Low-pass Filter Function Research Articles

A New CFA Based Current-Mode Universal Biquad Filter

The paper presents a new current-mode second order universal filter with single input and three outputs using two current feedback amplifiers, two grounded capacitors, two grounded resistors and only one floating resistor. The circuit implements lowpass, band-pass and high-pass filter functions simultaneously without changing configuration and passive components. All the passive components are grounded except one floating resistor. The grounded capacitors make circuit suitable for integration. The circuit has low active and passive sensitivities. Simulation results agree well with the theoretical analysis.

Electronically tunable current-mode biquadratic filter and four-phase quadrature oscillator

This paper presents a current-mode biquadratic filter based on ZC-CFTAs. It employs only three ZC-CFTAs, one resistor and two grounded capacitors. It can simultaneously realize not only highpass and lowpass filtering functions but also two different forms of bandpass ones; one has a pass-band gain of Q, the other, a pass-band gain of unity. Its ωo and Q can be tuned orthogonally through adjusting bias currents of ZC-CFTAs. Moreover, the proposed circuit can also be modified to be a current controlled four-phase quadrature oscillator with small distortion. Non-ideal analysis and sensitivity analysis are provided. The results of circuit simulations are in agreement with theory.

Generalised Christoffel–Darboux formula most directly applied in generating fully symmetric doubly resistively terminated LC lossless ladder filters

In this article, the approximation problem of a continuous analogue filter function of even and odd order is solved mathematically most directly applying the proposed generalised Christoffel–Darboux formula for two continuous orthogonal polynomials (Chebyshev first and second kind) on the equal finite segment of orthogonality in a compact explicit representative form. A set of analytic expressions of the proposed formula for the representative examples of odd-orders is given. Additionally, these expressions are applied in generating new excellent class all pole low-pass prototype analogue filter functions of odd orders (7, 9, 11, and 13th order). Based on the generated functions, the fully symmetric doubly resistively terminated LC ladder filter networks are realised by Darlington realisation. The generated filters are analysed, and their characteristics are presented. The effects of finite tolerance of a critical reactance of these ladder filters on the filter characteristics are considered. The filters generated by the proposed formula show excellent properties and possess important advantages in comparison to the corresponding filters generated by other methods.

Explicit form of new class of extremal filter functions with mini-max behaviour of summed sensitivity function

In this article, the all-pole low-pass filter function with mini-max for the summed sensitivity function in the pass-band is considered. With the application of Chebyshev polynomials of the first kind, the proposed filter function is obtained in an explicit form with a maximum number of oscillations of the summed sensitivity function in the pass-band. The calculation of the filter function is derived by using the summed sensitivity function as a starting point. New original approximation function is derived in order to achieve a mini-max summed sensitivity function in the filter pass-band. Sensitivity analysis is carried out and a comparison of the summed sensitivity and the group delay of the proposed and classical all-pole filters is given. Minimisation of the summed sensitivity function is important for reduction of the deviation of the magnitude response caused by temperature changes of the continuous-time active filters implemented into the analogue front end or as programmable chips.

New class of filter functions generated most directly by the Christoffel–Darboux formula for classical orthonormal Jacobi polynomials

The new originally capital general solution of determining the prototype filter function as the response that satisfies the specifications of all pole low-pass continual time filter functions of odd and even order is presented in this article. In this article, two new classes of filter functions are proposed using orthogonal and orthonormal Jacobi polynomials. The approximation problem of filter function was solved mathematically, most directly applying the summed Christoffel–Darboux formula for the orthogonal polynomials. The starting point in solving the approximation problem is a direct application of the Christoffel–Darboux formula for the initial set of continual Jacobi orthogonal polynomials in the finite interval in full respect to the weighting function with two free real parameters. General solution of the filter functions is obtained in a compact explicit form, which is shown to enable generation the Jacobi filter functions in a simple way by choosing the numerical values of the free real parameters. For particular specifications of free parameters, the proposed solution is used with the same criterion of approximation to generate the appropriate particular filter functions as are: the Gegenbauer, Legendre and Chebyshev filter functions of the first and second kind as well. The examples of proposed filter functions of even and odd order are illustrated and compared with classical solutions.

