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  • 1
    Electronic Resource
    Electronic Resource
    On better heuristics for Steiner minimum trees (1992)
    Springer
    Mathematical programming 57 (1992), S. 193-202 
    Details
    ISSN: 1436-4646
    Keywords: Steiner trees ; approximation performance ratio
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science , Mathematics
    Notes: Abstract Finding a shortest network interconnecting a given set of points in a metric space is called the Steiner minimum tree problem. The Steiner ratio is the largest lower bound for the ratio between lengths of a Steiner minimum tree and a minimum spanning tree for the same set of points. In this paper, we show that in a metric space, if the Steiner ratio is less than one and finding a Steiner minimum tree for a set of size bounded by a fixed number can be performed in polynomial time, then there exists a polynomialtime heuristic for the Steiner minimum tree problem with performance ratio bigger than the Steiner ratio. It follows that in the Euclidean plane, there exists a polynomial-time heuristic for Steiner minimum trees with performance ratio bigger than $${\textstyle{1 \over 2}}\sqrt 3 $$ . This solves a long-standing open problem.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01581080
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    Paper (German National Licenses)
    Fulltext
  • 2
    Electronic Resource
    Electronic Resource
    On heuristics for minimum length rectilinear partitions (1990)
    Springer
    Algorithmica 5 (1990), S. 111-128 
    Details
    ISSN: 1432-0541
    Keywords: Rectilinear figure ; Rectilinear partition ; Monotonic histogram ; Dynamic programming
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science , Mathematics
    Notes: Abstract The problem of partitioning a rectilinear figure into rectangles with minimum length is NP-hard and has bounded heuristics. In this paper we study a related problem,Elimination Problem (EP), in which a rectilinear figure is partitioned into a set of rectilinear figures containing no concave vertices of a fixed direction with minimum length. We show that a heuristic for EP within a factor of 4 from optimal can be computed in timeO(n 2), wheren is the number of vertices of the input figure, and a variant of this heuristic, within a factor of 6 from optimal, can be computed in timeO(n logn). As an application, we give a bounded heuristic for the problem of partitioning a rectilinear figure into histograms of a fixed direction with minimum length. An auxiliary result is that an optimal rectangular partition of a monotonic histogram can be computed in timeO(n 2), using a known speed-up technique in dynamic programming.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01840380
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    Paper (German National Licenses)
    Fulltext
  • 3
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    Hydraulic fracturing pressures in laboratorial Hot Dry Rock borehole injection (2018)
    PANGAEA
    In:  Supplement to: Cheng, Yuxiang; Zhang, Yanjun (submitted): A study about microearthquakes caused by hydraulic fracturing in hot dry rocks. Environmental Earth Sciences
    Details
    Publication Date: 2023-01-13
    Description: We use a true-triaxial apparatus to monitor hydraulic fracturing in the laboratorial Hot Dry Rock reservoir environment. The borehole injection and propagate fractures are in 300×300×300 mm3 heated granite specimens under triaxial confining pressures. The granite specimens can be heated to 60-120 degrees Celsius. We use pressures to record the triaxial stress and hydraulic fracturing pressures. Every 10 seconds, the data are recorded. The data reflect the variation of hydraulic fracturing with time.
    Type: Dataset
    Format: application/zip, 32.3 kBytes
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    DATA PANGAEA
  • 4
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    Seawater carbonate chemistry and the decrease of H+ concentration in the phycosphere and thickness of the pH boundary layer of marine diatoms Coscinodiscus wailesii (2022)
    PANGAEA
    Details
    Publication Date: 2024-03-15
    Description: Surface ocean pH is declining due to anthropogenic atmospheric CO2 uptake with a global decline of ~0.3 possible by 2100. Extracellular pH influences a range of biological processes, including nutrient uptake, calcification and silicification. However, there are poor constraints on how pH levels in the extracellular microenvironment surrounding phytoplankton cells (the phycosphere) differ from bulk seawater. This adds uncertainty to biological impacts of environmental change. Furthermore, previous modelling work suggests that phycosphere pH of small cells is close to bulk seawater, and this has not been experimentally verified. Here we observe under 140 μmol photons/m**2/s the phycosphere pH of Chlamydomonas concordia (5 µm diameter), Emiliania huxleyi (5 µm), Coscinodiscus radiatus (50 µm) and C. wailesii (100 µm) are 0.11 ± 0.07, 0.20 ± 0.09, 0.41 ± 0.04 and 0.15 ± 0.20 (mean ± SD) higher than bulk seawater (pH 8.00), respectively. Thickness of the pH boundary layer of C. wailesii increases from 18 ± 4 to 122 ± 17 µm when bulk seawater pH decreases from 8.00 to 7.78. Phycosphere pH is regulated by photosynthesis and extracellular enzymatic transformation of bicarbonate, as well as being influenced by light intensity and seawater pH and buffering capacity. The pH change alters Fe speciation in the phycosphere, and hence Fe availability to phytoplankton is likely better predicted by the phycosphere, rather than bulk seawater. Overall, the precise quantification of chemical conditions in the phycosphere is crucial for assessing the sensitivity of marine phytoplankton to ongoing ocean acidification and Fe limitation in surface oceans.
