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We use tools of the equilibrium statistical mechanics of disordered systems to study analytically the statistical properties of an ecosystem composed of N species interacting via random mutual interactions, as well as via deterministic self-interactions of order p>/=2. We show that the main effect of increasing the order of the interactions among the species is to make the system less competitive, in the sense that the fraction of extinct species is greatly reduced. In addition, we find that for p>2 there is a threshold value which gives a lower bound to the concentration of the surviving species, preventing then the existence of rare species and, consequently, increasing the robustness of the ecosystem to external perturbations. 相似文献
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Allison M Fox Mike Anderson Corinne Reid Tim Smith Dorothy VM Bishop 《BMC neuroscience》2010,11(1):1-15
Background
We examined development of auditory temporal integration and inhibition by assessing electrophysiological responses to tone pairs separated by interstimulus intervals (ISIs) of 25, 50, 100, 200, 400, and 800 ms in 28 children aged 7 to 9 years, and 15 adults.Results
In adults a distinct neural response was elicited to tones presented at ISIs of 25 ms or longer, whereas in children this was only seen in response to tones presented at ISIs above 100 ms. In adults, late N1 amplitude was larger for the second tone of the tone pair when separated by ISIs as short as 100 ms, consistent with the perceptual integration of successive stimuli within the temporal window of integration. In contrast, children showed enhanced negativity only when tone pairs were separated by ISIs of 200 ms. In children, the amplitude of the P1 component was attenuated at ISIs below 200 ms, consistent with a refractory process.Conclusions
These results indicate that adults integrate sequential auditory information into smaller temporal segments than children. These results suggest that there are marked maturational changes from childhood to adulthood in the perceptual processes underpinning the grouping of incoming auditory sensory information, and that electrophysiological measures provide a sensitive, non-invasive method allowing further examination of these changes. 相似文献3.
James W. Pavlik Heather S T. Martin Karen A. Lambert Jennifer A. Lowell Vikki M. Tsefrikas Cheryl K. Eddins Naod Kebede 《Journal of heterocyclic chemistry》2005,42(2):273-281
5‐Phenylisoxazole ( 4 ) and 4‐phenylisoxazole ( 22 ) underwent phototransposition to 5‐phenyloxazole ( 5 ) and 4‐phenyloxazole ( 24 ) respectively. Labeling with deuterium or methyl confirmed that these phototranspositions occurred via the P4 pathway which involves only interchange of the N2 and C3 ring position. Thus, 4‐deuterio‐5‐phenylisoxazole ( 4‐4d ), 4‐methyl‐5‐phenylisoxazole ( 10 ), and 5‐methyl‐4‐phenylisoxazole ( 23 ) phototransposed to 4‐deuterio‐5‐phenyloxazole ( 5‐4d ), 4‐methyl‐5‐phenyloxazole ( 11 ), and 5‐methyl‐4‐phenyloxazole ( 25 ) respectively. In addition to phototransposition, isoxazoles 4, 10 , and 23 also underwent photo‐ring cleavage to yield benzoylacetonitrile (9), α‐benzoylpropionitrile ( 15 ), and aceto‐α‐phenylacetonitrile ( 26 ) respectively. Irradiation of 5‐phenyl‐3‐(trifluoromethyl)isoxazole ( 16 ) in acetonitrile led to 5‐phenyl‐2‐(trifluoromethyl)oxazole ( 17 ), the P4 phototransposition product. Irradiation of 16 in methanol led to a substantial decrease in the yield of 17 and to the formation of a mixture of (E) and (Z)‐2‐methoxy‐2‐(trifluoromethyl)‐3‐benzoylaziridines 18a and 18b . 相似文献
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Tsefrikas VM Arns S Merner PM Warford CC Merner BL Scott LT Bodwell GJ 《Organic letters》2006,8(23):5195-5198
[Structure: see text] Flash vacuum pyrolysis of 7,10-bis(2-bromophenyl)acenaphtho[1,2-d]pyridazine (C26H14Br2N2) has resulted in a surprising transformation, including dinitrogen loss, to give benzo[a]acecorannulene, a novel C26H12 bowl-shaped fullerene fragment. 相似文献
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Irradiation of 5-phenyl-1,2,4-thiadiazole (6) resulted in the formation of benzonitrile (5), 3-phenyl-1,2,4-thiadiazole (4), phenyl- and diphenyl-1,3,5-triazines (7 and 8), and a trace quantity of diphenyl-1,2,4-thiadiazole (9). The formation of 4,5, 7, and 8 can be explained in terms of photoinduced electrocyclic ring closure resulting in the formation of an intermediate 4-phenyl-1,3-diaza-5-thiabicyclo[2.1.0]pentene. 15N-labeling experiments revealed that sulfur can undergo sigmatropic shifts around all four sides of the diazetine ring. Thus, irradiation of 6-4-15N led to the formation of 6-2-15N and an equimolar mixture of 4-2-15N and 4-4-15N. The thiabicyclo[2.1.0]pentene intermediate is also suggested to undergo sulfur elimination resulting in the formation of phenyldiazacyclobutadiene, which can undergo complete fragmentation to benzonitrile or [4+2] cycloaddition leading to unstable tricyclic adducts, the suggested precursors of the 1,3,5-triazine products 7 and 8. The observed 15N distribution in 7 and 8 is consistent with this mechanism. Irradiation of 4 led only to the formation of 5. 15N-labeling experiments show that 4 does not undergo electrocyclic ring closure but reacts exclusively by photofragmentation of the thiadiazole ring. 相似文献
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