Bright laser-driven neutron source based on the relativistic transparency of solids.

Neutrons are unique particles to probe samples in many fields of research ranging from biology to material sciences to engineering and security applications. Access to bright, pulsed sources is currently limited to large accelerator facilities and there has been a growing need for compact sources over the recent years. Short pulse laser driven neutron sources could be a compact and relatively cheap way to produce neutrons with energies in excess of 10 MeV. For more than a decade experiments have tried to obtain neutron numbers sufficient for applications. Our recent experiments demonstrated an ion acceleration mechanism based on the concept of relativistic transparency. Using this new mechanism, we produced an intense beam of high energy (up to 170 MeV) deuterons directed into a Be converter to produce a forward peaked neutron flux with a record yield, on the order of 10(10) n/sr. We present results comparing the two acceleration mechanisms and the first short pulse laser generated neutron radiograph.

Effects of natal habitat odour, reinforced by adult experience, on choice of oviposition site in the mosquito Aedes aegypti.

The effects of natal experience on the oviposition behaviour of adult female mosquitoes were investigated in the laboratory using Aedes aegypti (L.) (Diptera: Culicidae). 'Treatment' mosquitoes were exposed to a dilute repellent (inducing stimulus) in their breeding water (aquatic stages) and/or in the air (adults) during various combinations of life stages [larval only (L regime); larval and pupal (LP regime); larval, pupal and emergent adult (LPE regime); larval, pupal, emergent adult and adult (LPEA regime); pupal, emergent adult and adult (PEA regime); adult only (A regime)]. 'Control' mosquitoes were raised in an identical manner, but were not exposed to the inducing stimulus. The oviposition behaviour of treatment and control females was assessed in an oviposition assay that presented a choice of water with or without the inducing stimulus. Of the 435 mosquitoes tested in the experiment, 176 were non-distributors (i.e. laid all of their eggs in only one of the choices). Treatment females (distributors plus non-distributors) reared in the presence of the inducing stimulus throughout their lives (LPEA regime) showed a significant preference for the oviposition option containing the inducing stimulus (24/36 females) compared with corresponding controls (5/39 females). Distributors reared under the LPEA and PEA regimes also showed this preference (6/6 treatment vs. 2/29 control females, and 13/18 treatment vs. 7/23 control females, respectively). Females that had been exposed to the inducing stimulus as either immatures or adults only showed no preference for, and some showed an aversion to, the treatment oviposition option. This is interpreted as evidence for a natal habitat preference induction (NHPI) in this species, albeit one that requires extensive reinforcement in the adult stage. This adult experience-reinforced NHPI (AER-NHPI) is discussed in terms of its adaptive significance for container breeders, the possible timing mechanism and sensory basis of induction and potential practical consequences.

Observation of persistent species temperature separation in inertial confinement fusion mixtures.

The injection and mixing of contaminant mass into the fuel in inertial confinement fusion (ICF) implosions is a primary factor preventing ignition. ICF experiments have recently achieved an alpha-heating regime, in which fusion self-heating is the dominant source of yield, by reducing the susceptibility of implosions to instabilities that inject this mass. We report the results of unique separated reactants implosion experiments studying pre-mixed contaminant as well as detailed high-resolution three-dimensional simulations that are in good agreement with experiments. At conditions relevant to mixing regions in high-yield implosions, we observe persistent chunks of contaminant that do not achieve thermal equilibrium with the fuel throughout the burn phase. The assumption of thermal equilibrium is made in nearly all computational ICF modeling and methods used to infer levels of contaminant from experiments. We estimate that these methods may underestimate the amount of contaminant by a factor of two or more.

Characterization of the Mercury pulsed power x-ray source spectrum using multichannel density aerogel Cherenkov detectors.

The Aerogel Cherenkov Detector for Cygnus (ACD/C) is a time-dependent, x-ray spectral detector that uses SiO2 aerogels spanning an index of refraction (n = 1.02-1.07) corresponding to a 1.1-2.3 MeV x-ray energy threshold. The ACD/C was developed for pulsed power x-ray sources like Cygnus located at the Nevada National Site and Mercury located at the Naval Research Laboratory (NRL). Aerogels sit between the measurement capabilities of gas (>2 MeV) and solids such as fused silica (>0.3 MeV). The detector uses an aluminum converter to Compton scatter incoming x-rays and create relativistic electrons, which produce Cherenkov light in an aerogel or a fused silica medium. The ACD/C was fielded at the NRL when Mercury was tuned to produce up to 4.8 MeV endpoint bremsstrahlung. Despite a high radiation and electromagnetic interference background, the ACD/C was able to achieve high signal over noise across five aerogel densities and fused silica, including a signal to noise for a 1.1 MeV aerogel threshold. Previous experiments at Cygnus observed a signal that was comparable to the noise (1×) at the same threshold. The ACD/C observed time-resolved rise and fall times for different energy thresholds of the photon spectrum. Monte Carlo simulations of the ACD/C's aerogel response curves were folded with a simulation of Mercury's photon energy spectrum and agree within the error to the observed result.

