255 research outputs found
A stochastic model of Min oscillations in Escherichia coli and Min protein segregation during cell division
The Min system in Escherichia coli directs division to the centre of the cell
through pole-to-pole oscillations of the MinCDE proteins. We present a one
dimensional stochastic model of these oscillations which incorporates membrane
polymerisation of MinD into linear chains. This model reproduces much of the
observed phenomenology of the Min system, including pole-to-pole oscillations
of the Min proteins. We then apply this model to investigate the Min system
during cell division. Oscillations continue initially unaffected by the closing
septum, before cutting off rapidly. The fractions of Min proteins in the
daughter cells vary widely, from 50%-50% up to 85%-15% of the total from the
parent cell, suggesting that there may be another mechanism for regulating
these levels in vivo.Comment: 19 pages, 12 figures (25 figure files); published at
http://www.iop.org/EJ/journal/physbi
Dimension of the Torelli group for Out(F_n)
Let T_n be the kernel of the natural map from Out(F_n) to GL(n,Z). We use
combinatorial Morse theory to prove that T_n has an Eilenberg-MacLane space
which is (2n-4)-dimensional and that H_{2n-4}(T_n,Z) is not finitely generated
(n at least 3). In particular, this recovers the result of Krstic-McCool that
T_3 is not finitely presented. We also give a new proof of the fact, due to
Magnus, that T_n is finitely generated.Comment: 27 pages, 9 figure
Acenaphthenoannulation Induced by the Dual Lewis Acidity of Alumina
We have discovered a dual (i.āe., soft and hard) Lewis acidity of alumina that enables rapid one-pot Ļ-extension through the activation of terminal alkynes followed by CāF activation. The tandem reaction introduces an acenaphthene fragment ā an essential moiety of geodesic polyarenes. This reaction provides quick access to elusive non-alternant polyarenes such as Ļ-extended buckybowls and helicenes through three-point annulation of the 1-(2-ethynyl-6-fluorophenyl)naphthalene moiety. The versatility of the developed method was demonstrated by the synthesis of unprecedented structural fragments of elusive geodesic graphene nanoribbons
Synthesis, characterization and biological activity of Pt(II) complexes with steroidal thiosemicarbazones
In this work, Pt(II) complexes of previously synthesized steroidal thiosemicarbazones were synthesized and characterized. The ligands and their metal complexes were studied by analytical and spectroscopic data (elemental analysis, IR, 1D-NMR and 2D-NMR, HSQC, HMBC, NOESY, COSY), the analysis of which enabled complete 1H and 13C assignments of each compound including E and Z isomers. All the synthesized ligands and complexes were screened for their cytotoxic and antimicrobial activity. The results demonstrate that the new steroidal thiosemicarbazone complexes were significantly less cytotoxic than the corresponding steroidal thiosemicarbazones. In addition, complexes showed lower antimicrobial activity than the standard drugs, similar to the activity of the starting thiosemicarbazones
Markerless Vision-Based Skeleton Tracking in Therapy of Gross Motor Skill Disorders in Children
This chapter presents a research towards implementation of a computer vision system for markerless skeleton tracking in therapy of gross motor skill disorders in children suffering from mild cognitive impairment. The proposed system is based on a low-cost 3D sensor and a skeleton tracking software. The envisioned architecture is scalable in the sense that the system may be used as a stand-alone assistive tool for tracking the effects of therapy or it may be integrated with an advanced autonomous conversational agent to maintain the spatial attention of the child and to increase her motivation to undergo a long-term therapy
Hubble Space Telescope Angular Velocity Estimation During the Robotic Servicing Mission
In 2004 NASA began investigation of a robotic servicing mission for the Hubble Space Telescope (HST). Such a mission would require estimates of the HST attitude and rates in order to achieve a capture by the proposed Hubble robotic vehicle (HRV). HRV was to be equipped with vision-based sensors, capable of estimating the relative attitude between HST and HRV. The inertial HST attitude is derived from the measured relative attitude and the HRV computed inertial attitude. However, the relative rate between HST and HRV cannot be measured directly. Therefore, the HST rate with respect to inertial space is not known. Two approaches are developed to estimate the HST rates. Both methods utilize the measured relative attitude and the HRV inertial attitude and rates. First, a non-linear estimator is developed. The nonlinear approach estimates the HST rate through an estimation of the inertial angular momentum. Second, a linearized approach is developed. The linearized approach is a pseudo-linear Kalman filter. Simulation test results for both methods are given. Even though the development began as an application for the HST robotic servicing mission, the methods presented are applicable to any rendezvous/capture mission involving a non-cooperative target spacecraft
