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排序方式: 共有224条查询结果,搜索用时 15 毫秒
121.
Lerner B Yeshaya J Koushnir L 《IEEE/ACM transactions on computational biology and bioinformatics / IEEE, ACM》2007,4(2):204-215
Solving a multiclass classification task using a small imbalanced database of patterns of high dimension is difficult due to the curse-of-dimensionality and the bias of the training toward the majority classes. Such a problem has arisen while diagnosing genetic abnormalities by classifying a small database of fluorescence in situ hybridization signals of types having different frequencies of occurrence. We propose and experimentally study using the cytogenetic domain two solutions to the problem. The first is hierarchical decomposition of the classification task, where each hierarchy level is designed to tackle a simpler problem which is represented by classes that are approximately balanced. The second solution is balancing the data by up-sampling the minority classes accompanied by dimensionality reduction. Implemented by the naive Bayesian classifier or the multilayer perceptron neural network, both solutions have diminished the problem and contributed to accuracy improvement. In addition, the experiments suggest that coping with the smallness of the data is more beneficial than dealing with its imbalance 相似文献
122.
Scott A. Field Phillip W. Taylor Boaz Yuval 《Entomologia Experimentalis et Applicata》1999,92(3):271-276
Previous studies have reported considerable variation in copula duration in the Mediterranean Fruit Fly (medfly), Ceratitis capitata Weidemann (Diptera: Tephritidae). Presently, however, this variation is largely unexplained. In this study we measure copula duration in two medfly strains used in applied research in Israel and examine how much of the variation in copula duration is due to the strain, age, the time of day the mating begins and the relative size of the mating pair. We found the following: flies of a strain reared in the laboratory since 1976 (Vienna) copulated for longer than flies of a strain collected in 1969 and periodically refreshed with wild males (Sade); older flies copulated for longer than young flies; and pairs in which males were smaller than females copulated for longer than pairs in which males were larger or the sexes were more evenly size-matched. The time of day the mating commenced (morning vs afternoon) had no effect. We discuss potential mechanisms underlying these variations in medfly copula duration. 相似文献
123.
Jack J. Middelburg Joop Nieuwenhuize Frederik J. Slim Boaz Ohowa 《Biogeochemistry》1996,34(3):133-155
The biogeochemistry of mangrove sediments was investigated in several mangrove forest communities in Gazi Bay, a coastal lagoon in Kenya, Africa. Carbon dioxide fluxes, sediment median grain sizes, sedimentary organic carbon, nitrogen and phosphorus contents and pore-water characteristics (ammonium, nitrate, sulfate and chloride) could be related to forest type. Mangrove sediments have pH values that range from 3.5 to 8.3 due to the limited buffer capacity of these sediments and intense acidifying processes such as aerobic degradation of organic matter, oxidation of reduced components, ammonium uptake by roots and root respiration. The mangrove sediments are nitrogen-rich compared to mangrove litter, as a result of microbial nitrogen retention, uptake and fixation, and import of nitrogen-rich material. It appears that mangrove sediments in Gazi Bay act as a nutrient and carbon sink rather than as a source for adjacent seagrass and reef ecosystems. 相似文献
124.
Tirosh B Furman MH Tortorella D Ploegh HL 《The Journal of biological chemistry》2003,278(9):6664-6672
We examined the effects of protein folding on endoplasmic reticulum (ER)-to-cytosol transport (dislocation) by exploiting the well-characterized dihydrofolate reductase (DHFR) domain. DHFR retains the capacity to bind folate analogues in the lumen of microsomes and in the ER of intact cells, upon which it acquires a conformation resistant to proteinase K digestion. Here we show that a Class I major histocompatibility complex heavy chain fused to DHFR is still recognized by the human cytomegalovirus-encoded glycoproteins US2 and US11, resulting in dislocation of the fusion protein from the ER in vitro and in vivo. A folded state of the DHFR domain does not impair dislocation of Class I MHC heavy chains in vitro or in living cells. In fact, a slight acceleration of the dislocation of DHFR heavy chain fusion was observed in vitro in the presence of a folate analogue. These results suggest that one or more of the channels used for dislocation can accommodate polypeptides that contain a tightly folded domain of considerable size. Our data raise the possibility that the Sec61 channel can be modified to accommodate a folded DHFR domain for dislocation, but not for translocation into the ER, or that a channel altogether distinct from Sec61 is used for dislocation. 相似文献
125.
