Geophysics. Longitudinal variation in springtime ozone trends

Satellite measurements indicate that mid-latitude ozone depletion in the Northern Hemisphere spring during 1979-97 was worst over Europe and Russia. Here we show that these longitudinal differences in ozone trends are due to a combination of decadal variations in the circulation and transport of ozone-depleted air from the polar vortex. Any increase in ozone depletion in the polar vortex as a result of future cooling of the stratosphere would therefore be particularly bad over Europe and Russia.     

Top-down gain control of the auditory space map by gaze control circuitry in the barn owl

High-level circuits in the brain that control the direction of gaze are intimately linked with the control of visual spatial attention. Immediately before an animal directs its gaze towards a stimulus, both psychophysical sensitivity to that visual stimulus and the responsiveness of high-order neurons in the cerebral cortex that represent the stimulus increase dramatically. Equivalent effects on behavioural sensitivity and neuronal responsiveness to visual stimuli result from focal electrical microstimulation of gaze control centres in monkeys. Whether the gaze control system modulates neuronal responsiveness in sensory modalities other than vision is unknown. Here we show that electrical microstimulation applied to gaze control circuitry in the forebrain of barn owls regulates the gain of midbrain auditory responses in an attention-like manner. When the forebrain circuit was activated, midbrain responses to auditory stimuli at the location encoded by the forebrain site were enhanced and spatial selectivity was sharpened. The same stimulation suppressed responses to auditory stimuli represented at other locations in the midbrain map. Such space-specific, top-down regulation of auditory responses by gaze control circuitry in the barn owl suggests that the central nervous system uses a common strategy for dynamically regulating sensory gain that applies across modalities, brain areas and classes of vertebrate species. This approach provides a path for discovering mechanisms that underlie top-down gain control in the central nervous system.     

Summer sea-surface temperatures and climate events on the North Icelandic shelf through the last 3000 years

Diatom data from core MD992271 on the North Icelandic shelf record a cooling trend through the last 3000 years. This is indicated by a general decrease in warm water species and an increase in cold water taxa. The relative abundance of these two diatom groups changed periodically, suggesting that the climate also fluctuated within this time period. The results of diatom-based transfer function calculation show that the summer sea-surface temperatures (SSTs) before 1400 cal. a BP were generally higher than the mean value for the last 3000 years and the summer SSTs fluctuated around the mean between 1400 and 700 cal. a BP, and dropped to the values below the mean after 700 cal. a BP. Four cooling events were distinguished, centered at around 2600, 1900, 1300 and 600 cal. a BP respectively. The results are not only consistent with the data from neighbouring cores HM107-03 and MD992275, but also comparable with those from the GISP2 ice core and from other marine sediment records in the North Atlantic. This suggests that changes in the summer SSTs reflect regional climate variations in the North Atlantic. On the North Icelandic shelf, the summer SST variation is a result of changes in the in-teraction between the cold and the warm currents in the area.     

Incremental training increases the plasticity of the auditory space map in adult barn owls

The plasticity in the central nervous system that underlies learning is generally more restricted in adults than in young animals. In one well-studied example, the auditory localization pathway has been shown to be far more limited in its capacity to adjust to abnormal experience in adult than in juvenile barn owls. Plasticity in this pathway has been induced by exposing owls to prismatic spectacles that cause a large, horizontal shift of the visual field. With prisms, juveniles learn new associations between auditory cues, such as interaural time difference (ITD), and locations in visual space, and acquire new neurophysiological maps of ITD in the optic tectum, whereas adults do neither. Here we show that when the prismatic shift is experienced in small increments, maps of ITD in adults do change adaptively. Once established through incremental training, new ITD maps can be reacquired with a single large prismatic shift. Our results show that there is a substantially greater capacity for plasticity in adults than was previously recognized and highlight a principled strategy for tapping this capacity that could be applied in other areas of the adult central nervous system.     

废弃羽毛资源化利用研究进展

综述了废弃羽毛资源化利用的方式和途径,对微波法促进废羽毛制备氨基酸及资源化利用进行了展望.指出了改善即时控制,加强微波化学反应及机理的研究,并继续羽毛水解后固体废物的资源化利用是其主要研究发展方向.     

原子核电四极矩跃迁强度新经验公式

通过分析8≤Z≤100偶偶原子核电四极矩跃迁强度B(E2:0+→2+)与2+态激发能E(2+)实验数据,提出了原子核电四极矩跃迁强度新经验公式B(E2:0+→2+)=33.65Z2 A-0.71 E-1(2+).     

预应力T梁产生裂纹的原因及处理

分析了京大高速公路工程预应力砼T梁在冬季施工中产生裂纹的原因，指出通过修改部分钢筋设计，将抽拔管改为波纹管，以及加强各工序规范施工即可避免裂纹的产生，同时对已有裂纹的处理办法进行了探讨。     

The optic tectum controls visually guided adaptive plasticity in the owl's auditory space map.

The midbrain contains an auditory map of space that is shaped by visual experience. When barn owls are raised wearing spectacles that horizontally displace the visual field, the auditory space map in the external nucleus of the inferior colliculus (ICX) shifts according to the optical displacement of the prisms. Topographic visual activity in the optic tectum could serve as the template that instructs the auditory space map. We studied the effects of a restricted, unilateral lesion in the portion of the optic tectum that represents frontal space. Here we show that such a lesion eliminates adaptive adjustments specifically in the portion of the auditory map that represents frontal space on the same side of the brain, while the rest of the map continues to adjust adaptively. Thus, activity in the tectum calibrates the auditory space map in a location-specific manner. Because the site of adaptive changes is the ICX, the results also indicate that the tectum provides a topographic instructive signal that controls adaptive auditory plasticity in the ICX.     

Instructed learning in the auditory localization pathway of the barn owl

A bird sings and you turn to look at it a process so automatic it seems simple. But is it? Our ability to localize the source of a sound relies on complex neural computations that translate auditory localization cues into representations of space. In barn owls, the visual system is important in teaching the auditory system how to translate cues. This example of instructed plasticity is highly quantifiable and demonstrates mechanisms and principles of learning that may be used widely throughout the central nervous system.