Retardation Tests Research Articles

Perirhinal cortex lesions impair feature-negative discrimination

The role of the perirhinal cortex in inhibitory eyeblink conditioning was examined. In Experiment 1, rats were given lesions of the perirhinal cortex or control surgery and subsequently trained with a feature-negative discrimination procedure followed by summation and retardation tests for conditioned inhibition. Perirhinal cortex lesions impaired, but did not prevent acquisition of feature-negative discrimination. Results from the summation test showed that rats with perirhinal cortex lesions could not generalize feature-negative discrimination to a new stimulus. There were no group differences during the retardation test. Experiment 2 showed that lesions of the perirhinal cortex did not impair simple excitatory conditioning. Experiment 3 showed that perirhinal cortex lesions had no effect on acquisition of a simple tone-light discrimination. The results suggest that the perirhinal cortex plays a role in eyeblink conditioning when using discrimination procedures involving overlapping stimuli.

The Espinet and the perceptual learning effects in flavour aversion conditioning: Do they depend on a common inhibitory mechanism?

In three experiments rats were given short or long preexposure (4 or 10 sessions) to two compound flavours, AX and BX, according to an intermixed or a blocked schedule. Following preexposure, aversion conditioning trials were given with AX as the conditioned stimulus (CS). In Experiments 1 and 2, retardation and summation tests were then carried out to assess the inhibitory properties of B (an Espinet procedure). In Experiment 3, test trials evaluated generalization from AX to BX (the standard perceptual learning procedure). The results showed that B performed as an inhibitor of the unconditioned stimulus (US; an Espinet effect) only after long intermixed preexposure, whereas a reliable perceptual learning effect was observed both after short and after long preexposure. The observation that B had no detectable inhibitory properties after short preexposure casts doubt on the suggestion that inhibitory learning is responsible for perceptual learning after brief exposure to AX and BX.

A comparator view of Pavlovian and differential inhibition.

In 3 experiments using rats as subjects, the authors varied trial spacing to investigate the conditions under which Pavlovian and differential inhibition are observed. Experiment 1 compared Pavlovian and differential inhibition with spaced training trials. Spaced trials resulted in only the Pavlovian inhibitor passing both summation and retardation tests. Conversely, Experiment 2 compared these 2 types of inhibition with massed training trials. This training resulted in only the differential inhibitor passing both tests for conditioned inhibition. Finally, in Experiment 3 all subjects experienced Pavlovian inhibition training with massed trials. Although this training by itself did not result in behavior indicative of inhibition, subjects that also experienced posttraining extinction of the training context did pass both tests for inhibition. Overall, these results are anticipated by the extended comparator hypothesis (Denniston, Savastano, & Miller, 2001) but are problematic for most contemporary associative learning theories.

Thermal Stability and Flame Retardancy of Polypropylene with Phosphorus, Nitrogen and Silicon-Containing Compounds

Flame retardants containing phosphorus, nitrogen and silicone elements have been synthesized. The thermal stabilities of polypropylene (PP), PSiN and PP/PSiN have been studied by thermogravimetric (TG) analysis in nitrogen, air and oxygen atmospheres. The initial decomposition temperature (IDT), maximum-rate degradation temperature (Tmax), integral procedure decomposition temperature (IPDT) and char yield at 800 °C in various atmospheres have been investigated. Although the IDT of PP was reduced by the introduction of PSiN, the Tmax, IPDT and char yield were all increased. The flame retardancy of PP/PSiN composites were evaluated by measuring their Limiting Oxygen Index (LOI) values. Their thermal stabilities agreed with the results of the flame retardancy tests: the PP/PSiN-A exhibited good flame retardancy with LOI of 26.0 and its char yields at 800 °C were 27 wt.% (in nitrogen), 12 wt.% (air) and 12 wt.% (in oxygen). The activation energies of PP, PSiN and PP/PSiN composites in various atmospheres were calculated using the method of Horowitz-Metzger.

Dynamic Modelling and Simulation of Squirrel-Cage Asynchronous Machine with Non-Linear Effects

Abstract The paper presents the dynamic modelling and computer simulation of a squirrel-cage induction machine with non-linear effects. The computer simulation for the transient operation is obtained from the non-linear differential system of equations, which describe the induction machine in the rotor reference frame and with currents as state variables. It is shown that by using the characteristic data available from d.c. measurement, no-load, Blocked rotor, and retardation tests of the machine as well as the results obtained from the optimization of the T-model rotor circuit, accurate simulation of the machine under dynamic condition is possible. The simulated time function of the transient current, mechanical speed, and shaft torque characteristics of the machine are compared with the experimental results.

