A study of rotational brain injury

Of concern in the paper is an investigation on brain injuries which may occur owing to an input angular acceleration of the head. The study is based on the use of an improved mathematical model for the cranium. The eccentricity of the braincase is incorporated through the consideration of a prolate spheroidal shell as the representative of the skull. Also the dissipative mechanical behaviour of the brain material (as per the observations of experimenters) has been accounted for by considering the material contained in the shell as viscoelastic. The problem is formulated in terms of prolate spheroidal coordinates. The singularities of the governing equations of motion (when expressed in the prolate coordinate system) are removed by a suitable transformation of the concerned dependent variable, viz. the one that stands for the angular displacement of a representative point of the system. In the first place the solution of the boundary value problem is sought in the Laplace transform space, by employing a finite difference technique. Use of the alternating-direction-implicit method together with Thomas algorithm was made for obtaining the angular acceleration in the transformed space. The Laplace inversion is also carried out with the help of numerical procedures (Gauss quadrature formula is used for this purpose). The results of the parametric study are presented through graphs. The plots illustrate the shear stresses and strains in the brain medium. A meaningful comparison of the computational results with those of previous investigations indicate that the eccentricity of the braincase plays a significant role in causing injury to the brain.     

福建宁化晚石炭世有孔虫Pseudoendothyra动物群的发现及其意义

报道了福建宁化晚石炭世黄龙组下部白云岩中的Pseudoendothyra动物群,共描述鲢类化石1属21种,包括4个未定种。该动物群壳体微小,一般为扁圆形及凸镜形,轴率小于1,旋壁四层式,化石保存尚好,且具排它性分布。该动物群的发现丰富了筵类古生态学及其生物地层学研究领域的新资料。     

Oblate Spheroidal Triboelectric Nanogenerator for All‐Weather Blue Energy Harvesting

Triboelectric nanogenerators (TENGs) provide one of the most promising techniques for large‐scale blue energy harvesting. However, lack of reasonable designs has largely hindered TENG from harvesting energy from both rough and tranquil seas. In this paper, an oblate spheroidal TENG assembled by two novel TENG parts is elaborately designed for both situations. The TENG in the upper part is based on spring steel plates without other substrate materials, which makes it possible to output considerable power in rough seas and occupy small space. The TENG in the lower part consists of two copper‐coated polymer films and a rolling ball which can capture small wave energy from tranquil seas. The working mechanism and output performance are systematically studied. A maximum open‐circuit voltage of 281 V and a short‐circuit current of 76 µA can be achieved by one upper part, enough to charge a commercial capacitor for potential applications. More important, the proposed oblate spheroidal shell not only guarantees high sensitivity of the TENG in the lower part, but also qualifies the TENG with unique self‐stabilization and low consumables for the next generation of TENGs with new structural design toward all‐weather blue energy harvesting.     

Analysis of repeated signals during shell fights in the hermit crab Pagurus bernhardus

Shell exchanges between hermit crabs may occur after a period of shell rapping, when the initiating or attacking crab brings its shell rapidly and repeatedly into contact with the shell of the non-initiator or defender, in a series of bouts. There are two opposing models of hermit crab shell exchange and the function of shell rapping. The negotiation model views shell exchange as a mutualistic activity, in which the initiator supplies information about the quality of its shell via the fundamental frequency of the rapping sound. The aggression model views shell rapping as either detrimental to the defending crab, or as providing it with information about the initiator''s ability or motivation to continue, or both. The negotiation model makes no predictions about the temporal pattern of rapping, but under the aggression model it would be expected that crabs that rapped more vigorously would be more likely to effect an exchange. Repeating the signal could be expected under either model. Crabs that achieve an exchange rap more vigorously, rapping is more persistent when a clear gain in shell quality may be achieved, and the vigour is greater when the relative resource-holding potential (or ''fighting ability'') is high. These findings support the aggression model rather than the negotiation model. Contrary to the predictions of game theory, crabs that do not effect an exchange appear to signal that they are about to give up. The data suggest that rapping is performed repeatedly because the accumulation of all of the performances acts as a signal of stamina.     

A polarization model overcoming the geometric restrictions of the laplace solution for spheroidal cells: obtaining new equations for field-induced forces and transmembrane potential.

