Mechanical Deflection Research Articles

Temporal precision in population-but not individual neuron-dynamics reveals rapid experience-dependent plasticity in the rat barrel cortex.

Cortical reorganization following sensory deprivation is characterized by alterations in the connectivity between neurons encoding spared and deprived cortical inputs. The extent to which this alteration depends on Spike Timing Dependent Plasticity (STDP), however, is largely unknown. We quantified changes in the functional connectivity between layer V neurons in the vibrissal primary somatosensory cortex (vSI) (barrel cortex) of rats following sensory deprivation. One week after chronic implantation of a microelectrode array in vSI, sensory-evoked activity resulting from mechanical deflections of individual whiskers was recorded (control data) after which two whiskers on the contralateral side were paired by sparing them while trimming all other whiskers on the rat's mystacial pad. The rats' environment was then enriched by placing novel objects in the cages to encourage exploratory behavior with the spared whiskers. Sensory-evoked activity in response to individual stimulation of spared whiskers and adjacent re-grown whiskers was then recorded under anesthesia 1–2 days and 6–7 days post-trimming (plasticity data). We analyzed spike trains within 100 ms of stimulus onset and confirmed previously published reports documenting changes in receptive field sizes in the spared whisker barrels. We analyzed the same data using Dynamic Bayesian Networks (DBNs) to infer the functional connectivity between the recorded neurons. We found that DBNs inferred from population responses to stimulation of each of the spared whiskers exhibited graded increase in similarity that was proportional to the pairing duration. A significant early increase in network similarity in the spared-whisker barrels was detected 1–2 days post pairing, but not when single neuron responses were examined during the same period. These results suggest that rapid reorganization of cortical neurons following sensory deprivation may be mediated by an STDP mechanism.

Effect of Rotor Eccentricity in Large Synchronous Machines

This paper addresses the effects of rotor eccentricity on the unbalanced magnetic pull (UMP) and induced electromotive forces (EMFs) in permanent magnet and wound field machines with particular emphasis on wind applications. It is shown that in both machines, the UMP can be of similar or greater magnitude than the gravitational force acting on the rotor. It is also shown that although rotor eccentricity may have a noticeable effect on the induced EMF in individual coils, albeit the effects on the phase EMF may depend on the coil connections. Furthermore, the mechanical deflections and forces on the bearings are determined using Euler-Bernoulli beam theory taking into account the UMP and gravitational forces as well as the non-linear stiffness characteristics of the bearings. It is shown that the UMP could have a significant effect on bearing forces.

Frequency response properties of primary afferent neurons in the posterior lateral line system of larval zebrafish.

The ability of fishes to detect water flow with the neuromasts of their lateral line system depends on the physiology of afferent neurons as well as the hydrodynamic environment. Using larval zebrafish (Danio rerio), we measured the basic response properties of primary afferent neurons to mechanical deflections of individual superficial neuromasts. We used two types of stimulation protocols. First, we used sine wave stimulation to characterize the response properties of the afferent neurons. The average frequency-response curve was flat across stimulation frequencies between 0 and 100 Hz, matching the filtering properties of a displacement detector. Spike rate increased asymptotically with frequency, and phase locking was maximal between 10 and 60 Hz. Second, we used pulse train stimulation to analyze the maximum spike rate capabilities. We found that afferent neurons could generate up to 80 spikes/s and could follow a pulse train stimulation rate of up to 40 pulses/s in a reliable and precise manner. Both sine wave and pulse stimulation protocols indicate that an afferent neuron can maintain their evoked activity for longer durations at low stimulation frequencies than at high frequencies. We found one type of afferent neuron based on spontaneous activity patterns and discovered a correlation between the level of spontaneous and evoked activity. Overall, our results establish the baseline response properties of lateral line primary afferent neurons in larval zebrafish, which is a crucial step in understanding how vertebrate mechanoreceptive systems sense and subsequently process information from the environment.

Sensitivity enhancement of a flexible MEMS strain sensor by a field effect transistor in an all organic approach

We report a low-cost piezoresistive nanocomposite based organic micro electro mechanical system (MEMS) strain sensor that has been combined to an organic field effect transistor (OFET) with the objective of amplifying the sensitivity of the sensor. When the MEMS cantilever is strained by a mechanical deflection, the resulting variation of resistivity influences the gate voltage (VGS) of the OFET and, hence, changes the drain current (IDS) of the transistor. The present combination allows an enhancement of sensitivity to strain by a factor 3.7, compared to the direct detection of resistance changes of the nanocomposite. As a consequence, a low limit of detection of 24ppm has been estimated in terms of strain transduction efficiency. Furthermore, the organic microsystem exhibits a short response time and operates reversibly with an excellent robustness.

