Wyniki wyszukiwania - Biblioteka Nauki

1

Bistability and dual-frequency nematic liquid crystals

100%

Palto S. P. , Barnik M. I.

Opto-Electronics Review

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2007

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tom Vol. 15, No. 1

52-59

EN

Different modes of bistable switching in liquid crystals with frequency inversion of the dielectric anisotropy sign are discussed. The study is performed by numerical simulation and experimentally. It is shown that dual frequency driving can be effectively used to control switching between topologically equivalent and non-equivalent director field distributions. The experimental results on temperature performance of the dual-frequency switching and possible driving methods for energy consumption and expanding the temperature range are presented.

2

Bistability of Feshbach resonance in optical cavity

80%

Xu X.-Q. , Li Y.-Q.

Open Physics

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2014

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tom 12

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nr 6

427-432

EN

We consider Feshbach resonance in an optical cavity where photons interact with atoms and molecules dispersively. From mean-field theory we obtain multiple fixed-point solutions, which is strongly related to the phenomenon of bistability. Adiabatic evolutions demonstrate hysteretic behaviors by varying pump-cavity detuning from opposite directions. We also use the quantum model to check mean-field results which match perfectly. The analysis here may enrich the study of particle-photon interaction systems.

3

Power-induced lasing state switching and bistability in a two-state quantum dot laser subject to optical injection

80%

Jiang Z. , Wu Z. , Jayaprasath E. , Yang W. , Hu C. , Cui B. , Xia G.

Optica Applicata

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2020

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tom Vol. 50, nr 2

257--269

EN

We theoretically investigate power-induced lasing state switching and bistability in a two-state quantum dot laser subject to optical injection. The simulated results show that, for a free-running two-state quantum dot laser operating at the ground state under low current, a power-induced lasing state switching between the ground state and the excited state can be achieved through introducing optical injection with a frequency (winj) close to the lasing frequency of excited state (wES). The injection power required for the state switching depends on the scanning route of injection power, i.e. there may exist state bistability for the injection power within a certain region. For forward scanning injection power, with the increase of frequency detuning (ΔΩ = winj – wES), the injection power required for the state switching shows a decreasing trend accompanied by slight fluctuations. However, for backward scanning injection power, the injection power required for the state switching exhibits obvious fluctuations with the increase of ΔΩ. The width of the hysteresis loop fluctuates with ΔΩ, and the fluctuation amplitude is increased with the increase of the injection current. Additionally, the influences of the inhomogeneous broadening factor and the electron escape rate on the bistability performances are analyzed.

4

Harvesting mechanical vibrations energy using nonlinear electromagnetic minigenerators - a survey of concepts and problems

80%

Kulik M. , Jagieła M.

Poznan University of Technology Academic Journals. Electrical Engineering

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2017

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tom No. 90

347--358

EN

The state of knowledge in the field of conversion of energy of mechanical vibrations into electrical energy using nonlinear electromagnetic generators is presented. The principle of operation of the considered converters is based on the Faraday law. The electromotive force is induced by the relative movement of the coil or permanent magnets under impact of externally applied vibrations. In order to diminish the disadvantages of conventional generators, namely the narrow frequency bandwidth, in recent years the nonlinear systems were introduced that exhibit the nonlinear resonance phenomenon. Broadening the frequency bandwidth, in which the power generated by the system is relatively high, is realized via introduction of nonlinear force into system kinematics. Designing such systems becomes a big challenge. Based on thorough survey of recent publications as well as on own expertise in the field, the work compares a few concepts of nonlinear electromechanical minigenerators in term of their functional characteristics and design problems. Sample calculations of frequency characteristics using time- and frequency-domain models are presented.

5

Asymmetric multiple quantum well heterostructure laser systems : conception, performance, and characteristics

70%

Kononenko V. K. , Afonenko A. A. , Manak I. S. , Nalivko S. V.

Opto-Electronics Review

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2000

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tom Vol. 8, No. 3

241-250

EN

A new type of laser diodes and amplifiers based on asymmetric quantum-well heterostructures having active layers of different thickness and / or compositions has been considered. Bistable switching and regimes of regular radiation pulsation at two or three remote wavelengths in the range 790 - 850 nm in the GaAs-AlGaAs bi- and triple - quantum-well heterostructures are described. Influence of non-linear processes including gain suppression due to carrier heating on lasing regimes has been examined. Transformation of gain bands for TE and TM modes in dependence on the pump current has been studied for asymmetric four-quantum-well structures. The interval of tuning amplification wavelengths in the system reaches up to 70 nm.

6

Interplay of viral miRNAs and host mRNAs and proteins

60%

Zhdanov V.

Open Physics

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2011

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tom 9

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nr 5

1366-1371

EN

Recent experiments indicate that several viruses may encode microRNAs (miRNAs) in cells. Such RNAs may interfere with the host mRNAs and proteins. We present a kinetic analysis of this interplay. In our treatment, the viral miRNA is considered to be able to associate with the host mRNA with subsequent degradation. This process may result in a decline of the mRNA population and also in a decline of the population of the protein encoded by this mRNA. With these ingredients, we first show the types of the corresponding steady-state kinetics in the cases of positive and negative regulation of the miRNA synthesis by the protein. In addition, we scrutinize the situation when the protein regulates the virion replication or, in other words, provides a feedback for the replication. For the negative feedback, the replication rate is found to increase with increasing the intracellular virion population. For the positive feedback, the replication rate first increases and then drops. These features may determine the stability of steady states.

