Sympatric speciation by sexual selection

There is increasing evidence for the process of sympatric speciation, in which reproductive isolation of species occurs without physical isolation. Theoretical models have focused on disruptive natural selection as the crucial pressure for splitting a species. Here we report the theoretical finding that sympatric speciation may be caused by sexual selection even without disruptive natural selection. Specifically, we show that variation in a male secondary sexual character with two conspicuous extremes and the corresponding variance in female mating preference around no preference may jointly evolve into bimodal distributions with increasing modal divergence of the male and female traits, pulling a population apart into two prezygotically isolated populations. This mode of speciation, driven by two runaway processes in different directions, is promoted by an increase in the efficiency of females in discriminating among males or a decrease in the cost of male conspicuousness, indicating that sympatric speciation may occur more readily if barrier-free or predator-free conditions arise. Although even a slight cost of female preference would cancel the runaway process of sexual selection, it would not cancel the divergent runaway processes of sympatric speciation.     

A simple procedure for removal of intra- and extra-tumoral macrophages from primary tumor cultures

Summary Improved growth of tumor cells in primary cell suspensions isolated from solid tumors can be achieved by addition of an antifungal agent, mycostatin, to the culture medium. Mycostatin inhibits the cytotoxicity of macrophages and also quickly detaches phagocytes without any apparent retardation of the growth of tumor cells. This method is particularly useful for obtaining cultures of lung tumor cells or cells from lung metastases of other tumors.This research was supported in part by grants CA-22839 and CA-28482 awarded by the National Cancer Institute, DHEW, USA. This is publication No. 406 from the Department of Basic and Clinical Immunology and Microbiology, Medical University of South Carolina.We thank Charles L. Smith for editorial assistance. Address correspondence to Y. Y., Department of Basic and Clinical Immunology and Microbiology, Medical University of South Carolina, 171 Ashley Avenue, Charleston, SC 29403, USA.     

A synthetic glycolipid prevents autoimmune encephalomyelitis by inducing TH2 bias of natural killer T cells

Experimental autoimmune encephalomyelitis (EAE) is a prototype autoimmune disease mediated by type 1 helper T (TH1) cells and under the control of regulatory cells. Here we report that a synthetic glycolipid ligand for CD1d-restricted natural killer T (NKT) cells expressing the semi-invariant T-cell receptor (Valpha14+) is preventive against EAE. The ligand is an analogue of alpha-galactosylceramide (alpha-GC), a prototype NKT cell ligand, with a truncated sphingosine chain. alpha-GC causes NKT cells to produce both interferon (IFN)-gamma and interleukin (IL)-4 (refs 4, 5). However, this new ligand can induce a predominant production of IL-4 by the NKT cells. A single injection of this glycolipid, but not of alpha-GC, consistently induced TH2 bias of autoimmune T cells by causing NKT cells to produce IL-4, leading to suppression of EAE. The lack of polymorphism of CD1d and cross-reactive response of mouse and human NKT cells to the same ligand indicates that targeting NKT cells with this ligand may be an attractive means for intervening in human autoimmune diseases such as multiple sclerosis.     

Modulated structure of solid iodine during its molecular dissociation under high pressure

The application of pressure to solid iodine forces the molecules in the crystal to approach each other until intermolecular distances become comparable to the bond length of iodine; at this point, the molecules lose their identity and are essentially dissociated. According to room-temperature X-ray diffraction studies, this process involves direct dissociation of iodine molecules at about 21 GPa, whereas spectroscopic observations have identified intermediate molecular phases at pressures ranging from 15 to 30 GPa. Here we present quasi-hydrostatic powder X-ray diffraction measurements that clearly reveal an intermediate phase during the pressure-induced dissociation of solid iodine. We find that, similar to the behaviour seen in uranium, the structure of this intermediate phase is incommensurately modulated, with the nearest interatomic distances continuously distributed over the range 2.86-3.11 A. The shortest of these interatomic distances falls between the bond length of iodine in the molecular crystal (2.75 A) and the nearest interatomic distance in the fully dissociated monatomic crystal (2.89 A), implying that the intermediate phase is a transient state during molecular dissociation. We expect that further measurements at different temperatures will help to elucidate the origin and stability of the incommensurate structure, which might lead to a better understanding of the molecular-level mechanism of the pressure-induced dissociation seen here and in the molecular crystals of hydrogen, oxygen and nitrogen.     