Absence of plastin 1 causes abnormal maintenance of hair cell stereocilia and a moderate form of hearing loss in mice.

Hearing relies on the mechanosensory inner and outer hair cells (OHCs) of the organ of Corti, which convert mechanical deflections of their actin-rich stereociliary bundles into electrochemical signals. Several actin-associated proteins are essential for stereocilia formation and maintenance, and their absence leads to deafness. One of the most abundant actin-bundling proteins of stereocilia is plastin 1, but its function has never been directly assessed. Here, we found that plastin 1 knock-out (Pls1 KO) mice have a moderate and progressive form of hearing loss across all frequencies. Auditory hair cells developed normally in Pls1 KO, but in young adult animals, the stereocilia of inner hair cells were reduced in width and length. The stereocilia of OHCs were comparatively less affected; however, they also showed signs of degeneration in ageing mice. The hair bundle stiffness and the acquisition of the electrophysiological properties of hair cells were unaffected by the absence of plastin 1, except for a significant change in the adaptation properties, but not the size of the mechanoelectrical transducer currents. These results show that in contrast to other actin-bundling proteins such as espin, harmonin or Eps8, plastin 1 is dispensable for the initial formation of stereocilia. However, the progressive hearing loss and morphological defects of hair cells in adult Pls1 KO mice point at a specific role for plastin 1 in the preservation of adult stereocilia and optimal hearing. Hence, mutations in the human PLS1 gene may be associated with relatively mild and progressive forms of hearing loss.

Microstructural and elasto-plastic material parameters identification by inverse finite elements method of Ti(1 − x)AlxN (0 < x < 1) sputtered thin films from Berkovich nano-indentation experiments

The mechanical properties of Ti(1−x)AlxN (0<x<1) films of different thicknesses deposited by r.f. reactive magnetron sputtering on Si <100> and high speed steel substrates have been investigated. The as-deposited coatings have been characterized by X-ray diffraction, atomic force microscopy, four-probe electric resistivity method, mechanical deflection of cantilever beams and Berkovich nano-indentation tests associated with inverse finite elements analysis. The coatings with x<0.58–0.59 present a cubic structure whereas for x>0.7 a hexagonal structure is observed. Between these two compositions cubic and hexagonal structures coexist. The roughness depends on the film thickness and on the Al content and a minimum associated to a very fine microstructure is clearly observed in the two-phase coatings. The electric resistivity sharply increases as soon as the hcp structure appears (x~0.6). The mean residual stresses are compressive, except for the AlN coating, and present a minimum at the neighborhood of x~0.64 where a mixed structure is observed.The indentation modulus M<hkl> and the Berkovich hardness HB<hkl> greatly depend on the Al content and a progressive decreasing has been observed for 0.58<x<0.7. For the M<hkl> evolution, a simple model taking into account the stiffness coefficients of TiN and AlN structures, the mean residual stress level and the variations of the lattice parameters in the two structure domains is proposed.Knowing the elastic properties of these films, inverse finite elements analysis of the indentation curves considering a simple isotropic linear elasto-plastic behavior allows, as a function of the composition, the yield stress σY and the linear hardening coefficient Hp⁎ to be estimated. σY and Hp⁎ are in the ranges 4.2 to 6.8GPa and 60 to 400GPa, respectively. The maximum value of Hp⁎/σY which characterizes the ability of these coatings to exhibit plastic strain hardening is maximum for x=0.5 and 0.6. The quality of the estimation was discussed through a practical identifiability study and quantified using an identifiability index. Tip radius and elasticity of the Berkovich indenter are two very relevant parameters to improve identifiability and correctly extract the plastic parameters of the behavior law. Scratch crack propagation resistance shows an evolution similar to those of Hp⁎/σY.

Magnetic gear scaling analysis using magnetomechanical deflection analysis

In this paper the mechanical deflection of steel bars, of different length, in a flux focusing magnetic gear is studied. The mechanical deflection is caused by the magnetic attraction between the steel bars and the inner and outer rotor magnets of the magnetic gear. An iterative magnetomechanical approach using commercial finite element analysis software has been adopted. Two different diameter magnetic gear models with different axial lengths have been modeled and the deflection has been calculated for each model. Experimental verification for one model is also shown. The paper shows that when operating with a small air-gap and long axial length the mechanical deflection can become significant.