    Keywords: Acid-base regulation; Alkalinity, total; Aragonite saturation state; Bicarbonate ion; Bottles or small containers/Aquaria (〈20 L); Calcite saturation state; Calculated using seacarb after Nisumaa et al. (2010); Carbon, inorganic, dissolved; Carbonate ion; Carbonate system computation flag; Carbon dioxide; Chromista; Coscinodiscus wailesii; Figure; Fugacity of carbon dioxide (water) at sea surface temperature (wet air); Hydrogen ion concentration; Laboratory experiment; Laboratory strains; Not applicable; OA-ICC; Ocean Acidification International Coordination Centre; Ochrophyta; Partial pressure of carbon dioxide (water) at sea surface temperature (wet air); Pelagos; pH; Phytoplankton; Proton gradients; Salinity; Single species; Species, unique identification; Temperature, water; Thickness; Treatment; Type
    Type: Dataset
    Format: text/tab-separated-values, 3286 data points
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    DATA PANGAEA
  • 5
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    Phycosphere pH of unicellular nano- and micro- phytoplankton cells and consequences for iron speciation (2022)
    Nature Research
    Details
    Publication Date: 2024-02-07
    Description: Surface ocean pH is declining due to anthropogenic atmospheric CO2 uptake with a global decline of ~0.3 possible by 2100. Extracellular pH influences a range of biological processes, including nutrient uptake, calcification and silicification. However, there are poor constraints on how pH levels in the extracellular microenvironment surrounding phytoplankton cells (the phycosphere) differ from bulk seawater. This adds uncertainty to biological impacts of environmental change. Furthermore, previous modelling work suggests that phycosphere pH of small cells is close to bulk seawater, and this has not been experimentally verified. Here we observe under 140 μmol photons·m−2·s−1 the phycosphere pH of Chlamydomonas concordia (5 µm diameter), Emiliania huxleyi (5 µm), Coscinodiscus radiatus (50 µm) and C. wailesii (100 µm) are 0.11 ± 0.07, 0.20 ± 0.09, 0.41 ± 0.04 and 0.15 ± 0.20 (mean ± SD) higher than bulk seawater (pH 8.00), respectively. Thickness of the pH boundary layer of C. wailesii increases from 18 ± 4 to 122 ± 17 µm when bulk seawater pH decreases from 8.00 to 7.78. Phycosphere pH is regulated by photosynthesis and extracellular enzymatic transformation of bicarbonate, as well as being influenced by light intensity and seawater pH and buffering capacity. The pH change alters Fe speciation in the phycosphere, and hence Fe availability to phytoplankton is likely better predicted by the phycosphere, rather than bulk seawater. Overall, the precise quantification of chemical conditions in the phycosphere is crucial for assessing the sensitivity of marine phytoplankton to ongoing ocean acidification and Fe limitation in surface oceans.
    Type: Article , PeerReviewed
    Format: text
    Format: text
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 6
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    Contribution of recycled moisture to precipitation in oases of arid central Asia: A stable isotope approach (2016)
    Wiley-Blackwell
    Details
    Publication Date: 2016-04-07
    Description: Terrestrial moisture contributed by surface evaporation and transpiration, also known as recycled moisture, plays an important role in hydrological processes especially across arid central Asia. The stable hydrogen and oxygen isotopes can be used for water budget analysis to calculate the contribution of recycled moisture to precipitation between two locations along the moisture flow. Based on a three-component isotopic mixing model, the moisture recycling in oasis stations of arid central Asia during summer months is assessed. At large oases of Urumqi, the proportional contribution of recycled moisture to local precipitation is approximately 16.2%, and the mean proportions of surface evaporation and transpiration are 5.9%±1.5% and 10.3%±2.2%, respectively. At small oases like Shihezi and Caijiahu the contribution of recycled moisture is less than 5%, and the proportion of surface evaporation is much less than that of transpiration. The vegetative cover in arid central Asia is generally sparse, but the evapotranspiration contribution to precipitation cannot be ignored at the widely distributed oases. The oasis effect shows great variability depending on locations and water availability for evapotranspiration. This article is protected by copyright. All rights reserved.
    Print ISSN: 0043-1397
    Electronic ISSN: 1944-7973
    Topics: Architecture, Civil Engineering, Surveying , Geography
    Published by Wiley-Blackwell on behalf of American Geophysical Union (AGU).
