Decreased venous return is neither sufficient nor necessary to elicit ultrasonic vocalisations of infant rat pups.

It has been proposed that all ultrasonic vocalizations (USVs) in young rats are by-products of a cardiovascular response to decreased venous return, the abdominal compression reaction. To test the hypothesis, venous return was decreased in infant rats while USV and cardiovascular measures were monitored. Neither injection of the vasodilator sodium nitroprusside nor blood withdrawal from the superior vena cava or carotid artery elicited USV from pups in their home cage. Thus, decreased venous return by itself is not sufficient to elicit USV. To test whether venous return is a necessary mechanism for USV production, 5% dextrose in water or blood was infused intravenously into isolated pups that were producing USV. This artificial increase of venous return did not affect the rate of USV. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The isolation and companion comfort responses of 7- and 3-day-old rat pups are modulated by drugs active at the opioid receptor.

Rat pups emit ultrasonic vocalizations (USVs) when isolated in a novel environment. In 10-day-olds, USV has been shown to be reduced by either the administration of 0.125 mg/kg morphine (MOR) or the presence of a littermate; these effects were both reversed by naltrexone (NLX), an opioid receptor blocker. The present study reports that the same dose of MOR produced NLX-antagonized quieting without sedation in 7- and 3-day-old pups; higher doses of MOR decreased USV but produced motor deficits as well. The 0.125 mg/kg dose of MOR is less effective in reducing USV in 3- and 7-day-olds; calling rates declined by no more than 42%, compared with 65% at 10 days of age. The presence of a companion also lowered the USV of 3- and 7-day-olds by a lesser amount (55–57%) than the 67% seen in 10-day-olds or the 90% decline when pups are 2 weeks old. This suggests that age-related changes in the opioid system may be relevant to the increased salience of a social companion that comes with maturity. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Change in the electrical resistance of porous powder and fiber compacts during heating and compressive loading

The effect of heating at a constant rate in vacuum and compressive loading in the pressing direction on the electrical resistance of fiber compacts was investigated. Considerable decrease in electrical resistance occurred at 200–400°C. The significant effect of small compressive deformations on the electrical resistance of fiber compacts, and the absence of such in powder compacts, as well as a hysteresis in resistance occurring upon loading and unloading the fiber compacts, is explained by the nature of interparticle bonds. These are rigid in the powder compacts, and flexible-rigid in the fiber compacts.     

Brief Maternal Interaction Increases Number, Amplitude, and Bout Size of Isolation-Induced Ultrasonic Vocalizations in Infant Rats (Rattus norvegicus).

The number, amplitude, duration, and bout structure of isolation-induced ultrasonic vocalization (USV) of infant rats (Rattus norvegicus) were measured on postnatal Day 10. Measurements were made before and after a brief, 1-min, active interaction with their mother or before and after a "pick-up" control procedure. Consistent with prior studies, the number of USVs emitted was significantly increased in the period following the maternal reunion but not after the control procedure. The average amplitude of USVs was also greater following maternal reunion. Finally, analyses characterizing the bout structure of USV production indicated that the average bout size (i.e.. number of USVs/bout) was increased severalfold following the reunion with the mother, accounting for the greater rate of USV production during the second isolation period. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Strength of Unsintered Powder Compacts with Axial and Radial Loading

Cohesion and the internal friction angle characterizing the fracture region for the contour of Drucker-Prager limiting states are determined by experiment for green copper and iron powder compacts. With an increase in density the increase in cohesion is more marked for iron compacts. With an increase in compaction density the internal friction angle increases from 67° to 70° for copper compacts and it decreases from 70.5° to 69.9° for iron powder specimens.     

THE PROPERTIES OF POROUS NICKEL PRODUCED BY PRESSING AND SINTERING

Abstract

The effects of compacting pressure and of sintering temperature and time on the properties of porous sintered nickel compacts have been studied, using three carbonyl and two reduced nickel powders. For all five powders, the density of the green compacts and the porosity of the sintered compacts were linearly related to the log compacting pressure. Similar relationships with pressure were observed for strength and electrical conductivity.

Photomicrographs of sections through the sintered compacts made from the reduced nickel powders show that there are pores in two different size ranges, originating from the porosity between the original powder particles and the pores within the particles. It is concluded that sintered compacts from all five powders containing 40–50% porosity have adequate strength and conductivity for use in fuel-cell electrodes.     

