A New Angle on Microscopic Suspension Feeders near Boundaries

Microscopic sessile suspension feeders are a critical component in aquatic ecosystems, acting as an intermediate trophic stage between bacteria and higher eukaryotic taxa. Because they live attached to boundaries, it has long been thought that recirculation of the feeding currents produced by sessile suspension feeders inhibits their ability to access fresh fluid. However, previous models for the feeding flows of these organisms assume that they feed by pushing fluid perpendicular to surfaces they live upon, whereas we observe that sessile suspension feeders often feed at an angle to these boundaries. Using experiments and calculations, we show that living suspension feeders (Vorticella) likely actively regulate the angle that they feed relative to a substratum. We then use theory and simulations to show that angled feeding increases nutrient and particle uptake by reducing the reprocessing of depleted water. This work resolves an open question of how a key class of suspension-feeding organisms escapes physical limitations associated with their sessile lifestyle.     

A Neo-Boasian Conception of Cultural Boundaries

For the past 30 years, anthropology's critics have repeatedly questioned the notion of "cultural boundaries," arguing that concepts of culture inappropriately posit stable and bounded "islands" of cultural distinctiveness in an ever-changing world of transnational cultural "flows." This issue remains an Achilles' heel—or at least a recurring inflamed tendon—of anthropology. However, in the conception of boundaries, we still have much to learn from Boasian anthropologists, who conceived of boundaries not as barriers to outside influence or to historical change, but as cultural distinctions that were irreducibly plural, perspectival, and permeable. In this article, I retheorize and extend the Boasians' open concept of cultural boundaries, emphasizing how people's own ideas of "the foreign"—and the "own" versus the "other" distinction—give us a way out of the old conundrum in which the boundedness of culture, as conceived in spatial terms, seems to contradict the open-ended nature of cultural experience.     

不同饲养层对鸡胚胎干细胞培养效果的影响

目的:为探索鸡胚胎干细胞培养的优化条件,比较不同饲养层对鸡胚胎干细胞离体培养的效果。方法:用传至第2代的鸡胚成纤维细胞与鸭胚成纤维细胞,经丝裂霉素处理后制作饲养层,比较这2种饲养层以及不用饲养层对鸡胚胎干细胞离体培养效果的影响。结果:在以鸡胚成纤维细胞和鸭胚成纤维细胞作为饲养层的培养体系中,鸡胚胎干细胞均可保持良好的生长状态,而且2种饲养层对鸡胚胎干细胞克隆形成的影响差异不显著(P0.05)。结论:鸡胚成纤维细胞和鸭胚成纤维细胞均可作为较好的饲养层细胞用于鸡胚胎干细胞的离体培养。     

A New Angle on Second Harmonic Generation from a Small Hole in a Metal Film

Plasmonics - Bethe’s theory treats a subwavelength aperture in a metal film as the combination of a parallel magnetic dipole and transverse electric dipole. For linear optics, this gives the...     

X-Ray Small Angle Scattering: A New Deconvolution Method for Evaluating Electron Density Distributions from Small Angle Scattering Diagrams

The direct determination of the electron density distributions of multilayered specimens with a small number of unit cells from X-ray small angle scattering experiments via the Q-function method of Hosemann and Bagchi includes the deconvolution of the so-called Q_o-function, the generalized Patterson function of one unit cell. In this paper a new and direct deconvolution method on the basis of Fourier series is presented which is suitable for one-dimensional centrosymmetrical (or antisymmetrical) density distributions. A FORTRAN-program has been written which has an execution time of ca. 20 s on an UNIVAC 1106-computer. The procedure has been successfully tested on some convolution functions generated by membrane-type electron density distributions.     

Y-box Binding Protein 1: Providing a New Angle on Translational Regulation

Current models of translational regulation are mostly focused on how translational factors engage a messenger mRNA to the ribosome to initiate translation. Since the majority of mRNAs in eukaryotes are translated in a cap-dependent manner, the mRNA 5’ cap-binding protein eIF4E was characterized as a key player responsible for the recruitment of mRNAs to the initiation complex. The availability of eIF4E is believed to be especially critical for translational activation of mRNAs with extensive secondary structures in their 5’UTRs, many of which code for labile regulatory proteins essential for cell growth or viability. Surprisingly, little attention is paid to the other side of translational control, e.g., to define mechanisms responsible for translational silencing and storage of the above messages. In this review, we discuss the possibility that eIF4E per se may not be sufficient to release mRNAs from translational block. We found that many growth- and stress-related mRNAs are associated with the translational repressor YB-1, which can compete with the eIF4E-driven translation initiation complex for binding to the capped 5’ mRNA terminus. Moreover, the cap-dependent repressor activity of YB-1 appears to be negatively regulated via Akt-mediated phosphorylation of the Ser-102 residue of YB-1. Taken together with recent evidence suggesting that translational activation of growth-related messages is a primary cellular response to activation of Ras-Erk and PI3K-Akt signaling pathways, our data suggest that differential expression of specific mRNA subsets is regulated by the PI3K-Akt pathway and achieved via coordinated activation of the components of translational machinery and inactivation of general translational repressors such as YB-1.     