We present a new model for a variety of electric polarization effects on oblate and prolate homogeneous and single-shell spheroids. For homogeneous spheroids the model is identical to the Laplace model. For single-shell spheres of cell-like geometry the calculated difference of the induced dipole moments is in the thousandths range. To solve Laplace's equation for nonspherical single-shell objects it is necessary to assume a confocal shell, which results in different cell membrane properties in the pole and equator regions, respectively. Our alternative model addresses this drawback. It assumes that the disturbance of the external field due to polarization may project into the medium to a characteristic distance, the influential radius. This parameter is related to the axis ratio of the spheroid over the depolarizing factors and allows us to determine the geometry for a finite resistor-capacitor model. From this model the potential at the spheroid's surface is obtained and, consequently, the local field inside a homogeneous spheroid is determined. In the single-shell case, this is the effective local field of an equivalent homogeneous spheroid. Finally, integration over the volume yields the frequency-dependent induced dipole moment. The resistor-capacitor approach allowed us to find simple equations for the critical and characteristic frequencies, force plateaus and peak heights of deformation, dielectrophoresis and electrorotation for homogeneous and single-shell spheroids, and a more generalized equation for the induced transmembrane potential of spheroidal cells.     

陕南寒武系下部宽川铺组帽球状化石*

陕南寒武纪早期宽川铺组微体球状化石类型多样,如何正确辨别这些球状化石的生物属性是当前早期生命演化古生物学研究中的一个难点。我们在宽川铺组中发现了一类为数众多,具有一个或者多个不规则的帽状隆起结构以及翻边帽沿的帽状化石。研究表明这些帽状化石均为不完整的个体,其完整形态呈不规则的凹球形。根据帽球状化石帽身的数量和相对位置,这类化石可划分为"单帽型"、"双帽型"和"复帽型"三种类型。这些凹球状化石呈双层壳壁,内壁光滑,外壁粗糙。因为凹球状化石形态及其表面小孔与微体藻类、后生动物的胚胎以及壳体化石差异都非常显著,所以推测这类化石可能与带壳原生动物亲缘关系最为紧密。     

Chemically Based Mathematical Model for Development of Cerebral Cortical Folding Patterns

The mechanism for cortical folding pattern formation is not fully understood. Current models represent scenarios that describe pattern formation through local interactions, and one recent model is the intermediate progenitor model. The intermediate progenitor (IP) model describes a local chemically driven scenario, where an increase in intermediate progenitor cells in the subventricular zone correlates to gyral formation. Here we present a mathematical model that uses features of the IP model and further captures global characteristics of cortical pattern formation. A prolate spheroidal surface is used to approximate the ventricular zone. Prolate spheroidal harmonics are applied to a Turing reaction-diffusion system, providing a chemically based framework for cortical folding. Our model reveals a direct correlation between pattern formation and the size and shape of the lateral ventricle. Additionally, placement and directionality of sulci and the relationship between domain scaling and cortical pattern elaboration are explained. The significance of this model is that it elucidates the consistency of cortical patterns among individuals within a species and addresses inter-species variability based on global characteristics and provides a critical piece to the puzzle of cortical pattern formation.     

Fast ignition upon the implosion of a thin shell onto a precompressed deuterium-tritium ball

Fast ignition of a precompressed inertial confinement fusion (ICF) target by a hydrodynamic material flux is investigated. A model system of hydrodynamic objects consisting of a central deuterium-tritium (DT) ball and a concentric two-layer shell separated by a vacuum gap is analyzed. The outer layer of the shell is an ablator, while the inner layer consists of DT ice. The igniting hydrodynamic flux forms as a result of laser-driven acceleration and compression of the shell toward the system center. A series of one-dimensional numerical simulations of the shell implosion, the collision of the shell with the DT ball, and the generation and propagation of thermonuclear burn waves in both parts of the system are performed. Analytic models are developed that describe the implosion of a thin shell onto a central homogeneous ball of arbitrary radius and density and the initiation and propagation of a thermonuclear burn wave induced by such an implosion. Application of the solution of a model problem to analyzing the implosion of a segment of a spherical shell in a conical channel indicates the possibility of fast ignition of a spherical ICF target from a conical target driven by a laser pulse with an energy of 500?C700 kJ.     

Pollen Morphology of Xyridaceae Systematic (Poales) and its Potential

Xyridaceae are a predominantly tropical family of five genera that exhibit two pollen morphologies often considered to be of taxonomic importance. Xyris comprises about 95% of the species and is characterized by medium to large, elliptic, sulcate pollen grains. The other pollen class is spheroidal grains without an evident aperture. Many of the species with spheroidal grains have remarkably large and ornamented pollen found to be species specific in earlier research. A scanning electron microscopy investigation of 23 taxa representing all genera with spheroidal pollen revealed new data to further distinguish the genera based on pollen characters. Reliable specific pollen characters need to be evaluated in a statistical study.     

