Changes In Beat Frequency Research Articles

Ciliary beating patterns map onto a low-dimensional behavioural space

Biological systems are robust to perturbations at both the genetic and environmental levels, although these same perturbations can elicit variation in behaviour. The interplay between functional robustness and behavioural variability is exemplified at the organellar level by the beating of cilia and flagella. Cilia are motile despite wide genetic diversity between and within species, differences in intracellular concentrations of ATP and calcium, and considerable environment fluctuations in temperature and viscosity. At the same time, these perturbations result in a variety of spatio-temporal patterns that span a rich behavioural space. To investigate this behavioural space we analysed the dynamics of isolated cilia from the unicellular algae Chlamydomonas reinhardtii under many different environmental and genetic conditions. We found that, despite large changes in beat frequency and amplitude, the space of waveform shapes is low-dimensional in the sense that two features account for 80% of the observed variation. The geometry of this behavioural space accords with the predictions of a simple mechanochemical model in the low-viscosity regime. This allowed us to associate waveform shape variability with changes in only the curvature response coefficients of the dynein motors.

Side-Polished DBR Fiber Laser with Enhanced Sensitivity for Axial Force and Refractive Index Measurement

A highly sensitive optical fiber sensor for the measurement of axial force and refractive index (RI) is presented. The optical sensor consists of a distributed Bragg reflector (DBR) based fiber laser, the laser cavity of the DBR is polished to D-shape by the wheel fiber polishing system. Birefringence has been introduced with side polishing of the fiber, and then, it is utilized for sensing applications. The working principle of the device is based on the principle of the change in beat frequency of the two orthogonal polarization modes of the DBR fiber laser with external perturbations. In this work, it has been shown that the dual polarization beat frequency can be used for RI-based measurement applications along with the measurement of the axial force. The sensitivity of the DBR fiber laser sensor with change in axial force is enhanced significantly with side polishing. Such a device is robust, simple in fabrication and most importantly low-cost interrogation techniques can be used for the detection purpose. A resolution of 5.6014 × 10–8 N has been achieved in case of recognition of axial force and 1.9259 × 10–5 RIU is the observable detection limit for the RI based measurement.

Ciliomotor circuitry underlying whole-body coordination of ciliary activity in the Platynereis larva.

Ciliated surfaces harbouring synchronously beating cilia can generate fluid flow or drive locomotion. In ciliary swimmers, ciliary beating, arrests, and changes in beat frequency are often coordinated across extended or discontinuous surfaces. To understand how such coordination is achieved, we studied the ciliated larvae of Platynereis dumerilii, a marine annelid. Platynereis larvae have segmental multiciliated cells that regularly display spontaneous coordinated ciliary arrests. We used whole-body connectomics, activity imaging, transgenesis, and neuron ablation to characterize the ciliomotor circuitry. We identified cholinergic, serotonergic, and catecholaminergic ciliomotor neurons. The synchronous rhythmic activation of cholinergic cells drives the coordinated arrests of all cilia. The serotonergic cells are active when cilia are beating. Serotonin inhibits the cholinergic rhythm, and increases ciliary beat frequency. Based on their connectivity and alternating activity, the catecholaminergic cells may generate the rhythm. The ciliomotor circuitry thus constitutes a stop-and-go pacemaker system for the whole-body coordination of ciliary locomotion.

Compact dual-frequency fiber laser accelerometer with sub-μg resolution

We demonstrate a compact and high-resolution dual-polarization fiber laser accelerometer. A spring-mass like scheme is constructed by fixing a 10-gram proof mass on the laser cavity to transduce applied vibration into beat-frequency change. The loading is located at the intensity maximum of intracavity light to maximize the optical response. The detection limit reaches 107 ng/Hz1/2 at 200 Hz. The working bandwidth ranges from 60 Hz to 600 Hz.

Spatial Sensitivity Characterization of Dual-Polarization Fiber Grating Laser Sensors

In this paper, the spatial sensitivity of a dual-polarization fiber grating laser sensor is characterized by measuring the response in terms of beat–frequency change to localized transverse loading at different longitudinal positions. The induced frequency shift is proportional to the induced local birefringence change and the normalized light intensity, as a result of the resonant nature of the cavity. Measured result suggests that the sensitivity profile is mainly determined by the cavity length, as well as the grating reflectivities and the gain. We found that higher mass (or force) sensitivity can be obtained by shortening the laser cavities. Sensitivity as high as 51.1 MHz/g (or 5.192 GHz/N) has been achieved with a laser which has an effective cavity length close to 1 mm. The corresponding mass resolution reaches $9.78 \times 10^{-5}$ g. The result offers useful guidance for the transducer design for fiber laser sensors toward the detection of extremely small mass or weak perturbations.