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    PAPER CURRENT
  • 7
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    Minerals, Vol. 8, Pages 90: Sequential Transformation Behavior of Iron-Bearing Minerals during Underground Coal Gasification (2018)
    MDPI Publishing
    In: Minerals
    Details
    Publication Date: 2018-03-06
    Description: Minerals, Vol. 8, Pages 90: Sequential Transformation Behavior of Iron-Bearing Minerals during Underground Coal Gasification Minerals doi: 10.3390/min8030090 Authors: Shuqin Liu Weiping Ma Yixin Zhang Yanjun Zhang Kaili Qi Detailed mineralogical information from underground coal gasification (UCG) is essential to better understand the chemical reactions far below the surface. It is of great scientific significance to study the mineral transformation and identify the typical minerals in certain process conditions, because it may help to ensure the stable operation of gasification processes and improve the utilization efficiency of coal seams. The transformation of iron-bearing minerals has the typical characteristics during the UCG process and is expected to indicate the process parameters. In this paper, UCG progress was subdivided into pyrolysis, reduction and oxidation stages, and the progressive coal conversion products were prepared. Two types of lignite with different iron contents, Ulankarma and Ulanqab coals, were used in this study. The minerals in the coal transformation products were identified by X-ray diffraction (XRD) and a scanning electron microscope coupled with an energy-dispersive spectrometer (SEM-EDS). The thermodynamic calculation performed using the phase diagram of FactSage 7.1 was used to help to understand the transformation of minerals. The results indicate that the transformation behavior of iron-bearing minerals in the two lignites are similar during the pyrolysis process, in which pyrite (FeS2) in the raw coal is gradually converted into pyrrhotite (Fe1−xS). In the reduction stage, pyrrhotite is transformed into magnetite (Fe3O4) and then changes to FeO. The reaction of FeO and Al2O3 in the low iron coal produces hercynite above 1000 °C because of the difference in the contents of Si and Al, while in the high iron coal, FeO reacts with SiO2 to generate augite (Fe2Si2O6). When the temperature increases to 1400 °C, both hercynite and augite are converted to the thermodynamically-stable sekaninaite.
    Electronic ISSN: 2075-163X
    Topics: Geosciences
    Published by MDPI Publishing
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  • 8
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    Effects of Fuel Properties on Ignition Characteristics of Parallel-Bias Pulverized-Coal Jets (2017)
    American Chemical Society (ACS)
    Details
    Publication Date: 2017-10-14
    Description: Energy & Fuels DOI: 10.1021/acs.energyfuels.7b02055
    Print ISSN: 0887-0624
    Electronic ISSN: 1520-5029
    Topics: Chemistry and Pharmacology , Energy, Environment Protection, Nuclear Power Engineering , Process Engineering, Biotechnology, Nutrition Technology
    Published by American Chemical Society (ACS)
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  • 9
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    Advanced investigation on the change in the streamflow into the water source of the middle route of China's water diversion project (2017)
    Wiley-Blackwell
    Details
    Publication Date: 2017-07-02
    Description: To alleviate water shortage in northern China, the middle route of the South to North Water Diversion Project (MRP) was constructed by the Chinese government. A dramatic reduction in the annual streamflow into Danjiangkou Reservoir (ASDR), the water source of MRP, during 1990 has raised some concerns on the MRP's operation. This paper employed an advanced segmented regression model with more recent data to have a clear picture and understand the changing pattern of the ASDR. Our study firstly revealed a zigzag changing pattern (decreasing-increasing-decreasing-increasing) of ASDR during 1960-2013, which was supported by statistical criteria compared with a monotonic or single abrupt change. Particularly, the significantly decreasing trend from 1990s was reversed after 2000, and such change may relieve the concern about the water availability in the future. Sensitivity analysis showed that changes in streamflow were largely influenced by the combined effects of precipitation ( P ) and potential evapotranspiration ( ET 0 ), and were more sensitive to P than ET 0 . As ET 0 is estimated from other primary variables, further analysis was conducted to understand the sensitivities of ET 0 to its primary driving variables (wind speed, actual vapor pressure, temperature and sunshine duration), and indicated that ET 0 is mostly sensitive to actual vapor pressure during 1960-2013. The findings will assist the MRP's operation and management. Moreover, the results in this study also indicates that an adaptive water diversion plan, rather than the current plan with a constant annual amount of diversion water, might be a better option in the MRP's operation.
    Print ISSN: 0148-0227
    Topics: Geosciences , Physics
    Published by Wiley-Blackwell on behalf of American Geophysical Union (AGU).
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  • 10
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    Rapid Screening of Oxygen States in Carbon Quantum Dots by Chemiluminescence Probe (2017)
    American Chemical Society (ACS)
    Details
    Publication Date: 2017-11-11
    Description: Analytical Chemistry DOI: 10.1021/acs.analchem.7b03711
    Print ISSN: 0003-2700
    Electronic ISSN: 1520-6882
    Topics: Chemistry and Pharmacology
    Published by American Chemical Society (ACS)
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