Light Lever Research Articles

Fabrication and Resonance Characteristics of PZT Cantilevers

Thin films of lead zirconate titanate Pb(Zr0,52Ti0,48)O3 (PZT) with thickness of 1.4 μm were prepared on Si/SiO2/TiO2/Pt substrates by chemical solutions deposition. Based on the obtained films, the structures of PZT cantilevers were formed, with a length from 500 to 1000 /um and wide from 100 to 500 μm. Platinum (100 nm) as the bottom and top electrode, has been deposited by magnetron sputtering. PZT cantilevers werereleased by etching the sacrificial layer in SF6. The resonance characteristics of the PZT cantilevers were determined by the light lever method using a special optical measuring stand. Output characteristics of the PZT cantilevers, can be used in MEMS devices, specially, in MEMS resonators.

Treatment with a muscarinic acetylcholine receptor antagonist impairs the acquisition of conditioned reward learning in rats

The neural mechanisms whereby a reward-associated stimulus gains reinforcing properties and comes to function as a conditioned reward (CR) are not understood. We propose that muscarinic acetylcholine (mACh) receptor stimulation is necessary for this type of learning. Here we tested the hypothesis that mACh receptor antagonism, with scopolamine, would attenuate the acquisition by a food-related stimulus of the capacity to function as a CR. Rats were exposed to 5 pre-exposure sessions during which two levers were present, one producing a light and the other a tone when pressed. This was followed by 3 conditioning sessions in which the levers were absent and the rats were presented with 30 light-food pairings delivered randomly. In the test session, the levers were present and presses on both levers were recorded. Different groups of rats received intraperitoneal injections of scopolamine (0, 0.375, 0.75 and 1mg/kg) either prior to each conditioning session or prior to the test session. All groups showed significantly greater responding on the light lever in the test compared to the pre-exposure sessions, demonstrating the CR effect. In animals treated prior to conditioning the scopolamine groups pressed significantly less on the light lever than the vehicle group. In animals treated prior to the test the increased lever pressing for light was similar for all groups. These data suggest that scopolamine impaired the acquisition of CR but not its expression. The results support the hypothesis that mACh receptor stimulation is important for the acquisition by reward-associated stimuli of the ability to function as CRs.

Effects of systemic phencyclidine on firing activity of ventral tegmental area neurons in a classical conditioning paradigm

The neural mechanisms whereby a reward-associated stimulus gains reinforcing properties and comes to function as a conditioned reward (CR) are not understood. We propose that muscarinic acetylcholine (mACh) receptor stimulation is necessary for this type of learning. Here we tested the hypothesis that mACh receptor antagonism, with scopolamine, would attenuate the acquisition by a food-related stimulus of the capacity to function as a CR. Rats were exposed to 5 pre-exposure sessions during which two levers were present, one producing a light and the other a tone when pressed. This was followed by 3 conditioning sessions in which the levers were absent and the rats were presented with 30 light-food pairings delivered randomly. In the test session, the levers were present and presses on both levers were recorded. Different groups of rats received intraperitoneal injections of scopolamine (0, 0.375, 0.75 and 1 mg/kg) either prior to each conditioning session or prior to the test session. All groups showed significantly greater responding on the light lever in the test compared to the pre-exposure sessions, demonstrating the CR effect. In animals treated prior to conditioning the scopolamine groups pressed significantly less on the light lever than the vehicle group. In animals treated prior to the test the increased lever pressing for light was similar for all groups. These data suggest that scopolamine impaired the acquisition of CR but not its expression. The results support the hypothesis that mACh receptor stimulation is important for the acquisition by reward-associated stimuli of the ability to function as CRs.

Focus on nanoscience and nanotechnology

Focus on nanoscience and nanotechnology

Effect of required response force on rats’ performance on a VI+ schedule of reinforcement

Three experiments were performed to examine the effect of response force on rats' performance on various schedules of reinforcement. Response force was manipulated by changing the weight of the lever in the operant chamber--a heavy lever for high response force and a light lever for low response force. Using a within-subjects design, Experiment 1 replicated previous findings that rats respond more quickly on variable ratio (VR) than on equivalent variable-interval-plus-linear-feedback (VI+) schedules. Experiment 2 replicated this finding but also showed that the use of a smaller response force abolished the response rate difference between the VR and VI+ schedules. Experiment 3 used a between-subjects design and showed a response rate difference between the VR and VI+ schedules with a high response force but no response rate difference with a low response force. This suggests that under conditions of low force, when the rats' responding can continue at prolonged high rates, these subjects show little difference in their response rates between VR and VI + schedules. These data are similar to those found for human subjects.

