Secondary Bodies Research Articles

Bodily tides near the 1:1 spin-orbit resonance: correction to Goldreich’s dynamical model

Spin-orbit coupling is often described in an approach known as “the MacDonald torque”, which has long become the textbook standard due to its apparent simplicity. Within this method, a concise expression for the additional tidal potential, derived by MacDonald (Rev Geophys 2:467–541, 1994), is combined with a convenient assumption that the quality factor Q is frequency-independent (or, equivalently, that the geometric lag angle is constant in time). This makes the treatment unphysical because MacDonald’s derivation of the said formula was, very implicitly, based on keeping the time lag frequency-independent, which is equivalent to setting Q scale as the inverse tidal frequency. This contradiction requires the entire MacDonald treatment of both non-resonant and resonant rotation to be rewritten. The non-resonant case was reconsidered by Efroimsky and Williams (Cel Mech Dyn Astron 104:257–289, 2009), in application to spin modes distant from the major commensurabilities. In the current paper, we continue this work by introducing the necessary alterations into the MacDonald-torque-based model of falling into a 1-to-1 resonance. (The original version of this model was offered by Goldreich (Astron J 71:1–7, 1996). Although the MacDonald torque, both in its original formulation and in its corrected version, is incompatible with realistic rheologies of minerals and mantles, it remains a useful toy model, which enables one to obtain, in some situations, qualitatively meaningful results without resorting to the more rigorous (and complicated) theory of Darwin and Kaula. We first address this simplified model in application to an oblate primary body, with tides raised on it by an orbiting zero-inclination secondary. (Here the role of the tidally-perturbed primary can be played by a satellite, the perturbing secondary being its host planet. A planet may as well be the perturbed primary, its host star acting as the tide-raising secondary). We then extend the model to a triaxial primary body experiencing both a tidal and a permanent-figure torque exerted by an orbiting secondary. We consider the effect of the triaxiality on both circulating and librating rotation near the synchronous state. Circulating rotation may evolve toward the libration region or toward a spin faster than synchronous (the so-called pseudosynchronous spin). Which behaviour depends on the orbit eccentricity, the triaxial figure of the primary, and the mass ratio of the secondary and primary bodies. The spin evolution will always stall for the oblate case. For libration with a small amplitude, expressions are derived for the libration frequency, damping rate, and average orientation. Importantly, the stability of pseudosynchronous spin hinges upon the dissipation model. Makarove and Efroimsky (Astrophys J, 2012) have found that a more realistic tidal dissipation model than the corrected MacDonald torque makes pseudosynchronous spin unstable. Besides, for a sufficiently large triaxiality, pseudosynchronism is impossible, no matter what dissipation model is used.

In vitro propagation of Paphiopedilum orchid through formation of protocorm-like bodies

Paphiopedilum orchids are among the world’s most popular orchid due to their impressively beautiful flowers. Propagation of these orchid genera has been hampered by the naturally slow growth rate of the plant, which renders it very difficult to be propagated through conventional methods. In vitro culture techniques have provided a useful alternative technology for propagating this recalcitrant species. In this study, the propagation of P. rothschildianum was achieved through the in vitro formation of secondary protocorm-like bodies (PLBs) from the primary PLB that developed from stem-derived callus. The PLBs were cultured on half-strength MS medium supplemented with different concentrations (1.0, 2.0, 3.0, and 4.0 μM) of 6-benzyladenine (BA) and kinetin for the induction of secondary PLBs. The highest number of secondary PLBs formed was obtained on half-strength MS medium supplemented with 4.0 μM kinetin, with an average of 4.1 PLBs per explant after 8 weeks of culture. The secondary PLBs continued to proliferate further and formed 9.5–12.1 new PLBs per secondary PLB after being subcultured onto half-strength plant growth regulator-free MS medium supplemented with 60 g/L banana homogenate (BH). These tertiary PLBs were subcultured onto media containing different organic additives, such as BH, coconut water, potato homogenate, and tomato homogenate, for plantlet regeneration. Among the organic additives tested, the addition of 20% CW to half-strength MS medium resulted in the best average plantlet regeneration percentage from the PLBs, 67.9%, after 8 weeks of culture.

