一种目视激光显微镜

本文介绍一种目视激光显微镜。该装置采用白炽灯和激光做光源。通过调压器衬底亮度可以调整到零。由于激光的高亮度和强相干性,与普通显微镜相比,该显微镜具有景深长,分辨率高,层次丰富的特点。使用该显微镜时能实现镜象的假色彩编码,且镜象具有立体感。文中报导了该显微镜的原理和使用效果。     

A visually evoked escape response of the housefly

Summary Flies (Musca domestica) avoid danger by initiating a rapid jump followed by flight. To identify the visual cues that trigger the escape response in the housefly, we measured the timing and probability of escapes when the fly was presented with a variety of visual stimuli created by moving targets toward it. Our results show that an escape response is triggered by an approaching dark disk, but not by a receding dark disk. On the other hand, a bright disk elicits escape only when it recedes. A disk with black and white rings is less effective at eliciting escape than is a dark solid disk of the same size. This indicates that the darkening contrast produced by an approaching stimulus is a more crucial parameter than expansion cues contained in the optical flow. Escape is also triggered by a horizontally moving dark edge, but not by a moving bright edge or by a grating. An examination of several visual parameters reveals that the darkening contrast, measured from the onset of stimulation to the start of escape is nearly constant for a variety of stimuli that trigger escape reliably. Thus darkening contrast, coupled with motion may be crucial in eliciting the visually evoked escape response. Other visual parameters such as time-to-contact or target angular velocity seem to be relatively unimportant to the timing of escapes.Abbreviations P _s Probability of successful escape - r _disk radius of disk target - r _arena radius of shielding arena - v _disk linear velocity of disk target - v _edge linear velocity of edge - d _disk angular velocity of disk target boundary - _edge angular velocity of edge - _escape target distance at escape - d _start target distance before onset of target movement - h _edge height of the edge above fly - x _start distance from corner of triangle to start position of edge (0 or 50 mm) - x _escape distance from corner of triangle to the position of the edge when the fly escapes - x _center distance from corner of triangle to point above the center of the pad - x _total distance from the corner of the triangle to the base (height of triangle = base of triangle)     

Purification and properties of xylanase fromAureobasidium

Summary The yeast-like fungusAureobasidium is a promising source of xylanase (EC 3.2.1.8) with an exceptionally high specific activity. For enzyme production in volumes of several liters, xylose was the preferred carbon source and inducer. Xylanase in clarified cultures was concentrated by reversible adsorption to cation-exchange matrix to 5% of the initial volume, and recovered at nearly 2 million IU/1. Selective conditions permitted 97% recovery of xylanase with a 1.8-fold enrichment in specific activity, to 70% of purity. The predominant xylanase species (20 kDa) was subsequently purified to >99% of homogeneity by gel filtration chromatography. Purified enzyme exhibited an isoelectric point of 8.5, and specific activity of 2100 IU/mg under optimal conditions, determined to be pH 4.5 and 45°C. The activity of purified enzyme was specific for polymeric xylan.The mention of firm names or trade products does not imply that they are endorsed or recommended by the U.S. Dept. of Agirculture over other firms or similar products not mentioned.     

New Mechanism of Melanosomes Transport into Hair of Lambs of Different Breeds and Genotypes

By light microscopic investigation of skin and wool specimens of newborn lambs, we discovered a previously unknown mechanism for melanosomes transport in the process of dermal papilla melanocytes regular mitosis and migration into the hair shaft. This mechanism plays a great role in hair pigmentation especially in dominant (E^D/E^D) and recessive (A^a/A^a) black lambs of all investigated breeds. The rate of pigment cell mitosis, proliferation, and migration differs greatly in lambs of investigated color genotypes. In black genotypes the rate of melanocyte mitosis is very high and is approximately the same as in the hair bulb matrix cells, whereas in brown and red genotypes this rate is much lower. Melanocyte mitosis in the light red and tan groups was not found.     

Pattern recognition in honeybees: chromatic properties of orientation analysis

The spectral properties of the discrimination of pattern orientation in freely flying honeybees (Apis mellifera) were examined. Bees were trained to discriminate between two random black/white gratings oriented perpendicularly to each other, one of which was associated with a reward. Subsequently the bees were tested on two-colour gratings or gratings consisting of grey and coloured stripes, providing a range of different chromatic contrasts, luminance contrasts and specific channel contrasts. The results of these experiments indicate that orientation analysis in the honeybee is mediated almost exclusively by the green receptor channel, although the bee's visual system as a whole is endowed with excellent trichromatic colour vision.     