Vegetation Spatial Heterogeneity of Different Soil Regions in Inner Mongolia, China

The vegetation spatial heterogeneity and ecological characteristics in different soil regions were analyzed by surveying the vegetation in 12 different soil regions of Inner Mongolia, China, including conifer- ous-broadleaf deciduous forests, shrub, grassland, and desert regions with 1122 large 2 cm × 2 cm quad- rats (actual size 30 km × 30 km, referred to as L-quadrat hereafter) in about 1.18 million km2. Each L- quadrat was divided into four small 1 cm × 1 cm quadrats (actual size 15 km × 15 km, S-quadrat). The vegetation was analyzed based on the beta-binomial distribution to describe the frequency of occurrence and spatial heterogeneity for each kind of vegetation. The weighted average of the heterogeneity of all vegeta- tion in the same soil region provides a measure of the soil regional landscape level heterogeneity which de- scribes the spatial complexity of the regional landscape composition of the existing vegetation. Comparison of the vegetation characteristics in the 12 soil regions shows that, the calcic gray soil has the highest average vegetation type per quadrat. The largest soil region is calcic chestnut soil and has the most vegetation types. Every soil region has its own dominant vegetation sequence which dominates in occurrence and dominant vegetation types which dominates in spatial heterogeneity. For the Inner Mongolian vegetation, the weighted average of the heterogeneity is 0.60 and the vegetation diversity index is 4.47.     

陈国达矿(Ag9FeTe2S4): 胶东地区金矿床中发现的硫碲化物新矿物

陈国达矿(Ag9FeTe₂S₄), 产于中国胶东金矿区埠南金矿的含金-银的黄铜矿-石英脉中, 呈5~70 μm的半自形-他形粒状与方铅矿、黄铜矿、碲银矿、银金矿、自然银、未定名的Ag₆TeS₂, Ag₁₆FeBiTe₃S₈共生, 并被自然银和螺状硫银矿包围交代. 其平均化学成分(16个EPMA分析值)为Ag_8.97Fe_1.00Te_1.99S_4.04, 理想化学式Ag₉FeTe₂S₄. 利用甘多菲照相及同步辐射迴摆照相技术, 获得陈国达矿的67个衍射线, 主要衍射强线的d值和相对强度(括号中)为: 6.742(69), 6.416(39), 5.951(33), 3.265(100), 2.981(24), 2.649(22), 2.25(24), 2.188(71), 2.142(22), 2.123(31), 2.044(23), 1.949(33). 该衍射数据指标化为斜方晶系, a = 12.769 (2) Å, b = 14.814(2) Å, c = 16.233 (1) Å, V = 3070.6 ų, Z = 9, d_cal = 6.85 g/cm³. 反光显微镜下, 陈国达矿的光学性质与硫银锡矿接近, 浅灰色, 无明显非均质性, 摩氏硬度2~3, 颜色指数: x = 0.3027, y = 0.3076, Y = 25.78%, λ_d = 474 nm, Pe = 3.68%. 该矿物以中国地质学家、地洼学说的创立人陈国达教授的姓名命名. 该矿物及命名经IMA-CNMMN于2004年投票通过. 2005年作者补充数据后, 由CNMMN主席正式公布, 批准号2004-042a.     

反复变动轴力作用下钢柱的数值分析模型

当承受水平地震荷载时，高层框架结构的低层柱子通常受到困倾覆力矩而引起的反复变动轴力．文中提出一弹塑性数值分析模型以考虑变动轴力对柱子抗育强度的影响，并提出单轴移动骨架式恢复为模式来表现钢柱的恢复力特性．通过荷载试验结果对这一数值分析模型进行了检验．     

Recent Advances in High Efficiency Solar Cells

1 Results The conversion efficiency of sunlight to electricity is limited around 25%,when we use single junction solar cells. In the single junction cells,the major energy losses arise from the spectrum mismatching. When the photons excite carriers with energy well in excess of the bandgap,these excess energies were converted to heat by the rapid thermalization. On the other hand,the light with lower energy than that of the bandgap cannot be absorbed by the semiconductor,resulting in the losses. One way...     

Data crystallization applied for designing new products

It is only the observable part of the real world that can be stored in data. For such incomplete and ill-structured data, data crystallizing aims at presenting the hidden structure among events including unobservable events. This is realized by data crystallization, where dummy items, corresponding to potential existence ofunobservable events, are inserted to the given data. These dummy items and their relations with observable events are visualized by applying KeyGraph to the data with dummy items, like the crystallization of snow where dusts are involved in the formation of crystallization of water molecules. For tuning the granularity level of structure to be visualized, the tool of data crystallization is integrated with human＇s process of understanding significant scenarios in the real world. This basic method is expected to be applicable for various real world domains where previous methods of chance-discovery lead human to successful decision making. In this paper, we apply the data crystallization with human-interactive annealing （DCHA） to the design of products in a real company. The results show its effect to industrial decision making.