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1.
根据树木年轮图像的特点,提出了一种基于直方图变化特征的椭圆分块和最大类间方差法的树木年轮图像自适应分割方法。并运用该方法对落叶松的年轮图像进行分割,结果表明,该方法对树木年轮图像的分割效果非常理想。 相似文献
2.
大熊猫分布区珍稀濒危物种丰富度空间格局与热点区分析 总被引：2，自引：1，他引：1
分析物种丰富度格局和热点区是保护生物多样性的有效手段和途径。本文基于珍稀濒危物种名录信息,结合遥感影像、文献信息和专家经验,研究了大熊猫分布区内珍稀濒危物种及中国特有珍稀濒危物种的丰富度空间格局,确定了物种丰富度热点区,分析了大熊猫保护区对热点区保护的有效性。结果表明:大熊猫分布区内,与大熊猫同域分布的珍稀濒危物种有293种,包括哺乳动物109种、鸟类58种、爬行动物18种、两栖动物35种、高等植物73种;其中,IUCN极危物种11种、濒危物种48种、易危物种111种、近危物种74种,列入CITES附录Ⅱ2种,国家一级保护植物7种,国家二级保护植物36种;293种珍稀濒危物种中,133种为中国特有,19种为大熊猫分布区特有。大熊猫分布区中,岷山的文县和平武,邛崃山的汶川、宝兴和康定珍稀濒危物种丰富度最高,达到15~19种/km2,物种密集区呈块状或线状破碎化分布;秦岭山系、岷山山系和邛崃山系为中国特有珍稀濒危物种丰富度最高的集中分布区,丰富度为5~6种/km2;海拔1400~1600m和1800~2000m,分别为珍稀濒危物种和中国特有珍稀濒危物种丰富度最高的海拔区段,物种丰富度达186种和77种;800~2800m是珍稀濒危物种和中国特有珍稀濒危物种分布最密集的海拔范围,分别覆盖了88.4%的珍稀濒危物种和87.2%的中国特有珍稀濒危物种。大熊猫分布区有6个珍稀濒危物种丰富度热点区,占分布区总面积的10.5%,覆盖了分布区85%的珍稀濒危物种;中国特有珍稀濒危物种热点区,占分布区总面积的17.2%,覆盖了85%的中国特有珍稀濒危物种。大熊猫保护区,覆盖了27.6%的珍稀濒危物种热点区和21.4%的中国特有珍稀濒危物种热点区,保护了71.7%的珍稀濒危物种和70.7%的中国特有珍稀濒危物种。本研究结果可为提高大熊猫保护区的有效性和维护大熊猫种群的持续生存提供科学依据。 相似文献
3.
Flasar FM Achterberg RK Conrath BJ Pearl JC Bjoraker GL Jennings DE Romani PN Simon-Miller AA Kunde VG Nixon CA Bézard B Orton GS Spilker LJ Spencer JR Irwin PG Teanby NA Owen TC Brasunas J Segura ME Carlson RC Mamoutkine A Gierasch PJ Schinder PJ Showalter MR Ferrari C Barucci A Courtin R Coustenis A Fouchet T Gautier D Lellouch E Marten A Prangé R Strobel DF Calcutt SB Read PL Taylor FW Bowles N Samuelson RE Abbas MM Raulin F Ade P Edgington S Pilorz S Wallis B Wishnow EH 《Science (New York, N.Y.)》2005,307(5713):1247-1251
Stratospheric temperatures on Saturn imply a strong decay of the equatorial winds with altitude. If the decrease in winds reported from recent Hubble Space Telescope images is not a temporal change, then the features tracked must have been at least 130 kilometers higher than in earlier studies. Saturn's south polar stratosphere is warmer than predicted from simple radiative models. The C/H ratio on Saturn is seven times solar, twice Jupiter's. Saturn's ring temperatures have radial variations down to the smallest scale resolved (100 kilometers). Diurnal surface temperature variations on Phoebe suggest a more porous regolith than on the jovian satellites. 相似文献
4.
We compared near-infrared observations of the recently discovered outer rings of Uranus with Hubble Space Telescope results. We find that the inner ring, R/2003 U 2, is red, whereas the outer ring, R/2003 U 1, is very blue. Blue is an unusual color for rings; Saturn's enigmatic E ring is the only other known example. By analogy to the E ring, R/2003 U 1 is probably produced by impacts into the embedded moon Mab, which apparently orbits at a location where nongravitational perturbations favor the survival and spreading of submicron-sized dust. R/2003 U 2 more closely resembles Saturn's G ring, which is red, a typical color for dusty rings. 相似文献
5.