RULING OUT POSSIBLE SECONDARY STARS TO EXOPLANET HOST STARS USING THE CHARA ARRAY

Of the over 450 exoplanets known to date, more than 420 of them have been discovered using radial velocity studies, a method that tells nothing about the inclination of the planet's orbit. Because it is more likely that the companion is a planetary-mass object in a moderate- to high-inclination orbit than a low-mass stellar object in a nearly face-on orbit, the secondary bodies are presumed to be planets. Interferometric observations allow us to inspect the angular diameter fit residuals to calibrated visibilities in order to rule out the possibility of a low-mass stellar companion in a very low-inclination orbit. We used the Center for High Angular Resolution Astronomy (CHARA) Array interferometer to observe 20 exoplanet host stars and considered five potential secondary spectral types: G5 V, K0 V, K5 V, M0 V, and M5 V. If a secondary star is present and is sufficiently bright, the effects of the added light will appear in interferometric observations where the planet will not. All secondary types could be eliminated from consideration for 7 host stars and no secondary stars of any spectral type could be ruled out for 7 more. The remaining 6 host stars showed a range of possible secondary types.

Energy Levels of Periodic Solutions of the Circular 2 + 2 Sitnikov Problem

We study a 2+2 body problem introduced in a previous paper as the circular double Sitnikov problem. Since the secondary bodies are moving on the same perpendicular line where evolve the primaries, almost every solution is a collision orbit. We extend the solutions beyond collisions with a symplectic regularization and study the set of energy surfaces that contain periodic orbits and their foliations .

Tightrope Walking: A Memoir by Josephine Pasternak by Pasternak Ramsay , Rimgaila Helen , Rimgaila Salys (review)