Overview of recent developments in the flame retardancy of polycarbonates

AbstractThis paper presents an overview of the recent literature on flame retardancy of polycarbonate (PC) and polycarbonate‐based resins. A brief survey of the major mechanisms of thermal decomposition of PC is also presented because it gives insight in the mechanisms of flame retardant action. Mostly industrial laboratories are involved in the development of new flame retardants for PC and, to a much lesser extent, academic laboratories are doing research on the mechanistic aspects of flame retardancy. The number of patents published annually on the flame retardancy of PC and its blends significantly exceeds the number of patents on flame retardancy of any other polymer. Because PC is a naturally high charring polymer, the condensed phase active flame retardants, in particular phosphorus‐based ones, are widely used in PC‐based blends. Plain PC can pass stringent flame retardant tests with very low additions of some sulfur‐ or silicone‐based flame retardants. Copyright © 2005 Society of Chemical Industry

Some of the properties of flame retardant medium density fiberboard made from rubberwood and recycled containers containing aluminum trihydroxide

The flame retardancy of medium density fiberboard (MDF) made from mixture of rubberwood fibers and recycled old corrugated containers was studied. Aluminum trihydroxide (ATH) was used as a fire retardant additive and mixed with the fibers to manufacture experimental MDF panels using wet process. Phenol formaldehyde (PF) resin in liquid, 2% based on oven dry weight of fibers, was used along with 0%, 10%, 15% and 20% of ATH. The flame retardant test was done using the limiting oxygen index (LOI) test. The other properties investigated include internal bond strength, thickness swelling and water absorption. The results showed that ATH loading increased as the LOI of MDF increased. This demonstrated that ATH could improved the fire retardant property of MDF at sufficient loading. An increase in concentration of ATH showed an increase in the IB values of MDF made without resin. MDF panels made without resin showed a progressive increase in internal bond as the composition of recycled old corrugated containers fiber increased. Addition of resin improved internal bond strength and reduced thickness swelling, and water absorption. Thickness swelling of panel increased as the composition of recycled old corrugated containers fiber increased. Scanning electron microscopy (SEM) and energy dispersive X-ray analysis (EDAX) showed that there is indication of ATH and resin filling the void space in between fibers.

Thwarting the renewal (relapse) of conditioned fear with the explicitly unpaired procedure: Possible interpretations and implications for treating human fears and phobias

In three experiments using the barpress conditioned suppression task with albino rats, we studied the renewal (relapse) of conditioned fear in an ABA fear-renewal paradigm. We found that explicitly unpaired (EU) deliveries of conditioned stimuli (CSs) and unconditioned stimuli (USs) in Context B thwarted fear renewal in Context A. Evidence contraindicated a suggestion by Rauhut, Thomas, and Ayres (2001) that US habituation plays a key role in this effect. For example, renewal was thwarted only when EU CSs and USs were intermingled rather than given in succession. The possibility that EU treatments thwart renewal by creating a CS that inhibits fear in the test context also received no support. Thus, summation and retardation tests in Context A found no evidence that the EU CS became inhibitory, finding instead evidence for a residual excitation. Other possible interpretations of the results and some implications for clinical practice are noted.

Enhancement of Pavlovian conditioned inhibition achieved by posttraining inflation of the training excitor

In two conditioned lick suppression experiments using water-deprived rats, we examined the effects of following Pavlovian conditioned inhibition training (i.e., A–US/AX-NoUS) with pairings of the training excitor (A) and the unconditioned stimulus (US). Experiments 1 and 2 assessed the effects of this posttraining inflation treatment on Pavlovian conditioned inhibition using a summation test and a retardation test, respectively. Both experiments revealed that subjects exposed to inflation treatment demonstrated behavior indicative of enhanced conditioned inhibition compared to subjects that did not receive inflation treatment. The results in conjunction with other recent findings suggest that posttraining associative deflation (i.e., extinction of A) and inflation effects are more symmetrical than has previously been realized.

