Density-functional and shell-model calculations of the energetics of basal-plane stacking faults in sapphire

We report the generation of fullerenes and nanotubes using an arc discharge on graphite in a high-pressure nozzle. The vapour from the arc is quenched via collisions with helium gas, forming carbon clusters within a localized highpressure region. The carbon molecules are entrained in the gas jet as it expands into the vacuum and deposited onto a silicon substrate in a low-pressure (6 mT) environment. Mass spectroscopy measurements of the plasma reveal the presence of C molecules in the expanding plume. Microstructural examination of films deposited using this method revealed clustered regions of larger fullerenes and nanotubes surrounded by an amorphous matrix. Films containing fullerenes and nanotubes were found to be significantly harder and more elastic than amorphous carbon films deposited under identical parameters but without conditions for fullerene and/or nanotube formation.     

Identifying the character of intrinsic stacking faults in the A15 compound Nb3Al

The character of intrinsic stacking faults on {001} in the A15 intermetallic compound Nb₃Al has been investigated using energy-dispersive X-ray spectroscopy in a field-emission-gun transmission electron microscope. Line scans were obtained across edge-on faults with an electron beam of approximate diameter 0.5 nm and it was found that the Al concentration is enhanced at the fault. Taken in conjunction with crystallographic data obtained previously, this implies that a {004} layer composed of Nb atoms only is removed to form these intrinsic stacking faults in Nb₃Al. The configuration of these faults implies that they may form by Nb vacancy coalescence and could act as embryonic nuclei for the precipitation of the D8_bcompound Nb₂Al.     

Transformation of Shockley into Frank stacking faults in a ZnS 0.04 Se 0.96 /GaAs (001) heterostructure

We report the transformation of Shockley partial dislocations (PDs) into Frank PDs in lattice-matched ZnS 0.04 Se 0.96 /GaAs(001) as investigated by transmission electron microscopy. The ZnS 0.04 Se 0.96 layers, with a nominal thickness of 70 nm, were grown on GaAs(001) by metal-organic chemical vapour deposition at 350°C. We mainly find stacking-fault pairs on the (111) and planes that are bound by Shockley PDs with Burgers vector . Different reactions are observed between PDs taking place in situ in the electron microscope, leading to the transformation of Shockley PDs into Frank PDs with and stacking faults on the or planes.     

Threading dislocation with b=c+2a in 4H-SiC as determined by LACBED

The Burgers vectors of the so-called threading screw dislocations (a total of 28 dislocations) in 4H-SiC were determined by large-angle convergent-beam electron diffraction. A new type of TSD, that is, b = c + 2a dislocation, was identified. Thus, all of the four types of TSD predicted by Onda et al. [Phil. Mag. Lett. 93 (2013) p.591] were identified.     

Possible participation of D3 and D4 dopaminergic receptors on genital reflexes induced by cocaine in paradoxical sleep deprived male rats

Previous studies have demonstrated that paradoxical sleep deprivation (PSD) potentiates cocaine-induced genital reflexes in male rats and both D1 and D2 receptors may play a role in those effects, and to examine the possibility that such might involve other dopaminergic receptors, we investigated the effects of D3 and D4 receptor subtype antagonists on cocaine-induced reflexes in sleep-deprived rats. Separate groups of PSD rats received saline, D3 (U9919A; 0.75, 1.5 and 3 mg/kg) or D4 (L745870; 0.75, 1.5 and 3 mg/kg) antagonists prior to acute cocaine challenge. Results demonstrated that U9919A induced significant reduction in the number of animals that displayed erection and the frequency of erection at two smaller doses, while no significant difference was reported for the D4 receptor antagonist. Although our studies indicate that there is a relevant participation of D3 receptors in male sexual function, D4 receptors seem not to exert an essential role in this model.     

Polydipsia induced in rats by second-order schedules of reinforcement.

Three rats were exposed to a second-order schedule in which fixed-interval components ended either with food or with a brief stimulus that was never paired with food. Food and the brief stimulus occurred in a random sequence (variable-ratio 2 overall schedule). Another three rats were exposed to a similar second-order schedule, the only difference being that the food or the stimulus was presented independently of operant behavior (fixed-time components). The three rats exposed to the fixed-interval components licked at a water spout after each food presentation. These rats also licked in the intervals after the brief stimulus. Although the discriminative properties of food and of the brief stimulus were identical in relation to subsequent reinforcement, licking after the stimulus was less than after food. The three rats exposed to the second-order schedules with fixed-time components also licked at the water spout after food, but these rats did not lick consistently after brief stimulus presentations.     