Deformation of PEM fuel cell gas diffusion layers under compressive loading: An analytical approach

In the PEM fuel cell stack, the fibrous porous gas diffusion layer (GDL) provides mechanical support for the membrane assembly against the compressive loads imposed by bipolar plates. In this study, a new mechanistic model is developed using fundamental beam theory that can accurately predict the mechanical deflection of GDL under compressive loads. The present analytical model is built on a unit cell approach, which assumes a simplified geometry for the complex and random GDL microstructure. The model includes salient microstructural parameters and properties of the fibrous porous medium including: carbon fiber diameter, fiber elastic modulus, pore size distribution, and porosity. Carbon fiber bending is proved to be the main deformation mechanism at the unit cell level. A comprehensive optical measurement study with statistical analysis is performed to determine the geometrical parameters of the model for a number of commercially available GDL samples. A comparison between the present model and our experimental stress–strain data shows a good agreement for the linear deformation region, where the compressive pressure is higher than 1 MPa.

An Iterative Magnetomechanical Deflection Model for a Magnetic Gear

This paper investigates the mechanical deflection within steel bars in a flux focusing magnetic gear. The deflection is caused by the magnetic attraction between the steel bars and the inner and outer rotor magnets. The non-linearity within the steel is considered. Experimental results are presented.

Out-of-plane MEMS-based mechanical airflow sensor co-integrated in SOI CMOS technology

This paper demonstrates the monolithic integration of an airflow sensor based on out-of-plane movable cantilevers with a CMOS integrated circuit providing small footprint and low-power sensing. Airflow is sensed by mechanical deflection of cantilevers without static power consumption contrary to classical thermal flow sensors based on micro-heater. The interfacing circuit is a CMOS ring oscillator (RO), fabricated on the same chip with silicon-on-insulator (SOI) technology, offering unique properties such as harsh environment resistance and lower power consumption. Moreover, the additional post-processing steps required by the built-in of out-of-plane cantilevers are minimum thanks to the use of standard CMOS materials and dry etching of the sacrificial layer.The developed microsystem demonstrates 10% variation of the RO frequency for an airflow varying from 0m/s to 120m/s, with a static power consumption of the order of 1μW.

Biofunctionalization of carbon nanofiber tips for scanning probe microscopy using thin Au coating and immobilized biorecognition molecules

Individual carbon nanofibers (CNFs) synthesized on the apices of tetrahedral-type Si cantilever tips via argon-ion (Ar+) bombardment, i.e., CNF-tipped scanning probe microscopy (SPM) probes, were sputter coated with a Au film without undergoing any obvious deformations. Indentations made using the Au-coated CNF tips showed that the buckling force of the tips increased with the thickness of the Au film. The CNF tip coated with a thin Au film less than approximately 8nm in thickness elastically buckled when subjected to mechanical deflection, which was similar to the bare CNF tips. After annealing the Au-coated CNF-tipped SPM probes, we biofunctionalized them by immobilizing thiol-derivatized, single-stranded DNA (ssDNA) molecules, used as representative biorecognition molecules, on the Au(111)-coated surfaces. The ability of the immobilized ssDNA molecules to bind with complimentary RNA targets was confirmed via field-emission scanning electron microscopy and energy-dispersive X-ray spectroscopy-based analysis of quantum dots bound to the ssDNA/RNA hybrids formed on the surfaces of the biofunctionalized CNF-tipped SPM probes.

Large Stroke Staggered Vertical Comb-Drive Actuator for the Application of a Millimeter-Wave Tunable Phase Shifter

This paper presents the design, fabrication, and characterization of a MEMS actuator with large static deflection as a waveguide-mounted variable millimeter-wave phase shifter. The actuator is composed of a pair of interdigitated microplates actuated by vertical comb-drives and suspended by SU-8 torsional springs. The SU-8 spring possesses a thin metallization top layer and a reverse-T-shaped cross-section enabling low torsional stiffness and high in-plane stability. A maximum mechanical deflection of 10.3 <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex Notation="TeX">$^{\circ}$</tex></formula> is obtained under a dc actuation voltage of 35 V. The dynamic characterization of the device shows that the resonance frequency of the torsional mode is well separated from the other three bending modes, confirming the designed low torsional stiffness and high in-plane stability. The torsional viscoelastic creeping is measured as a function of time at different loads and shows a maximum of 0.5 <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex Notation="TeX">$^{\circ}$</tex></formula> for an applied voltage of 27.5 V. A high operation cycle test is conducted and the metalized SU-8 spring withstands 800 million cycles without showing fatigue. RF measurements show that a variable mechanical deflection angle between 0 <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$^{\circ}$</tex></formula> and 8.2 <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$^{\circ}$</tex></formula> results in a variable transmission phase shift up to 58.0 <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$^{\circ}$</tex></formula> . The measured insertion loss is always below 5.1 dB at 98 GHz, corresponding to a figure of merit of 11.5 <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$^{\circ}/{\rm dB}$</tex> </formula> . [2012-0338]

