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Miniature eye movements enhance fine spatial detail 总被引:1,自引:0,他引:1
Our eyes are constantly in motion. Even during visual fixation, small eye movements continually jitter the location of gaze. It is known that visual percepts tend to fade when retinal image motion is eliminated in the laboratory. However, it has long been debated whether, during natural viewing, fixational eye movements have functions in addition to preventing the visual scene from fading. In this study, we analysed the influence in humans of fixational eye movements on the discrimination of gratings masked by noise that has a power spectrum similar to that of natural images. Using a new method of retinal image stabilization, we selectively eliminated the motion of the retinal image that normally occurs during the intersaccadic intervals of visual fixation. Here we show that fixational eye movements improve discrimination of high spatial frequency stimuli, but not of low spatial frequency stimuli. This improvement originates from the temporal modulations introduced by fixational eye movements in the visual input to the retina, which emphasize the high spatial frequency harmonics of the stimulus. In a natural visual world dominated by low spatial frequencies, fixational eye movements appear to constitute an effective sampling strategy by which the visual system enhances the processing of spatial detail. 相似文献
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Bipolar supercurrent in graphene 总被引:3,自引:0,他引:3
Graphene--a recently discovered form of graphite only one atomic layer thick--constitutes a new model system in condensed matter physics, because it is the first material in which charge carriers behave as massless chiral relativistic particles. The anomalous quantization of the Hall conductance, which is now understood theoretically, is one of the experimental signatures of the peculiar transport properties of relativistic electrons in graphene. Other unusual phenomena, like the finite conductivity of order 4e(2)/h (where e is the electron charge and h is Planck's constant) at the charge neutrality (or Dirac) point, have come as a surprise and remain to be explained. Here we experimentally study the Josephson effect in mesoscopic junctions consisting of a graphene layer contacted by two closely spaced superconducting electrodes. The charge density in the graphene layer can be controlled by means of a gate electrode. We observe a supercurrent that, depending on the gate voltage, is carried by either electrons in the conduction band or by holes in the valence band. More importantly, we find that not only the normal state conductance of graphene is finite, but also a finite supercurrent can flow at zero charge density. Our observations shed light on the special role of time reversal symmetry in graphene, and demonstrate phase coherent electronic transport at the Dirac point. 相似文献
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在钢水浇铸过程中,需要严格控制钢包到中间包的钢渣量.通过对国外多种下渣检测技术的调研分析及国内多个钢厂的现场试验,提出了一种高灵敏性的钢包下渣检测装置,从硬件上改变了传统采集的单一检测方式,同时在软件上简化了下渣特征提取的算法.通过在现场使用,取得了较好的检测效果,有效控制了进入中间包内的钢渣量,提高了钢厂的经济效益. 相似文献
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Jorge A. Duran-Encalada Alberto Paucar-Caceres 《Systemic Practice and Action Research》2009,22(2):77-99
This paper reports on an on-going project on urban sustainability, the Puerto Aura in the region of the Valsequillo Lake in
Puebla, Mexico. As part of the project, a simulation model was built to explore the dynamic interaction of the dimensions
inherent in sustainable urban development. After reviewing literature on sustainable urban development (SUD) frameworks and
tools, we identify key variables that intervene in SUD. We propose a System Dynamics model to simulate the dimensions that
intervene in a sustainable development and to anticipate the consequences of the decision making process. The structure and
inter-relationships of four sectors in the proposed model are described, the sustainability indicators in each sector explained.
Preliminary conclusions are drawn stating that a complete run of the model simulating a 20 years horizon in monthly periods
is expected when the full data from the Puerto Aura master plan becomes available.
相似文献
Alberto Paucar-Caceres (Corresponding author)Email: |
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Mutations in kelch-like 3 and cullin 3 cause hypertension and electrolyte abnormalities 总被引:2,自引:0,他引:2
Boyden LM Choi M Choate KA Nelson-Williams CJ Farhi A Toka HR Tikhonova IR Bjornson R Mane SM Colussi G Lebel M Gordon RD Semmekrot BA Poujol A Välimäki MJ De Ferrari ME Sanjad SA Gutkin M Karet FE Tucci JR Stockigt JR Keppler-Noreuil KM Porter CC Anand SK Whiteford ML Davis ID Dewar SB Bettinelli A Fadrowski JJ Belsha CW Hunley TE Nelson RD Trachtman H Cole TR Pinsk M Bockenhauer D Shenoy M Vaidyanathan P Foreman JW Rasoulpour M Thameem F Al-Shahrouri HZ Radhakrishnan J Gharavi AG Goilav B 《Nature》2012,482(7383):98-102
Hypertension affects one billion people and is a principal reversible risk factor for cardiovascular disease. Pseudohypoaldosteronism type II (PHAII), a rare Mendelian syndrome featuring hypertension, hyperkalaemia and metabolic acidosis, has revealed previously unrecognized physiology orchestrating the balance between renal salt reabsorption and K(+) and H(+) excretion. Here we used exome sequencing to identify mutations in kelch-like 3 (KLHL3) or cullin 3 (CUL3) in PHAII patients from 41 unrelated families. KLHL3 mutations are either recessive or dominant, whereas CUL3 mutations are dominant and predominantly de novo. CUL3 and BTB-domain-containing kelch proteins such as KLHL3 are components of cullin-RING E3 ligase complexes that ubiquitinate substrates bound to kelch propeller domains. Dominant KLHL3 mutations are clustered in short segments within the kelch propeller and BTB domains implicated in substrate and cullin binding, respectively. Diverse CUL3 mutations all result in skipping of exon 9, producing an in-frame deletion. Because dominant KLHL3 and CUL3 mutations both phenocopy recessive loss-of-function KLHL3 mutations, they may abrogate ubiquitination of KLHL3 substrates. Disease features are reversed by thiazide diuretics, which inhibit the Na-Cl cotransporter in the distal nephron of the kidney; KLHL3 and CUL3 are expressed in this location, suggesting a mechanistic link between KLHL3 and CUL3 mutations, increased Na-Cl reabsorption, and disease pathogenesis. These findings demonstrate the utility of exome sequencing in disease gene identification despite the combined complexities of locus heterogeneity, mixed models of transmission and frequent de novo mutation, and establish a fundamental role for KLHL3 and CUL3 in blood pressure, K(+) and pH homeostasis. 相似文献
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