Electron Tomography of Metaphase Nucleolar Organizer Regions: Evidence for a Twisted-Loop Organization

Metaphase nucleolar organizer regions (NORs), one of four types of chromosome bands, are located on human acrocentric chromosomes. They contain r-chromatin, i.e., ribosomal genes complexed with proteins such as upstream binding factor and RNA polymerase I, which are argyrophilic NOR proteins. Immunocytochemical and cytochemical labelings of these proteins were used to reveal r-chromatin in situ and to investigate its spatial organization within NORs by confocal microscopy and by electron tomography. For each labeling, confocal microscopy revealed small and large double-spotted NORs and crescent-shaped NORs. Their internal three-dimensional (3D) organization was studied by using electron tomography on specifically silver-stained NORs. The 3D reconstructions allow us to conclude that the argyrophilic NOR proteins are grouped as a fiber of 60–80 nm in diameter that constitutes either one part of a turn or two or three turns of a helix within small and large double-spotted NORs, respectively. Within crescent-shaped NORs, virtual slices reveal that the fiber constitutes several longitudinally twisted loops, grouped as two helical 250- to 300-nm coils, each centered on a nonargyrophilic axis of condensed chromatin. We propose a model of the 3D organization of r-chromatin within elongated NORs, in which loops are twisted and bent to constitute one basic chromatid coil.

Force-free twisted magnetospheres of neutron stars

Context. The X-ray spectra observed in the persistent emission of magnetars are evidence for the existence of a magnetosphere. The high-energy part of the spectra is explained by resonant cyclotron upscattering of soft thermal photons in a twisted magnetosphere, which has motivated an increasing number of efforts to improve and generalize existing magnetosphere models. Aims. We want to build more general configurations of twisted, force-free magnetospheres as a first step to understanding the role played by the magnetic field geometry in the observed spectra. Methods. First we reviewed and extended previous analytical works to assess the viability and limitations of semi-analytical approaches. Second, we built a numerical code able to relax an initial configuration of a nonrotating magnetosphere to a force-free geometry, provided any arbitrary form of the magnetic field at the star surface. The numerical code is based on a finite-difference time-domain, divergence-free, and conservative scheme, based of the magneto-frictional method used in other scenarios. Results. We obtain new numerical configurations of twisted magnetospheres, with distributions of twist and currents that differ from previous analytical solutions. The range of global twist of the new family of solutions is similar to the existing semi-analytical models (up to some radians), but the achieved geometry may be quite different. Conclusions. The geometry of twisted, force-free magnetospheres shows a wider variety of possibilities than previously considered. This has implications for the observed spectra and opens the possibility of implementing alternative models in simulations of radiative transfer aiming at providing spectra to be compared with observations.

The builder's complete assistant, or, A library of arts and sciences, absolutely necessary to be understood by builders and workmen in general : viz. I. Arithmetick, vulgar and decimal, in whole numbers and fractions. II. Geometry, lineal, superficial, and solid. III. Architecture, universal. IV. Mensuration. V. Plain trigonometry. VI. Surveying of land, &c. VII. Mechanick powers. VIII. Hydrostaticks : illustrated by above thirteen hundred examples of lines, superficies, solids, mouldings, pedestals, columns, pilasters, entablatures, pediments, imposts, block cornices, rustick quoins, frontispieces, arcades, porticos, &c. : proportioned by modules and minutes, according to Andrea Palladio, and by equal parts : likewise great varieties of trussed roofs, timber bridges, centerings, arches, groins, twisted rails, compartments, obelisks, vases, pedestals for bustos, sun-dials, fonts, &c. and methods for raising heavy bodies by the force of levers, pulleys, axes in peritrochio, screws, and wedges, as also water, by the common pump, crane, etc. : wherein the properties, and pressure of the air on water, &c. are explained : the whole exemplified by 77 large quarto copper-plates /

All of the numbered plates in the atlas are double plates, and thus are counted twice in the adjusted plate count.

Some twisted results

The Drinfeld twist for the opposite quasi-Hopf algebra, H-COP, is determined and is shown to be related to the (second) Drinfeld twist on a quasi-Hopf algebra. The twisted form of the Drinfeld twist is investigated. In the quasi-triangular case, it is shown that the Drinfeld u-operator arises from the equivalence of H-COP to the quasi-Hopf algebra induced by twisting H with the R-matrix. The Altschuler-Coste u-operator arises in a similar way and is shown to be closely related to the Drinfeld u-operator. The quasi-cocycle condition is introduced and is shown to play a central role in the uniqueness of twisted structures on quasi-Hopf algebras. A generalization of the dynamical quantum Yang-Baxter equation, called the quasi-dynamical quantum Yang-Baxter equation, is introduced.