STUDIES OF THE SINTERING AND HOMOGENIZATION OF NICKEL-COPPER COMPACTS

Abstract

Studies are described of the progress of sintering and alloying in compacts of similar compositions made from nickel-coated copper, copper-coated nickel, and mixed nickel and copper powders. Density losses observed in the early stages of sintering were lower in magnitude and were more quickly recovered in the case of the composite powder compacts. Alloying by diffusion at both 1900 and 2200°F (1040 and 1205°C) progressed most rapidly in compacts prepared from nickel-coated copper powders, and the probable reasons for this observation are discussed in detail. Electrical resistivity was used to follow homogenization of the compacts, and samples were rendered nearly 100% dense by cold working and annealing before making resistivity measurements. Resistivity / sintering-time curves for dense specimens showed no maxima of the type reported by earlier investigators for porous compacts, which were attributed to alloying effects.     

Influence of Manganese Oxide and Silica on the Morphological Structure of Hematite Compacts

Dry compacts of pure Fe₂O₃ and Fe₂O₃ doped with either (2–6 mass%) MnO₂, (2.5–7.5 mass%) SiO₂ or with both (2–6% MnO₂ + 7.5% SiO₂) were indurated at 1373 K for 6 hours and physically and chemically characterized. The fired compacts were isothermally reduced with pure CO gas at 1073–1373 K. The O₂‐weight loss was continuously recorded as a function of time using TGA technique. The external volume of pure and doped compacts was measured at different reduction conditions and the volume change was calculated. The structural changes accompanying the reduction process were visually and microscopically examined and the different phases were identified by X‐ray diffraction analysis. After firing, manganese ferrite (MnFe₂O₄) phase was identified in MnO₂‐doped compacts. In pure Fe₂O₃ compacts, the external volume of compacts was increased with reduction temperature, showing a maximum swelling value at 1198 K. Catastrophic swelling was observed in MnO₂‐doped Fe₂O₃ compacts, the volume change increased with MnO₂ content showing catastrophic swelling in compacts containing 6%MnO₂ at 1248 K. The catastrophic swelling was attributed to the formation of dense metallic iron whiskers and plates in a highly porous structure. Unlike in MnO₂‐doped samples, no considerable volume changes were detected in SiO₂‐doped Fe₂O₃ and (MnO₂ + SiO₂)‐doped Fe₂O₃ compacts where the presence of silica greatly hindered the swelling phenomenon at all reduction temperatures.     

Effect of boron on vacuum carburising depth of iron powder metallurgy compacts

Abstract

The work was aimed at determining the effect of boron on vacuum carburising of iron compacts with density over 7·2 g cm^–3. An attempt was made to determine the effectiveness of boron on carbon diffusion rate into the material of compacts with no additional effect of interconnected porosity. Vacuum carburising of compacts made of iron powder with an addition of boron was carried out at 1050°C in a laboratory vacuum furnace.

The effect of boron content within 0·005 to 0·02% on the vacuum carburising depth was analysed. It was found that the boron addition up to 0·01% increased the carburising depth by ～0% in comparison with the compacts of pure iron.     

OBSERVATIONS ON THE SINTERING OF COMPACTSFROM A MIXTURE OF IRON AND COPPER POWDERS

Abstract

Three grades of iron powder-an atomized steel powder, a sponge iron powder reduced from magnetite with carbon, and a powder reduced from mill scale with hydrogen were mixed with 3% of copper powder and pressed into compacts. The diametral dimensional changes of the compacts during sintering below and above the melting point of copper were measured, their microstructures examined, and both related to the characteristics of the powders, particularly their specific surface. During sintering below the melting point of copper, compacts of all three powders shrank. Micrographic examination showed that the copper is transported by solid-state diffusion along the surfacesand grain boundaries of the iron powder particles. During sintering above the melting point of copper, compacts of the atomized and the MH-100 sponge iron powders grew while those of the hydrogen reduced mill-scale powder shrank. This phenomenon is related to the different mode of penetration of liquid copper in the compacts from the three powders, observed in the microstructures of the compacts.     