340 SEER, 87, 2, APRIL 200g unhappymarriage, arguesthatSokhanskaiahas createdan 'almostentirely matriarchal worldin whichmen playlittlepart' (p. 64). He thusfindsthe storyto be more about 'narrative death and resurrection' than about an unhappymarriage(p. 65). Unexpectedly we findthatoutsidespace, rather thanthetypical domainofindoors, is thearenawheretheheroinefinds her identity. Andrewsuggests thatbothSokhanskaia and Khvoshchinskaia foreshadowwhatbecomesa centralmotif of twentieth-century feminist fiction: 'friendship amongwomen'(p. 77). (Khvoshchinskaia' s novel,however,also takeson thedarkthemeofwomenpolicing each other[pp. 103-09]whichis likewisepresentin the threestoriesof Dostoevskii's which he discusses.) Although I foundthisnotionoftheemphasis on femalefriendship as a dominantthemecompelling , itseemsto me thatthisidea aboundsin nineteenthcentury literature generally - whether amongAusten's heroines orevenwith AnnaKarenina,whois inpartdriven tohersuicidebecauseofherexclusion from theworldofwomen. Andrew's analysis of'FamilyHappiness'uncovers a crucialgenericswitch betweenpartsone and twofromthepastoraleto thesocietytale; hisfinal chapteron Chekhov's'The Fiancée' exploresthewaysin whichChekhov, evenas he deliberately returns tothestyle and evocation ofan earlier period, is also in dialoguewithTolstoi'sstory.I foundespeciallyfascinating the lastsection,'Chekhov'sTestament'.Here Andrewexploreshow thisstory, Chekhov's last,isbotha retrospective and a capstone.'Mostofthecharacters couldbe saidto comefrom theChekhov"repertory company'"(p. 177), and he concludes, 'Butthis,hislast,testamental workdoes,at least,seemto call on Russiatoawake,likehislastshort story heroine, whosefullnameis never usedinthestory, butis,ofcourse[.. .] Hope' (p. 179).As notedearlier, atthis pointthereaderflips thepage,eagerfora conclusion tohighlight theinsights culledalong theway. But it is herethatthisinteresting, well argued,and convincing volumecomesto itsend. Department ofGerman, Russian RobinFeuer Miller andAsian Languages andLiterature Brandeis University, Massachusetts PasternakRamsay,Helen and Salys,Rimgaila (eds). Tightrope Walking: A Memoir by Josephine Pasternak. Slavica,Bloomington, IN, 2005. xv + 296 pp. Illustrations. Chronology.Notes. Bibliography.Index. $24.95 (paperback). Memoirspresent us witha doubleinterest: we wishto learnmoreabout a particular lifeorlives, butwe alsoreadthememoir as a workofartinitsown right. Josephine Pasternak's Tightrope Walking belongstoa particular sub-genre of memoirs, depicting the livesof notablepersonsthrough the eyes of a closerelative. Withsuchmemoirs thenarrator himself orherself can become invisible, withdrawn to a background, made onlyto illuminate greatlives. Pasternak's memoirdefinitely does not followsuch constraints. Poet and philosopher Josephine Pasternak writes a detailedexploration ofherownlife, REVIEWS 34I and evenmoreso ofherown emotionaland mentalworld.The book was intended to concentrate on herlife,yetto also makeprominent thebiographiesoffamily members, Nobel Prizelaureatepoet and prosewriter Boris Pasternak (Josephine's brother), landscapeandportrait artist LeonidPasternak (herfather), and pianistRosalia KaufmanPasternak (hermother). Josephine Pasternak'smemoir,writtenin English, spans from her childhoodin pre-Revolutionary Russia, through the Revolution,to lifein emigration in Germany, and endsat thepointofherarriving at theage of twenty-seven. The memoiris constructed aroundthe 'threecentralsunsin (her)family [herfather, mother and brother Boris]and thethreesatellites, or secondary bodies- Shura[hereldestbrother] , Lydia[hersister] ' and herself (p. 60). Indeed, much of the book is devotedto the personaland artistic development ofthese'threesuns',especially Borisand Leonid.She mentions Boris'svariousyouthful infatuations and discusseshis turbulent relationship withhisfirst wife.But she also stresses theaffinity ofartistic sensibility she and Borisfelt. Josephine discusses Leonid'sartand claimsthat'hisflights of inspiration werenotlessboldthanthoseofhisson' (p. 212),butshealso gives an accountoftheinternal conflict thefather alwaysfelt betweenhiscommitmenttohisfamily and hisvocation.It seemsthat Josephine isconcerned with pureart,and sees anything lessthanabsolutededicationas a lossofartistic potential. As to Rosalia,Josephine talksoftheeffect ofhermother's playing on herearliest impressions, noting an affinity toMarinaTsvetaeva,forwhom hermother and musicwerealso formative influences. By virtueofbeingclose to herbrother Boris, Josephinehad been introducedto a number ofpoetsand writers oftheperiod.She describes in detail a visitwithBoris to Lilia and Osip Brik,when she was exhilaratedby themutualaffection betweenPasternak and Maiakovskii. Regardlessofthe difference in poetictemperament betweenthem,she ascertains, theyunderstoodand admiredeach other's work.Atthesameevening Josephine recalls a curiousscenewhenBoriskissedherin an eroticmanner.Significantly, she says thatwhile she feltno eroticresponse,insteadof being shockedshe believedthat'to remaincold in answerto hispassionateappeal - [was] a desecration' (p. 93). It seemsthatforherpassionis relatedto artand both are,forher,highest ideals.Conventions matter less,surprisingly fora young womanwhogrewup in a strict Victorian-style household. In spiteoftheprofessed emphasison 'thesuns'in herfamily, Josephine devoteslargepartsof her memoirto her own psychological and religious turmoil, and also refers to a numberofmentalbreakdowns laterin life.She describes in detailreligious and sexualpassionsand compulsions shehad felt from an earlyage. Her approachis psychoanalytical and she seeksmeaning in the Freudianset of images.How much of thisinterpretation is a true reflection ofJosephine's mentalstateand how muchofher experienceshe constructs mentally becauseoftheintellectual influence ofpsychoanalysis on herviewsis hardto tell. A curiouscollision is seenagainand againinthememoir, whenJosephine on theone hand professes deep attachment to herfamily and on theother hand confessesto feelingtrappedin the familycircle.When she finally decidedtomovetoBerlintostudy shefeelsthehappiness offreedom butalso 342 SEER, 87, 2, APRIL 200g excruciating nostalgia...