Transfer Function Analysis of the Micro Cantilever Used in Atomic Force Microscopy

Current approaches to study the system response of the different modes of dynamic atomic force microscopy (AFM) use model simplification such as single mode approximations or are based on the nontrivial solution of the equation of motion. As an alternative to these approaches, the transfer function analysis gives a more complete description of system dynamics considering the cantilever as an extended vibrating structure. In order to describe the dynamics correctly, the precise experimental configuration has to be taken into account. This includes distinguishing between point loads (mechanical tip sample interaction) and distributed loads induced, e.g., by inertial driving or electrostatic forces. In this work we focus on a transfer function study of two different AFM configurations, the point force and distributed force driven cantilever. Exact analytical expressions of the infinite dimensional transfer function are derived for both possible system outputs: cantilever deflection and slope, which correspond to an interferometric and a light lever deflection detection system, respectively. Frequency response and transfer function infinite product expansion are obtained for the case where system outputs are set at the free end of the cantilever. In the frequency response, it is reflected the full complexity of cantilever dynamics affected by the presence of an infinite number of poles and zeros. An analytical expression for all the zeros and poles of the system is obtained. Using the transfer function, system dynamics are analyzed obtaining modal and antiresonant cantilever shapes along with its step response. From the frequency response, pole-zero investigations, and system dynamics, it is shown that both cantilever actuation and output measurement affect AFM operation. Transfer function analysis of AFM cantilevers improves the possibility of model-based AFM operation to increase imaging and manipulation performance

Optical lever detection in higher eigenmode dynamic atomic force microscopy

The optical lever detection scheme is widely used in atomic force microscopy for the detection of the cantilever deflection. Laser spot size as well as adjustment of the laser along the cantilever determine the zeros of the transfer function of the signal path from the tip-sample forces to the optical readout. This can cause (almost) pole-zero cancellations which lead to a significantly reduced sensitivity in the detection of higher mode vibrations of the cantilever. Physically, the light lever detection integrates over the slope of the cantilever. However, the sign of the slope of higher flexural modes varies along the cantilever. Thus, integration can lead to a significantly decreased sensitivity to higher eigenmode vibrations. Illuminating only the area between the free end and the next zero crossing of the slope of the modal shape provides a good compromise between high and low frequency sensitivity.

Formation of Micronuclei Responsible for Decompression Sickness

In this report, the origin of micronuclei responsible for the onset of decompression sickness is investigated. The formation of cavities by tribonucleation between hydrophobic and hydrophilic surfaces has been studied using a new force measuring device, LLIFE (Light Lever Instrument for Force Evaluation). Using this instrument, the interaction force between silica surfaces in equilibrium with the cationic surfactant cetylpyridinium chloride has been measured above and below the critical micelle concentration. A long range hydrophobic attraction is evident between adsorbed monolayers and a DLVO repulsion is apparent between adsorbed bilayers. It is shown that the formation of cavities on separation occurs not only between hydrophobic monolayers but between hydrophilic bilayers, should the bilayers be squeezed sufficiently to cause rupture. The demonstration that cavities may arise upon separation between bilayers is new and leads to the postulate that cavities are formedin vivoby the rupture of cell membrane bilayers, thereby providing the nucleation sites for bubble formation should sufficient gas supersaturation occur.

Mechanical measures during maximal velocity knee extension exercise and their relation to fibre composition of the human vastus lateralis muscle.

A method for measuring the maximal velocity of knee extension exercise is described using a very light lever arm. Instrumentation of the lever arm with a potentiometer and accelerometer also allows for the measurement of peak acceleration, time to peak acceleration, the average rate of development of acceleration (jerk) and peak torque. With this apparatus and surface electromyography, electromechanical delay (EMD) was also determined. This apparatus was tested using 17 female and 10 male subjects, and the measures obtained were related to the percentage of fast twitch fibres (% FT) and the relative area of fast twitch fibres (% FTA) in the vastus lateralis determined from duplicate muscle biopsy samples. Peak velocity of unloaded knee extension averaged 12.1 +/- 1.2 and 12.2 +/- 1.7 rad.s-1 for females and males, respectively, and were not significantly different. As well, peak acceleration, time to peak acceleration jerk and EMD values were not significantly different between the female and male subjects, but the mean peak torque for the female subjects (73.5 +/- 14.7 N.m) was significantly lower than that for the males (98.4 +/- 31.5 N.m). Peak acceleration was significantly correlated with %FT (r = 0.40, P = 0.04) for the total subject population. None of the other measures was significantly related to either %FT or %FTA for the male and female subjects or the combined population of subjects.

The effects of pimozide on the establishment of conditioned reinforcement as a function of the amount of conditioning.

