55 research outputs found
Integration of CFD Methods into Concurrent Design of Internal Combustion Engine
This paper describes patterns of algorithms for different innovative levels of design at parametric, configuration and conceptual levels. They can be applied to Computer-aided Engine Design (CED). Data structures, process simulation hierarchy, engine simulation modules and the requirements for further development are described. An example of advanced thermodynamics modeling of combustion engines is included
Complicated variations of early optical afterglow of GRB 090726
We report on a detection of an early rising phase of optical afterglow (OA)
of a long GRB 090726. We resolve a complicated profile of the optical light
curve. We also investigate the relation of the optical and X-ray emission of
this event. We make use of the optical photometry of this OA obtained by the
0.5 m telescope of AI AS CR, supplemented by the data obtained by other
observers, and the X-ray Swift/XRT data.
The optical emission peaked at ~ 17.5 mag (R) at t-T0 ~ 500 s. We find a
complex profile of the light curve during the early phase of this OA: an
approximately power-law rise, a rapid transition to a plateau, a weak flare
superimposed on the center of this plateau, and a slowly steepening early
decline followed by a power-law decay. We discuss several possibilities to
explain the short flare on the flat top of the optical light curve at t-T0 ~
500 s; activity of the central engine is favored although reverse shock cannot
be ruled out. We show that power-law outflow with Theta_obs/Theta_c > 2.5 is
the best case for OA of GRB 090726. The initial Lorentz factor is Gamma_0 ~
230-530 in case of propagation of the blast wave in a homogeneous medium, while
propagation of this wave in a wind environment gives Gamma_0 ~ 80-300. The
value of Gamma_0 in GRB 090726 thus falls into the lower half of the range
observed in GRBs and it may even lie on the lower end. We also show that both
the optical and X-ray emission decayed simultaneously and that the spectral
profile from X-ray to the optical band did not vary. This OA belongs to the
least luminous ones in the phase of its power-law decay corresponding to that
observed for the ensemble of OAs of long GRBs.Comment: 5 pages, 5 figures, accepted to A&
Short-term streambed drying events alter amphipod population structure in a central European stream
Temporary streams are becoming increasingly common, but ecological responses to streambed drying are poorly characterized in the temperate continental region of central Europe. In addition, global research has focused on community responses to drying, whereas effects on individual populations remain unknown. We explored the population structure of Gammarus fossarum (Crustacea: Amphipoda) in a central European temporary stream. Benthic gammarids were sampled on five dates during a flow recession, one date between two drying events (of 10 and 20 days, respectively), and five dates after flow resumed. Additional benthic samples were taken from isolated pools and dry sediments during drying events, and freeze cores were collected to compare the vertical distribution of amphipods during wet and dry phases. Gammarids were measured, adults distinguished from juveniles, adults sexed, and female reproductive state determined. Densities increased during flow recession, potentially reflecting both a decline in submerged habitat availability and seasonal increases in juvenile abundance. Persistence within dry benthic sediments was minimal, whereas pools and saturated subsurface sediments supported high population densities. Juveniles comprised 80 % of the subsurface population, suggesting that their ability to inhabit small interstices promotes persistence within the dry reach. Juveniles also comprised 92 % of pool inhabitants, despite their potential exposure to predation. Adults dominated after flow resumed, and population structure was altered post-drying by the loss of spring-recruited juveniles and reproductive females. Our results suggest that streambed drying may have longer-term effects than typically characterized by community-level studies. We recommend management actions that support populations of ecologically important species as they adapt to changing flow regimes
Cascade Dissociations of Peptide Cation-Radicals. Part 2. Infrared Multiphoton Dissociation and Mechanistic Studies of z-Ions from Pentapeptides
Sediment respiration pulses in intermittent rivers and ephemeral streams
Intermittent rivers and ephemeral streams (IRES) may represent over half the global stream network, but their contribution to respiration and carbon dioxide (CO2) emissions is largely undetermined. In particular, little is known about the variability and drivers of respiration in IRES sediments upon rewetting, which could result in large pulses of CO2. We present a global study examining sediments from 200 dry IRES reaches spanning multiple biomes. Results from standardized assays show that mean respiration increased 32–66‐fold upon sediment rewetting. Structural equation modelling indicates that this response was driven by sediment texture and organic matter quantity and quality, which, in turn, were influenced by climate, land use and riparian plant cover. Our estimates suggest that respiration pulses resulting from rewetting of IRES sediments could contribute significantly to annual CO2 emissions from the global stream network, with a single respiration pulse potentially increasing emission by 0.2–0.7%. As the spatial and temporal extent of IRES increases globally, our results highlight the importance of recognizing the influence of wetting‐drying cycles on respiration and CO2 emissions in stream networks
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The recovery of European freshwater biodiversity has come to a halt
Owing to a long history of anthropogenic pressures, freshwater ecosystems are among the most vulnerable to biodiversity loss. Mitigation measures, including wastewater treatment and hydromorphological restoration, have aimed to improve environmental quality and foster the recovery of freshwater biodiversity. Here, using 1,816 time series of freshwater invertebrate communities collected across 22 European countries between 1968 and 2020, we quantified temporal trends in taxonomic and functional diversity and their responses to environmental pressures and gradients. We observed overall increases in taxon richness (0.73% per year), functional richness (2.4% per year) and abundance (1.17% per year). However, these increases primarily occurred before the 2010s, and have since plateaued. Freshwater communities downstream of dams, urban areas and cropland were less likely to experience recovery. Communities at sites with faster rates of warming had fewer gains in taxon richness, functional richness and abundance. Although biodiversity gains in the 1990s and 2000s probably reflect the effectiveness of water-quality improvements and restoration projects, the decelerating trajectory in the 2010s suggests that the current measures offer diminishing returns. Given new and persistent pressures on freshwater ecosystems, including emerging pollutants, climate change and the spread of invasive species, we call for additional mitigation to revive the recovery of freshwater biodiversity
Electron capture in spin-trap capped peptides. An experimental example of ergodic dissociation in peptide cation-radicals
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