On the periodic orbits of the circular double Sitnikov problem

We introduce a restricted four body problem in a 2 + 2 configuration extending the classical Sitnikov problem to the Double Sitnikov problem. The secondary bodies are moving on the same perpendicular line to the plane where the primaries evolve, so almost every solution is a collision orbit. We extend the solutions beyond collisions with a symplectic regularization and study the set of energy surfaces that contain periodic orbits. To cite this article: H. Jiménez Pérez, E.A. Lacomba, C. R. Acad. Sci. Paris, Ser. I 347 (2009).

Dynamics of tidal synchronization and orbit circularization of celestial bodies

We take a dynamical-systems approach to study the qualitative dynamical aspects of the tidal locking of the rotation of secondary celestial bodies with their orbital motion around the primary. We introduce a minimal model including the essential features of gravitationally induced elastic deformation and tidal dissipation that demonstrates the details of the energy transfer between the orbital and rotovibrational degrees of freedom. Despite its simplicity, our model can account for both synchronization into the 1:1 spin-orbit resonance and the circularization of the orbit as the only true asymptotic attractors, together with the existence of relatively long-lived metastable orbits with the secondary in p:q synchronous rotation.

Tidal disruptions: II. A continuum theory for solid bodies with strength, with applications to the Solar System

We present a comprehensive theory for the breakup conditions for ellipsoidal homogeneous secondary bodies subjected to the tidal forces from a nearby larger primary: for materials ranging from purely fluid ones, to granular rubble-pile gravel-like ones, and to those with either cohesive or granular strength including cohesive rocks and metals. The theory includes but greatly extends the classical analyses given by Roche in 1847, which dealt only with fluids, and also our previous analysis [Holsapple, K.A., Michel, P., 2006. Icarus 183, 331–348], which dealt only with solid but non-cohesive bodies. The results here give the distance inside of which breakup must occur, for both a steadily orbiting satellite and for a passing or impacting object. For the fluid bodies there is a single specific shape (a “Roche Ellipsoid”) that can be in equilibrium at any given distance from a primary, and especially only one shape that can exist at the overall minimum distance ( d / R ) ( ρ / ρ p ) 1 / 3 = 2.455 , the classical well-known “Roche limit.” In contrast, solid bodies can exist at a given distance from a primary with a range of shapes. Here we give multiple plots of the minimum distances for various important combinations of body shape, spin, mass density, and the strength parameters characterized by an angle of friction and cohesive strength. Such results can be used in different ways. They can be used to estimate limits on strengths and mass densities for orbiting bodies at a known distance and shape. They can be used to determine breakup distances for passing bodies with an assumed strength and shape. They can be used to constraint physical properties such as bulk density of bodies with a known shape that were known to breakup at a given distance. A collection of approximately 40 satellites of the Solar System is used for comparison to the theory. About half of those bodies are closer than the Roche fluid limit and must have some cohesion and/or friction angle to exist at their present orbital distance. The required solid strength for those states is determined. Finally, we apply the theory to the break up of the SL9 comet at close approach with Jupiter. Our results make clear that the literature estimates of its bulk density depend markedly on unknown parameters such as shape, orientation and spin, and most importantly, material strength characterization.

