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931.
PurposeTo conduct a simplified lesion-detection task of a low-dose (LD) PET-CT protocol for frequent lung screening using 30% of the effective PETCT dose and to investigate the feasibility of increasing clinical value of low-statistics scans using machine learning.MethodsWe acquired 33 SD PET images, of which 13 had actual LD (ALD) PET, and simulated LD (SLD) PET images at seven different count levels from the SD PET scans. We employed image quality transfer (IQT), a machine learning algorithm that performs patch-regression to map parameters from low-quality to high-quality images. At each count level, patches extracted from 23 pairs of SD/SLD PET images were used to train three IQT models – global linear, single tree, and random forest regressions with cubic patch sizes of 3 and 5 voxels. The models were then used to estimate SD images from LD images at each count level for 10 unseen subjects. Lesion-detection task was carried out on matched lesion-present and lesion-absent images.ResultsLD PET-CT protocol yielded lesion detectability with sensitivity of 0.98 and specificity of 1. Random forest algorithm with cubic patch size of 5 allowed further 11.7% reduction in the effective PETCT dose without compromising lesion detectability, but underestimated SUV by 30%.ConclusionLD PET-CT protocol was validated for lesion detection using ALD PET scans. Substantial image quality improvement or additional dose reduction while preserving clinical values can be achieved using machine learning methods though SUV quantification may be biased and adjustment of our research protocol is required for clinical use. 相似文献
932.
Jianfu Zhou Gevorg Grigoryan 《Protein science : a publication of the Protein Society》2015,24(4):508-524
Finding backbone substructures from the Protein Data Bank that match an arbitrary query structural motif, composed of multiple disjoint segments, is a problem of growing relevance in structure prediction and protein design. Although numerous protein structure search approaches have been proposed, methods that address this specific task without additional restrictions and on practical time scales are generally lacking. Here, we propose a solution, dubbed MASTER, that is both rapid, enabling searches over the Protein Data Bank in a matter of seconds, and provably correct, finding all matches below a user-specified root-mean-square deviation cutoff. We show that despite the potentially exponential time complexity of the problem, running times in practice are modest even for queries with many segments. The ability to explore naturally plausible structural and sequence variations around a given motif has the potential to synthesize its design principles in an automated manner; so we go on to illustrate the utility of MASTER to protein structural biology. We demonstrate its capacity to rapidly establish structure–sequence relationships, uncover the native designability landscapes of tertiary structural motifs, identify structural signatures of binding, and automatically rewire protein topologies. Given the broad utility of protein tertiary fragment searches, we hope that providing MASTER in an open-source format will enable novel advances in understanding, predicting, and designing protein structure. 相似文献
933.
934.
935.
We observed female beaugregory damselfish (Stegastes leucostictus) as they interacted with males to see whether their movements fit the predictions of different mate-search models. We established
high-quality and low-quality groups with low variance in breeding site quality and a medium-quality, high-variance breeding
site group and compared focal observations of female nonforaging forays in each group. Only 8% of 137 forays monitored resulted
in spawning events. Eighty-nine percent of the forays were less than 240 s and were within 7 m of the focal female’s territory.
Average foray times and straight-line foray distances did not differ for females traveling between males in each group. Females
entered high-quality breeding sites at a higher rate than low-quality sites and round-trip distances were also greatest in
high-quality groups, indicating that females were following a more convoluted path. We interpret these results to mean that
(a) female beaugregories separate the tasks of mate assessment and mate choice by conducting information-gathering forays
between mating events, (b) forays are energetically costly and therefore usually short in duration and overall distance traveled,
(c) information collection takes approximately the same time for high-quality and low-quality mates, but (d) females will
alter their foray patterns in high-quality areas to collect additional information. These data are also consistent with the
hypothesis that females optimize their search by employing a tiered process of assessment during information-gathering forays,
first using an adjustable threshold to accept or reject each male based on his courtship and subsequently a fixed threshold
to assess the quality of each breeding site. 相似文献
936.