Surface stress sensor using MEMS-based Fabry–Perot interferometer for label-free biosensing

We have recently developed a surface stress sensor based on a microelectromechanical system Fabry–Perot interferometer integrated with a photodiode, which utilizes the nonlinear optical transmittance change in the Fabry–Perot interference to enhance the sensitivity of the surface stress. The novel signal transducing technique from the surface stress caused by molecular adsorption to the electrical readout is carried out in three steps, namely, mechanical deflection, transmittance change, and photocurrent change. Parylene-C was used as a deformable membrane in the sensor because of its high optical transmittance, low Young's modulus, and negligible residual stress, which provides a flat freestanding membrane. The theoretical minimum detectable surface stress of the proposed sensor was predicted to be −1μN/m, which is two orders of magnitude greater than that of the piezoresistor-embedded surface stress sensor. The Fabry–Perot surface stress sensor was fabricated using a semiconductor fabrication process and sacrificial release process. An encapsulating structure for the Fabry–Perot cavity that uses a dry film resist by a roll-to-roll technique enabled us to use wet condition for detection of biomolecules. Amino-methyl-functionalized parylene was coated on the parylene-C membrane for immobilization of the biomolecules via electrostatic coupling between biomolecules and the amino group. The photocurrent was demonstrated to shift by 23.7nA at a 3-V reverse bias voltage with immobilized antibodies. This Fabry–Perot sensor allows the use of a universal biochemical sensing platform in a label-free manner.

STUDY OF TALC FILLED POLYPROPYLENE- A CONCEPT FOR IMPROVING MECHANICAL PROPERTIES OF POLYPROPYLENE

Talc is a important filler for polypropylene (PP) and Non halogen flame retardants (ammonium polyphosphate) is used with PP. It does not generate toxic gases and corrosive smokes during combustion. The addition of flame retardants will lower the flammability of PP. Talc improves the mechanical properties (stiffness, flexural strength, modulus etc) and heat deflection temperature. Two types of mechanical testing have been done to determine the mechanical properties, which are flexural test and tensile test .In this study, the improvement of mechanical properties have shown with increasing suitable percentage (by weight) of talc for a new applications . Keyword- Stiffness, Talc, FR, PP

High-performance spinning device for DVD-based micromechanical signal transduction

Here we report a high-throughput spinning device for nanometric scale measurements of microstructures with instrumentation details and experimental results. The readout technology implemented in the designed disc-like device is based on a DVD data storage optical pick-up unit (OPU). With a spinning mechanism, this device can simultaneously measure surface topography, mechanical deflections and resonance frequencies of several microfabricated beams at a high speed. In biochemical sensing applications, the OPU can measure bending changes of functionalized microcantilevers, providing a statistically robust and label-free bio-detection analysis of multiple compounds. The signal-to-noise ratio (S/N) is demonstrated from statistical measurements as 1.2 with arginine detection at 750 nM concentration. Practically, the OPU can measure up to 480 individual cantilever sensors per second with nanometer resolution. The opto-mechanical optimization of the device design and settings for biochemical detection are described.

Comprehensive Analysis of Repair/Reinforcement Materials for Polymethyl Methacrylate Denture Bases: Mechanical and Dimensional Stability Characteristics

Fracture of complete denture is a common problem as acrylic resins hold inherent limitations. This necessitates affirmation of a selection criterion by evaluating the critical requirements of repair materials. The study intended to evaluate mechanical properties and dimensional stability of common denture base repair and reinforcement materials under standard experimental protocol. Seven types of denture reinforcement materials were chosen. Forty cuboidal samples were made in accordance with ISO 178 for three point bending test and divided to eight groups of five samples each. One group acted as control and samples of seven groups were sectioned and repaired with chosen materials. Five mechanical properties-fracture load, deflection, flexural strength, fracture toughness and elastic modulus were evaluated for all groups. Forty mandibular complete denture specimens were utilized for evaluating fracture load and deflection under loading. Dimensional stability after repair with seven different repair materials was analyzed in two planes (Linear and curvilinear) utilizing separate set of denture samples. Heat cure polymethyl methacrylate with polyethylene fiber was affirmed as material of choice based on this study as it accomplishes the most critical norms of requirement.