Differential Effects of Cerebellar Inactivation on Eyeblink Conditioned Excitation and Inhibition

The neural mechanisms underlying excitatory and inhibitory eyeblink conditioning were compared using muscimol inactivation of the cerebellum. In experiment 1, rats were given saline or muscimol infusions into the anterior interpositus nucleus ipsilateral to the conditioned eye before each of four daily excitatory conditioning sessions. Postinfusion testing continued for four more excitatory conditioning sessions. All rats were given a final test session after muscimol infusions. The muscimol infusions inactivated the cerebellar nuclei, lateral anterior lobe, crus I, rostral crus II, and lobule HVI ipsilateral to the conditioned eye. Acquisition of excitatory conditioning was completely prevented by muscimol inactivation. In experiment 2, there were four experimental phases. Phase 1 consisted of excitatory conditioning. In phase 2, rats were given saline or muscimol infusions before conditioned inhibition training. Phase 3 consisted of continued conditioned inhibition training with no drug infusions. In phase 4, all rats received a retardation test in which the inhibitory stimulus was paired with the unconditioned stimulus. Muscimol infusions blocked the expression of conditioned responses during phase 2. However, robust conditioned inhibition was evident in phases 3 and 4. The findings indicate that conditioned excitation and inhibition depend on different mechanisms.

アルミナ水和物を配合したゴムの補強効果と難燃特性

Etylene-propylene-diene terpolymer (EPDM) filled with mixtures of aluminium hydrate, carbon black and silica were evaluated. The aluminium hydroxides used were gibbsite (Al(OH)3) and boehmite (AlO(OH)). Silane treated boehmite was also evaluated. Mechanical and flame retardancy tests were carried out in order to find the relative amounts of fillers which would give the best balance of properties. A composite consisting of 100phr of gibbsite and 50phr of silane-treated boehmite showed the best balance between flame resistance and mechanical properties.

A study of the effect of locust bean gum on the rheological behaviour and microstructure of a β-lactoglobulin gel at pH 7

The effect of locust bean gum (LBG), a non-gelling polysaccharide, on the thermal gelation of β-lactoglobulin, at 80 °C, and on the gel properties after quenching to 20 °C was studied by small deformation rheology and by confocal laser scanning microscopy (CLSM). The concentration of β-lactoglobulin was kept constant at 10 wt% and that of LBG varied from 0 to 0.78 wt%. For all the concentrations studied, the presence of LBG enhanced the aggregation rate and the strength of the protein gel, but the magnitude of these effects depended on the β-lactoglobulin/LBG ratio: 0.35 wt% LBG resulted only in a very slight increase of G′, whereas 0.45 wt% LBG caused a ~fivefold jump; for higher LBG concentrations, the differences between the systems were quite small. The linear viscoelastic behaviour, at 20 °C, was characterized over the 10−5 to 100 rad/s frequency range by combining the dynamic and retardation tests. Compliance data were converted from the time to the frequency domain. The viscoelastic plateau was seen to extend down in the 0.001–0.0001 rad/s range and its lower limit seemed not to vary much with LBG concentration. Its upper limit was visibly beyond 100 rad/s. The observed microstructure of the gels showed that they were two-phase and that the state of aggregation of β-lactoglobulin was influenced by the β-lactoglobulin/LBG ratio.

Safety signals from avoidance learning but not from yoked classical conditioning training pass both summation and retardation tests for inhibition.

In one experiment half of the animals were trained to avoid a signaled footshock by jumping (30 or 160 trials), whereas the rest of the animals received the same events as yoked. For all of them the termination of the warning signal and of the shock was followed by a safety signal. Several tests were conducted to assess the ability of the stimuli to suppress licking by measuring the latency in completing 25 consecutive licks in the presence of the stimuli. Fear of the warning signal and inhibitory properties of the safety signal (summation and retardation tests) were measured. The results showed that there were no differences in fear to the warning signal, and that the safety signal behaves as a conditioned inhibitor only for animals trained with a long avoidance procedure, but not in the yoked (classical conditioning) procedure. These results highlight the role played by the avoidance response and its consequences in avoidance learning.

Outcome-specific conditioned inhibition in Pavlovian backward conditioning.