Mammalian DRC, Ciliary, Motility and Left‐Right Body Asymmetry

Many advances made in our understanding of the molecular basis of ciliopathies in humans have come through the identification and analysis of candidate ciliary proteins in lower model systems. For example, Growth Arrest Specific 8 (Gas8) has been implicated in cilia motility based on its Chlamydomonas homolog pf2 showing it is a component of the Nexin-dynein regulatory complex (NDRC). However, the study of Gas8 in mammalian systems is very limited, and unexpectedly, recent data indicate that Gas8 localizes to the base of primary non-motile cilia and knockdown studies indicate that Gas8 has a role as a positive regulator of Smoothened activity and its ciliary localization. Here we investigate the in vivo role of Gas8 by generating a mutant mouse line. Gas8 mutant mice did not have any overt phenotypes expected if Hedgehog signaling is affected. Gas8 mutants did present with situs inversus implicating the NDRC in mammalian left-right body axis specification and in the normal function of node cilia. In addition, to the LR defects, Gas8 mutants invariably develop hydrocephalus and were sterile. Our analyses of cilia motility in the ventricles of the brain and trachea show abnormalities in cilia generated fluid movement associated with changes in beat frequency, waveform, and structure of the cilium. We show Gas8 is required for proper assembly of the inner dynein arms (IDA) and the Nexin-Dynein Regulatory Complex (NDRC). Additionally, a screen for GAS8 mutations in human patients with situs defects identified two independent homozygous missense mutations. The two independent mutations at c.595G>A and c.1172C>T interrupt the Gas8 Microtubule Association Domain (GMAD) and the putative Smoothened binding domain, respectively. We hypothesize that both of these mutations will result in disruption of NDRC assembly and cause dyskinetic motile cilia. The pathogenicity of these mutations and their effect on NDRC formation is being analyzed in Chlamydomonas, zebrafish, and mouse lines that express the human disease alleles.

Effect of Pump Light Polarization and Beat Note Stabilization for Dual-Polarization Fiber Grating Laser Sensors

Dual-polarization fiber grating lasers have been exploited as high-sensitivity photonic sensors for a variety of measurands by monitoring the frequency of the output beat signal. In this paper, we demonstrate that the environmentally induced perturbations on polarization orientation of the pump light can cause considerable changes in output beat frequency, which can significantly affect the resolution of the sensor especially for static or quasi-static measurements. We found that the beat frequency change with the pump orientation is mainly caused by the resonantly enhanced nonlinearity associated with the generation of green fluorescent light, rather than thermal effect or Kerr electro-optic effect. In order to obtain stable beat signal and improve the accuracy of the fiber laser sensor, the fiber lasers are annealed in advance and then connected to polarization-maintaining fibers and devices to avoid the influence of external perturbations. The frequency fluctuation has been reduced from 1.5 to about 0.1 MHz, and the corresponding resolution of the sensor to static transverse load is improved from 1.76 × 10 -4 to 1.17 × 10 -5 N/mm.

From channelrhodopsins to optogenetics

We did not expect that research on the molecular mechanism of algal phototaxis or archaeal light‐driven ion transport might interest readers of a medical journal when we conceived and performed our experiments a decade ago. On the other hand, it did not escape our attention that channelrhodopsin is helping an ever‐increasing number of researchers to address their specific questions. For example, the channelrhodopsin approach is used to study the molecular events during the induction of synaptic plasticity or to map long‐range connections from one side of the brain to the other, and to map the spatial location of inputs on the dendritic tree of individual neurons. The current applications have been summarized in a number of recent reviews (Fenno et al, 2011; Yizhar et al, 2011; Zhang et al, 2011). Here, we give personal insight into the history of the discovery of channelrhodopsin and a biophysical perspective on this remarkable class of proteins that has been the main topic of our research since the 1990s. The discovery of channelrhodopsin is based on two quite different research fields, studies on living algae and experiments on reconstituted microbial rhodopsins. A number of researchers have characterized the swimming behaviour and light responses of motile microalgae over at least 140 years (Fig 1A). Early studies on green microalgae root back to L.G. Treviranus (Treviranus, 1817) and behavioural responses were described by A. Famintzin from St. Petersburg University in 1878 (Famintzin, 1878). During helical swimming of the green alga Chlamydomonas , its orange eye signals to the flagella to alter the flagellar beating plane (Mast, 1916). Researchers at Stanford University implicated Mg2+ and Ca2+ in the behavioural responses and identified the role of Ca2+ influx in flagellar beat frequency changes (Halldal, 1957, Schmidt & Eckert, 1976). Then Oleg Sineshchekov …