The flow of reality’s development: from postmodernism to post-postmodernism in John Irving’s The World According to Garp and Last Night in Twisted River

In this master’s thesis, I examine the development of writer-characters and metafiction from John Irving’s The World According to Garp to Last Night in Twisted River and how this development relates to the development of late twentieth century postmodern literary theory to twenty-first century post-postmodern literary theory. The purpose of my study is to determine how the prominently postmodern feature metafiction, created through the writer-character’s stories-within-stories, has changed in form and function in the two novels published thirty years apart from one another, and what possible features this indicates for future post-postmodern theory. I establish my theoretical framework on the development of metafiction largely on late twentieth-century models of author and authorship as discussed by Roland Barthes, Wayne Booth and Michel Foucault. I base my close analysis of metafiction mostly on Linda Hutcheon’s model of overt and covert metafiction. At the end of my study, I examine Irving’s later novel through Suzanne Rohr’s models of reality constitution and fictional reality. The analysis of the two novels focuses on excerpts that feature the writer-characters, their stories-within-stories and the novels’ other characters and the narrators’ evaluations of these two. I draw examples from both novels, but I illustrate my choice of focus on the novels at the beginning of each section. Through this, I establish a method of analysis that best illustrates the development as a continuum from pre-existing postmodern models and theories to the formation of new post-postmodern theory. Based on my findings, the thesis argues that twenty-first century literary theory has moved away from postmodern overt deconstruction of the narrative and its meaning. New post-postmodern literary theory reacquires the previously deconstructed boundaries that define reality and truth and re-establishes them as having intrinsic value that cannot be disputed. In establishing fictional reality as self-governing and non-intrudable, post-postmodern theory takes a stance against postmodern nihilism, which indicates the re-founded, non-questionable value of the text’s reality. To continue mapping other possible features of future post-postmodern theory, I recommend further analysis solely on John Irving’s novels’ published in the twenty-first century.

Superlattice structures in twisted bilayers of folded graphene

The electronic properties of bilayer graphene strongly depend on relative orientation of the two atomic lattices. Whereas Bernal-stacked graphene is most commonly studied, a rotational mismatch between layers opens up a whole new field of rich physics, especially at small interlayer twist. Here we report on magnetotransport measurements on twisted graphene bilayers, prepared by folding of single layers. These reveal a strong dependence on the twist angle, which can be estimated by means of sample geometry. At small rotation, superlattices with a wavelength in the order of 10 nm arise and are observed by friction atomic force microscopy. Magnetotransport measurements in this small-angle regime show the formation of satellite Landau fans. These are attributed to additional Dirac singularities in the band structure and discussed with respect to the wide range of interlayer coupling models.

Elliptic curves, group law, and efficient computation

This thesis is about the derivation of the addition law on an arbitrary elliptic curve and efficiently adding points on this elliptic curve using the derived addition law. The outcomes of this research guarantee practical speedups in higher level operations which depend on point additions. In particular, the contributions immediately find applications in cryptology. Mastered by the 19th century mathematicians, the study of the theory of elliptic curves has been active for decades. Elliptic curves over finite fields made their way into public key cryptography in late 1980’s with independent proposals by Miller [Mil86] and Koblitz [Kob87]. Elliptic Curve Cryptography (ECC), following Miller’s and Koblitz’s proposals, employs the group of rational points on an elliptic curve in building discrete logarithm based public key cryptosystems. Starting from late 1990’s, the emergence of the ECC market has boosted the research in computational aspects of elliptic curves. This thesis falls into this same area of research where the main aim is to speed up the additions of rational points on an arbitrary elliptic curve (over a field of large characteristic). The outcomes of this work can be used to speed up applications which are based on elliptic curves, including cryptographic applications in ECC. The aforementioned goals of this thesis are achieved in five main steps. As the first step, this thesis brings together several algebraic tools in order to derive the unique group law of an elliptic curve. This step also includes an investigation of recent computer algebra packages relating to their capabilities. Although the group law is unique, its evaluation can be performed using abundant (in fact infinitely many) formulae. As the second step, this thesis progresses the finding of the best formulae for efficient addition of points. In the third step, the group law is stated explicitly by handling all possible summands. The fourth step presents the algorithms to be used for efficient point additions. In the fifth and final step, optimized software implementations of the proposed algorithms are presented in order to show that theoretical speedups of step four can be practically obtained. In each of the five steps, this thesis focuses on five forms of elliptic curves over finite fields of large characteristic. A list of these forms and their defining equations are given as follows: (a) Short Weierstrass form, y2 = x3 + ax + b, (b) Extended Jacobi quartic form, y2 = dx4 + 2ax2 + 1, (c) Twisted Hessian form, ax3 + y3 + 1 = dxy, (d) Twisted Edwards form, ax2 + y2 = 1 + dx2y2, (e) Twisted Jacobi intersection form, bs2 + c2 = 1, as2 + d2 = 1, These forms are the most promising candidates for efficient computations and thus considered in this work. Nevertheless, the methods employed in this thesis are capable of handling arbitrary elliptic curves. From a high level point of view, the following outcomes are achieved in this thesis. - Related literature results are brought together and further revisited. For most of the cases several missed formulae, algorithms, and efficient point representations are discovered. - Analogies are made among all studied forms. For instance, it is shown that two sets of affine addition formulae are sufficient to cover all possible affine inputs as long as the output is also an affine point in any of these forms. In the literature, many special cases, especially interactions with points at infinity were omitted from discussion. This thesis handles all of the possibilities. - Several new point doubling/addition formulae and algorithms are introduced, which are more efficient than the existing alternatives in the literature. Most notably, the speed of extended Jacobi quartic, twisted Edwards, and Jacobi intersection forms are improved. New unified addition formulae are proposed for short Weierstrass form. New coordinate systems are studied for the first time. - An optimized implementation is developed using a combination of generic x86-64 assembly instructions and the plain C language. The practical advantages of the proposed algorithms are supported by computer experiments. - All formulae, presented in the body of this thesis, are checked for correctness using computer algebra scripts together with details on register allocations.