Phase Synchronization Control of Robotic Networks on Periodic Ellipses with Adaptive Network Topologies
This paper presents a novel formation control method for a large number of robots or vehicles described by Euler-Lagrange (EL) systems moving in elliptical orbits. A new
coordinate transformation method for phase synchronization of networked EL systems in elliptical trajectories is introduced to define desired formation patterns. The proposed phase synchronization controller synchronizes the motions of agents, thereby yielding a smaller synchronization error than an uncoupled control law in the presence of bounded disturbances. A complex time-varying and switching network topology, constructed by the
adaptive graph Laplacian matrix, relaxes the standard requirement of consensus stability, even permitting stabilization on an arbitrary unbalanced graph. The proofs of stability are constructed by robust contraction analysis, a relatively new nonlinear stability tool. An
example of reconfiguring swarms of spacecraft in Low Earth Orbit shows the effectiveness of the proposed phase synchronization controller for a large number of complex EL systems moving in elliptical orbits
AkustiÄkoāmehaniÄki model govornog trakta
Modelling voice tract using an acousticalāmechanical analogy is shown in this article. The process of modelling voice tract is often reduced to one-dimensional acoustical model, i.e. planar waveguide model. With this acousticalmechanical model, computer programs are utilized to analyze and synthesize the voice tract. Hence, it is possible to calculate models which describe the voice tract with satisfactory quality and detail level and these models can be used in practice and applied to particular cases. In this article the process of producing a voice tract model is presented. The process includes the usage of three different computer programs, each of them dedicated to one segment of modelling. Recordings for three speakers were made and the analysis of voice parameters was performed. After the analysis is completed, a two-dimensional model of the voice tract was made, which resulted in a mechanical model consisting of specific number of tubes. Finally, the evaluation procedure for the model is done by applying a software developed specifically for this purpose, in order to determine whether the resulting model truly represents the voice tract of each speaker.Ovaj Älanak daje primjer izrade modela govornog trakta zasnovanog na akustiÄko-mehaniÄkim analogijama, za tri govornika, pomoÄu raÄunalno zasnovanog sustava. Definiranje modela govornog trakta Äesto se svodi na jednodimenzionalni akustiÄki model, planarni valovodni model. Kad je napravljen akustiÄko-mehaniÄki model, u analizu i sintezu uvode se raÄunala i raÄunalni programi. PomoÄu njih se dobivaju modeli i izraÄuni koji sa zadovoljavajuÄom kvalitetom i preciznoÅ”Äu opisuju govorni trakt, pa takve modele možemo koristiti u praksi i primjenjivati na konkretne sluÄajeve. U Älanku su za dobivanje modela govornog trakta koriÅ”tene tri razliÄite programske podrÅ”ke, svaka u svom segmentu izrade modela. Snimljena su tri govornika i napravljena je analiza glasa. Nakon toga je, opet koristeÄi raÄunalo, izmodeliran dvodimenzionalni model govornog trakta, koji kao rezultat daje mehaniÄki model s odre.enim brojem cjevÄica. Na kraju je napravljena provjera tog modela sa programskom podrÅ”kom koja je napisana za tu svrhu, kako bi se utvrdilo da dobiveni model zaista predstavlja govorni trakt pojedinog govornika
Ionization of hydrogen and hydrogenic ions by antiprotons
Presented here is a description of the ionization of hydrogen and hydrogenic
ions by antiproton-impact, based on very large scale numerical solutions of the
time-dependent Schr\"odinger equation in three spatial dimensions and on
analysis of the topology of the electronic eigenenergy surfaces in the plane of
complex internuclear distance. Comparison is made with other theories and very
recent measurements.Comment: RevTex document, 11 pages, 4 Postscript figures are available from
the authors, in press Phys. Rev. Let
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