Polarimetric Heterodyning Fiber Grating Laser Sensors

Fiber grating laser sensors have been attracting great interest because of their high signal-to-noise ratio and narrow linewidth that permit high resolution sensing. According to the working principle, fiber grating laser sensors can be classified into two types: wavelength encoding sensor and polarimetric heterodyning sensor. The former responds to external perturbations in terms of shift in the operation wavelength of the fiber laser, which is similar to that of fiber grating sensor. The latter converts measurand into change in beat frequency between the two orthogonal polarization modes from the fiber laser. The polarimetric fiber grating laser sensor not only has almost all advantages of passive fiber grating sensors, but also has a distinctive advantage of ease of interrogation. This is because the beat frequency is in the RF domain, which avoids the employment of expensive wavelength measurement devices. This type of sensor has been demonstrated for measurement of temperature, axial strain, lateral force, hydrostatic pressure, bending, displacement, acceleration, electric current, and acoustic and ultrasonic signal. In this paper, we review the principle, fabrication, characterization, and implementation of the polarimetric heterodyning fiber grating laser sensors, and the sensor multiplexing in the RF domain.

Two-Dimensional Spectroscopy Can Distinguish between Decoherence and Dephasing of Zero-Quantum Coherences

Recent experiments on a variety of photosynthetic antenna systems have revealed that coherences among electronic states persist longer than previously anticipated. In an ensemble measurement, the observed dephasing of a coherent state can occur because of either disorder across the ensemble or decoherence from interactions with the bath. Distinguishing how much such disorder affects the experimentally observed dephasing rate is paramount for understanding the role that quantum coherence may play in energy transfer through these complexes. Here, we show that two-dimensional electronic spectra can distinguish between the limiting cases of homogeneous dephasing (decoherence) and inhomogeneous dephasing by examining how the quantum beat frequency changes within a cross peak. For the antenna complex LH2 isolated from Rhodobacter sphaeroides , we find that dephasing of the coherence between the B850 and B800 rings arises predominantly from inhomogeneity. In contrast, within the Fenna-Matthews-Olson (FMO) complex from Chlorobium tepidum , dephasing of the coherence between the first two excitons appears quite homogeneous. Thus, the observed dephasing rate sets an upper bound on decoherence for the LH2 complex while establishing both an upper and lower bound for the FMO complex.

Highly sensitive bending sensor based on Er^3+-doped DBR fiber laser

A short cavity Er(3+)-doped distributed-Bragg-reflector (DBR) fiber laser with a low polarization beat frequency has been demonstrated for bending measurement. The polarization beat frequency of the DBR laser is extremely sensitive to bending and can measure curvature changes as small as 1.8 x 10(-2) m(-1). Excellent agreement between experimental and theoretical results was obtained for bending curvatures from 0 m(-1) to 58.8 m(-1) with corresponding changes in beat frequency from 18.6 MHz to 253 MHz. The sensor is insensitive to temperature fluctuations and has a temperature coefficient of the beat frequency of -25.4 kHz/degrees C, making the temperature compensation unnecessary in most practical applications. The very low beat frequency of the DBR fiber laser makes frequency down-conversion unnecessary. This can greatly simplify the demodulation scheme and thus, allow the realization of low-cost but highly sensitive optical bending sensor systems.

How 5000 independent rowers coordinate their strokes in order to row into the sunlight: phototaxis in the multicellular green alga Volvox.