Neuron dynamics in the presence of1/fnoise

Interest in understanding the interplay between noise and the response of a nonlinear device cuts across disciplinary boundaries. It is as relevant for unmasking the dynamics of neurons in noisy environments as it is for designing reliable nanoscale logic circuit elements and sensors. Most studies of noise in nonlinear devices are limited to either time-correlated noise with a Lorentzian spectrum (of which the white noise is a limiting case) or just white noise. We use analytical theory and numerical simulations to study the impact of the more ubiquitous "natural" noise with a 1/f frequency spectrum. Specifically, we study the impact of the 1/f noise on a leaky integrate and fire model of a neuron. The impact of noise is considered on two quantities of interest to neuron function: The spike count Fano factor and the speed of neuron response to a small steplike stimulus. For the perfect (nonleaky) integrate and fire model, we show that the Fano factor can be expressed as an integral over noise spectrum weighted by a (low-pass) filter function given by F(t,f)=sinc(2)(πft). This result elucidates the connection between low-frequency noise and disorder in neuron dynamics. Under 1/f noise, spike dynamics lacks a characteristic correlation time, inducing the leaky and nonleaky models, to exhibit nonergodic behavior and the Fano factor, increasing logarithmically as a function of time. We compare our results to experimental data of single neurons in vivo [Teich, Heneghan, Lowen, Ozaki, and Kaplan, J. Opt. Soc. Am. A 14, 529 (1997)] and show how the 1/f noise model provides much better agreement than the usual approximations based on Lorentzian noise. The low-frequency noise, however, complicates the case for an information-coding scheme based on interspike intervals by introducing variability in the neuron response time. On a positive note, the neuron response time to a step stimulus is, remarkably, nearly optimal in the presence of 1/f noise. An explanation of this effect elucidates how the brain can take advantage of noise to prime a subset of the neurons to respond almost instantly to sudden stimuli.

An explicit form of all‐pole filter function with decreasing envelope of the summed sensitivity function

AbstractIn this paper, the all‐pole lowpass filter function with the decreasing envelope of the summed sensitivity in the pass‐band is considered. The filter transfer function with maximal number of the ripples of the summed sensitivity in the pass‐band is obtained in the explicit form, by the application of the Chebyshev polynomials of the first kind. The slope of the decrease of the summed sensitivity envelope can be controlled by a free‐parameter α.We derived a new approximation function in order to achieve small summed sensitivity in the filter pass‐band. Consequently, the sensitivity analysis was carried out and a comparison of the summed sensitivity and the group delay with respect to the classic all‐pole filters was given. The approach presented in this paper is based on that the minimization of the summed sensitivity is important for the reduction of the deviation of the magnitude response caused by temperature changes of the continuous‐time active filters implemented into the analog front end or as programmable chips. Copyright © 2010 John Wiley & Sons, Ltd.

Continuous Dynamic Photostimulation - inducing defined, in-vivo-like fluctuating stimuli with Channelrhodopsins