Production of regular rhythm induced by external stimuli in rats

Animal Cognition - Rhythmic ability is important for locomotion, communication, and coordination between group members during the daily life of animals. We aimed to examine the rhythm perception...     

Mecamylamine prevents the enhancement of retention induced by lysine vasopressin in mice

Lysine vasopressin (0.03 microgram/kg, sc) enhanced retention of a one-trial, step-through inhibitory avoidance task when injected into male Swiss mice immediately post-training, as indicated by retention performance 48 h later. A low dose of the vasopressin antagonist, AAVP (0.01 microgram/kg, sc), did not significantly affect retention, whereas a higher dose (0.03 microgram/kg, sc) impaired retention. Neither lysine vasopressin nor AAVP modified latencies to step-through of mice that had not received a footshock during training. The simultaneous injection of AAVP (0.01 microgram/kg, sc) prevented the enhancement of retention induced by lysine vasopressin. The influence of lysine vasopressin on retention was antagonized by the simultaneous administration of mecamylamine (5 mg/kg, sc) but not by hexamethonium (5 mg/kg, sc), atropine (0.5 mg/kg, sc), or methylatropine (0.5 mg/kg, sc). A modulatory role of vasopressin on the activity of central cholinergic nicotinic mechanisms which participate in memory formation is suggested.     

Delayed backward conditioning of place preference induced by wheel running in rats

Backward conditioning of place preference has been obtained in hungry rats when wheel running (the rewarding US) is followed immediately by exposure to a distinctive chamber (the CS). We tested whether such backward conditioning would occur with a 10-min delay. In each of four paired exposures, a period of wheel running (2 or 22 h, in separate experiments) was followed by 10 min in the home cage and then 30 min in the CS chamber. Control rats were put in the CS chamber without wheel running. In other similar experiments, a 0-, 10-, or 30-min delay separated wheel running from exposure to the CS chamber. Reliable conditioned place preference (CPP) occurred when the delay was 0 or 10 but not 30 min. The strength of CPP decreased as the delay increased. These findings imply that the reward process initiated by wheel running remains active for some time after running stops. They support the view that the suppression of feeding produced by wheel running in hungry rats (activity anorexia) is mediated by this reward process.     

Type of motion in inverted self-motion perception induced by a foreground stimulus

Slowly moving foreground induces an illusory self-motion perception in the same direction as its motion direction (inverted vection). In this study, the effects of motion type of the foreground stimulus on inverted vection were investigated using a sample of 3 men and 1 woman. As indices of perceived strength of the inverted vection, duration and estimated magnitude were measured. Analysis of the psychophysical experiment indicated that a translating foreground induced inverted linear vection in the same direction as the stimulus motion. However, a rotating foreground did not induce an inverted roll vection. Statistical analyses indicate that there is a significant difference between two foreground motion conditions (Duration: t3=14.54, p <.01; Estimation: t3=16.92, p<.01). This result supports the hypothesis that eye-movement information is responsible for the occurrence of inverted vection.     

Modulations of muscle modes in automatic postural responses induced by external surface translations

The authors applied principal component analysis to investigate muscle activation patterns (M-modes) involved in the automatic postural responses induced by external surface perturbations. They focused on M-mode modulations as responses to the effects of practice, stability of the conditions and perturbed directions. While peak center of mass velocity reduced with practice, M-modes were similar with practice and across stability conditions. In contrast, atypical sway mode coactivations that combined proximal trunk muscles with distal muscles of the opposite lower extremity of the ventral-dorsal side were observed under the unstable conditions in both forward and backward perturbations after practice. In addition, M-modes in the forward translations were characterized by increased cocontraction patterns. Results suggest that compositions of the underlying M-modes show minor differences in each perturbed direction, but practice enhances coactivation patterns combining proximal muscles with distal muscles, and with accompanying cocontraction patterns, under more challenging conditions.     