BackgroundThe evolution of multicellular motile organisms from unicellular ancestors required the utilization of previously evolved tactic behavior in a multicellular context. Volvocine green algae are uniquely suited for studying tactic responses during the transition to multicellularity because they range in complexity from unicellular to multicellular genera. Phototactic responses are essential for these flagellates because they need to orientate themselves to receive sufficient light for photosynthesis, but how does a multicellular organism accomplish phototaxis without any known direct communication among cells? Several aspects of the photoresponse have previously been analyzed in volvocine algae, particularly in the unicellular alga Chlamydomonas.ResultsIn this study, the phototactic behavior in the spheroidal, multicellular volvocine green alga Volvox rousseletii (Volvocales, Chlorophyta) was analyzed. In response to light stimuli, not only did the flagella waveform and beat frequency change, but the effective stroke was reversed. Moreover, there was a photoresponse gradient from the anterior to the posterior pole of the spheroid, and only cells of the anterior hemisphere showed an effective response. The latter caused a reverse of the fluid flow that was confined to the anterior hemisphere. The responsiveness to light is consistent with an anterior-to-posterior size gradient of eyespots. At the posterior pole, the eyespots are tiny or absent, making the corresponding cells appear to be blind. Pulsed light stimulation of an immobilized spheroid was used to simulate the light fluctuation experienced by a rotating spheroid during phototaxis. The results demonstrated that in free-swimming spheroids, only those cells of the anterior hemisphere that face toward the light source reverse the beating direction in the presence of illumination; this behavior results in phototactic turning. Moreover, positive phototaxis is facilitated by gravitational forces. Under our conditions, V. rousseletii spheroids showed no negative phototaxis.ConclusionsOn the basis of our results, we developed a mechanistic model that predicts the phototactic behavior in V. rousseletii. The model involves photoresponses, periodically changing light conditions, morphological polarity, rotation of the spheroid, two modes of flagellar beating, and the impact of gravity. Our results also indicate how recently evolved multicellular organisms adapted the phototactic capabilities of their unicellular ancestors to multicellular life.

Force Generation and Dynamics of Individual Cilia under External Loading

Motile cilia are unique multimotor systems that display coordination and periodicity while imparting forces to biological fluids. They play important roles in normal physiology, and ciliopathies are implicated in a growing number of human diseases. In this work we measure the response of individual human airway cilia to calibrated forces transmitted via spot-labeled magnetic microbeads. Cilia respond to applied forces by 1), a reduction in beat amplitude (up to an 85% reduction by 160–170 pN of force); 2), a decreased tip velocity proportionate to applied force; and 3), no significant change in beat frequency. Tip velocity reduction occurred in each beat direction, independently of the direction of applied force, indicating that the cilium is “driven” in both directions at all times. By applying a quasistatic force model, we deduce that axoneme stiffness is dominated by the rigidity of the microtubules, and that cilia can exert 62 ± 18 pN of force at the tip via the generation of 5.6 ± 1.6 pN/dynein head.

Frequency-Shifted Feedback Fiber Laser Oscillation with Monolithically Integrated Tandem Waveguide-Type Acoustooptic Modulator Driven by Surface Acoustic Waves

Frequency-shifted feedback fiber laser oscillation and optical frequency domain ranging using a monolithically integrated tandem acoustooptic modulator driven by surface acoustic waves (SAWs) were demonstrated. The linear relationships between the beat frequency change and the optical path difference in the Mach–Zehnder interferometer with three slopes were obtained by combining the upward and downward frequency shifts in the first and second SAWs.

Hyperactivation is the mode conversion from constant‐curvature beating to constant‐frequency beating under a constant rate of microtubule sliding

Flagellar beating of hyperactivated golden hamster spermatozoa was analyzed in detail using digital image analysis and was compared to that of nonhyperactivated (activated) spermatozoa in order to understand the change in flagellar beating during hyperactivation and the active microtubule sliding that brought about the change in flagellar beating. Hyperactivated flagellar beating, which was characterized by a sharp bend in the proximal midpiece and low beat frequency, was able to alter the waveform with little change in beat frequency (constant-frequency beating), whereas activated flagellar beating, which was characterized by a slight bend in the proximal midpiece and high beat frequency, was able to alter beat frequency with little change in the waveform (constant-curvature beating). These results demonstrate that flagellar beating of hyperactivated and activated spermatozoa were essentially different modes and that hyperactivation was the mode conversion from constant-curvature beating to constant-frequency beating. Detailed analysis of flagellar bends revealed that the increase in curvature in the proximal midpiece during hyperactivation was due to the increase in total length of microtubule sliding in a nearly straight region between bends, while the rate of microtubule sliding remained almost constant.

Modulation of Chlamydomonas reinhardtii flagellar motility by redox poise.