Kaplun A Vyazmensky M Zherdev Y Belenky I Slutzker A Mendel S Barak Z Chipman DM Shaanan B 《Journal of molecular biology》2006,357(3):951-963
The enzyme acetohydroxyacid synthase (AHAS) catalyses the first common step in the biosynthesis of the three branched-chain amino acids. Enzymes in the AHAS family generally consist of regulatory and catalytic subunits. Here, we describe the first crystal structure of an AHAS regulatory subunit, the ilvH polypeptide, determined at a resolution of 1.75 A. IlvH is the regulatory subunit of one of three AHAS isozymes expressed in Escherichia coli, AHAS III. The protein is a dimer, with two beta alpha beta beta alpha beta ferredoxin domains in each monomer. The two N-terminal domains assemble to form an ACT domain structure remarkably close to the one predicted by us on the basis of the regulatory domain of 3-phosphoglycerate dehydrogenase (3PGDH). The two C-terminal domains combine so that their beta-sheets are roughly positioned back-to-back and perpendicular to the extended beta-sheet of the N-terminal ACT domain. On the basis of the properties of mutants and a comparison with 3PGDH, the effector (valine) binding sites can be located tentatively in two symmetrically related positions in the interface between a pair of N-terminal domains. The properties of mutants of the ilvH polypeptide outside the putative effector-binding site provide further insight into the functioning of the holoenzyme. The results of this study open avenues for further studies aimed at understanding the mechanism of regulation of AHAS by small-molecule effectors. 相似文献
126.
David I. Kline Lida Teneva Claudine Hauri Kenneth Schneider Thomas Miard Aaron Chai Malcolm Marker Rob Dunbar Ken Caldeira Boaz Lazar Tanya Rivlin Brian Gregory Mitchell Sophie Dove Ove Hoegh-Guldberg 《PloS one》2015,10(6)
Understanding the temporal dynamics of present thermal and pH exposure on coral reefs is crucial for elucidating reef response to future global change. Diel ranges in temperature and carbonate chemistry parameters coupled with seasonal changes in the mean conditions define periods during the year when a reef habitat is exposed to anomalous thermal and/or pH exposure. Anomalous conditions are defined as values that exceed an empirically estimated threshold for each variable. We present a 200-day time series from June through December 2010 of carbonate chemistry and environmental parameters measured on the Heron Island reef flat. These data reveal that aragonite saturation state, pH, and pCO2 were primarily modulated by biologically-driven changes in dissolved organic carbon (DIC) and total alkalinity (TA), rather than salinity and temperature. The largest diel temperature ranges occurred in austral spring, in October (1.5 – 6.6°C) and lowest diel ranges (0.9 – 3.2°C) were observed in July, at the peak of winter. We observed large diel total pH variability, with a maximum range of 7.7 – 8.5 total pH units, with minimum diel average pH values occurring during spring and maximum during fall. As with many other reefs, the nighttime pH minima on the reef flat were far lower than pH values predicted for the open ocean by 2100. DIC and TA both increased from June (end of Fall) to December (end of Spring). Using this high-resolution dataset, we developed exposure metrics of pH and temperature individually for intensity, duration, and severity of low pH and high temperature events, as well as a combined metric. Periods of anomalous temperature and pH exposure were asynchronous on the Heron Island reef flat, which underlines the importance of understanding the dynamics of co-occurrence of multiple stressors on coastal ecosystems. 相似文献
127.