Visualization of expanding warm dense gold and diamond heated rapidly by laser-generated ion beams.

With the development of several novel heating sources, scientists can now heat a small sample isochorically above 10,000 K. Although matter at such an extreme state, known as warm dense matter, is commonly found in astrophysics (e.g., in planetary cores) as well as in high energy density physics experiments, its properties are not well understood and are difficult to predict theoretically. This is because the approximations made to describe condensed matter or high-temperature plasmas are invalid in this intermediate regime. A sufficiently large warm dense matter sample that is uniformly heated would be ideal for these studies, but has been unavailable to date. Here we have used a beam of quasi-monoenergetic aluminum ions to heat gold and diamond foils uniformly and isochorically. For the first time, we visualized directly the expanding warm dense gold and diamond with an optical streak camera. Furthermore, we present a new technique to determine the initial temperature of these heated samples from the measured expansion speeds of gold and diamond into vacuum. We anticipate the uniformly heated solid density target will allow for direct quantitative measurements of equation-of-state, conductivity, opacity, and stopping power of warm dense matter, benefiting plasma physics, astrophysics, and nuclear physics.

Maternal sensitivity during infancy and subsequent life events relate to attachment representation at early adulthood.

A prospective longitudinal research study of 86 prematurely born children from birth to age 18 years provided empirical evidence for continuity from infancy experience to representations of attachment at age 18 years. Young adults whose representation of attachment was dismissing had been objectively observed during infancy, 16-17 years earlier, to receive less sensitive maternal care than those infants who were later judged at early adulthood to have secure or preoccupied representations. Infancy experience alone did not differentiate young adults with secure representations from those with preoccupied representations. Rather, adverse life events through age 12, particularly parental divorce, reduced the likelihood of secure representations and increased the likelihood of preoccupied representations. The absence of adverse life events did not increase the likelihood of security for those who had not experienced early sensitive caregiving.

Single-frequency, injection-seeded Ti:sapphire ring laser with high temporal precision.

A three-mirror Ti:sapphire ring laser with a cavity length of 11 cm is injection seeded with a single-mode laser diode operating at 784 nm. The seed beam is injected into the ring cavity through the output coupler. The incident seed power is 11 mW. The ring laser is pumped with a frequency-doubled Nd:YAG laser. An efficiency of 40% is demonstrated. With the seed beam present, oscillation in the ring cavity is unidirectional, and the output is single frequency. The duration of the output pulse is 4 ns FWHM, and the temporal jitter with respect to the 532-nm pump pulse is less than +/-300 ps. The spatial profile of the output beam is near diffraction limited (M(2) < 1.1).

Continuity and discontinuity of attachment from infancy through adolescence.

This study reports relations between infant Ainsworth Strange Situation classifications, negative life events, and Adolescent Attachment Interview classifications. Overall, the stability of secure versus insecure classifications was 77%, and infant attachment classification was a significant predictor of adolescent attachment classification. Chi-square analyses indicate that negative life events are significantly related to change in attachment classification. The sample (n = 30) is drawn from the Family Lifestyles Project (FLS), an ongoing longitudinal study of children's development within the context of nonconventional family lifestyles. The distribution of family lifestyles within this study, unlike those in the full FLS sample, represent a higher proportion of conventional two-parent families (40%). There were no differences between adolescents reared in conventional or nonconventional families in the distribution of adolescent attachment security, the experience of negative life events, or the continuity of attachment from infancy through adolescence.

Children's relationships with caregivers: mothers and child care teachers.

Infant, toddler, and preschool children's relationships with mothers and teachers were examined in this study. 110 children were observed with their mothers during child care arrivals and reunions. 403 children were observed with their teachers in child care. 3 categories of relationships were derived from these observations. Children in the secure relationship category experienced more teacher involvement than children in the avoidant or ambivalent relationship categories. Children in the ambivalent relationship categories experienced more teacher involvement than children in avoidant relationship categories. A subsample (n = 23) of children were seen with their mothers both during child care arrivals and reunions and in the Strange Situation. Relationship classifications were similar.

Children's relationships with child care teachers: stability and concordance with parental attachments.

In order to examine caregiving relationships of children enrolled in childcare, two longitudinal samples of children, n = 72 and n = 106, were followed from infancy through preschool. Maternal attachment as assessed by the Strange Situation, 4-year-old reunion behavior, and by the Attachment Q-Set tended to be stable across time. Children's teacher-child relationship quality, as measured by the Attachment Q-Set, was stable if the teacher remained the same. When the teacher changed, teacher-child relationship quality tended to be unstable until the children were 30 months old. After 30 months, relationship quality with teachers tended to be stable regardless of whether or not the teacher changed. Maternal and teacher relationships were nonconcordant. There were few interactions between adult caregiver relationship quality and age of entry into child care or intensity of child care.