Fullerene tubular structures can be generated by vapor condensation of carbon on an atomically flat graphite surface. Scanning tunneling microscope (STM) images revealed the presence of tubes with extremely small diameters (from 10 to 70 angstroms), most of which are terminated by hemispherical caps. Atomic resolution images of such structures showed that the tubes have a helical graphitic nature. The formation of the tubes under the quasi-free conditions suggests that the growth to tubular rather than spherical configurations is preferred for "giant fullerenes." 相似文献
6.
Jupiter's main ring shows vertical corrugations reminiscent of those recently detected in the rings of Saturn. The Galileo spacecraft imaged a pair of superimposed ripple patterns in 1996 and again in 2000. These patterns behave as two independent spirals, each winding up at a rate defined by Jupiter's gravity field. The dominant pattern originated between July and October 1994, when the entire ring was tilted by about 2 kilometers. We associate this with the Shoemaker-Levy 9 impacts of July 1994. New Horizons images still show this pattern 13 years later and suggest that subsequent events may also have tilted the ring. Impacts by comets or their dust streams are regular occurrences in planetary rings, altering them in ways that remain detectable decades later. 相似文献
7.
Detection, isolation, and continuous production of cytopathic retroviruses (HTLV-III) from patients with AIDS and pre-AIDS 总被引：450，自引：0，他引：450
A cell system was developed for the reproducible detection of human T-lymphotropic retroviruses (HTLV family) from patients with the acquired immunodeficiency syndrome (AIDS) or with signs or symptoms that frequently precede AIDS (pre-AIDS). The cells are specific clones from a permissive human neoplastic T-cell line. Some of the clones permanently grow and continuously produce large amounts of virus after infection with cytopathic (HTLV-III) variants of these viruses. One cytopathic effect of HTLV-III in this system is the arrangement of multiple nuclei in a characteristic ring formation in giant cells of the infected T-cell population. These structures can be used as an indicator to detect HTLV-III in clinical specimens. This system opens the way to the routine detection of HTLV-III and related cytopathic variants of HTLV in patients with AIDS or pre-AIDS and in healthy carriers, and it provides large amounts of virus for detailed molecular and immunological analyses. 相似文献
8.
Cassini images of Saturn's small inner satellites (radii of less than approximately 100 kilometers) have yielded their sizes, shapes, and in some cases, topographies and mean densities. This information and numerical N-body simulations of accretionary growth have provided clues to their internal structures and origins. The innermost ring-region satellites have likely grown to the maximum sizes possible by accreting material around a dense core about one-third to one-half the present size of the moon. The other small satellites outside the ring region either may be close to monolithic collisional shards, modified to varying degrees by accretion, or may have grown by accretion without the aid of a core. We derived viscosity values of 87 and 20 square centimeters per second, respectively, for the ring material surrounding ring-embedded Pan and Daphnis. These moons almost certainly opened their respective gaps and then grew to their present size early on, when the local ring environment was thicker than it is today. 相似文献
9.
Shearer A Stappers B O'Connor P Golden A Strom R Redfern M Ryan O 《Science (New York, N.Y.)》2003,301(5632):493-495
We detected a correlation between optical and giant radio pulse emission from the Crab pulsar. Optical pulses coincident with the giant radio pulses were on average 3% brighter than those coincident with normal radio pulses. Combined with the lack of any other pulse profile changes, this result indicates that both the giant radio pulses and the increased optical emission are linked to an increase in the electron-positron plasma density. 相似文献
10.
Lamb LD Huffman DR Workman RK Howells S Chen T Sarid D Ziolo RF 《Science (New York, N.Y.)》1992,255(5050):1413-1416
High-temperature, high-pressure extracts of soot produced by the Kr?tschmer-Huffman technique (KH carbon) were characterized by mass spectrometry and imaging with scanning tunneling microscopes (STMs). The mass spectra of these samples are similar to those of ambient-pressure, high-boiling-point solvent extractions, supporting the idea that solvent temperature and possibly pressure are key parameters in extraction of the giant fuilerenes. The STM images show that the giant fullerenes in these samples are roughly spherical in shape and range in diameter from approximately 1 to 2 nanometers, corresponding to fullerenes containing 60 to 330 atoms. No evidence of bucky tubes was found. 相似文献
11.