Naama Yahalom-Mack Dafna Langgut Omri Dvir Ofir Tirosh Adi Eliyahu-Behar Yigal Erel Boaz Langford Amos Frumkin Mika Ullman Uri Davidovich 《PloS one》2015,10(12)
In the deepest section of a large complex cave in the northern Negev desert, Israel, a bi-conical lead object was found logged onto a wooden shaft. Associated material remains and radiocarbon dating of the shaft place the object within the Late Chalcolithic period, at the late 5th millennium BCE. Based on chemical and lead isotope analysis, we show that this unique object was made of almost pure metallic lead, likely smelted from lead ores originating in the Taurus range in Anatolia. Either the finished object, or the raw material, was brought to the southern Levant, adding another major component to the already-rich Late Chalcolithic metallurgical corpus known to-date. The paper also discusses possible uses of the object, suggesting that it may have been used as a spindle whorl, at least towards its deposition. 相似文献
128.
Some of the oxygen produced during oxygenic photosynthesis is consumed but little is known about the extent of the processes
involved. We measured the 17O/16O and 18O/16O ratios in O2 produced by certain marine and freshwater phytoplankton representing important groups of primary producers. When the cells
were performing photosynthesis under very low dissolved oxygen concentrations (<3 μM), we observed significant enrichment
in both 18O and 17O with respect to the substrate water. The difference in δ18O between O2 and water was about 4.5, 3, 5.5, and 7‰ in the diatom Phaeodactylum tricornutum, Nannochloropsis sp. (Eustigmatophyceae), the coccolithophore Emiliania huxleyi and the green alga Chlamydomonas reinhardtii, respectively. The difference in δ17O was about 0.52 that of δ18O. As explained, the observed enrichments most probably stem from considerable oxygen consumption during photosynthesis even
when major O2-consuming reactions such as photorespiration were minimized. These enrichments increased linearly with rising O2 levels but with different δ17O/δ18O slopes for the various organisms, suggesting engagements of different O2-consuming reactions with rising O2 levels. Consumption of O2 may be important for energy dissipation during photosynthesis. The isotope enrichment observed here, not accounted for in
earlier assessments, closes an important gap in our understanding of the difference between the isotopic compositions of atmospheric
oxygen and that of seawater, i.e., the Dole effect. 相似文献
129.
Harel E Rubinstein A Chen W Breuer E Tirosh B 《Bioorganic & medicinal chemistry letters》2010,20(22):6518-6523
Some carbamoylphosphonates (CPOs) inhibit matrix metalloproteinases (MMPs). Although MMPs are involved in inflammatory processes, the anti-inflammatory activity of CPOs has not been reported. In this context we compared the biological activity of the three aminoCPOs, PYR-CPO, PIP-CPO and cis-ACCP. We were particularly interested in their capability to modulate the secretion of tumor necrosis factor alpha (TNFα). LPS-activated mouse peritoneal macrophages and LPS-activated mouse splenocytes were used to explore this question. It was found that the aminoCPOs were able to reduce TNFα secretion to a level equivalent to the reduction caused by the steroid drug budesonide (BUD). The reduction in TNFα levels was neither accompanied by cytotoxicity, nor did it inhibit cell proliferation. To explicate whether the aminoCPOs affect TNFα processing by TNFα-converting enzyme (TACE), TACE inhibitory properties of the three molecules was tested in vitro. Only PIP-CPO exerted TACE inhibitory activity at therapeutic (non-cytotoxic) concentrations, indicating on its potential to serve as an anti-inflammatory agent by reducing TNFα secretion. 相似文献
130.
Sandhya Vasan Sarah J. Schlesinger Yaoxing Huang Arlene Hurley Angela Lombardo Zhiwei Chen Soe Than Phumla Adesanya Catherine Bunce Mark Boaz Rosanne Boyle Eddy Sayeed Lorna Clark Daniel Dugin Claudia Schmidt Yang Song Laura Seamons Len Dally Martin Ho Carol Smith Martin Markowitz Josephine Cox Dilbinder K. Gill Jill Gilmour Michael C. Keefer Patricia Fast David D. Ho 《PloS one》2010,5(1)