The remarkable inefficiency of word recognition

Do we recognize common objects by parts, or as wholes? Holistic recognition would be efficient, yet people detect a grating of light and dark stripes by parts. Thus efficiency falls as the number of stripes increases, in inverse proportion, as explained by probability summation among independent feature detectors. It is inefficient to detect correlated components independently. But gratings are uncommon artificial stimuli that may fail to tap the full power of visual object recognition. Familiar objects become special as people become expert at judging them, possibly because the processing becomes more holistic. Letters and words were designed to be easily recognized, and, through a lifetime of reading, our visual system presumably has adapted to do this as well as it possibly can. Here we show that in identifying familiar English words, even the five most common three-letter words, observers have the handicap predicted by recognition by parts: a word is unreadable unless its letters are separately identifiable. Efficiency is inversely proportional to word length, independent of how many possible words (5, 26 or thousands) the test word is drawn from. Human performance never exceeds that attainable by strictly letter- or feature-based models. Thus, everything seen is a pattern of features. Despite our virtuosity at recognizing patterns and our expertise from reading a billion letters, we never learn to see a word as a feature; our efficiency is limited by the bottleneck of having to rigorously and independently detect simple features.     

Solar chromospheric spicules from the leakage of photospheric oscillations and flows

Spicules are dynamic jets propelled upwards (at speeds of approximately 20 km s(-1)) from the solar 'surface' (photosphere) into the magnetized low atmosphere of the Sun. They carry a mass flux of 100 times that of the solar wind into the low solar corona. With diameters close to observational limits (< 500 km), spicules have been largely unexplained since their discovery in 1877: none of the existing models can account simultaneously for their ubiquity, evolution, energetics and recently discovered periodicity. Here we report a synthesis of modelling and high-spatial-resolution observations in which numerical simulations driven by observed photospheric velocities directly reproduce the observed occurrence and properties of individual spicules. Photospheric velocities are dominated by convective granulation (which has been considered before for spicule formation) and by p-modes (which are solar global resonant acoustic oscillations visible in the photosphere as quasi-sinusoidal velocity and intensity pulsations). We show that the previously ignored p-modes are crucial: on inclined magnetic flux tubes, the p-modes leak sufficient energy from the global resonant cavity into the chromosphere to power shocks that drive upward flows and form spicules.     

格群的积扭类及积拟扭类

讨论了两灯格群根式类－积扭类及积拟扭类，给出了积扭根式映射及积拟扭根式映射的特征性质，并具体刻画了积扭类格及积扭类格中的极运算。     

Females increase offspring heterozygosity and fitness through extra-pair matings

Females in a variety of species commonly mate with multiple males, and there is evidence that they benefit by producing offspring of higher genetic quality; however, the nature of these genetic benefits is debated. Enhanced offspring survival or quality can result from intrinsic effects of paternal genes---'good genes'--or from interactions between the maternal and paternal genomes--'compatible genes'. Evidence for the latter process is accumulating: matings between relatives lead to decreased reproductive success, and the individual level of inbreeding--measured as average heterozygosity--is a strong fitness predictor. Females should thus benefit from mating with genetically dissimilar males. In many birds, social monogamy restricts mate choice, but females may circumvent this by pursuing extra-pair copulations. Here we show that female blue tits, Parus caeruleus, increase the heterozygosity of their progeny through extra-pair matings. Females thereby produce offspring of higher reproductive value, because less inbred individuals have increased survival chances, a more elaborate male secondary sexual trait (crown colour) and higher reproductive success. The cost of inbreeding may therefore be an important factor driving the evolution of female extra-pair mating.     

Electronic spin transport and spin precession in single graphene layers at room temperature

Electronic transport in single or a few layers of graphene is the subject of intense interest at present. The specific band structure of graphene, with its unique valley structure and Dirac neutrality point separating hole states from electron states, has led to the observation of new electronic transport phenomena such as anomalously quantized Hall effects, absence of weak localization and the existence of a minimum conductivity. In addition to dissipative transport, supercurrent transport has also been observed. Graphene might also be a promising material for spintronics and related applications, such as the realization of spin qubits, owing to the low intrinsic spin orbit interaction, as well as the low hyperfine interaction of the electron spins with the carbon nuclei. Here we report the observation of spin transport, as well as Larmor spin precession, over micrometre-scale distances in single graphene layers. The 'non-local' spin valve geometry was used in these experiments, employing four-terminal contact geometries with ferromagnetic cobalt electrodes making contact with the graphene sheet through a thin oxide layer. We observe clear bipolar (changing from positive to negative sign) spin signals that reflect the magnetization direction of all four electrodes, indicating that spin coherence extends underneath all of the contacts. No significant changes in the spin signals occur between 4.2 K, 77 K and room temperature. We extract a spin relaxation length between 1.5 and 2 mum at room temperature, only weakly dependent on charge density. The spin polarization of the ferromagnetic contacts is calculated from the measurements to be around ten per cent.     

From Single Droplet to Column Design

The technique state to design counter-current extraction columns is based on the performance of pilot plant experiments. The modelling is then either with the equilibrium or dispersion model, whereas in the latter the dispersion coefficient accounts for all hydrodynamic non-idealities. A new approach uses single droplet experiments to obtain the basic laws and functions governing droplet breakage, coalescence, relative velocity, and axial dispersion when using droplet populance balance models （DPBM）. The hydrodynamics simulation results show that the mean Sauter diameter, hold-up, and concentration profiles could be well predicted, which promotes the use of DPBM models for further applications in industrial scale.