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  • Articles  (18)
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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)
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  • 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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  • 3
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    Whole-genome sequencing reveals that mutations in myosin-5 confer resistance to the fungicide phenamacril in Fusarium graminearum (2015)
    Nature Publishing Group (NPG)
    Details
    Publication Date: 2015-02-05
    Description: To determine the mechanism of resistance to the fungicide phenamacril (JS399-19) in Fusarium graminearum, the causal agent of Fusarium head blight, we sequenced and annotated the genome of the resistant strain YP-1 (generated by treating the F. graminearum reference strain PH-1 with phenamacril). Of 1.4 million total reads from an Illumina-based paired-end sequencing assay, 92.80% were aligned to the F. graminearum reference genome. Compared with strain PH-1, strain YP-1 contained 1,989 single-nucleotide polymorphisms that led to amino acid mutations in 132 genes. We sequenced 22 functional annotated genes of another F. graminearum sensitive strain (strain 2021) and corresponding resistant strains. The only mutation common to all of the resistant mutants occurred in the gene encoding myosin-5 (point mutations at codon 216, 217, 418, 420, or 786). To confirm whether the mutations in myosin-5 confer resistance to phenamacril, we exchanged the myosin-5 locus between the sensitive strain 2021 and the resistant strain Y2021A by homologous double exchange. The transformed mutants with a copy of the resistant fragment exhibited resistance to phenamacril, and the transformed mutant with a copy of the sensitive fragment exhibited sensitivity to phenamacril. These results indicate that mutations in myosin-5 confers resistance to phenamacril in F. graminearum. Scientific Reports 5 doi: 10.1038/srep08248
    Electronic ISSN: 2045-2322
    Topics: Natural Sciences in General
    Published by Nature Publishing Group (NPG)
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  • 4
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    Large variations of δ13C values in stalagmites from southeastern China during historical times: implications for anthropogenic deforestation (2015)
    Wiley-Blackwell
    In: Boreas
    Details
    Publication Date: 2015-04-02
    Description: Variations in speleothem δ 13 C values can reflect changes in overlying surface vegetation, which, over historical time scales, may represent the influence of human activities. Here, we examined δ 13 C variations in two stalagmites growing for the last 2200 years in Shennong Cave, Jiangxi Province, SE China. The two δ 13 C records corroborate well one another and show a prominent 6‰ enrichment of the δ 13 C values from AD 700 to 1100. The isotopic equilibrium for modern calcite and negative correlation between δ 18 O and δ 13 C values along the growth axis suggest that the influences of kinetic fractionation are negligible. Varied correlations between Mg / Ca and Sr / Ca ratios and divergent changes between δ 13 C values and Mg / Ca and Sr / Ca ratios from AD 700 to 1100 reveal that the prior calcite precipitation (PCP) and water–rock interaction did not dominate the increase of δ 13 C values. It is plausible that the obvious δ 13 C variation was largely influenced by the changes in vegetation cover overlying the cave. Our δ 13 C results, together with the records of climate and human activity from historical documentary records, suggest that: (i) prior to AD 700, small fluctuations in relatively light δ 13 C values reflect the presence of lush forest coverage above the cave, which was minimally disturbed by human activities; (ii) during AD 700–1100, the drastic increase in δ 13 C values indicates persistent and massive deforestation associated with large-scale immigration into northern Jiangxi after the Rebellion of An & Shi (AD 755–763) in the Tang Dynasty and the subsequent development of agriculture and economic activity; and (iii) since AD 1100, fluctuations in relatively high δ 13 C values suggest that local vegetation during the last millennium has been sparse. Since the Rebellion of An & Shi , southeastern China was progressively developed, coincident with deforestation and vegetation deterioration caused by human disturbance in the form of deforestation and cultivation.