Histogenesis of the Intravitreal Membrane and Secondary Vitreous in the Mouse

The intravitreal membrane (IVM) is a membranous structure between the primary and secondary vitreous bodies in developing mammalian eyes. In this study, for the first time the histogenesis of the IVM and the relationship between the hyaloid vasculature and the IVM was characterized in newborn mice. Eyes of mice less than 12 days old were fixed and embedded. From these, serial paraffin-embedded sections were made for lectin histochemistry, immunohistochemistry, and picrosirius red (PSR) staining, and ultrathin sections were made for transmission electron microscopy (TEM). Eight biotinylated lectins and antibodies for laminin and type IV collagen were used. Among the eight lectins tested, concanavalin A (Con A) agglutinin, Ricinus communis agglutinin I, and wheat germ agglutinin demonstrated strong positive staining in the IVM and vitreous fibrils of the primary and secondary vitreous bodies. They also bound to the internal limiting membrane (ILM) of the retina. At postgestational day 4, the secondary vitreous first appeared between the ILM and the vasa hyaloidea propria (VHP). Immunohistochemical staining revealed that the IVM consists of extracellular matrix components including laminin and type IV collagen, whereas PSR staining and TEM showed that collagen fibrils in the IVM are bundled and continuous with the basement membrane of hyaloid capillaries or the VHP. Lectin histochemistry and immunohistochemistry provided good methods for visualizing the structures of the IVM and vitreous fibrils. These results suggest that the IVM is separated from the basement membrane of the retinal ILM along with the vascular network of the VHP when the secondary vitreous begins to form.

Multiple laryngeal foreign bodies composed of dried fish vertebral bones: a case report

We present a rare case of tracheostomy for removal of laryngeal foreign bodies consisting of three connected fish vertebral bones in a 15-month-old girl. Recent endoscopic techniques have made it possible to extract nearly all tracheobronchial foreign bodies with rigid bronchoscopes. However, the three connected foreign bodies in this report could not be extracted entirely by single endoscopy because the glottis as an exit was narrow due to severe oedema. Accordingly, tracheostomy was required to assist ventilation, prevent prolonged post-operative endotracheal intubation, remove the secondary tracheal foreign bodies and to provide a conduit for the introduction of a bronchoscope. This suggests that tracheostomy should be considered to avoid the potential dangers of severe laryngeal oedema and to secure the route for removal of foreign bodies from the trachea when treating patients with multiple laryngeal foreign bodies and laryngeal oedema.

Management of Osteochondritis Dissecans of the Knee

Osteochondritis dissecans of the knee is being seen with increased frequency in pediatric and young adult athletes and is thought to be, in part, owing to earlier and increasingly competitive sports participation. Despite much speculation, the cause of both juvenile and adult osteochondritis dissecans remains unclear. Early recognition is essential. Whereas adult osteochondritis dissecans lesions have a greater propensity to instability, juvenile osteochondritis dissecans lesions are typically stable, and those with an intact articular surface have a potential to heal with nonoperative treatment through cessation of repetitive impact loading. The value of adjunctive immobilization, protected weightbearing, and unloader bracing has not been established. Skeletally immature patients with stable lesions that have not healed with nonoperative treatment should have consideration given to arthroscopic drilling to promote healing before the lesion progresses and requires more involved treatment with a less optimistic prognosis. Magnetic resonance imaging may allow early prediction of lesion healing potential. The majority of adult osteochondritis dissecans cases as well as those skeletally immature patients with unstable lesions and secondary loose bodies require fixation and possible bone grafting. Many unstable lesions will heal after stabilization, but long-term prognosis is not clear. Chronic loose fragments can be difficult to fix and have poor healing potential. Results of excision of large lesions from weightbearing zones are poor. Chondral resurfacing techniques have limited long-term data for cases of osteochondritis dissecans in skeletally immature patients.