In the present experiments, the outcome specificity of learning was explored in an appetitive Pavlovian backward conditioning procedure with rats. The rats initially were administered Pavlovian backward training with two qualitatively different unconditioned stimulus conditioned-stimulus (US-CS) pairs of stimuli (e.g., pellet --> noise or sucrose --> light), and then the effects of this training were assessed in Pavlovian-to-instrumental transfer (Experiment 1) and retardation-of-learning (Experiment 2) tests. In the transfer test, it was shown that during the last 10-sec interval, the CSs selectively reduced the rate of the instrumental responses with which they shared a US, relative to the instrumental responses with which they did not share a US. The opposite result was obtained when the USs (in the absence of the CSs) were presented noncontingently. In the retardation test, conditioned magazine approach, responding to the CSs was acquired more slowly when the stimulus-outcome combinations in the backward and the forward conditioning phases were the same, as compared with when they were reversed. These results are collectively in accord with the view that Pavlovian backward conditioning can result in the formation of outcome-specific inhibitory associations. Alternative views of backward conditioning are also examined.

A phenomenological analysis of wheat gluten viscoelastic response in retardation and in dynamic experiments over a large time scale

Dynamic measurements and retardation tests (creep and creep recovery) were combined systematically to characterise the different aspects of gluten rheology. Gluten flow behaviour exhibits extreme shear thinning and time-dependent viscosity. The viscoelastic contribution to the total strain behaves linearly over large strain and stress ranges; however, the material shows physical ageing and does not exhibit time translational invariance. In spite of these difficulties, it was possible, in the case of fresh gluten samples or after the material has been submitted to mechanical loading for a period long enough, to obtain the linear viscoelastic response over seven logarithmic decades of time or frequency by combining the data from dynamic measurements and from retardation tests. The method of Kaschta was used to calculate the discrete retardation spectrum from creep recovery data; the spectrum was then used to convert recovery data into storage and loss compliance and modulus. Converted recovery data match dynamic data satisfactorily in the case of fresh gluten. Some discrepancy was observed in the case of gluten submitted to previous mechanical history; it has been attributed to the effect of physical ageing. The storage and nonviscous loss compliance functions show that the extension of the viscoelastic plateau of gluten is very large. Their shape suggests a bimodal spectrum; however, this point would need further confirmation.

Low molecular weight protamine as an efficient and nontoxic gene carrier: in vitro study.

The structural similarity between low molecular weight protamine (LMWP), prepared by enzymatic digestion of protamine, and HIV-TAT protein transduction peptide suggested the feasibility of LMWP as an efficient carrier for delivering therapeutic genes while alleviating the cytotoxicity of currently employed gene carriers. LMWP was prepared by enzymatic digestion of protamine with thermolysine. The prepared LMWP peptide and TAT peptide, as well as their complexes with plasmid DNA (pDNA), were examined for cellular uptake behaviors by using confocal microscopy and flow cytometry. The complexation of pDNA and LMWP was monitored by gel retardation test as well as size and zeta potential measurements, and was then further assessed by DNase I protection assay. The transfection efficiency of pDNA/LMWP was examined by varying the pDNA content and charge ratio in the complex, and then compared with that of pDNA/PEI. Cytotoxicity induced by pDNA/LMWP and pDNA/PEI was also examined. Prepared LMWP showed similar transcellular localization behavior and kinetics to those of TAT, and efficiently transferred the pDNA into nucleus and cytoplasm in a short time period. The size and zeta potential of the pDNA/LMWP complex were 120 nm and 30 mV, respectively, which were adequately suitable for cellular uptake. After forming the complex, LMWP appeared to effectively protect pDNA against DNase I attack. The pDNA/LMWP complex showed significantly enhanced gene transfer than both naked pDNA and the pDNA/PEI complex, while exhibiting a markedly reduced cytotoxicity than that of the pDNA/PEI complex. The present study suggested that LMWP could be a useful and safe tool for enhancing delivery of bioactive molecules and therapeutic DNA products into cells when applied in gene therapy.