Event Abstract Back to Event Continuous Dynamic Photostimulation - inducing defined, in-vivo-like fluctuating stimuli with Channelrhodopsins Andreas Neef1*, Ahmed ElHady1, Jatin Nagpal2, Kai Broking2, Ghazaleh Afshar2, Theo Geisel1, 2, Ernst Bamberg3, Ragnar Fleischmann2, Walter Stühmer1, 4 and Fred Wolf1, 2 1 BCCN Göttingen, Germany 2 MPI DS, Germany 3 MPI Biophysics, Germany 4 MPI Experimental Medicine, Germany Central neurons typically operate in a noise driven regime: thousands excitatory and inhibitory synapses give rise to a constantly fluctuating conductance. Its statistic is similar to low-pass filtered white noise conductance that can be parameterized by is average, standard deviation and correlation time. An understanding of action potential generation and encoding in the noise driven regime requires the detection of action potential times during stimulation with defined time dependent conductance. Channelrhodopsin variants, expressed in neurons have been almost exclusively used to drive action potentials by illumination with very brief, intense light flashes; effectively imprinting action potential patterns, that are largely independent of the neurons intrinsic response properties. Using the only known weakly inactivating channelrhodopsin variant ChIEF under continuously fluctuating illumination by an LED, we achieve a defined, reproducible conductance modulation that mimicks the naturally occurring synaptic inputs . Cultured hippocampal neurons subjected to this continuous dynamic photostimulation (CoDyPs) generate seemingly random, but reproducible patterns of action potentials, even in experiments lasting several hours. Within the range of illumination intensities used (up to 0.3 mW/µm²) the induced conductance change can be predicted, up to a factor describing the number of expressed ChIEF-Molecules, by convolution of the light signal with the light-conductance transfer function of ChIEF. This Transfer function was determined from light-induced currents, recorded in voltage clamped cultured cells (HEK-293), transiently expressing ChIEF. It resembles the transfer function of a simple single pole low-pass filter with a corner frequency of 20-25 Hz. Together with non-invasive action potential detection by extracellular electrodes, CoDyPs lays the foundation for very long-lasting studies of action potential generation in a fluctuation driven regime. This promises to allow the measurement of dynamical response properties and the respective cut-off frequencies from individual neurons. It might also prove a useful addition to conventional flash-evoked imprinting of action potential patterns for in-vivo experiments. Figure 1 Acknowledgements Supported by funding through BFNT and BCCN Göttingen Keywords: channelrhodopsin, dynamic gain, Neurons, networks and dynamical systems, neurotechnology, optogenetics Conference: BC11 : Computational Neuroscience & Neurotechnology Bernstein Conference & Neurex Annual Meeting 2011, Freiburg, Germany, 4 Oct - 6 Oct, 2011. Presentation Type: Poster Topic: neurons, networks and dynamical systems (please use "neurons, networks and dynamical systems" as keywords) Citation: Neef A, ElHady A, Nagpal J, Broking K, Afshar G, Geisel T, Bamberg E, Fleischmann R, Stühmer W and Wolf F (2011). Continuous Dynamic Photostimulation - inducing defined, in-vivo-like fluctuating stimuli with Channelrhodopsins. Front. Comput. Neurosci. Conference Abstract: BC11 : Computational Neuroscience & Neurotechnology Bernstein Conference & Neurex Annual Meeting 2011. doi: 10.3389/conf.fncom.2011.53.00045 Copyright: The abstracts in this collection have not been subject to any Frontiers peer review or checks, and are not endorsed by Frontiers. They are made available through the Frontiers publishing platform as a service to conference organizers and presenters. The copyright in the individual abstracts is owned by the author of each abstract or his/her employer unless otherwise stated. Each abstract, as well as the collection of abstracts, are published under a Creative Commons CC-BY 4.0 (attribution) licence (https://creativecommons.org/licenses/by/4.0/) and may thus be reproduced, translated, adapted and be the subject of derivative works provided the authors and Frontiers are attributed. For Frontiers’ terms and conditions please see https://www.frontiersin.org/legal/terms-and-conditions. Received: 23 Aug 2011; Published Online: 04 Oct 2011. * Correspondence: Dr. Andreas Neef, BCCN Göttingen, Göttingen, Germany, aneef@gwdg.de Login Required This action requires you to be registered with Frontiers and logged in. To register or login click here. Abstract Info Abstract The Authors in Frontiers Andreas Neef Ahmed ElHady Jatin Nagpal Kai Broking Ghazaleh Afshar Theo Geisel Ernst Bamberg Ragnar Fleischmann Walter Stühmer Fred Wolf Google Andreas Neef Ahmed ElHady Jatin Nagpal Kai Broking Ghazaleh Afshar Theo Geisel Ernst Bamberg Ragnar Fleischmann Walter Stühmer Fred Wolf Google Scholar Andreas Neef Ahmed ElHady Jatin Nagpal Kai Broking Ghazaleh Afshar Theo Geisel Ernst Bamberg Ragnar Fleischmann Walter Stühmer Fred Wolf PubMed Andreas Neef Ahmed ElHady Jatin Nagpal Kai Broking Ghazaleh Afshar Theo Geisel Ernst Bamberg Ragnar Fleischmann Walter Stühmer Fred Wolf Related Article in Frontiers Google Scholar PubMed Abstract Close Back to top Javascript is disabled. 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Current Mode Biquad Filter with Minimum Component Count

The paper presents a new current mode biquadratic filter with one input and three outputs using differential voltage current conveyor (DVCC) and four passive components. The proposed circuit can simultaneously realize low-pass, band-pass, and high-pass filter functions without changing the circuit topology and passive elements. The circuit exhibits a good frequency performance and low-sensitivity figures. PSPICE simulation using 0.5 μm CMOS parameters are given to validate the proposed circuit. The circuit provides a simple yet novel solution to the current-mode filtering after appropriate incorporation of current sensing elements in form of current buffers.

