Reversal of particle size/shock sensitivity relationship at small particle size for pressed heterogeneous explosives under sustained shock loading

Abstract

Shock initiation of pressed heterogeneous explosives has been reviewed. The key processes of ignition and buildup and their relative importance under sustained and short duration shock are described. Particle size effects on shock sensitivity are shown to depend on both density (ZTMD) and shock duration. A series of RDX samples of narrow particle size range were subjected to sustained shock (gap test). Sensitivity increased over the series 250 < 138 < 100.0 < 21.2 μm median particle size but decreased for a 3.9 μm sample. These results combined with earlier published data support published modelling studies which predict decreased shock sensitivity at small particle size.     

Rapid and robust olfactory conditioning with milk before suckling experience: Promotion of nipple attachment in the newborn rat.

An olfactory conditioning paradigm tested the hypothesis that newborn rats are able to learn about events associated with their first experience with milk as early as 3–5 hr after birth. Exposure to lemon odor (conditioned stimulus, [CS]) paired with intraoral milk infusions (unconditioned stimulus, [US]) resulted in strong conditioning: In the presence of the CS, sustained attachment occurred to an empty nipple as if it provided milk, whereas pups in control conditions showed little attachment. A single CS–US pairing was sufficient for strong conditioning, which was evident with a trace interval as long as 60 s. Conditioning was robust enough to promote attachment to a nipple providing saline, which is aversive to the newborn rat, and comparably strong conditioning occurred with sucrose or saccharin as the US. These findings suggest that olfactory conditioning has the potential to modify suckling behavior. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Alterations in the reinforcing efficacy of cocaine in adult rats following prenatal exposure to cocaine.

Adult male rats gestationally exposed to cocaine and nonexposed control offspring were examined for differences in operant responding for cocaine and sucrose reinforcement. Offspring were derived from dams that had received subcutaneous injections of 40 mg/kg/3cc cocaine hydrochloride daily on gestational Days 8–20 and nontreated control dams. Although no prenatal treatment differences were seen when the animals lever pressed for sucrose pellets on a progressive-ratio (PR) schedule, adult offspring prenatally exposed to cocaine were observed to exhibit an enhanced rate of cocaine intravenous self-administration on a fixed-ratio 5 (FR-5) schedule along with a marked decrease in break point on the PR reinforcement schedule. These results suggest that the reinforcing efficacy of cocaine may be reduced in animals with a prenatal history of cocaine exposure. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Conditioned opioid activity in the rat fetus.

Classical conditioning in the rat fetus (Embryonic Day 20) was investigated in 4 experiments. Reexposure to a CS (sucrose), after 3 pairings with an unconditioned stimulus (UCS; milk), reduced fetal facial wiping in a bioassay of perioral cutaneous responsiveness. Reduced responsiveness was evident only in Ss that received paired presentations of the CS and UCS and cannot be attributed to habituation, sensitization to the CS, or protracted effects of UCS exposure during conditioning trials. Fetuses attended to the chemosensory, not the tactile, qualities of the sucrose infusion during CS reexposure. Changes in fetal responsiveness resulted from conditioned activity in the endogenous opioid system, specifically at mu opioid receptors. These data confirm that the rat fetus is capable of exhibiting a conditioned opioid response in utero. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Monolithic integration of an InP/InGaAs four-channel transimpedance optical receiver array

Fully functional four-channel transimpedance receiver array OEICs have been fabricated on 2" diameter InP substrates. Each receiver channel has a bandwidth of 200 MHz and an average input equivalent noise current of around 6 pA/ square root (Hz). The array chip is 3.7 mm*3.2 mm in size and contains 88 components. This is believed to represent the highest level of optoelectronic integration yet reported on InP.<>     

Age-related differences in short-term retention of separable elements of an odor aversion.

The rate of forgetting over short intervals was tested in preweanling rats, 8, 12, or 18 days postnatal, using procedures that may have analytical advantages over other tests of short-term retention. Separate tests of retention were conducted for the simple occurrence of an odor and for the occurrence of an odor paired with a mild footshock. Forgetting of odors with either of two histories, incidental or target, was more rapid the younger the preweanling, over intervals of less than an hour. There was some indication of more rapid forgetting for incidental than target odors. Finally, although exposure to a CS– (conditioned stimulus [an odor not paired with footshock]) was necessary for conditioning of the CS+ (an odor paired with footshock) in rats 8 or 12 days of age, exposure to a CS– had no influence on conditioning of the CS+ in preweanlings 18 days of age. The age-related differences in forgetting over intervals less than an hour long suggest that substantial age-related differences in forgetting can occur that, it is likely, are not accounted for by differential growth. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Effects of fasting and 3,3',4,4',5,5'-hexabromobiphenyl on plasma transport of thyroxine and retinol: fasting reverses elevation of retinol

Male Wistar rats were injected ip with 0 or 20 mg/kg 3,3',4,4',5,5'-hexabromobiphenyl and blood samples were collected 1, 3, 6, 7, and 8 d later. At 8 d after the injection, serum retinol was increased 30% and serum thyroxine was decreased 26% relative to control values. These effects were apparently unrelated to transthyretin in that the biphenyl did not alter the proportion of thyroxine binding in vitro to the prealbumin fraction of serum proteins. Separate groups of control and HBBP-injected rats did not receive food on d 7 (i.e., 24-h fast) and d 8 after injection (i.e., 48-h fast). Fasting decreased the serum retinol and thyroxine concentrations as well as the proportion of thyroxine binding in vitro to the prealbumin fraction of serum. The decreases in retinol and thyroxine concentrations associated with fasting are therefore ascribed to a decrease in the concentration of transthyretin in circulation.