The role of temporal variables in inhibition produced through extinction

In two experiments with rats as subjects, the temporal characteristics of inhibition produced through extinction were investigated. Each experiment established two independent signals for unconditioned stimulus presentation, one trace and one delay. Following initial training, either the trace or the delay conditioned stimulus (CS) was massively extinguished. In Experiment 1, a summation test established that an extinguished delay CS (but not a neutral CS) passed a summation test with a delay, but not with a trace, transfer excitor, and an extinguished trace CS (but not a neutral CS) passed a summation test with a trace, but not with a delay, transfer excitor. In Experiment 2, a retardation test showed retarded behavioral control by an extinguished delay CS when the CS was retrained as a delay CS, but not as a trace CS, and by an extinguished trace CS when the CS was retrained as a trace CS, but not as a delay CS. The results are discussed in terms of contemporary theories of extinction.

Retardation of fatigue crack propagation by indentation technique

This paper used indentations to retard crack development and thus to prolong the crack growth life. The growth retardation resulting from the indentation-induced strain hardening and the crack closure due to indentation-induced residual stresses were explored. The retardation tests using 3–10 kN indentation loads were performed on different thickness specimens of AISI 4130 low alloy steel and AISI 304 stainless steel. These loads were applied using a hemispherical indenter to both sides of the expected crack path on the specimen surfaces. Loads of 4.5 kN and greater increased the microhardness at and around the indentation position, indicating that at those loads the hardness or the strain hardening contributed to retarding crack growth. In addition, all the loads caused different levels of crack closure. The greater the loads, the stronger were the crack closure effect and the accompanying growth retardation. In the 3.5 mm thick AISI 4130 specimens, a 10 kN load exerted the strongest growth retardation to arrest the post-indentation crack propagation.

Whatman plc, UK

Developing a strong, flame resistant, and thermally insulating structural material is essential for reducing energy consumption and improving safety in buildings. Wood is a pervasive structural material with natural thermally insulating properties. However, its flammability and insufficient mechanical strength compromises its safety, particularly in mid-rise and high-rise buildings that have higher safety and structural requirements. Herein, we demonstrate a strong, flame-retardant, and thermally insulating wood laminate featuring a compact structure that we synthesized by infiltrating delignified basswood with bentonite nanosheets, followed by hot-pressing to densify the material. Bentonite nanosheets can be infiltrated into the microchannel of the delignified wood to achieve a good compatible and 3D flame resistant protective surface. Flame retardant tests show that the peak heat release rate of this wood laminate is reduced by more than 50% compared to natural basswood. Additionally, the wood laminate does not start to burn until after 7 min of direct exposure to an open flame, and then self-extinguishing when removed from the igniting flame, suggesting the excellent flame resistance of the composite. The wood laminate also exhibits a high tensile strength of 330 MPa that is more than 8-times higher than the starting material. In addition, the wood laminate exhibits lower thermal conductivities of 0.2 and 0.18 W m−1 K−1 in the axial and radial direction, respectively. The demonstrated wood laminate shows great promise as a high-performance structural material with strong flame-retardant, thermally insulating, and mechanical robust properties that are needed for the construction of energy efficient buildings.

Blockade of GABAA receptors in the interpositus nucleus modulates expression of conditioned excitation but not conditioned inhibition of the eyeblink response.

The cerebellum and related brainstem structures are essential for excitatory eyeblink conditioning. Recent evidence indicates that the cerebellar interpositus and lateral pontine nuclei may also play critical roles in conditioned inhibition (CI) of the eyeblink response. The current study examined the role of GABAergic inhibition of the interpositus nucleus in retention of CI. Male Long-Evans rats were implanted with a cannula positioned just above or in the anterior interpositus nucleus before training. The rats were trained with two different tones and a light as conditioned stimuli, and a periorbital shock as the unconditioned stimulus. CI training consisted of four phases: 1) excitatory conditioning (8 kHz tone paired with shock); 2) feature-negative discrimination (2 kHz tone paired with shock or 2 kHz tone concurrent with light); 3) summation test (8 kHz tone or 8 kHz tone concurrent with light); and 4) retardation test (light paired with shock). After reaching a criterion level of performance on the feature-negative discrimination (40% discrimination), 0.5 microl picrotoxin (a GABAA receptor antagonist) was infused at one of four concentrations, each concentration infused during separate test sessions. Picrotoxin transiently impaired conditioned responses during trials with the excitatory stimulus (tone) in a dose-dependent manner, but did not significantly impact responding to the inhibitory compound stimulus (tone-light). The results suggest that expression of conditioned inhibition of the eyeblink conditioned response does not require GABAergic inhibition of neurons in the anterior interpositus nucleus.