Saturn's E ring is revealed by image processing of direct photographs of the 1966 edge-on presentation of the planet's ring plane. Two different techniques were used: scanning with an image quantizer operated in the derivative mode and computer-enhanced background subtraction from digitized images. 相似文献
12.
Smith BA Soderblom LA Beebe R Bliss D Boyce JM Brahic A Briggs GA Brown RH Collins SA Cook AF Croft SK Cuzzi JN Danielson GE Davies ME Dowling TE Godfrey D Hansen CJ Harris C Hunt GE Ingersoll AP Johnson TV Krauss RJ Masursky H Morrison D Owen T Plescia JB Pollack JB Porco CC Rages K Sagan C Shoemaker EM Sromovsky LA Stoker C Strom RG Suomi VE Synnott SP Terrile RJ Thomas P Thompson WR Veverka J 《Science (New York, N.Y.)》1986,233(4759):43-64
Voyager 2 images of the southern hemisphere of Uranus indicate that submicrometersize haze particles and particles of a methane condensation cloud produce faint patterns in the atmosphere. The alignment of the cloud bands is similar to that of bands on Jupiter and Saturn, but the zonal winds are nearly opposite. At mid-latitudes (-70 degrees to -27 degrees ), where winds were measured, the atmosphere rotates faster than the magnetic field; however, the rotation rate of the atmosphere decreases toward the equator, so that the two probably corotate at about -20 degrees . Voyager images confirm the extremely low albedo of the ring particles. High phase angle images reveal on the order of 10(2) new ringlike features of very low optical depth and relatively high dust abundance interspersed within the main rings, as well as a broad, diffuse, low optical depth ring just inside the main rings system. Nine of the newly discovered small satellites (40 to 165 kilometers in diameter) orbit between the rings and Miranda; the tenth is within the ring system. Two of these small objects may gravitationally confine the e ring. Oberon and Umbriel have heavily cratered surfaces resembling the ancient cratered highlands of Earth's moon, although Umbriel is almost completely covered with uniform dark material, which perhaps indicates some ongoing process. Titania and Ariel show crater populations different from those on Oberon and Umbriel; these were probably generated by collisions with debris confined to their orbits. Titania and Ariel also show many extensional fault systems; Ariel shows strong evidence for the presence of extrusive material. About halfof Miranda's surface is relatively bland, old, cratered terrain. The remainder comprises three large regions of younger terrain, each rectangular to ovoid in plan, that display complex sets of parallel and intersecting scarps and ridges as well as numerous outcrops of bright and dark materials, perhaps suggesting some exotic composition. 相似文献
13.
In the outer regions of Saturn's main rings, strong tidal forces balance gravitational accretion processes. Thus, unusual phenomena may be expected there. The Cassini spacecraft has recently revealed the strange "flying saucer" shape of two small satellites, Pan and Atlas, located in this region, showing prominent equatorial ridges. The accretion of ring particles onto the equatorial surfaces of already-formed bodies embedded in the rings may explain the formation of the ridges. This ridge formation process is in good agreement with detailed Cassini images showing differences between rough polar and smooth equatorial terrains. We propose that Pan and Atlas ridges are kilometers-thick "ring-particle piles" formed after the satellites themselves and after the flattening of the rings but before the complete depletion of ring material from their surroundings. 相似文献
14.
A mosaic of images shows the extended structure of the cD galaxy that resides at the center of the rich cluster of galaxies Abell 2029. After correcting for the scattered light of nearby stars and galaxies, the faint halo of this giant can be traced out to a distance of more than 1 megaparsec, making it one of the largest and most luminous galaxies known. The smoothness of this halo suggests that it was formed early in the history of the cluster. 相似文献
15.
从环境视角,结合房山区畜牧业实际状况,从土地的承载力、粪尿的经济运输距离、粪污处理模式等因素推断,得出畜牧养殖规模的差距是巨大的,必须从系统论的角度看畜牧养殖,结合农村能源建设,大力发展沼气发电,推进农牧结合建设生态畜牧业。 相似文献
16.