Contemporary take on deconstructed Medea : a review

THEATRE: The New Dead: Medea Material. By Heiner Muller. Stella Electrika in association with La Boite Theatre Company, Brisbane, November 19. THERE has been a lot of intensity in independent theatre in Brisbane during the past year, as companies, production houses and producers have begun building new programs and platforms to support an expansion of pathways within the local theatre ecology. Audiences have been exposed to works signalling the diversity of what Brisbane theatre makers want to see on stage, from productions of new local and international pieces to new devised works, and the results of residencies and development programs. La Boite Theatre Company closes its inaugural indie season with a work that places it at the contemporary, experimental end of the spectrum. The New Dead: Medea Material is emerging director Kat Henry's interpretation of Heiner Muller's 1981 text Despoiled Shore Medea Material Landscape with Argonauts. Start of sidebar. Skip to end of sidebar. End of sidebar. Return to start of sidebar. Muller is known for his radical adaptations of historical dramas, from the Greeks to Shakespeare, and for deconstructed texts in which the characters - in this case, Medea - violently reject the familial, cultural and political roles society has laid out for them. Muller's combination of deconstructed characters, disconnected poetic language and constant references to aspects of popular culture and the Cold War politics he sought to abjure make his texts challenging to realise. The poetry entices but the density, together with the increasing distance of the Cold War politics in the texts, leaves contemporary directors with clear decisions to make about how to adapt these open texts. In The New Dead: Medea Material, Henry works with some interesting imagery and conceptual territory. Lucinda Shaw as Medea, Guy Webster as Jason and Kimie Tsukakoshi as King Creon's daughter Glauce, the woman for whom Jason forsakes his wife Medea, each reference different aspects of contemporary culture. Medea is a bitter, drunken, satin-gowned diva with bite; Jason - first seen lounging in front of the television with a beer in an image reminiscent of Sarah Kane's in-yer-face characterisation of Hippolytus in Phaedra's Love - has something of the rock star about him; and Glauce is a roller-skating, karaoke-singing, pole-dancing young temptress. The production is given a contemporary tone, dominated by Medea's twisted love and loss, rather than by any commentary on her circumstances. Its strength is the aesthetic Henry creates, supported by live electro-pop music, a band stage that stands as a metaphor for Jason's sea voyage, and multimedia that inserts images of the story unfolding beyond these characters' speeches as sorts of subconscious flashes. While Tsukakoshi is engaging throughout, there are moments when Shaw and Webster's performances - particularly in the songs - are diminished by a lack of clarity. The result is a piece that, while slightly lacking in its realisation at times, undoubtedly flags Henry's facility as an emerging director and what she wants to bring to the Brisbane theatre scene.

A view from the edge of the forest : recent progress in understanding the relationships of the insect orders

