3,989 research outputs found
Knots and Classical 3-Geometries
It has been conjectured by Rovelli that there is a correspondence between the
space of link classes of a Riemannian 3-manifold and the space of 3-geometries
(on the same manifold). An exact statement of his conjecture will be
established and then verified for the case when the 3-manifold is compact,
orientable and closed.Comment: 14p. type-set in AmS-TeX version 2.
Computational Aspects of Protein Functionality
The purpose of this short article is to examine certain aspects of protein functionality
with relation to some key organizing ideas. This is important from a computational
viewpoint in order to take account of modelling both biological systems and
knowledge of these systems. We look at some of the lexical dimensions of the
function and how certain constructs can be related to underlying ideas. The pervasive
computational metaphor is then discussed in relation to protein multifunctionality,
and the specific case of von Willebrand factor as a ‘smart’ multifunctional protein
is briefly considered. Some diagrammatic techniques are then introduced to better
articulate protein function
Cell biological mechanisms of activity-dependent synapse to nucleus translocation of CRTC1 in neurons.
Previous studies have revealed a critical role for CREB-regulated transcriptional coactivator (CRTC1) in regulating neuronal gene expression during learning and memory. CRTC1 localizes to synapses but undergoes activity-dependent nuclear translocation to regulate the transcription of CREB target genes. Here we investigate the long-distance retrograde transport of CRTC1 in hippocampal neurons. We show that local elevations in calcium, triggered by activation of glutamate receptors and L-type voltage-gated calcium channels, initiate active, dynein-mediated retrograde transport of CRTC1 along microtubules. We identify a nuclear localization signal within CRTC1, and characterize three conserved serine residues whose dephosphorylation is required for nuclear import. Domain analysis reveals that the amino-terminal third of CRTC1 contains all of the signals required for regulated nucleocytoplasmic trafficking. We fuse this region to Dendra2 to generate a reporter construct and perform live-cell imaging coupled with local uncaging of glutamate and photoconversion to characterize the dynamics of stimulus-induced retrograde transport and nuclear accumulation
A multiple-cut analytic center cutting plane method for semidefinite feasibility problems
10.1137/S1052623400370503SIAM Journal on Optimization1241126-114
Spectral operators of matrices
The class of matrix optimization problems (MOPs) has been recognized in recent years to be a powerful tool to model many important applications involving structured low rank matrices within and beyond the optimization community. This trend can be credited to some extent to the exciting developments in emerging fields such as compressed sensing. The Löwner operator, which generates a matrix valued function via applying a single-variable function to each of the singular values of a matrix, has played an important role for a long time in solving matrix optimization problems. However, the classical theory developed for the Löwner operator has become inadequate in these recent applications. The main objective of this paper is to provide necessary theoretical foundations from the perspectives of designing efficient numerical methods for solving MOPs. We achieve this goal by introducing and conducting a thorough study on a new class of matrix valued functions, coined as spectral operators of matrices. Several fundamental properties of spectral operators, including the well-definedness, continuity, directional differentiability and Fréchet-differentiability are systematically studied. © 2017 Springer-Verlag Berlin Heidelberg and Mathematical Optimization Society
Binding of Basic Dyes by the Algae, Chara aspera
Non-living biomass of the algae Chara aspera is capable of binding two basic dyes, methylene blue and basic blue 3, from aqueous solution. Factors such as dye concentration, contact time, sorbent dosage and pH of solution were
studied. Maximum sorption capacities of the algae for methylene blue and basic blue 3 are 139.4 and 17.8 mg/g, respectively, as determined from the
Langmuir isothenns
Applications of Built-up Sections in Lightweight Steel Trusses
Lightweight steel structures have been widely used in the construction industry. It is flexible and thus can be designed to cater for different usages. To enhance the application of cold-formed steel structures, innovative configurations are developed. These include increasing the load bearing capacity of the structure and stretching it over a larger span. Built-up section of lipped channels, either back-to-back or boxed-up for the critical elements of a truss is often adopted when it may have practical limitations in increasing the truss depth. This paper presents some of such applications in the construction industry. The built-up section possesses apparent improvement in lateral stiffness. Although these sections act together, they are currently designed individually. Current design codes do not have comprehensive provision for the design of built-up sections reflecting the improvement in design strength. The modified slenderness ratio for built-up sections in the American Iron and Steel Institute (AISI) North American Specification for the Design of Cold-Formed Steel Structural Members is adopted from researches and recommendations for hot-rolled sections. From literature search, field observation and preliminary test conducted, it reveals that the modification rule can be further developed to better reflect the improvement in the slenderness ratio of the built-up sections
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