Tyrosine phosphatase SHP-1 acts at different stages of development to regulate hematopoiesis

AbstractMice lacking SHP-1 exhibit a plethora of perturbations in their hematopoietic and immune systems. To reveal the primary effects resulting from SHP-1 deficiency, we used embryonic stem (ES) cells to study the role of SHP-1 in developmental hematopoiesis. We expressed wild-type (WT) and dominant-negative (R459M) forms of SHP-1 in ES cells and used ES/OP-9 coculture and embryoid body development followed by hematopoietic colony assays to demonstrate that SHP-1 acts at multiple stages of hematopoietic differentiation to alter lineage balance. Expression of WT SHP-1 reduced myeloid colony numbers while increasing the numbers of secondary embryoid bodies and mixed hematopoietic colonies obtained. Conversely, expression of R459M SHP-1 resulted in a significant increase in the numbers and sizes of myeloid colonies observed while reducing the numbers of colonies derived from undifferentiated cells or hematopoietic precursor cells. Confining the expression of WT or R459M SHP-1 to the early phases of differentiation decreased and increased progenitor cell numbers, respectively, and influenced colony formation. Overall, our results are consistent with SHP-1 acting during multiple stages of hematopoietic development, and they suggest that the increases in granulocytes and macrophages observed in motheaten mice arise as the result of a cell autonomous effect early during development.

Immunocytochemical localization of polygalacturonase during tracheary element differentiation in Zinnia elegans

Polygalacturonase (PG) is a cell wall-associated protein that degrades pectin. A ZePG1 cDNA encoding a putative PG was isolated from Zinnia elegens L. and a rabbit antibody specific to the ZePG1 protein was generated. The level of the ZePG1 protein was up-regulated when tracheary element differentiation was initiated. Using gold-labeled secondary antibodies for light and electron microscopy, ZePG1 protein was localized in cultured Zinnia cells. This protein was preferentially distributed on tracheary elements (TEs). At the subcellular level, the protein was localized on secondary wall thickenings, primary walls, Golgi bodies and vesicles. Thus, the putative role of the ZePG1 protein might be the degradation of pectic substances before lignification. Some non-TE cells also accumulated ZePG1 protein on primary walls, Golgi bodies and vesicles. The accumulation of ZePG1 protein on primary walls seems to be at the elongating tips of non-TE cells. In plants, ZePG1 protein was localized on the secondary wall thickenings of differentiating TEs and phloem regions. These results suggest that the expression of the ZePG1 protein is highly regulated both spatially and temporally during in vitro and in situ TE differentiation.

On the regularities of the mean distances of secondary bodies in the solar system

Abstract In this paper new formulae for the computation of orbital periods and mean distances of secondary bodies from a primary central body are given as a function (i) of an integer orbit number, and (ii) of the mass of the primary. Not all orbits numbered by the consecutive integers are occupied by the secondaries; on the contrary, most of them remain empty. It has been found that the mass of the primary, for which the formulae are valid, must be greater than M o = 1.747M Earth. The mean primary/secondary distances and orbital periods agree surprisingly accurately with the real ones for all systems considered (Solar, Jovian, Saturnian, Uranian and Neptunian, Table 7).

Enhanced Green Fluorescence Protein (EGFP) as a Non-Invasive In Vivo Marker to Assess the Efficiency of Trangenesis and Nuclear Transplantation

Objective: We have successfully used mouse secondary polar bodies (2PBs) and female pronuclei (FPNs) to reconstruct viable embryos. However, factors attributing to the success of reconstruction remain unclear. The EGFP gene encoding a protein emitting green fluorescent light which can be easily observed by a fluorescent microscopy. In this study, we tried to established the method of integrating this exogenous DNA into the genome of the reconstructed embryos as a non-toxic biological marker to assess the efficiency of transgenesis and nuclear transplantation.

