Kink solitons in DNA

We here examine the nonlinear dynamics of artificial homogeneous DNA chain relying on the plain-base rotator model. It is shown that such dynamics can exhibit kink and antikink solitons of sine-Gordon type. In that respect we propose possible experimental assays based on single molecule micromanipulation techniques. The aim of these experiments is to excite the rotational waves and to determine their speeds along excited DNA. We propose that these experiments should be conducted either for the case of double stranded (DS) or single stranded (SS) DNA. A key question is to compare the corresponding velocities of the rotational waves indicating which one is bigger. The ratio of these velocities appears to be related with the sign of the model parameter representing ratio of the hydrogen-bonding and the covalent-bonding interaction within the considered DNA chain.Comment: 15 pages, 5 figure

ACL injuries identifiable for pre-participation imagiological analysis: Risk factors

Identification of pre-participation risk factors for noncontact anterior cruciate ligament (ACL) injuries has been attracting a great deal of interest in the sports medicine and traumatology communities. Appropriate methods that enable predicting which patients could benefit from pre- ventive strategies are most welcome. This would enable athlete-specific training and conditioning or tailored equipment in order to develop appropriate strategies to reduce incidence of injury. In order to accomplish these goals, the ideal system should be able to assess both anatomic and functional features. Complementarily, the screening method must be cost-effective and suited for widespread application. Anatomic study protocol requiring only standard X rays could answer some of such demands. Dynamic MRI/CT evaluation and electronically assisted pivot-shift evaluation can be powerful tools providing complementary information. These upcoming insights, when validated and properly combined, envision changing pre-participation knee examination in the near future. Herein different methods (validated or under research) aiming to improve the capacity to identify persons/athletes with higher risk for ACL injury are overviewed.

Primena metode MUSIC za određivanje smera dolaska radio-signala korišćenjem antenskih nizova ADCOCK / Application of the MUSIC method for direction of arrival estimation using the ADCOCK antenna arrays

Analiziran je problem procene smera dolaska radio-signala metodom MUSIC korišćenjem antenskih nizova ADCOCK. Formulisan je matematički model signala na antenskom nizu ADCOCK. Izvedene su relacije između vektora prostiranja ADCOCK i vektora prostiranja ukupnog antenskog niza (niza od koga se ADCOCK-ov niz formira). Definisana je kriterijumska funkcija algoritma MUSIC i funkcija neodređenosti antenskog niza ADCOCK. Prikazani su rezultati simulacije, kao i rezultati praktične verifikacije mogućnosti primene metode MUSIC na antenske nizove ADCOCK. / The MUSIC based Direction of Arrival estimation using the ADCOCK antenna arrays is considered. Starting from signal model formulation, the cost function of the MUSIC algorithm and the ambiguity functions for the ADCOCK antenna array have been formulated. Some simulation results and some preliminary results of the verification in practice are presented

Direct Wideband Coherent Localization by Distributed Antenna Arrays

We address wideband direct coherent localization of a radio transmitter by a distributed antenna array in a multipath scenario with spatially-coherent line-of-sight (LoS) signal components. Such a signal scenario is realistic in small cells, especially indoors in the mmWave range. The system model considers collocated time and phase synchronized receiving front-ends with antennas distributed in 3D space at known locations connected to the front-ends via calibrated coaxial cables or analog radio frequency over fiber links. The signal model assumes spherical wavefronts. We propose two ML-type algorithms (for known and unknown transmitter waveforms) and a subspace-based SCM-MUSIC algorithm for wideband direct coherent position estimation. We demonstrate the performance of the methods by Monte Carlo simulations. The results show that even in multipath environments, it is possible to achieve localization accuracy that is much better (by two to three orders of magnitude) than the carrier wavelength. They also suggest that the methods that do not exploit knowledge of the waveform have mean-squared errors approaching the Cramér–Rao bound

Position estimation with a millimeter-wave massive MIMO system based on distributed steerable phased antenna arrays