Research over the last two decades has significantly increased our understanding of the evolutionary position of the insects among other arthropods, and the relationships among the insect Orders. Many of these insights have been established through increasingly sophisticated analyses of DNA sequence data from a limited number of genes. Recent results have established the relationships of the Holometabola, but relationships among the hemimetabolous orders have been more difficult to elucidate. A strong consensus on the relationships among the Palaeoptera (Ephemeroptera and Odonata) and their relationship to the Neoptera has not emerged with all three possible resolutions supported by different data sets. While polyneopteran relationships generally have resisted significant resolution, it is now clear that termites, Isoptera, are nested within the cockroaches, Blattodea. The newly discovered order Mantophasmatodea is difficult to place with the balance of studies favouring Grylloblattodea as sister-group. While some studies have found the paraneopteran orders (Hemiptera, Thysanoptera, Phthiraptera and Psocoptera) monophyletic, evidence suggests that parasitic lice (Phthiraptera) have evolved from groups within the book and bark lice (Psocoptera), and may represent parallel evolutions of parasitism within two major louse groups. Within Holometabola, it is now clear that Hymenoptera are the sister to the other orders, that, in turn are divided into two clades, the Neuropteroidea (Coleoptera, Neuroptera and relatives) and the Mecopterida (Trichoptera, Lepidoptera, Diptera and their relatives). The enigmatic order Strepsiptera, the twisted wing insects, have now been placed firmly near Coleoptera, rejecting their close relationship to Diptera that was proposed some 15years ago primarily based on ribosomal DNA data. Phylogenomic-scale analyses are just beginning to be focused on the relationships of the insect orders, and this is where we expect to see resolution of palaeopteran and polyneopteran relationships. Future research will benefit from greater coordination between intra and inter-ordinal analyses. This will maximise the opportunities for appropriate outgroup choice at the intraordinal level and provide the background knowledge for the interordinal analyses to span the maximum phylogenetic scope within groups.

A computational model for BMP movement in sea urchin embryos

Bone morphogen proteins (BMPs) are distributed along a dorsal-ventral (DV) gradient in many developing embryos. The spatial distribution of this signaling ligand is critical for correct DV axis specification. In various species, BMP expression is spatially localized, and BMP gradient formation relies on BMP transport, which in turn requires interactions with the extracellular proteins Short gastrulation/Chordin (Chd) and Twisted gastrulation (Tsg). These binding interactions promote BMP movement and concomitantly inhibit BMP signaling. The protease Tolloid (Tld) cleaves Chd, which releases BMP from the complex and permits it to bind the BMP receptor and signal. In sea urchin embryos, BMP is produced in the ventral ectoderm, but signals in the dorsal ectoderm. The transport of BMP from the ventral ectoderm to the dorsal ectoderm in sea urchin embryos is not understood. Therefore, using information from a series of experiments, we adapt the mathematical model of Mizutani et al. (2005) and embed it as the reaction part of a one-dimensional reaction–diffusion model. We use it to study aspects of this transport process in sea urchin embryos. We demonstrate that the receptor-bound BMP concentration exhibits dorsally centered peaks of the same type as those observed experimentally when the ternary transport complex (Chd-Tsg-BMP) forms relatively quickly and BMP receptor binding is relatively slow. Similarly, dorsally centered peaks are created when the diffusivities of BMP, Chd, and Chd-Tsg are relatively low and that of Chd-Tsg-BMP is relatively high, and the model dynamics also suggest that Tld is a principal regulator of the system. At the end of this paper, we briefly compare the observed dynamics in the sea urchin model to a version that applies to the fly embryo, and we find that the same conditions can account for BMP transport in the two types of embryos only if Tld levels are reduced in sea urchin compared to fly.

The antigen 43 structure reveals a molecular velcro-like mechanism of autotransporter-mediated bacterial clumping

Aggregation and biofilm formation are critical mechanisms for bacterial resistance to host immune factors and antibiotics. Autotransporter (AT) proteins, which represent the largest group of outer-membrane and secreted proteins in Gram-negative bacteria, contribute significantly to these phenotypes. Despite their abundance and role in bacterial pathogenesis, most AT proteins have not been structurally characterized, and there is a paucity of detailed information with regard to their mode of action. Here we report the structure–function relationships of Antigen 43 (Ag43a), a prototypic self-associating AT protein from uropathogenic Escherichia coli. The functional domain of Ag43a displays a twisted L-shaped β-helical structure firmly stabilized by a 3D hydrogen-bonded scaffold. Notably, the distinctive Ag43a L shape facilitates self-association and cell aggregation. Combining all our data, we define a molecular “Velcro-like” mechanism of AT-mediated bacterial clumping, which can be tailored to fit different bacterial lifestyles such as the formation of biofilms.

3-Phenylisoquinolin-1(2H)-one

The title compound, C15H11NO, consists of a planar isoquinolinone group to which a phenyl ring is attached in a twisted fashion [dihedral angle = 39.44 (4)degrees]. The crystal packing is dominated by intermolecular N-H center dot center dot center dot O and C-H center dot center dot center dot O hydrogen bonds which define centrosymmetric dimeric entitities.

Equivariant Birch-Swinnerton-Dyer Conjecture for the Base Change of Elliptic Curves: An Example

Let E be an elliptic curve defined over Q and let K/Q be a finite Galois extension with Galois group G. The equivariant Birch-Swinnerton-Dyer conjecture for h(1)(E x(Q) K)(1) viewed as amotive over Q with coefficients in Q[G] relates the twisted L-values associated with E with the arithmetic invariants of the same. In this paper I prescribe an approach to verify this conjecture for a given data. Using this approach, we verify the conjecture for an elliptic curve of conductor 11 and an S-3-extension of Q.