ABSTRACT. The searching tactics of the housefly, Musca dormestica L. (Diptera: Muscidae), have been delineated from digitized pathways of flies walking in patches of sucrose drops arranged in linear (ROW) and hexagonal (HEX) arrays. The areas covered by flies in ROW and HEX patches are distinctly different, but flies seem not to employ different tactics for the two types of resource arrays. The number of drops located, if at least one drop is found, does not differ between ROW and HEX. Most quantitative measures of local search remain constant after the first interdrop interval, although feeding time decreases as flies sample successive drops. Local search intensifies after each drop is ingested, with locomotory rate decreasing and turning rate increasing, followed by decay of both measures toward ranging levels. Searching can be characterized by two movement tendencies resulting from specific, definable, locomotory functions: a forward-moving tendency is expressed by the fly as it leaves a resource in approximately the same direction as it arrives; and local search is characterized by looping, rather than straight walking, with a variable turning rate that generates a rough ‘zigzag’ superimposed on looping. The two movement tendencies, combined, allow flies to locate resources in a linear arrangement, because of the forward-moving tendency, and to locate resources not arranged in a linear array because of the ‘noisy’ loop. M. domestica does not appear to retain and use information gained from one patch of drops in another, so the search tactic of the fly seems therefore to be a compromise between straight movement and circular movement that may be adaptive for an environment subject to frequent changes in the spatial distribution of resources. Giving-up-time, the period between ingesting the last drop and leaving the patch, is a function of the rate of change in the transition from local search to ranging, which is constant in our experiments. If a fly does not encounter another drop while ranging, during which it walks relatively straight, the fly moves out of and away from the patch. 相似文献
937.
Renato Cavasini Marcos Roberto Dias Batista Louis Bernard Klaczko 《Genetics and molecular biology》2015,38(1):55-58
Drosophila mediopunctata has been used as a model organism for
genetics and evolutionary studies in the last three decades. A linkage map with 48
microsatellite loci recently published for this species showed five syntenic groups,
which had their homology determined to Drosophila melanogaster
chromosomes. Then, by inference, each of the groups was associated with one of the
five major chromosomes of D. mediopunctata. Our objective was to
carry out a genetic (chromosomal) analysis to increase the number of available loci
with known chromosomal location. We made a simultaneous analysis of visible mutant
phenotypes and microsatellite genotypes in a backcross of a standard strain and a
mutant strain, which had each major autosome marked. Hence, we could establish the
chromosomal location of seventeen loci; including one from each of the five major
linkage groups previously published, and twelve new loci. Our results were congruent
with the previous location and they open new possibilities to future work integrating
microsatellites, chromosomal inversions, and genetic determinants of physiological
and morphological variation. 相似文献
938.
1. Omnivorous woodland ant species trade off between the ability to find and behaviourally control food resources. Dominant species can limit the ability of subordinates to harvest certain food items. However, subordinate species, by being faster discoverers, could gain access to such food items by arriving at them first. 2. In this study, we tested the hypothesis that resource‐directed discovery occurs in ant communities and that good discoverers preferentially discover high value resources. We did this by measuring time to discovery and the number of discoveries of high and low levels of two resource types, crickets and honey, for species occurring in Texas and Arizona woodland ant communities. 3. Ants discovered resources roughly 10 times faster in Texas than in Arizona. They discovered crickets more rapidly than honey in both communities, but there was no difference in the discovery of different resource levels. We also found that species were not biased in their discovery of different resource types or levels. 4. These results provide indirect evidence that discovery is directed by resource stimuli but that such directedness does not impact interspecific exploitative competition. 相似文献
939.
940.
Masaki Tomonaga 《Primates; journal of primatology》1993,34(2):161-168
During a visual search performance by a chimpanzee (Pan troglodytes), horizontal location (column) of target was sequentially changed across 48-trial blocks. Reaction time was used for measure
of facilitatory and inhibitory effects of the blocked-trial fixation on her search performance. The chimpanzee showed significant
decrease of response time in the later phase of each block in comparison with the condition in which the target location was
changed to another column than before changing. Furthermore, difference in response time before and after changing column
monotonically and linearly increased as a function of distance between columns. In summary, the blocked-trial fixation of
the target location facilitated the chimpanzee's visual-search performance, and that when the pretrial information became
invalid, her performance was clearly disrupted. Pretrial information about target location could “prime” and modify the chimpanzee's
search strategy. 相似文献