Abstract In this paper, we propose a massive MIMO (multiple-input-multiple-output) architecture with distributed steerable phased antenna subarrays for position estimation in the mmWave range. We also propose localization algorithms and a multistage/multiresolution search strategy that resolve the problem of high side lobes, which is inherent in spatially coherent localization. The proposed system is intended for use in line-of-sight indoor environments. Time synchronization between the transmitter and the receiving system is not required, and the algorithms can also be applied to a multiuser scenario. The simulation results for the line-of-sight-only and specular multipath scenarios show that the localization error is only a small fraction of the carrier wavelength and that it can be achieved under reasonable system parameters including signal-to-noise ratios, antenna number/placement, and subarray apertures. The proposed concept has the potential of significantly improving the capacity and spectral/energy efficiency of future mmWave massive MIMO systems

Calcium signaling modulates the dynamics of cilia and flagella

To adapt to changing environments cells must signal and signaling requires messengers whose concentration varies with time in space. We here consider the messenger role of calcium ions implicated in regulation of the wave-like bending dynamics of cilia and flagella. The emphasis is on microtubules as polyelectrolytes serving as transmission lines for the flow of Ca2+ signals in the axoneme. This signaling is superimposed with a geometric clutch mechanism for the regulation of flagella bending dynamics and our modeling produces results in agreement with experimental data

A biophysical model of how alpha-tubulin carboxy-terminal tails tune kinesin-1 processivity along microtubule

It appears that so called post translational modifications of tubulin heterodimers are mostly focussed at positions of amino acid sequences of carboxy terminal tails. These changes have very profound effects on microtubule functions especially in connection with cellular traffic in terms of motor proteins. In this study, we elaborated the biophysical model aimed to explain the strategy governing these subtle interplays between structural and functional properties of microtubules. We relied onto Langevin equations including fluctuation dissipation processes. In that context we found out that small interaction between a charged motor neck domain and oppositely charged carboxy terminal tail of the a tubulin plays the decisive role in tuning kinesin-1 motor processivity along microtubules

Role of nonlinear localized Ca2+ pulses along microtubules in tuning the mechano-sensitivity of hair cells

This paper aims to provide an overview of the polyelectrolyte model and the current understanding of the creation and propagation of localized pulses of positive ions flowing along cellular microtubules. In that context, Ca2+ ions may move freely on the surface of microtubule along the protofilament axis, thus leading to signal transport. Special emphasis in this paper is placed on the possible role of this mechanism in the function of microtubule based kinocilium, a component of vestibular hair cells of the inner ear. We discuss how localized pulses of Ca2+ ions play a crucial role in tuning the activity of dynein motors, which are involved in mechano sensitivity of the kinocilium. A prevailing notion holds that the concentration of Ca2+ ions around the microtubules within the kinocilium represents the control parameter for Hopf bifurcation. Therefore, a key feature of this mechanism is that the velocities of these Ca2+ pulses be sufficiently high to exert control at acoustic frequencies. (C) 2015 Elsevier Ltd. All rights reserved

Are microtubules discrete or continuum systems?

In this paper we study nonlinear dynamics of microtubules (MTs) relying on so-called u-model. A crucial discrete differential equation is transformed into a partial differential equation using a continuum approximation. Both the continuum and the discrete equations are solved and an excellent agreement of the results shows that MTs can be viewed as continuum systems. Thus we proved that the continuum approximation is applicable in research of nonlinear dynamics of MTs. (C) 2014 Elsevier Inc. All rights reserved

Soliton Waves in Lossy Nonlinear Transmission Lines at Microwave Frequencies: Analytical, Numerical and Experimental Studies

In this paper, we performed analytical, numerical and experimental studies on the generation of soliton waves in discrete nonlinear transmission lines (NLTL) with varactors, as well as the analysis of the losses impact on the propagation of these waves. Using the reductive perturbation method, we derived a nonlinear Schrödinger (NLS) equation with a loss term and determined an analytical expression that completely describes the bright soliton profile. Our theoretical analysis predicts the carrier wave frequency threshold above which a formation of bright solitons can be observed. We also performed numerical simulations to confirm our analytical results and we analyzed the space–time evolution of the soliton waves. A good agreement between analytical and numerical findings was obtained. An experimental prototype of the lossy NLTL, built at the discrete level, was used to validate our proposed model. The experimental shape of the envelope solitons is well fitted by the theoretical waveforms, which take into account the amplitude damping due to the losses in commercially available varactors and inductors used in a prototype. Experimentally observed changes in soliton amplitude and half–maximum width during the propagation along lossy NLTL are in good accordance with the proposed model defined by NLS equation with loss term