Rapid and persistent suppression of feeding behavior induced by sensitization training in Aplysia

In Aplysia, noxious stimuli induce sensitization of defensive responses. However, it remains largely unknown whether such stimuli also alter nondefensive behaviors. In this study, we examined the effects of noxious stimuli on feeding. Strong electric shocks, capable of inducing sensitization, also led to the suppression of feeding. The use of multiple training protocols revealed that the time course of the suppression of feeding was analogous to that of sensitization. In addition, the suppression of feeding was present only at the time points in which sensitization was expressed. These results suggest that, in Aplysia, noxious stimuli may produce concurrent changes in neural circuits controlling both defensive and nondefensive behaviors.     

Aggressive behavior induced by electrical stimulation in the midbrain central gray of male rats

Electrical stimulation via electrodes implanted in the lateral hypothalamus may induce intraspecific aggressive behavior. Small electrolytic lesions placed via these electrodes resulted in a five– to tenfold increase in the current threshold for aggression. Degenerating fibers were stained by means of the Fink-Heimer method and could be followed caudally to the dorsal midbrain central gray and to the mammillary bodies. A few axons could be traced rostrally to the medial septum. Aggression could be induced from 10 of 112 electrodes implanted in the central gray; the other electrodes elicited either locomotion, vocalization, jump, or “alarm-like reactions.” The morphology of the induced aggression was similar to the morphology of the hypothalamically induced aggression, though it was often accompanied with motor disturbances and was less intense. Hypothalamic stimulation was combined with simultaneous central gray stimulation in rats with electrodes both in the hypothalamus and in the central gray. Hypothalamic thresholds for aggression could be lowered by this stimulation of the central gray, even when no aggressive responses were observed during central gray stimulation alone. This suggests that, although aggression is not manifest, electrical stimulation may activate neural tissue involved in aggressive behavior. It is concluded that in rats central gray and hypothalamus are part of the same neural network mediating intraspecific aggression.     

The development and the extinction of hyperthermia induced by conditioned avoidance behavior in rats

Hyperthermia was observed at the end of each conditioning session in rats trained to avoid electric shocks by jumping on a platform. The temperature rise was also observed after the conditioned behavioral response was well established and was elicited even in the absence of shocks. There was no tendency for the hyperthermia to diminish over the course of nine extinction sessions.     

Hepatic versus cerebral origin of stimulus for feeding induced by 2-deoxy-d-glucose in rats

Intravenous administration of 2-deoxy-D-glucose (2-DG), a competitive inhibitor of glucose utilization, increased the food intake of rats. Infusions of glucose or mannose abolished this effect, whereas equimolar fructose solutions did not affect 2-DG-induced feeding. Similar results were obtained when 2-DG and the hexoses were administered into the hepatic portal vein. These findings suggest that 2-DG elicits feeding due to glucoprivation at a site that is inaccessible to fructose. This site is likely to be in the brain, not the liver, because all three sugars can nourish peripheral tissue but only fructose cannot penetrate the blood-brain barrier. Moreover, 2-DG-induced feeding was abolished by intravenous infusion of beta-hydroxybutyrate, a substrate that can be oxidized by brain and other tissues but not by the liver.     

Modifications induced by neonatal steroids in reproductive organs and behavior of male rats.

Male rats injected on Day 3 neonatally with .01, .1, 1, 10, 100, or 1,000 micrograms of estradiol benzoate (EB), 10,000 microgram of testosterone propionate (TP), or sesame oil were subsequently examined for testicular, penile, and accessory organ development. Sexual behavior was evaluated during therapy with fluoxymesterone (FM) and then with TP. Estradiol benzoate in dosages greater than 1.0 micrograms delayed testicular descent, reduced the size and hormone responsiveness of reproductive organs, and decreased sexual behavior in a dose-dependent manner. The 10,000-microgram dosage of neonatal TP delayed testicular descent and reduced sexual behavior to levels near those of the 10--100 micrograms EB groups, but it produced no significant penile or accessory organ changes. Neither reduced peripheral organ development nor inhibited neonatal testicular secretions fully explain reductions in male behavior following large dosages of neonatal TP. Neonatal androgen may reduce the responsiveness of central nervous system neurons governing male sexual behavior after being converted to estrogen or by directly altering steroid receptor systems.