New class of filter functions generated most directly by Christoffel-Darboux formula for Gegenbauer orthogonal polynomials

A new original formulation of all pole low-pass filter functions is proposed in this article. The starting point in solving the approximation problem is a direct application of the Christoffel-Darboux formula for the set of orthogonal polynomials, including Gegenbauer orthogonal polynomials in the finite interval [−1, +1] with the application of a weighting function with a single free parameter. A general solution for the filter functions is obtained in a compact explicit form, which is shown to enable generation of the Gegenbauer filter functions in a simple way by choosing the value of the free parameter. Moreover, the proposed solution with the same criterion of approximation could be used to generate Legendre and Chebyshev filter functions of the first and second kind as well. The examples of proposed filter functions of even (10th) and odd (11th) order are illustrated. The approximation is shown to yield a good compromise solution with respect to the filter frequency characteristics (magnitude as well as phase characteristics). The influence of tolerance of the filter critical component (inductor) on the proposed magnitude and group delay characteristics of a resistively terminated LC lossless ladder filter is analysed as well. The proposed filter functions are superior in terms of the excellent magnitude characteristic, which approximates an ideal filter almost perfectly over the entire pass-band range and exhibits the summed sensitivity function better than that of a Butterworth filter. In the article, we present the filter function solution that exhibits optimum amplitude as well as optimum group delay characteristics that are of crucial importance for implementation of digital processing as well as RF analogue parts of communication networks. Derivation of the other band range filter functions, which could be realised either by continuous or digital filters, is also generally possible with the procedure proposed in this article.

Spatial filter by spike timing dependent plasticity

Spike timing dependent plasticity (STDP) is found in various areas of the brain, visual cortex, hippocampus and hindbrain of electric fish, etc. The synaptic modification by STDP depends on time difference between presynaptic spike arrival and postsynaptic firing. If presynaptic neuron fires earlier than postsynaptic neuron dose, synaptic weight is strengthened. If postsynaptic neuron fires earlier than presynaptic neuron dose, synaptic weight is weakened. This learning rule is one example of various rules (hippocampal type). The learning rule of electric fish type is reversed. Changes of synaptic efficiency precisely depend on timing of pre- and postsynaptic spikes under STDP. Because of this precise dependence, STDP is thought to play the important role in temporal processing of stimuli. Temporal processing by STDP is well known. However, the role of STDP in spatial processing is not enough understood. To investigate spatial processing by STDP, We studied the role in spatial processing on interconnected network with STDP, using computer simulation. In this study, we found two type spatial filter by STDP on interconnected network. One is low pass filter using the learning rule of electric fish type. Another is edge-enhancing filter using the learning rule of hippocampus type. In this study, we calculated the response of interconnected neural network with STDP learning. The structure of the network is one-dimensional array. The neuron of the network has connection to neighbour neurons. In the case of learning rule of electric fish type, the network provided the function of low pass filter. The network was stimulated by direct current rectangularly distributed with noise. We examined two cases. In one case, synaptic modification did not occur (Fig ​(Fig1a).1a). In another case, synaptic modification occurred (Fig ​(Fig1b).1b). In the first case, Noise presented in response of the network and covered the rectangular form of stimulus. In the second case, noise was eliminated and the rectangular form of stimulus was represented. In the case of learning rule of hippocampal type, the network provided the function of edge-enhancing filter. The network was stimulated by direct current rectangularly distributed. The firing rate of the neuron that represents the edge of stimulus was larger than one of the others. This result shows that the network with hipocampal type STDP plays the role of edge-enhancing filter. These results show that interconnected network with STDP provides the function of spatial filter, and suggest that STDP would plays the important role in spatial processing. Figure 1 Response of network. Vertical and horizontal line indicates response of the network and neuronal number, respectively. (a) and (b) show the response of the network without and with STDP learning, respectively.