Further study of the model of a human skull as a cupola with a plane base]

An experimental study of the base deformation of isolated human scull under conditions of scull collision with an obstacle has been carried out. The findings are compared with human cerebrospinal traums phenomena. An earlier suggested continuous scull model is modified on the basis of the data obtained. It is shown that the modified model (a part of spherical shell with the flat base) resembles scull behaviour in statics and dynamics better than the scull model in the form of spherical shell.     

Pollen Morphology in the Subtribe Aspidistrinae (Liliaceae s. l.)

Pollen morphology in the subtribe Aspidistrinae is reported and the main viewpoints are summarized as follows: (1) Two major types of pollen grains, i.e., monosulcate,ellipsoidal pollen and inaperturate, spheroidal pollen, are identified in the genus Tupistra. The species with monosulcate, ellipsoidal pollen usually have monomodal karyotypes, brightcolored flower, smaller stigma, and stamens inserted at upper or middle part of perianth tube, while the inaperturate and spheroidal pollen is always found in the species with bimodal karyotypes, dingy-colored flower, swollen stigma and stamens inserted at the base of perianth tube. (2) Pollen grains in the genus Rhodea are monosulcate and ellipsoidal, while those in the genus Aspidistra are inaperturate and spheroidal, correspondingly similar to the second type of pollen grains in the genus Tupistra. (3) The most primitive pollen in the subtribe Aspidistinae is regarded as monosulcate and ellipsoidal, having perforate or reticulate exine sculpture. The inaperturate, spheroidal pollen with verrucate, gemmate or rugulate exine sculpture is considered derived; (4) Unlike those reported in other groups of the family Liliaceae, the infraspecific pollen shape, aperture type and exine sculpture in Aspidistrinae are basically stable and may serve as a taxonomic character.     

Dynamic response of intraocular pressure and biomechanical effects of the eye considering fluid-structure interaction

The vibration characteristics of shell structures such as eyes have been shown to vary with intraocular pressure (IOP). Therefore, vibration characteristics of the eye have the potential to provide improved correlation to IOP over traditional IOP measurements. As background to examine an improved IOP correlation, this paper develops a finite element model of an eye subject to vibration. The eye is modeled as a shell structure filled with inviscid pressurized fluid in which there is no mean flow. This model solves a problem of a fluid with coupled structural interactions of a generally spherically shaped shell system. The model is verified by comparing its vibrational characteristics with an experimental modal analysis of an elastic spherical shell filled with water. The structural dynamic effects due to change in pressure of the fluid are examined. It is shown that the frequency response of this fluid-solid coupled system has a clear increase in natural frequency as the fluid pressure rises. The fluid and structure interaction is important for accurate prediction of system dynamics. This model is then extended to improve its accuracy in modeling the eye by including the effect of the lens to study corneal vibration. The effect of biomechanical parameters such as the thicknesses of different parts of the eye and eye dimensions in altering measured natural frequencies is investigated and compared to the influence of biomechanical parameters in Goldmann applanation tonometry models. The dynamic response of the eye is found to be less sensitive to biomechanical parameters than the applanation tonometry model.     

Stacking Increments: A New Model and Morphospace for the Analysis of Bivalve Shell Growth

A model employing stacking increments is introduced for the analysis of bivalve shell growth and form. The model is based on the components of shell growth that are potentially independent: the rate of mantle cell proliferation, the rate of precipitation of shell material, and the rate of translation of the pallial line, where the mantle is attached to the shell. This model is defined in terms of the following parameters: (1) the ratio of accretion of shell material at the shell margin to growth of the mantle by cell division, (2) the ratio of shell accretion at the pallial line to mantle growth, and (3) the ratio of the amount of pallial muscle translation, away from the umbo toward the shell margin, to mantle growth. In this model, the shape of a radial section through the shell is simulated by stacking of internal microgrowth increments. The mode of stacking of the increments is determined by the balance among the parameters defining growth. A theoretical morphospace defined on the basis of this model is largely consistent with the range of forms of naturally occurring bivalve shells. Analysis of the distribution of actual shell forms in relation to this morphospace suggests that the absolute rate of shell precipitation and the gradient in precipitation rate away from the shell margin along a radial cross-section are physiologically as well as geometrically constrained.     