A resonance scanning grating based on SOI for microspectrometer application

A scanning grating is designed and fabricated as a significant dispersing component of a microspectrometer. The designed scanning grating utilizes the slight vertical comb offsets induced mainly by the fabrication imperfections and residual stress in silicon on insulator (SOI) as starting electrodes. According to the spectral resolution and resonance frequency requirements, the scanning grating structure parameters are determined. Based on an SOI substrate, a V-shaped grating structure (〈111〉 plane with an angle of 54.74° to the surface of a 〈100〉 silicon substrate) can be obtained by wet etching on the microscanning mirror plate (3 × 3 mm2). Some measuring principles and experimental results on the main performance of the scanning grating including the resonance frequency, deflection angle and diffraction efficiency are discussed in detail. The mechanical deflection angle of the scanning grating can reach ±5°, corresponding to an optical scan range of 20° at a driving voltage of 30 V.

A New Look at the Physics of Rossby Waves: A Mechanical–Coriolis Oscillation

Abstract The presence of the latitudinal variation of the Coriolis parameter serves as a mechanical barrier that causes a mass convergence for the poleward geostrophic flow and divergence for the equatorward flow, just as a sloped bottom terrain does to a crossover flow. Part of the mass convergence causes pressure to rise along the uphill pathway, while the remaining part is detoured to cross isobars out of the pathway. This mechanically excited cross-isobar flow, being unbalanced geostrophically, is subject to a “half-cycle” Coriolis force that only turns it to the direction parallel to isobars without continuing to turn it farther back to its opposite direction because the geostrophic balance is reestablished once the flow becomes parallel to isobars. Such oscillation, involving a barrier-induced mass convergence, a mechanical deflection, and a half-cycle Coriolis deflection, is referred to as a mechanical–Coriolis oscillation with a “barrier-induced half-cycle Coriolis force” as its restoring force. Through a complete cycle of the mechanical–Coriolis oscillation, a new geostrophically balanced flow pattern emerges to the left of the existing flow when facing the uphill (downhill) direction of the barrier in the Northern (Southern) Hemisphere. The β barrier is always sloped toward the pole in both hemispheres, responsible for the westward propagation of Rossby waves. The β-induced mechanical–Coriolis oscillation frequency can be succinctly expressed as , where , and λ is the angle of a sloped surface along which the unbalanced flow crosses isobars, α is the angle of isobars with the barrier’s slope, and k is the wavenumber along the direction of the barrier’s contours.

Higher-Order Mode-Locking and Phase Slips in Hair Cell of the Inner Ear

Auditory system is known for its exquisite sensitivity, displaying sub-nanometer detection thresholds. Mechanical deflections evoked by external sound and ground vibrations are converted by the inner ear hair cells into electrical signals. In some species, hair cell bundles exhibit spontaneous oscillations under in vitro conditions. In Bullfrog sacculus, the oscillation profile is consistent with relaxation-type oscillation, in which a rapid motion of a bundle is followed by a slow drift along the same direction. A large number of hair bundles also show more complex temporal profiles, with quiescent intervals interspersed with bursts of oscillation. We study the dynamics of phase-locking of individual hair bundles to low-amplitude mechanical stimulations, where the amplitude of the oscillations remains unaffected by the stimulus. Under low-frequency stimulation, the signal entrains the bundle motility via higher-order mode-locking. The applied signal modulated both the quiescent intervals and the oscillatory bursts, across a broad range of frequencies. We compare these experimental findings with results from numerical simulations.

In situ synthesized carbon nanotube networks on a microcantilever for sensitive detection of explosive vapors

This paper reports a chemical sensor that consists of a suspended microcantilever and a carbon nanotube (CNT) network that is in situ synthesized on the microcantilever. The in situ synthesis achieves minimized thermal resistance of the interface between the CNTs and the microcantilever, which together with the low thermal mass and the high thermal conductivity allows the sensor to operate in microcalorimeter mode. By heating the CNT networks with an integrated heater, the explosive vapors adsorbed on the CNT surfaces are ignited to deflagration, which releases extra heat to deflect the microcantilever and thus changes the resistance of an integrated piezoresistor. This thermal-mechanical coupling transduction mechanism bridges the heat changes on the CNT networks and the mechanical deflection of the microcantilever. The large surface to volume ratio of CNTs enables fast adsorption of the chemical sensor to explosive vapors and improved equivalent limit of detection (LOD). An equivalent LOD of 2.4 pg is achieved for TNT detection, and run-to-run repeatability and device-to-device reproducibility are better than 4% and 10%. The preliminary results demonstrate the feasibility of development of sensitive CNT chemical sensors using in situ synthesized CNT networks and thermal-mechanical coupling transduction mechanism.