Electron Microscopic Studies on Opaque Colony Variants of Group A Streptococci

Opaque colony variants of two strains of group A streptococci have been compared with blue colonies of the same strains by electron microscopy. In opaque colonies, the cocci are joined into elongated chains by exaggerated intercellular septa that often occupy the major portion of each cell's circumference. The thickness and lamination of cell walls in opaque colony variants are identical to those aspects of cell walls in blue colony forms. The similarity in cell wall architecture is found between opaque and blue forms whether or not M protein (and M associated surface fimbriae) is present. Extensive, direct contact between the nucleoid and the cytoplasmic membrane beneath intercellular septa is seen in opaque colony variants. The relationship of this marked nucleoid-cytoplasmic membrane association to the unusual chain forms in the opaque colony variants is unclear.     

A Note on Scanning Electron Microscopic Assessment of Stomacher Action on Chicken Skin

Scanning electron microscopy was used in conjunction with normal microbiological procedures to evaluate the stomacher as a means of recovering bacteria from chicken skin. Stomaching removed most bacteria from the skin and viable counts of skin micro-organisms obtained by this method were not significantly different from those obtained by blending. The stomacher represents a useful alternative to blending techniques commonly used to assess contamination of poultry carcasses.     

DebtRank: A Microscopic Foundation for Shock Propagation

The DebtRank algorithm has been increasingly investigated as a method to estimate the impact of shocks in financial networks, as it overcomes the limitations of the traditional default-cascade approaches. Here we formulate a dynamical “microscopic” theory of instability for financial networks by iterating balance sheet identities of individual banks and by assuming a simple rule for the transfer of shocks from borrowers to lenders. By doing so, we generalise the DebtRank formulation, both providing an interpretation of the effective dynamics in terms of basic accounting principles and preventing the underestimation of losses on certain network topologies. Depending on the structure of the interbank leverage matrix the dynamics is either stable, in which case the asymptotic state can be computed analytically, or unstable, meaning that at least one bank will default. We apply this framework to a dataset of the top listed European banks in the period 2008–2013. We find that network effects can generate an amplification of exogenous shocks of a factor ranging between three (in normal periods) and six (during the crisis) when we stress the system with a 0.5% shock on external (i.e. non-interbank) assets for all banks.     

New fluorescence reactions in DNA cytochemistry. 1. Microscopic and spectroscopic studies on nonrigid fluorochromes

Some nonrigid DNA-binding antibiotics and fluorochromes that recognize adenine-thymine (AT) sequences are widely applied in biomedical research, but the microscopic use, spectral characteristics and DNA binding modes of other similar compounds have been overlooked or scarcely explored. After treatment with thioflavine T, auramine O and G, curcumin, bis-aminophenyl-oxadiazol, berenil and distamycin A, a bright DNA-dependent fluorescence reaction was found in the chromatin of interphase nuclei, meiotic and polytene chromosomes, spermatozoa heads and kinetoplasts of Trypanosoma cruzi epimastigotes. Nucleoli and basophilic cytoplasm showed low or no fluorescence; the highest emission occurred in the AT-rich kinetoplast DNA. When bound to DNA or in the presence of alpha-cyclodextrin and viscous solvents or cosolutes, nonrigid compounds revealed a striking enhancement of fluorescence. The results indicate that these new or poorly known fluorochromes bind selectively to DNA-containing structures and that the minor groove from AT-rich DNA regions could represent the specific and highly fluorescent binding site.     

水翁悬浮细胞系的建立及其悬浮培养的生长特性

建立了水翁悬浮细胞系,并对其悬浮培养的生长特性作了初步探讨。以水翁新生芽尖作为外植体,接种于添加有不同浓度和配比的生长调节物质及各种附加物的MS固体培养基中,诱导培养产生初代愈伤组织;挑选Ⅰ和Ⅱ型的愈伤组织进行继代培养改良,考察愈伤组织的生长状况和统计生长量来决定最佳继代培养基的配方和得到适合悬浮培养的愈伤组织;将以上得到的愈伤组织转接于最佳继代液体培养基中,于24±1℃,120r/min条件下振荡培养,筛选分散度好、较均匀、生长快、色浅透明的细胞作为种子传代,数次传代后得到性能良好的悬浮细胞系;以细胞生长量(鲜重)为指标,绘制了水翁悬浮细胞的生长曲线。研究表明:2.0mg/L的2,4-D的诱导率最高(92%,初代愈伤组织为Ⅰ型),Ⅱ型愈伤组织的最高诱导率为75%;最佳的继代培养基配方为MS 0.5mg/L 2,4-D 0.5mg/L 6-BA 1.0mg/L IAA 0.5mg/L IBA 0.5mg/L NAA 0.1mg/L KT 700mg/L LH,形成Ⅱ型愈伤组织的生长量可达3.28g/瓶(鲜重);液体继代培养3代后,可得到性能良好的悬浮细胞系;水翁悬浮细胞的生长曲线表明,最佳接种期为培养后的16~18d。     

A Use-Time Recorder for Application in Critical Microscopic Illumination

The recorder, controlled by a keyed lockable switch which activates a sealed lapsed-time meter and energizes a power outlet, is placed between the power mains electrical source and the illuminator, or other equipment, to be monitored. Electrical connection between the latter and the power outlet of the recorder is made with paired nonstandard locking connectors; one connector being attached to the power outlet and the other replacing the standard male convience plug on the power cord of the illuminator. The lockable switch maintains absolute control over use of the monitored equipment while the time meter provides an accurate record of use-time. Bypass of the locked recorder is prevented by the non-standard connectors. Total fabrication costs of the recorder are less than $25.00.