7

Electrical coupling and bistability in inhibitory neuronal networks

60%

Bem T. , Hallam J. , Meyrand P. , Rinzel J.

Biocybernetics and Biomedical Engineering

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2006

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tom Vol. 26, no. 2

3-14

EN

The role of gap junction-mediated electrical coupling in oscillatory networks is not yet fuIly understood. Such coupling is widespread in developing nervous systems and in many structures of the adult brain where it coexists with synaptic inhibition. Our results, both modeling and experimental, indicate that the effect of electrical coupling in networks of rhythmic inhibitory neurons is crucially dependent on the cells' duty cycle. In the Stomatogastric Nervous System, in which ceIls with large duty cycle are interconnected by reciprocal inhibition, electrical coupling may be responsible for masking adult-like properties of the embryonic network by coordinating the neuronal activity into a single rhythm with different phases. In a two-ceIl half-center oscillator model short duty cycle destabilizes antiphase activity which can be re-established by adding electrical coupling. Moreover, such a network expresses bistability of the in-phase and anti-phase patterns in some range of coupling strengths. AIso in a large-scale model network, in which ceIls are interconnected electrically and by synaptic inhibition, multistability of the in-phase and different anti-phase patterns may occur. A possible function of the multistability in the controI of movement is discussed.

8

Gravity-induced bistable 2DOF piezoelectric vibration energy harvester for broadband low-frequency operation

60%

Liu C. , Zhang W. , Yu K. , Liao B. , Zhao R. , Liu T.

Archives of Civil and Mechanical Engineering

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2023

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tom Vol. 23, no. 3

art. no. e208, 2023

EN

Bistability has been proven beneficial for vibration energy harvesting. However, previous bistable harvesters are usually cumbersome in structure and are not necessarily capable of low-frequency operation. To resolve this issue, this paper proposes a compact two-degree-of-freedom (2DOF) bistable piezoelectric energy harvester with simple structure by using an inverted piezoelectric cantilever beam elastically coupled with a swinging mass-bar. The swinging mass-bar possesses bistable property due to the combined effect of the gravity and the elastic joint. It is revealed that, under the inter-well periodic motion pattern which has large swinging amplitude, the swinging mass-bar can exert large force and moment on the piezoelectric cantilever beam, thereby generating large electrical output in this process. Moreover, the inter-well periodic swinging motion can occur in a very broad low-frequency region, enabling broadband low-frequency energy harvesting. An experimental prototype is tested under harmonic excitation and sine frequency sweeping excitation; high electrical output is gained in the frequency range of 2 Hz to 12.6 Hz with a peak power of 3.558mW and a normalized power density of 19.52mW/(g2·cm3), which validates the broadband low-frequency energy harvesting capability.

9

Non-coding RNAs and a layered architecture of genetic networks

60%

Zhdanov V.

Open Physics

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2010

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tom 8

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nr 6

864-872

EN

In eukaryotic cells, protein-coding sequences constitute a relatively small part of the genome. The rest of the genome is transcribed to non-coding RNAs (ncRNAs). Such RNAs form the cornerstone of a regulatory network that operates in parallel with the protein network. Their biological functions are based primarily on the ability to pair with and deactivate target messenger RNAs (mRNAs). To clarify the likely role of ncRNAs in complex genetic networks, we present and comprehensively analyze a kinetic model of one of the key counterparts of the network architectures. Specifically, the genes transcribed to ncRNAs are considered to interplay with a hierarchical two-layer set of genes transcribed to mRNAs. The genes forming the bottom layer are regulated from the top and negatively self-regulated. If the former regulation is positive, the dependence of the RNA populations on the governing parameters is found to be often non-monotonous. Specifically, the model predicts bistability. If the regulation is negative, the dependence of the RNA populations on the governing parameters is monotonous. In particular, the population of the mRNAs, corresponding to the genes forming the bottom layer, is nearly constant.

10

Bistability in epileptic phenomena

60%

Suffczyński P. , Kalitzin S. , da Silva F. L.

Bio-Algorithms and Med-Systems

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2005

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tom Vol. 1, no. 1/2

259--266

EN

It is currently believed that the mechanisms underlying spindle oscillations are related to those that generate spike and wave (SW) discharges. The mechanisms of transition between these two types of activity, however, are not well understood. In order to provide more insight into the dynamics of the neuronal networks leading to seizure generation in a rat experimental model of absence epilepsy we developed a computational model of thalamo-cortical circuits based on relevant (patho)physiological data. The model is constructed at the macroscopic level since this approach allows to investigate dynamical properties of the system and the role played by different mechanisms in the process of seizure generation, both at short and long time scales. The main results are the following: (i) SW discharges represent dynamical bifurcations that occur in a bistable neuronal network. (ii) The durations of paroxysmal and normal epochs have exponential distributions, indicating that transitions between these two stable states occur randomly over time with constant probabilities. (iii) The probabilistic nature of the onset of paroxysmal activity implies that it is not possible to predict its occurrence. (iv) The bistable nature of the dynamical system allows an ictal state to be aborted by a single counter-stimulus.