SPHEROIDAL AND RING NUCLEOLI IN AMPHIBIAN OOCYTES : Patterns of Uridine Incorporation and Fine Structural Features

In maturing oocytes of the newt Triturus viridescens, the nucleoli undergo a series of morphological changes that are very similar to those described by Callan for the axolotl, Ambystoma mexicanum. The nucleoli first assume the form of spheroids which then become extended into ring or necklace shapes that are DNase-sensitive; in mature oocytes the nucleoli revert to a spheroidal form. Short term in vitro incorporation studies with uridine-³H on both species show that RNA synthesis occurs in a restricted, eccentric portion of the spheroidal nucleoli, thereby producing an asymmetrical pattern of labeling. In the ring forms, however, the localization of the radioactivity suggests that synthesis takes place symmetrically throughout their entire length. The changes in nucleolar morphology apparently reflect the fact that the component DNA has undergone a redistribution from a localized region in the spheroidal nucleoli to an extended circle in the rings; the patterns of uridine-³H incorporation, therefore, parallel the distribution of DNA in both the spheroidal and the ring nucleoli. Ultrastructurally, the nucleoli contain a fibrillar component that corresponds in position to that of the DNA. The typical spheroidal nucleolus consists of a fibrillar core situated eccentrically and surrounded by a hull of granular, ribonucleoprotein material. The ring nucleoli are composed of a central fibrous region that is ensheathed all around its circumference by a layer of similar granular material. This granular substance is thicker at intervals along the length of the rings, representing the "beads" of the necklaces.     

Molecular mechanisms of trophoblast survival: from implantation to birth

Fetal development depends upon a coordinated series of events in both the embryo and in the supporting placenta. The initial event in placentation is appropriate lineage allocation of stem cells followed by the formation of a spheroidal trophoblastic shell surrounding the embryo, facilitating implantation into the uterine stroma and exclusion of oxygenated maternal blood. In mammals, cellular proliferation, differentiation, and death accompany early placental development. Programmed cell death is a critical driving force behind organ sculpturing and eliminating abnormal, misplaced, nonfunctional, or harmful cells in the embryo proper, although very little is known about its physiological function during placental development. This review summarizes current knowledge of the cell death patterns and molecular pathways governing the survival of cells within the blastocyst, with a focus on the trophoblast lineage prior to and after implantation. Particular emphasis is given to human placental development in the context of normal and pathological conditions. As molecular pathways in humans are poorly elucidated, we have also included an overview of pertinent genetic animal models displaying defects in trophoblast survival.     

Structure of the scaffold in bacteriophage lambda preheads removal of the scaffold leads to a change of the prehead shell

Small angle X-ray scattering was performed on unprocessed and processed preheads, intermediates in the morphogenesis of bacteriophage λ heads. Unprocessed preheads possess an internal structure (scaffold), necessary for efficient assembly of closed shells. Processed preheads, formed after removal of the scaffold, are able to pack and cut the viral DNA in vitro. Our data show that the scaffold fills out the inside of the shell in an almost (but not completely) homogeneous fashion; structures of the scaffold with the bulk of the mass in a small core inside the shell can be excluded. Unprocessed preheads are larger than processed ones. A change in shell architecture takes place upon transition from unprocessed to processed prehead; the shell becomes roughened up. Shrinking of the shell as well as roughening up can be triggered by accidental partial degradation of the scaffold. The lattice constant of type A polyheads is in agreement with the lattice constant derived from our icosahedral models of the shell, indicating a close relationship between processed preheads and type A polyheads. This observation, together with the type of subunit clustering found, leads us to propose a simple model for the interaction of prehead shell and protein pD, which stabilizes phage DNA after packaging.     

Three-dimensional spheroidal culture of cytotrophoblast cells mimics the phenotype and differentiation of cytotrophoblasts from normal and preeclamptic pregnancies

Normal placental development is dependent on the orchestrated differentiation of cytotrophoblast (CTB) cells. This study was aimed at studying cytotrophoblast cells from normal and preeclamptic pregnancies in a three-dimensional spheroid-based cell culture model. First trimester cytotrophoblast cells cultured as spheroids maintain their high proliferative and invasive phenotype and respond to different cytokines upon stimulation in a three-dimensional invasion assay. In contrast, third trimester cytotrophoblast spheroids maintain their quiescent nonproliferating phenotype and invasion can only be induced by EGF. Contrasting the regular spheroidal arrangement of cytotrophoblast cells from normal third trimester pregnancies, spheroidal organization of preeclamptic cytotrophoblast cells is disturbed and the cells downregulate CD105 in vivo and in vitro. Furthermore, the invasion of both normal and preeclamptic third trimester, but not first trimester cytotrophoblast cells, is inhibited by pro-inflammatory cytokines. Plasma samples from pregnant women with preeclampsia significantly stimulate the invasion of first trimester cytotrophoblast cells and the sprouting of human umbilical vein endothelial cells (HUVECs) compared to plasma samples from healthy pregnant women. Taken together, the data establish the spheroidal cytotrophoblast model as a powerful system to mimic the in vivo phenotype of first and third trimester and preeclamptic cytotrophoblast cells and demonstrate that plasma-derived factors modulate the differentiation of cytotrophoblast cells.