edge modification by abrasion, alteration, presence of aggregates, secondary minerals and coatings) were analyzed and described.Characteristic features were recognized for deposits from different eruptive phases. Samples from phreatomagmatic deposits show the following features:

• - glass alteration;

• - presence of secondary minerals on the external surfaces or inside the cavities;

• - coatings;

• - presence of aggregate formed by juvenile and lithic particles.

Other features, indicated by many authors as resulting from magma-water interaction, can arise from different mechanisms and cannot discriminate between phreatomagmatic and magmatic nature of deposits.The juvenile clasts from the phreatomagmatic phases of these eruptions of Vesuvius always show primary vesiculation; this observation supports the presence of fragmented magma at the time when interaction occurred.The conclusions from SEM observations are in perfect agreement with the results of granulometric and component analysis on the same eruptive sequences.     

Occurrence of minor toxic elements in volcanic-sedimentary aquifers: a case study in central Italy

The occurrence of minor toxic elements (arsenic, vanadium and fluoride among others) in the volcanic aquifers of central Italy, with concentrations often above the national standards for drinking waters, has been recognized since the 1970s. However, these groundwaters are still often used for human consumption. With the aim of providing insight into the water–rock interaction processes, as well as into the evolution of arsenic and other elements, water-sampling campaigns where undertaken within a 100 km² area at the eastern margin of the Viterbo region, where volcanites overlie an alluvial aquifer complex. The samples were analysed and geochemical modelling was applied to characterize the thermodynamic state of the waters. The results indicate the existence of direct relations among arsenic, vanadium and fluoride concentrations and of their inverse relationship with calcium concentration. An evolution scheme of groundwater composition from the upstream volcanic aquifer to the downstream sedimentary aquifer is also discussed. Two hypotheses are proposed which justify the observed decrease of the cited minor element concentrations, i.e. dilution processes and/or precipitation of fluorapatite, which can include in its structure small amounts of these elements. The precipitation hypothesis is supported by modelling results.     

Earthquake focal mechanisms and stress inversion in the Irpinia Region (southern Italy)

The goal of this study was to estimate the stress field acting in the Irpinia Region, an area of southern Italy that has been struck in the past by destructive earthquakes and that is now characterized by low to moderate seismicity. The dataset are records of 2,352 aftershocks following the last strong event: the 23 November 1980 earthquake (M 6.9). The earthquakes were recorded at seven seismic stations, on average, and have been located using a three-dimensional (3D) P-wave velocity model and a probabilistic, non-linear, global search technique. The use of a 3D velocity model yielded a more stable estimation of take-off angles, a crucial parameter for focal mechanism computation. The earthquake focal mechanisms were computed from the P-wave first-motion polarity data using the FPFIT algorithm. Fault plane solutions show mostly normal component faulting (pure normal fault and normal fault with a strike-slip component). Only some fault plane solutions show strike-slip and reverse faulting. The stress field is estimated using the method proposed by Michael (J Geophys Res 92:357–368, 1987a) by inverting selected focal mechanisms, and the results show that the Irpinia Region is subjected to a NE–SW extension with horizontal σ ₃ (plunge 0°, trend 230°) and subvertical σ ₁ (plunge 80°, trend 320°), in agreement with the results derived from other stress indicators.     

Recent contamination of mercury in an estuarine environment (Marano lagoon,Northern Adriatic,Italy)

The Marano Lagoon, in the northern Adriatic Sea (Italy), has been affected by mercury (Hg) contamination from industrial and mining activities. It has been estimated that 186,000 kg of Hg were deliberately discharged into the main drainage system (Aussa–Corno River) by a chlor-alkali plant (CAP) from 1940s to 1984. The lagoon has also experienced a secondary long-term Hg input, originated from mining activity in Idrija (Slovenia), due to the supply of fluvial suspended particles carried by the Isonzo River in the Gulf of Trieste. Since local fishing activities are extensively conducted, there is great concern on the risk posed by potentially harmful effects of Hg to the trophic chain.     

Lysosomal and lipid-associated parameters in the livers of three species of arctic seabird chicks: species differences and relationships with contaminant levels

Lysosomal membrane stability, lipofuscin (LF), malondialdehyde (MDA), neutral lipid (NL) levels, as well as halogenated organic compounds (HOCs), Cr, Cd, Pb and Fe concentrations were analyzed in liver of black-legged kittiwake (BK), herring gull (HG), and northern fulmar (NF) chicks. There were significant species differences in the levels of NL, LF and lysosomal membrane stability. These parameters were not associated with the respective HOC concentrations. LF accumulation was associated with increasing Cr, Cd and Pb concentrations. HG presented the lowest lysosomal membrane stability and the highest.LF and NL levels, which indicated impaired lysosomes in HG compared to NF and BK. Lipid peroxidation was associated with HOC and Fe²⁺ levels. Specific HOCs showed positive and significant correlations with MDA levels in HG. The study indicates that contaminant exposure can affect lysosomal and lipid associated parameters in seabird chicks even at low exposure levels. These parameters may be suitable markers of contaminant induced stress in arctic seabirds.     

Structure of the Prompt Emission of GRB 151027A Within the Fireshell Model

Long gamma-ray burst GRB 151027A was observed by all three detectors onboard the Swift spacecraft, and many more, including MAXI, Konus-Wind and Fermi GBM/LAT instruments. This revealed a complex structure of the prompt and afterglow emission, consisting of a double-peak gammaray prompt with a quiescent period and a HRF/SXF within the X-ray afterglow, together with multiple BB components seen within the time-resolved spectral analysis. These features, within the fireshell model, are interpreted as the manifestation of the same physical process viewed at different angles with respect to the HN ejecta. Here we present the time-resolved and time-integrated spectral analysis used to determine the energy of the e^?e⁺ plasma E_tot and the baryon load B. These quantities describe the dynamics of the fireshell up to the transparency point. We proceed with the light-curve simulation from which CBM density values and its inhomogeneities are deduced. We also investigate the properties of GRB 140206A, whose prompt emission exhibits a similar structure.