Microstructure and tensile properties of compacted,mechanically alloyed,nanocrystalline Fe-AI

Data on mechanical properties of nanocrystalline materials have been limited, due in part to the difficulty in producing consolidated nanocrystalline materials of sufficient quantity for characterization and evaluation. A second problem is consolidation and retention of the nanostructure. A vacuum hot-pressing consolidation program has been developed to produce full-dense compacts from attrition milled, mechanically alloyed, nanograin micron-size particles of Fe-2 wt pet Al powder. The resulting compacts were of sufficient size to allow evaluation of microstructure, density, hardness, and tensile properties. The compacted microstructure was a composite of pure iron submicrograins and Fe-A1 nanograin clusters. Tensile strength was found to be proportional to the sample’s density squared. For full-dense compacts, tensile strength of nanocrystalline compacts approaching 1 GPa was obtained.     

Ultrasonic vocalization, laryngeal braking, and thermogenesis in rat pups: A reappraisal.

Tested the hypothesis that the respiratory events underlying rat pup ultrasonic vocalization (USV) facilitate brown adipose tissue (BAT) thermogenesis, as proposed by M. S. Blumberg and J. R. Alberts (1990). Laryngeal denervation of tracheostomy were used to reduce or eliminate laryngeal braking and prevent USV in 9- to 10-day-old pups during recovery from deep hypothermia and during cooling induced by isolation for 1 hr at room temperature. Both forms of devocalization slowed rewarming of hypothermic pups, but neither had any effects on cooling rate or BAT thermogenesis in normothermic pups that were allowed to cool from 35°C to 29°C. Physiological effects of laryngeal braking on thermogenesis appear to be limited to conditions, such as severe hypothermia, in which ventilatory and oxygen transport functions are compromised. Results have implications for understanding the regulation and evolution of USV. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Synthesis of γ-TiAl by Reactive Spark Plasma Sintering of Cryomilled Ti and Al Powder Blend: Part II: Effects of Electric Field and Microstructure on Sintering Kinetics

The current study shows the dramatic effect of an electric field (EF) and use of nanosized cryomilled grains on accelerating sintering kinetics during spark plasma sintering of blended elemental powder compacts of Ti₅₃Al₄₇ targeted to produce γ-TiAl intermetallic compounds. The EF had the dominating effect since it reduced the activation barrier for diffusion through Al₃Ti leading to faster growth of Al₃Ti; the precursor to γ-TiAl. The Avrami exponent (n) determined for the micrograin compact lies between 1.0 and 1.5, which indicates that reaction sintering is controlled by bulk diffusion in these compacts, while for cryomilled compacts this is between 0.7 and 1.0 suggesting the important role of dislocations and grain boundaries on the transformation during reaction sintering. The activation energies were found to be in increasing order as: cryomilled compacts with EF (182 kJ/mol); micrograin compacts with EF (290 kJ/mol); cryomilled compacts without EF (331 kJ/mol); and micrograin compacts without EF (379 kJ/mol). The cryomilled microstructure also enhanced the sintering kinetics because of the availability of faster diffusing paths in Al and Ti including larger grain boundary area and dislocation density.     

Effect of conventional and microwave sintering on the properties of yttria alumina garnet-dispersed austenitic stainless steel

The current study examines the effect of heating mode, temperature, and varying yttria alumina garnet (YAG) addition (5 and 10 wt pct) on the densification and properties of austenitic (316L) stainless steel. The straight 316L stainless steel and 316L-YAG composites were heated in a radiatively heated (conventional) and 2.45 GHz microwave sintering furnace. The compacts were consolidated through solid state as well as supersolidus sintering at 1200 °C and 1400 °C, respectively. Both 316L and 316L-YAG compacts couple with microwaves and heat to the sintering temperature rapidly (∼45 °C/min). The overall processing time was reduced by about 90 pct through microwave sintering. As compared to conventional sintering, compacts sintered in microwaves exhibit higher densification and finer microstructure but no corresponding improvement in mechanical properties and wear resistance. This has been correlated to elongated, irregular pore structure in microwave-sintered compacts.     

Dynamic and static strengths of pressed specimens from single-fraction iron and rock salt powders

Conclusions A study was made of the strength of compacts from single-fraction iron and rock salt powders under dynamic and static loads. It has been demonstrated that the mechanism of rupture of compacts from iron and rock salt powders is apparently identical, so that the nature of the chemical bond in the material determines only the absolute value of strength of compacts.Translated from Poroshkovaya Metallurgiya, No. 2 (98), pp. 89–92, February, 1971.     