PL

Mechanizm spontanicznego powstawania oraz wygaszania napadów epileptycznych nie jest dobrze poznany. W celu lepszego zrozumienia tych mechanizmów opracowany został model symulacyjny układu wzgórzowo-korowego, odpowiedzialnego za powstawanie napadów nieświadomości u ludzi oraz zwierząt. Model wykorzystuje podejście populacyjne, co pozwoliło na zbadanie właściwości układu w skali krótko- i długoczasowej. Główne wyniki pracy to: (i) napady nieświadomości powstają w bistabilnej sieci neuronalnej, (ii) długości napadów oraz odcinków pomiędzy napadami mają rozkład eksponencjalny, co sugeruje, że przejścia pomiędzy stanem normalnym a napadem odbywają się losowo w czasie ze stałym prawdopodobieństwem (iii) probabilistyczna natura powstawania napadów sugeruje, że nie jest możliwe ich przewidywanie (iv) napady powstające w układzie bistabilnym mogą być zatrzymane poprzez stymulację pojedynczym impulsem elektrycznym.

11

Area of the unstable solution of rolling equation : jumps of the oscillations amplitude

60%

Wawrzyński W.

Journal of KONES

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2018

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tom Vol. 25, No. 3

489--496

EN

The most interesting motion of the ship is rolling. This is because the rolling amplitudes are much bigger than amplitudes of other degrees of freedom and under resonance conditions, which can exceed 40º. In such a case, when the maximum of the righting arm curve is placed at relatively small angles, the roll equation reveals a strongly nonlinear character and bistability areas as well as an area of unstable solutions of the roll equation occurs. Together with the appearance of the above-mentioned areas, amplitude jumps are possible. In the study, the case of strongly nonlinear rolling is analysed. For the purpose of numerical simulations, the 1DOF mathematical model of rolling with damping dependent on amplitude and frequency is used. The article presents the roll spectrum including the bistability areas and the area of unstable solutions for one loading condition of the offshore support vessel. It is demonstrated that for strongly nonlinear rolling, rolling with two different amplitudes for the same value of excitation is possible. It is also shown that transitions (jumps) between these amplitudes are possible too. A few scenarios of jumps of the rolling amplitude within the region of unstable solutions of the rolling equation are presented. The presented rolling scenarios show that under some circumstances rolling can be observed as chaotic.

12

On the Role of Specific Characteristics of the Streaming Mercury Electrode in the Generation of the Ni=onlinear Electrochemical Dynamical Phenomena

60%

Orlik M. , Jurczakowski R.

Polish Journal of Chemistry

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2004

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tom Vol. 78 / nr 9

1221-1234

EN

The streaming mercury electrode was recently found by us a very powerful electrode type for the observation of sustained oscillations and multistability accompanying the electrode processes with the region of the negative differential resistance (NDR) in their I-E characteristics. Following our earlier experimental and theoretical studies of the electroreduction of the pseudohalogenide complexes of nickel(II) at the streaming mercury electrode, we discuss the conditions for the onset of oscillations and multistability in these processes, taking into account the dependence of the double layer capacitance on the electrode potential. The improved stability criteria, involving both the differentialCd and integral K capacitances are derived and compared with our earlier simplified theory. Based on the experimental characteristics of the Ni(II)-SCN- electroreduction it is quantitatively shown, how the two factors specific to the streaming electrodes: the permanent flow of the capacitive current and - in particular - the relatively small thickness of the diffusion layer determine the characteristics of the bistable and oscillatory behaviour.

13

Bistability phenomenon in fluid dynamic

51%

Tesar V.

Zeszyty Naukowe. Mechanika / Akademia Techniczno-Rolnicza w Bydgoszczy

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1999

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tom Z. 44 (221)

161-170

EN

Several interesting fluid flow fields exhibit lack of unicity: instead of a single solution, they have two stable regimes - with an unstable equilibrium between them, which however becomes stable at low Reynolds numbers. A particular example is a trapped vortex ring held by a special cavity on periphery of a fluid jet. Dynamic models of this bistability show interesting bifurcation properties, period doubling phenomenon and existence of chaotic regimes indicating that this may be an important underlying effect for turbulence.

PL

Kilka interesujących obszarów przepływu płynu wykazuje brak jednoznaczności: zamiast pojedynczego rozwiązania posiadają one dwa stabilne stany - z niestabilną równowagą między nimi, która jednakże staje się stabilna przy niskich liczbach Reynoldsa. Szczególnym przykładem jest stabilizujący pierścień wirowy otrzymany przez specjalne wgłębienie na obrzeżu strumienia płynu. Model dynamiczny tej bistabilności wykazuje interesujące rozgałęziające własności, okresowe zjawisko zdwajania i istnienie stanów chaotycznych powoduje, że może to być istotny wspomagający efekt turbulencji.