Redox-based regulatory systems are essential for many cellular activities. Chlamydomonas reinhardtii exhibits alterations in motile behavior in response to different light conditions (photokinesis). We hypothesized that photokinesis is signaled by variations in cytoplasmic redox poise resulting from changes in chloroplast activity. We found that this effect requires photosystem I, which generates reduced NADPH. We also observed that photokinetic changes in beat frequency and duration of the photophobic response could be obtained by altering oxidative/reductive stress. Analysis of reactivated cell models revealed that this redox poise effect is mediated through the outer dynein arms (ODAs). Although the global redox state of the thioredoxin-related ODA light chains LC3 and LC5 and the redox-sensitive Ca2+-binding subunit of the docking complex DC3 did not change upon light/dark transitions, we did observe significant alterations in their interactions with other flagellar components via mixed disulfides. These data indicate that redox poise directly affects ODAs and suggest that it may act in the control of flagellar motility.

Body Size and Swimming Types in Carp Larvae; Effects of Being Small

The viscosity of water is a major hydrodynamic force and especially important for tiny objects (on or below a mm scale) moving at low speeds. Fish larvae between 4.8 and 8.1 mm total length (TL) are of intermediate size. During their growth the flow while swimming becomes dominated by inertial instead of viscosity forces. The present paper presents changes in beat frequency, wave speed, absolute speed, distance covered per swimming cycle and the distribution of body curvature along the trunk during larval growth. Just hatched larvae show only one type of swimming but further types develop during growth. Early wriggling (resistive) swimming is rapidly replaced by beating with tail and tail fin suggesting the increasing dominance of inertial hydrodynamic forces. Similar movements as in the 4.8 mm larvae are found in the first body wave of bigger larvae thus strengthening the hypothesis of the changing relationship between viscosity effects and swimming motion with size.

A polarimetric current sensor using an orthogonally polarized dual-frequency fibre laser

We demonstrate a novel -doped fibre laser operating in orthogonally polarized dual-frequency modes and its application to electric current sensing with frequency read-out. A Faraday rotating mirror and spatial hole burning effects in a gain medium and in a saturable absorber are utilized to control the lasing mode and polarization. The polarization mode beat frequency changes linearly in response to the non-reciprocal circular birefringence induced by an external magnetic field. When the laser was applied to sensing an alternating electric current with a simple phase-locked loop signal processing scheme, the slope coefficient of 8.0 kHz per turn and the noise equivalent current of 460 per turn were obtained. The new current sensor is immune to perturbations in the lead fibres.

Motility in the colonial and multicellular Volvocales: structure, function, and evolution

The colonial Volvocales are often said to be composed of Chlamydomonas-like cells, but there are substantial differences in motility and flagellar apparatus construction between the unicellular forms and the individual members of a colony or spheroid. These changes appear to be required for effective organismal motion and might possibly limit the rate at which new colonial forms evolve from unicellular ones. The flagellar-beat envelopes in colonial members are modified such that they beat in the same direction and in parallel planes with their effective strokes at right angles to the cellular anterior-posterior axis. These changes result from a series of developmental events of the flagellar apparatus of the colonial forms while the colony is still an embryo. Differences in the flagellar-apparatus structure in the members of the Goniaceae and Volvocaceae are not obviously correlated with the traditional placement of these algae in a simple volvocine lineage. Effective colonial motion clearly requires precise positioning and rotational orientation of the cells within the colony. Almost any arrangement where the cells are placed with rotational symmetry within the colony results in colonial progression with rotation. Such rotational symmetry is present from the time of embryogenesis. The mechanism that leads to organismal steering in behavioral responses (e.g., phototaxis) must likewise differ between colonial and unicellular forms. In at least some cases, this appears to result from changes in beat frequency in some parts of the spheroid, but changes in beat direction cannot be ruled out for all forms.

Cooperativity in axonemal motion: analysis of a four-state, two-site kinetic model.

A kinetic model for axonemal motion based upon a four-state mechanochemical cycle of dynein with two active sites is described. Our model analysis determines the pseudo-steady-state concentrations of enzyme species for specified rate constants, most of which are experimentally determined, with given substrate and product concentrations. The proportion of enzyme species in which both active sites are detached from the microtubule (denoted as "both detached"), numerically calculated from the model, appears to be proportional to experimental observations of flagellar beat frequency. This correlation between beat frequency and the both-detached enzyme species is maintained over a wide range of substrate concentrations and exhibited an apparent positive cooperativity at low substrate concentrations, which we call "obligate cooperativity." The unusual obligate cooperativity exhibited by flagellar beat frequency parallels that seen in the calculated proportion of the both-detached enzyme species and is interpreted as a requirement for a molecule of substrate to bind to each active site in a multimeric dynein in order to produce oscillatory motion. Furthermore, the proportion of the both-detached enzyme species correlates with experimentally observed changes in beat frequency with a nucleotide analog and with product inhibition.