A variational method for designing adaptive bandlimited wavelets

This paper proposes a new method of estimating an orthogonal bounded spectrum wavelet from a given signal. The method is based on minimizing the distance of the wavelet and the given signal in the sense of the metric of the L2 space. In this method, the amplitude and phase of the mother wavelet are optimized simultaneously. The Lagrange multipliers technique is applied to consider the constraints due to the bounded spectrum wavelet and orthogonality conditions. The variational method reduced the optimal matching problem to the solution of a set of functional equations for the amplitude and phase of the optimal-matched bandlimited wavelet spectrum. Continuous functional equations are written with respect to Fourier coefficients of phase of transfer function of the quadrate low-pass filter at the sampled frequencies, and asset of discrete algebraic equations allows us to design the wavelet directly from the signal of interest. To demonstrate the performance of the presented method in this paper, it is employed to determine the matched wavelets of some specified signals.

A variational method for designing wavelets to match a specified signal

In this paper, we have developed an efficient method for obtaining an orthonormal wavelet that is matched to a given signal. The error between the wavelet and the given signal is minimized subject to the constraints of the amplitude and phase of the band-limited wavelet spectrum. To consider the constraints of the minimization problem, the Lagrange multipliers technique is applied. Variational method reduced the optimal matching problem to the solution of a set of functional equations for the amplitude and phase of the wavelet spectrum. Continuous functional equations were written in terms of Fourier coefficients of the phase of the transfer function of the quadrature low pass filter at the sampled frequencies. Consequently, a set of discrete algebraic equations allows us to design the wavelet directly from the signal of interest. Specific examples are given for demonstrating the performance of wavelet matching equations for both known orthonormal wavelets and arbitrary signals.

Dynamic properties of Drosophila olfactory electroantennograms

Time-dependent properties of chemical signals are probably crucially important to many animals, but little is known about the dynamics of chemoreceptors. Behavioral evidence of dynamic sensitivity includes the control of moth flight by pheromone plume structure, and the ability of some blood-sucking insects to detect varying concentrations of carbon dioxide, possibly matched to host breathing rates. Measurement of chemoreceptor dynamics has been limited by the technical challenge of producing controlled, accurate modulation of olfactory and gustatory chemical concentrations over suitably wide ranges of amplitude and frequency. We used a new servo-controlled laminar flow system, combined with photoionization detection of surrogate tracer gas, to characterize electroantennograms (EAG) of Drosophila antennae during stimulation with fruit odorants or aggregation pheromone in air. Frequency response functions and coherence functions measured over a bandwidth of 0-100 Hz were well characterized by first-order low-pass linear filter functions. Filter time constant varied over almost a tenfold range, and was characteristic for each odorant, indicating that several dynamically different chemotransduction mechanisms are present. Pheromone response was delayed relative to fruit odors. Amplitude of response, and consequently signal-to-noise ratio, also varied consistently with different compounds. Accurate dynamic characterization promises to provide important new information about chemotransduction and odorant-stimulated behavior.

Experimental application of high precision k-space filters and stopping rules for fully automated near-field acoustical holography

In general, inverse acoustics problems are ill-posed. Without proper regularization action taken noisy measurements result in an increasingly disturbed solution of the inverse acoustics wave equation as the distance from the measurement plane to the desired source grows. Two distinctive steps take place in the regularization process for planar near-field acoustical holography (PNAH): first, a low-pass filter function is defined and secondly a stopping rule is applied to determine the parameter settings of the filter. In acoustical imaging practice, it turns out to be very hard to determine the right filter for a certain case, ideally by means of an automatic search for the (near-) optimal parameters. This paper presents the practical application of a novel automated method that combines fitted filters for a broad number of possible experimental sources combined with highly efficient stopping rules by taking advantage of k-space. Also, a number of well-known and newly developed filter functions and stopping rules are discussed and compared with one another. Results based on actual measurements demonstrate the effectiveness, applicability, and precision of the fully implemented and automated regularization process for PNAH. Practical results even show acoustic source visualization below one millimeter primarily by successful application of k-space regularization. Implementations include modifications of Tikhonov, exponential and truncation low-pass filters, L-curve Generalised Cross-Validation (GCV) and the novel Cut-Off and Slope (COS) parameter selection methods for PNAH COS iteration in combination with either a modified exponential or Tikhonov low-pass filter results in an automated selection of the regularization parameters and eventually a fully automated PNAH system.

Control of gyro system based on lowpass filter function feedback

This paper presents a method of controlling gyro system based on bounded damping feedback. Firstly，using LaSalle invariable theorem，a stability analysis is given theoretically. Then by introducing a two order Butterworth lowpass filter，a feedback controller is proposed on the basis of measured signals. The chaotic gyro system can be stabilized to different periodic obits or fixed points in the numerical simulation. Furthermore，the effects of control parameter and noise are investigated. The results show that the implementation of this control method is simple and easy. In addition，the controller has strong robustness against weak external noise.