The orientation behaviour of the lesser spearnosed bat, Phyllostomus discolor (Chiroptera) in a model roost

The orientation behaviour of bats (Phyllostomus discolor, Phyllostomidae), flying inside an octagonal roost-like chamber (ø: 100cm; h: 150cm) was examined.It has been shown that the bats begin turning manoeuvres during flight by turning their head towards the direction they intend to proceed to. During early phases of the flights, cumulative navigation errors were evident, indicating that endogenous spatial information plays a major role in the orientation of the bats. During later phases of the flight this error is diminished again. So it can be concluded that the bats start to use exogenous spatial information for orientation while approaching the target.In order to investigate the relative importance of vision, echolocation and endogenous spatial information for approaching the roost, the landing lattices inside the test arena were changed for non-grid dummies. We found that: 1. combined visual and endogenous information are more important than echoacoustical cues, 2. the bats learned quickly to switch their orientation behaviour in order to get a better performance in avoiding the dummies, 3. the learning performance was influenced by the visual similarity of dummies and the real landing lattice.     

Chemical and Electron Microscopic Studies of Cattle (Bos taurus) With Four Types of Phenotypic Pigmentation

The biological behavior of the pigmentary phenotypes of four breeds of cattle has been analysed: the black pigmentation of Holstein Friesian; the red pigmentation of Limousin; the dilution in Charolais; and the postnatal disappearance of red pigmentation in Chianina. The analytic techniques included the characterization of melanins by high-performance liquid chromatography, the examination of follicular melanocytes by light microscopy, and the examination of melanosomes by electron microscopy. The black phenotype was very strongly eumelanogenic. The red phenotype in Limousin is polymorphic: individual follicular melanocytes contain both mature eumelanosomes and pheomelanosomes. Charolais and Chianina cattle exhibited a dramatic reduction in melanogenic activity, which was characterized by the almost exclusive presence of prephaoemelanosomes in Charolais and of immature premelanosomes in Chianina. In the dilute Charolais phenotype, the density of distribution of follicular melanocytes also seemed to be reduced. The genes that are responsible for these four phenotypes seem to act on the maturation, differentiation, and density of distribution of the melanosomes.     

Ecomorphological adaptations to bioluminescence in Porichthys notatus

Synopsis The midshipman fish, Porichthys notatus, is a visually active nocturnal predator. It must acquire exogenous sources of luciferin to remain luminescent and feeds on a variety of luminescent prey. Its ecomorphological adaptations for nocturnal predation were examined by observing predation on zooplankton illuminated by dinoflagellates. Its visual sensitivity is well adapted for detection of its own luminescence and its prey's luminescence. P. notatus can detect the luminescence of dinoflagellates and use this indirect light to increase predation on nonluminescent prey. Flash frequency and duration modulated predation rates. The interval between flash onset and strike initiation regulated strike success. High prey concentration decreased predation success due to increased optical and mechanosensory noise. Other ecomorphological adaptations of this predator to its special photic environment include a pigmented digestive tract, duplex retina with the capacity to discriminate emission spectra, contractible pupil, and the potential to counter illuminate. These morphological adaptations combined with an ambush predator style allow effective predation while minimizing exposure risk.     

Light-dependent conformational change at rhodopsin's cytoplasmic surface detected by increased susceptibility to proteolysis

Rhodopsin in bovine photoreceptor disk membranes was subjected to limited proteolysis by thermolysin, removing twelve amino acids from rhodopsin's carboxyl terminus. (1) The rate of proteolysis is significantly faster with rhodopsin following exposure to light than with unbleached rhodopsin, provided that the incubation conditions (pH, temperature) favor the formation of metarhodopsin II. (2) If the disk membranes are illuminated under conditions in which metarhodopsin I is the predominant photoproduct (pH 8.5, 0°C), no increase in the rate of proteolysis is observed compared to unilluminated membranes. (3) The light-induced increase in the rate of proteolysis is transient: it slowly decays in the dark to the original rate found for unbleached rhodopsin. The enhanced susceptibility to proteolysis appears to measure a conformational change at rhodopsin's cytoplasmic surface which is first exhibited at the metarhodopsin II stage. This and possibly other light-dependent changes may allow rhodopsin to mediate its signal as a light-receptor protein by binding to and activating certain rod cell enzymes.     

色觉异常的数学模型

色盲是一种遗传性疾病,由于色觉机理尚未研究清楚,一向不能矫治。为了解除色盲患者的苦脑,增加他们在升学、就业和职业选择中的权利,我们通过色觉过程的拓扑学研究,建立了色觉异常的突变模型;论证了色盲矫治机理;研制了色盲电脑诊断矫正检测仪。为色盲眼镜的批量生产和患者的配镜提供准确的矫正曲线。