FACTORS AFFECTING THE RADIAL AND AXIAL SHRINKAGE IN SOFT-METAL POWDER COMPACTS

Abstract

The variables affecting the radial: axial (R/A) shrinkage ratio in copper-powder compacts have been investigated. The value of R/A is linearly dependent on compacting pressure, green density, and sintering temperature, and also increases with decrease in the particle size of the powder. The observed variation of R/A is attributed to the differences in density in the green compacts, which result in anisotropic stresses in sintering. Surface-tension forces or residual stresses introduced during compaction cannot alone be regarded as the main driving forces responsible for shrinkage; anisotropic stresses also play an important role in the densification of metal-powder compacts. By proper control of these variables, parts can be produced from the compacts to close dimensional tolerances.     

Characteristic of interconnected porosity in ferrous PM compacts

Abstract

The purpose of this work was to quantitatively describe the interconnected porosity in iron compacts, both in macro- and microscale. Size and volume fraction of micro-, meso- and macropores were examined in the compacts with density within 5˙6–6˙4 g cm^?3, made in laboratory conditions of two iron powders: NC100˙24 and ASC100˙29 manufactured by Höganäs Company. The interconnected porosity was determined using the method based on measuring the sorption isotherms of CO₂ and benzene at T=25°C in static conditions in a high vacuum gravimetric appliance equipped with McBain–Bakr weighers.

Volume distributions of individual size classes of micro- and mesopores in the compacts made of both iron powders with fixed density were compared.

Relationships between density and the interconnected micro- and macroporosity of the examined compacts were determined.     

IRON-COPPER-TIN SINTERED COMPACTS

Abstract

A wide range of copper and tin powder additions to iron powder sintered compacts hasbeen studied. From mechanical-property tests it has been shown that when using sinteririg temperatures of 900–1100°C in nitrogen/10% hydrogen atmospheres there is an optimum copper: tin ratio of 15:2. The mechanical properties obtained from compacts pressed from iron mixed with 4% copper+tin in this ratio and sintered at 900°C were similar to those obtained from iron ?l0% copper powder compacts sintered at 1100°C. Moreover, the iron-copper-tin components showed improved dimensional accuracy.

In a further series of experiments, it was shown that tin additions to iron-copper alloy compacts increased the solubility of iron in the liquid phase at the sintering temperature and simultaneously decreased the rate of diffusion of copper into the iron particles. At the same time, tin improved the wettability of the liquid, reducing its surface tension and allowing it to disperse more completely throughout the matrix. The mechanical properties of compacts containing larger amounts of tin were decreased by the presence of brittle compounds, although the sintering rate was increased. It is concluded that the optimum properties of iron-copper-tin compacts are obtained by making correct additions of copper and tin to the iron powder and giving careful consideration to the sintering atmosphere.     

Effect of storage on the properties of ultrafine nickel and copper powders

Conclusions Storage of ultrafine powders under unfavorable conditions, in particular in air, adversely affects their processing properties, bringing about marked changes in their compressibility and sinterability. Storage in argon of technical purity does not offer effective protection to particles against surface oxidation. Storage of UFPs in the form of compacts of relative density 0.5–0.6 almost completely inhibits the powder oxidation process, and granulated powders produced by disintegrating compacts possess superior processing characteristics A simple method is proposed for estimating the oxygen content of a powder from the electrical resistivities of compacts.Translated from Poroshkovaya Metallurgiya, No. 10(274), pp. 74–78, October, 1985.     

Fear conditioning to discontinuous auditory cues requires perirhinal cortical function.

Pretraining lesions of rat perirhinal (PR) cortex impair fear conditioning to ultrasonic vocalizations (USVs) but have no effect on conditioning to continuous tones. This study attempted to deconstruct USVs into simpler stimulus features that cause fear conditioning to be PR-dependent. Rats were conditioned to one of three cues: a multicall 19-kHz USV, a 19-kHz discontinuous tone, and a 19-kHz continuous tone. The discontinuous tone duplicated the on/off pattern of the individual calls in the USV, but it lacked the characteristic frequency modulations. Well-localized neurotoxic PR lesions impaired conditioning to the USV, the discontinuous tone, and the training context. However, PR lesions had no effect on conditioning to the continuous tone. The authors suggest that the lesion effects on fear conditioning to both cues and contexts reflect the essential role of PR in binding stimulus elements together into unitary representations. (PsycINFO Database Record (c) 2010 APA, all rights reserved)