In an attempt to understand some inconsistent findings, the present experiment investigated the effects of pimozide, a dopamine (DA) receptor blocker, on the establishment of conditioned reinforcement as a function of the amount of conditioning. In Experiment 1, rats received three phases of training in a two-lever box. The pre-exposure phase measured the operant rates of pressing the levers; one produced a 3-s tone and the other turned the lights off for 3 s. In the conditioning phase, with the levers absent, the light-off stimulus was paired with food for two or four sessions. The test phase again measured the rate of pressing the levers. Conditioned reinforcement was shown by a relative increase in responding on the light lever during the test. Of the groups receiving four conditioning sessions, pimozide (0.5, 1.0, 2.0 and 4.0 mg/kg) produced a dose-dependent attenuation of conditioned reinforcement, those rats treated with 4.0 mg/kg failing to demonstrate a significant effect. When 2 conditioning days were employed, pimozide treatment also produced a dose-dependent attenuation; however, in these less conditioned animals 2.0 mg/kg blocked the effect. The possibility that pimozide produced a conditioned taste aversion to the food was ruled out in Experiment 2. These data suggest that DA transmission may be necessary for the establishment of conditioned reinforcement and that the effects of receptor blockade may be related to the amount of conditioning.

Force requirements in lever-pressing and responding after haloperidol

One hypothesis regarding the actions of neuroleptic drugs on operant responding is that they interfere in some manner with the motoric capability of the animal. To further explore this possibility, we investigated the effects of haloperidol on a bar press response after animals were trained on levers with different force requirements. In the first experiment, two groups of rats were trained to press levers having either low (30 g) or high (100 g) force requirements. The effects of haloperidol on bar pressing when both groups were responding on the light lever were then examined. Under these conditions, the groups showed similar declines in response rates, indicating little transfer between previous experience on the heavy lever and responding in the presence of haloperidol. In the second experiment, the same groups of rats received further training exclusively on either the heavy or the light lever; the rate of responding was similar for the two groups. The effects of haloperidol on pressing either the heavy or the light lever were then examined. It was found that the rate-decreasing effects of haloperidol were similar in both groups. However, when the lever-pressing response was subsequently extinguished, rats working on the heavy lever were significantly more resistant to extinction than the light lever groups. The results of these experiments fail to indicate that the putative motoric effects of haloperidol interact significantly with response force demands. Furthermore, the data provide yet further evidence that blockade of dopamine receptors and removal of reinforcement are not equivalent.

Magnetic bearing torsional creep apparatus

AbstractA torsional creep and recovery apparatus has been designed and constructed to measure extremely wide ranges of recoverable creep compliance (10−10 to 10−2 cm.2/dyne) and viscosity (10−1 to 1016 poises) within the temperature range −60 to 220°C. Friction is avoided by supporting the moving element, the rotor, in a magnetic field, inducing the required torque with a drag cup motor, and monitoring the angular displacement with a light lever and a light following recorder. Measurements of recoverable compliance can be made further into the region of time scale which is dominated by viscous deformation than has been heretofore possible. In situ sample manipulation of viscoelastic liquids is utilized. Measurement is made on liquid cylinders between circular stainless steel platens. Results which have been obtained on a 1.22 × 105 molecular weight polystyrene are presented to illustrate the range of possible measurements and to indicate the value of such results covering up to six logarithmic decades of time scale.

Dynamic measurement of Young's modulus for short wires

The method consists essentially in the measurement of the time for a quarter vibration of a short wire clamped at one end. The wire breaks a circuit as it starts its transverse vibration, and is made to strike a very light lever and open another circuit just as it completes one-quarter of its first vibration. The time between the two events is measured ballistically. From a knowledge of the time of vibration, the length, the diameter and the density of the wire, Young's modulus can be readily calculated. The method is particularly suitable for thin wires having a diameter of the order of 0.015 cm. and a length of about 2 cm. The results are consistent to a few per cent. Comparison of the results with the accepted values for five different wires shows a good agreement.

A Rat Test for Drug Addiction.

Further experiments on the addiction liability of various drugs in the albino rat have been carried out by the method previously described. The test measures objectively progressive changes in the degree of irritability of the animal 24 hours after withdrawal of the drug throughout the period of administration. Advantage is thus taken of the most outstanding part of the abstinence syndrome clinically and experimentally, hyperirritability, to assess the ability of a drug to produce addiction. The irritability of the rat which is normally fairly constant for a series of animals is quantitatively measured by determining the struggle response to a uniformly uncomfortable situation. Such a situation is provided by lashing the animal in the supine position to a small animal board so constructed that the animal is free to struggle but can neither injure nor extricate itself. Graphic records of each struggle are made kymographically by a light lever attached to the skin overlying the xyphoid process. The response of the animal is expressed by the number of struggles per interval and is a quantitative index of the degree of irritability of the animal at that time. Daily administration of morphine, codeine, or heroine results consistently in progressive increase of 24-hour abstinence hyper-irritability as shown by the struggle response to the above described uniformly uncomfortable situation. Control animals receiving injections of water showed only a gradual decrease in irritability under the same experimental conditions. Dihydromorphinone hydrochloride (dilaudid): To completely eliminate the movements of rats in the device described above, dilaudid was 10 times as potent as morphine. Complete tranquilization was obtained with dilaudid in one-tenth of the dosage necessary with morphine. When daily doses of equal tranquilizing potency were given, no significant difference in addiction liability could be found between dilaudid and morphine.