Changing images of the State: overloaded, hollowed-out, congested

Three conceptualisations of the UK's state are identified: the overloaded state of the 1960s/1970s; the hollowed-out state of the 1980s/early 1990s; the congested state of the late 1990s. In this latter period the creation of collaborative institutions has become a core strategy in all areas of UK public policy. This rich web of linkages arose in response to the problems inherent in the fragmentation arising from hollowing-out. The resulting partnerships bring together public, private, voluntary and community sector actors. They operate between and around the core institutions of democratic government. These tertiary (partnership) structures have complex accountability relationships with primary (elected) and secondary (appointed) public bodies, as well as with other actors. The example of Northshire shows how inter-linked strategic and specific partnership boards create an alternative, collaborative governance structure for a locality which is largely outside democratic processes. This development has fundamental implications for our appreciation of the institutional framework of UK government, as well as for the debate about and practice of democratic renewal.

Secondary phase distribution analysis via finite body tessellation

The concept of a Dirichlet tessellation has been extended to that of a 'finite body' tessellation to provide a more meaningful description of the spatial distribution of non-spherical secondary phase bodies on two-dimensional sections. A finite body tessellation consists of a network of cells constructed from the interfaces of each individual secondary phase body such that every point within a cell is closer to the corresponding body than to any other. Spatial distribution related cell characteristics derived from Dirichlet tessellations have been extended to finite body tessellations. Quantitative comparisons between the two methods indicate that finite body tessellation measurements are more physically representative as well as more sensitive to local distribution characteristics of secondary phases. To reflect the potential application of finite body tessellations, a methodology is described for analysing the effects of particle distribution and morphology on short crack behaviour in particulate reinforced metal matrix composites.

Quantitative Assessment of Particle Distribution Effects on Short Crack Growth in SiCp Reinforced Al-Alloys

Ceramic reinforcements are known to have a marked effect on fatigue in Al-based materials. Critical physical processes include localized load transfer mechanics and associated stress/strain concentrations, the presence of matrix/reinforcement differential thermal contraction stresses and the modification of matrix microstructure by the presence of ceramic reinforcements (e.g. dislocation densities and precipitation characteristics). The extent to which reinforcements may affect crack growth will depend on a range of materials parameters, including component phase elastic moduli, thermal expansivities and strength levels, interfacial strength, reinforcement morphology (size, aspect ratios, volume fraction), and the spatial distribution of the reinforcement. The identification of Dirichlet cells around individual secondary phase bodies, such that every point within the cell is closer to the centroid of the associated body than any other, has been previously identified as a uniquely powerful analysis tool in describing distribution characteristics on a particle-by-particle basis. In a separate publication by the authors, such a tessellation process has been extended to finite bodies to provide a more physically meaningful description of non-spherical secondary phase bodies exhibiting a wide size range. A finite body tessellation consists of a network of cells such that every point within a cell is closer to the interface of themore » corresponding body than to any other. In an initial investigation of the effects of particle distribution on fatigue failure processes of MMCs, crack propagation associated with the short crack regime in an aluminum-based metal matrix composite has been analyzed quantitatively using finite body tessellations. The main aim of this paper is to illustrate the value of tessellation analysis for the study of crack tip interactions in particle reinforced materials.« less

The orbits structure for the subsystem of secondary bodies in the Solar system

The orbits structure for the subsystem of secondary bodies in the Solar system

Positional Information and Whorl Morphogenesis inPolysphondylium

Cellular slime molds of the genusPolysphondyliumperiodically release cell masses from the base of culminating fruiting bodies. These masses quickly undergo a change in symmetry from spherical to radial as they differentiate into distinctive arrays of secondary fruiting bodies arranged about a primary axis of stalk cells. Here we show that a major event in whorl morphogenesis is the activation of a prestalk-specific promoter early and globally in newly forming whorls. With time, transcript synthesis and amplification become restricted to the equator of the whorl and then to patches which define where secondary tip morphogenesis will occur. The localization of early prestalk message synthesis depends on positional information, in contrast to the establishment of early prestalk/prespore patterns in bothPolysphondyliumandDictyostelium.