High-resolution molecular line and continuum radio images from the Hat Creek Radio Observatory and the Very Large Array suggest that the core of the W49A star-forming region is undergoing gravitational collapse. The radio continuum shows a 2-parsec ring of at least ten distinct ultracompact H-II regions, each associated with at least one O star. The ring is a region of large-scale, organized massive star formation. Recombination line velocities and HCO(+) excitation requirements indicate that the ring is rotating around 50,000 solar masses of material. Because the HCO(+) (1-0) line shows red-shifted absorption but blue-shifted emission, the molecular cloud core is believed to be collapsing toward the center of the ring. The HCO(+) radial velocities, as well as H-I, H(2)CO, and magnetic-field measurements, fit a simple model of inside-out gravitational collapse of a once magnetically supported cloud. 相似文献
17.
Showalter MR 《Science (New York, N.Y.)》1995,267(5197):490-493
Careful reprocessing of the Voyager images reveals that the Uranìan lambda ring has marked longitudinal variations in brightness comparable in magnitude to those in Saturn's F ring and Neptune's Adams ring. The ring's variations show a dominant five-cycle (72-degree) periodicity, although additional structure down to scales of about 0.5 degree is also present. The ring's shape is defined by a small overall eccentricity plus a six-cycle (60-degree) sinusoidal variation of radial amplitude around 4 kilometers. Both of these properties can be explained by the resonant perturbations of a moon at a semimajor axis of 56,479 kilometers, but no known moon orbits at this location. Unfortunately, the mass required suggests that such a body should have been imaged by Voyager. 相似文献
18.
为了解各地动物园圈养大熊猫的毕氏肠微孢子虫感染情况及其人畜共患风险,采用基于ITS基因的巢氏PCR方法,对江苏、福建、浙江等10个省(市、自治区)的动物园圈养大熊猫毕氏肠微孢子虫的感染情况及基因分型进行调查和检测。在31份大熊猫粪便样品中,共检测到毕氏肠微孢子虫阳性14份,总感染率45.2%,检测出SC02(13/14)和Peru6(1/14)两种毕氏肠微孢子虫基因型。种系发育分析表明,SC02和Peru6都属于具有人畜共患潜能的group 1b。本实验首次发现SC02基因型毕氏肠微孢子虫感染大熊猫,表明大熊猫可能作为毕氏肠微孢子虫的储存宿主引起人微孢子虫病,拓宽了基因型SC02的毕氏肠微孢子虫宿主范围。 相似文献
19.
《（《农业科学与技术》）编辑部》2017,(8)
Chinese giant salamander(CGS, Andrias davidianus) is experiencing the threat of extinction. It is disappearing gradually, because of overharvesting, environmental pollution, specially river pollution, activity of human exploitation, and so on. We conducted community interview fieldworks to collect respondent data from Xieba Country(not reserve) situated in Zhengan County of Guizhou Province, where one of the places known by historical giant salamander records in Guizhou. Through the analysis of the collected data, we created quantitative data of use for conservation management on the local status of salamander populations, and we compared our data with those available data of Y. Pan et al., who investigated the status of CGS in 3 reserves in Guizhou Province in 2015.The conclusions have a similar trend, which proved that the collected data were creditable. Through statistical analysis of the comparison data, the number of wild CGS decreased actually followed the increase of artificial framing.Because of the source of breeding to catch wild CGS, overharvesting was likely the most reason to make wild CGS decline. 相似文献
20.
Chinese giant salamander (CGS, Andrias davidianus ) is experiencing the threat of extinction. It is disappearing gradually, because of overharvesting, environmental pollution, specially river pollution, activity of human exploitation, and so on. We conducted community interview fieldworks to collect respondent data from Xieba Country (not reserve) situated in Zhengan County of Guizhou Province, where one of the places known by historical giant salamander records in Guizhou. Through the analysis of the collected data, we created quantitative data of use for conservation management on the local status of salamander populations, and we compared our data with those available data of Y. Pan et al., who investigated the status of CGS in 3 reserves in Guizhou Province in 2015.The conclusions have a similar trend, which proved that the collected data were creditable. Through statistical analysis of the comparison data, the number of wild CGS decreased actually followed the increase of artificial framing. Because of the source of breeding to catch wild CGS, overharvesting was likely the most reason to make wild CGS decline. 相似文献