    Print ISSN: 0300-9483
    Electronic ISSN: 1502-3885
    Topics: Geography , Geosciences
    Published by Wiley-Blackwell
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  • 5
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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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  • 6
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    Down-regulation of c-fos by shRNA sensitizes adriamycin-resistant MCF-7/ADR cells to chemotherapeutic agents via P-glycoprotein inhibition and apoptosis augmentation (2013)
    Wiley-Blackwell
    Details
    Publication Date: 2013-03-14
    Description: Multidrug resistance (MDR) is a major hurdle in the treatment of cancer. Research indicated that the main mechanisms of most cancers included so-called “pump” (P-glycoprotein, P-gp) and “non-pump” (apoptosis) resistance. Identification of novel signaling molecules associated with both P-gp and apoptosis will facilitate the development of more effective strategies to overcome MDR in tumor cells. Since the proto-oncogene c-fos has been implicated in cell adaptation to environmental changes, we analyzed its role in mediating “pump” and “non-pump” resistance in MCF-7/ADR, an adriamycin (ADR)-selected human breast cancer cell line with the MDR phenotype. Elevated expression of c-fos in MCF-7/ADR cells and induction of c-fos by ADR in the parental drug-sensitive MCF-7 cells suggested a link between c-fos and MDR phenotype. Down-regulation of c-fos expression via shRNA resulted in sensitization of MCF-7/ADR cells to chemotherapeutic agents, including both P-gp and non-P-gp substrates. Further results proved that c-fos down-regulation in MCF-7/ADR cells resulted in decreased P-gp expression and activity, enhanced apoptosis, and altered expression of apoptosis-associated proteins (i.e., Bax, Bcl-2, p53 and PUMA). All above facts indicate that c-fos is involved in both P-gp- and anti-apoptosis-mediated MDR of MCF-7/ADR cells. Based on these results, we propose that c-fos may represent a potential molecular target for resistant cancer therapy, and suppressing c-fos gene expression may therefore be an effective means to temper breast cancer cell's MDR to cytotoxic chemotherapy. J. Cell. Biochem. © 2013 Wiley Periodicals, Inc.
    Electronic ISSN: 0091-7419
    Topics: Biology , Chemistry and Pharmacology , Medicine
    Published by Wiley-Blackwell
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  • 7
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    Sensors, Vol. 14, Pages 431-442: The Performance Analysis of Distributed Brillouin Corrosion Sensors for Steel Reinforced Concrete Structures (2013)
    MDPI Publishing
    In: Sensors
    Details
    Publication Date: 2013-12-28
    Description: The Brillouin optical time-domain analysis (BOTDA)-based optical fiber method has been proposed to measure strain variations caused by corrosion expansion. Spatial resolutions of 1 m can be achieved with this kind of Brillouin sensor for detecting the distributed strain. However, when the sensing fiber is wound around the steel rebar in a number of circles in a range of several meters, this spatial resolution still has limitations for corrosion monitoring. Here, we employed a low-coherent fiber-optic strain sensor (LCFS) to survey the performance of Brillouin sensors based on the fact that the deformation measured by the LCFS equals the integral of the strains obtained from Brillouin sensors. An electrochemical accelerated corrosion experiment was carried out and the corrosion expansion was monitored by both BOTDA and the LCFS. Results demonstrated that the BOTDA can only measure the expansion strain of about 1,000 με, which was generated by the 18 mm steel rebar corrosion, but, the LCFS had high sensitivity from the beginning of corrosion to the destruction of the structure, and no obvious difference in expansion speed was observed during the acceleration stage of the corrosion developed in the reinforced concrete (RC) specimens. These results proved that the BOTDA method could only be employed to monitor the corrosion inside the structure in the early stage.
    Electronic ISSN: 1424-8220
    Topics: Chemistry and Pharmacology , Electrical Engineering, Measurement and Control Technology
    Published by MDPI Publishing
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  • 8
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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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  • 9
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    Electronic and spin dynamics in the insulating iron pnictide ${\mathrm{NaFe}}_{0.5}{\mathrm{Cu}}_{0.5}\mathrm{As}$ (2017)
    American Physical Society (APS)
    Details
    Publication Date: 2017-12-22
    Description: Author(s): Shunhong Zhang, Yanjun He, Jia-Wei Mei, Feng Liu, and Zheng Liu NaFe 0.5 Cu 0.5 As represents a rare exception in the metallic iron pnictide family, in which a small insulating gap is opened. Based on first-principles study, we provide a comprehensive theoretical characterization of this insulating compound. The Fe 3 + spin degree of freedom is quantified as a quasi-o... [Phys. Rev. B 96, 245128] Published Thu Dec 21, 2017
    Keywords: Electronic structure and strongly correlated systems
    Print ISSN: 1098-0121
    Electronic ISSN: 1095-3795
    Topics: Physics
    Published by American Physical Society (APS)
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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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