The coherence between the IMF and high-latitude ionospheric flows: The dayside magnetosphere–ionosphere low-pass filter

This study seeks to establish a new system characteristic describing dayside convective flows in the coupled magnetosphere–ionosphere: the low-pass filter function through which interplanetary magnetic field (IMF) fluctuations are processed as they are communicated from the magnetopause to the high-latitude ionosphere near local noon. In doing so, this study confirms that variations in the ionospheric flows at high-latitudes near local noon are well correlated with variations in the IMF orientation and magnitude on short timescales. We construct the filter function by comparing time series of the ionospheric equivalent flows at a fixed location at magnetic local noon and 80° latitude with time series of the IMF. The coherence spectra of these two parameters—averaged over 330 h of comparison—indicate that there is a low-pass cutoff in the ionospheric response to IMF driving at a periods shorter than 20 min (frequencies higher than 0.8 mHz). When there is sufficient power in the IMF fluctuations, this cutoff is relatively sharp—the coherence drops by roughly a factor of three between the periods 32 and 21 min (0.5 and 0.8 mHz). The results also show that on average the coherence between the east–west component of the equivalent flows and IMF B y tends to be less than the coherence between the north–south component of the equivalent flows and IMF B z .

BK channel β4 subunit reduces dentate gyrus excitability and protects against temporal lobe seizures

Synaptic inhibition within the hippocampus dentate gyrus serves a 'low-pass filtering' function that protects against hyperexcitability that leads to temporal lobe seizures. Here we demonstrate that calcium-activated potassium (BK) channel accessory beta4 subunits serve as key regulators of intrinsic firing properties that contribute to the low-pass filtering function of dentate granule cells. Notably, a critical beta4 subunit function is to preclude BK channels from contributing to membrane repolarization and thereby broaden action potentials. Longer-duration action potentials secondarily recruit SK channels, leading to greater spike frequency adaptation and reduced firing rates. In contrast, granule cells from beta4 knockout mice show a gain-of-function for BK channels that sharpens action potentials and supports higher firing rates. Consistent with breakdown of the dentate filter, beta4 knockouts show distinctive seizures emanating from the temporal cortex, demonstrating a unique nonsynaptic mechanism for gate control of hippocampal synchronization leading to temporal lobe epilepsy.

Single DDCC Biquads with High Input Impedance and Minimum Number of Passive Elements

Two new configurations for the design of biquad filters with high input impedance are presented. The first configuration can synthesize low-pass and high-pass filter functions according to the passive components used. The second one can synthesize a band-pass filter function. The proposed configurations employ only one differential difference current conveyor (DDCC) as active elements and minimum number of passive elements, namely two resistors and two capacitors. Another filter topology based on DDCC is presented that allows modifying the quality factor without changing its natural frequency. All the filters enjoy low sensitivities. SPICE simulation results are given to confirm the validity of the analysis and to point out the high performance of the filters.

In Silico Stochastic Network Models that Emulate the Molecular Sieving Characteristics of Bone

Recent studies implicate bone's extracellular matrix as a "living electrophoresis and ion exchange column" with low pass filter function at the matrix level; whereas small molecules pass through the matrix microporosity, larger molecules penetrate the tissue through the pericellular space. In this study, stochastic network modeling principles were applied, for the first time to our knowledge, to build in silico, nano- to microscale models of bone. Small volumes of bone were modeled to include hierarchical levels of porosity comprising the bone matrix microporosity and the pericellular network. Flow and transport through the network was calculated for molecules from 1,000 to 100,000 datons (Da). On the basis of this study, two contrasting effects determine the rate and direction of transport of different size molecules through the hierarchical porous network of bone. Whereas diffusivity of a given molecule decreases with increasing molecular size, the size exclusion effects of bone's low pass molecular sieve translate into increasing flow velocities for large molecular species along transport paths located in the immediate vicinity of the cells. Both phenomena are expected to have a profound effect on the formation of molecular gradients at a tissue level, providing cues for tissue generation and repair by cellular "micromachines," i.e., osteoclasts and osteoblasts.