Systemic and developmental toxicity of dermally applied syntower bottoms in rats.

Syntower bottoms (STB) was evaluated for subchronic and developmental toxicity. In the subchronic study, undiluted STB was applied on the shaved backs of male and female rats at dose levels of 0, 8, 30, 125, and 500 mg/kg for 13 weeks, 5 days per week. Exposure sites were not covered. In the developmental toxicity study, STB was similarly applied, but to pregnant rats at dose levels of 0, 8, 30, and 125 mg/kg on Gestation Days 0-19. In addition, 4 mg/kg was dosed as 8 mg/kg every other day, starting on Gestation Day 0, and 500 mg/kg was dosed on Gestation Days 10-12. Evidence of toxicity observed in the subchronic study included death, decreased body weights, aberrant serum chemistry and hematology values, altered organ weights, and histopathologic changes in a variety of organs. A no observed adverse effect level for systemic toxicity could not be established. Evidence of maternal toxicity was observed at all exposure levels in the development study. Regardless of the length of the exposure period, STB was toxic to the developing conceptus. Evidence of developmental toxicity observed included increased resorptions with a concomitant decrease in litter size and reduced fetal body weights. Cleft palate was observed in fetuses exposed in utero to STB during Gestation Days 10-12 at 500 mg/kg. No evidence of teratogenicity was observed when the exposure period was throughout gestation. Ossification delays were observed in fetuses exposed in utero to STB at doses in excess of 4 mg/kg. A no observed adverse effect level for maternal and developmental toxicity could not be established.

Maternal, teacher, and child care history correlates of children's relationships with peers.

Mother and teacher correlates of social competence with familiar and unfamiliar peers in 84 children who entered child care at three different times are examined. Social competence at age 4 was assessed with both familiar and unfamiliar peers. Relationships with both initial and 4-year-old teachers were related to social competence with peers. Maternal attachment relationships at 12 months and at 4 years did not predict social competence with peers.

Children's relationships with peers: differential associations with aspects of the teacher-child relationship.

Associations between children's social competence with peers and differential aspects of their teacher-child relationships were examined in a longitudinal sample of 48 4-year-old children enrolled in child care as infants. Toddler security with teacher was negatively associated with hostile aggression and positively with complex peer play and gregarious behaviors. Prosocial behaviors and withdrawing behaviors were associated with preschool security with teacher. Dependence on teachers as a preschooler was associated with social withdrawal and hostile aggression. Positive toddler teacher socialization was associated with higher perceived peer acceptance. Preschool teacher negative socialization was negatively associated with complex peer play, teacher ratings of hesitancy, friendly enactment, and accidental attribution and positively related to teacher ratings of difficulty.

Systemic and developmental toxicity of dermally applied distillate aromatic extract in rats.

Distillate aromatic extract (DAE) was evaluated for subchronic and developmental toxicity. In the subchronic study, undiluted DAE was applied on the shaved backs of male and female rats at dose levels of 0, 30, 125, 500, and 1250 mg/kg for 13 weeks, 5 days per week. Exposure sites were not covered. In the developmental toxicity study, DAE was similarly applied, but to pregnant rats at dose levels of 0, 8, 30, and 125 mg/kg on Gestation Days 0-19, 500 mg/kg on Gestation Days 0-16, and 1000 mg/kg on Gestation Days 10-12. Evidence of toxicity observed in the subchronic study included death, decreased body weights, aberrant serum chemistry and hematology values, altered organ weights, and histopathologic changes in a variety of organs. Regardless of the length of the exposure period, DAE was toxic to the developing conceptus. Evidence of developmental toxicity observed included increased resorptions and reduced fetal body weights. Cleft palate and ossification delays were observed in fetuses exposed in utero to DAE on Gestation Days 10-12, but not when exposure spanned all (Gestation Days 0-19) or most (Gestation Days 0-16) of gestation.

The stability of attachment security from infancy to adolescence and early adulthood: general introduction.

Current attachment theory hypothesizes that attachment security during infancy influences individual differences in adult representations of attachment. We present three long-term longitudinal studies using three different samples relevant to this hypothesis. Each study assesses infant attachment by using the Ainsworth Strange Situation and adult attachment by using the Berkeley Adult Attachment Interview (AAI). Attachment security was significantly stable in the first two studies. Discontinuity in all three studies was related to negative life events and circumstances. Comparison of the results across these complementary studies affords a degree of replication and sheds light on alternative interpretations. Various mechanisms underlying the stability and instability of attachment security are discussed.

The stability of attachment security from infancy to adolescence and early adulthood: general discussion.

For over three decades, critics of the developmental and psychometric paradigms have argued that individual differences are neither stable, coherent, nor clinically significant. The present studies extend a long line of research demonstrating the coherence of individual development in attachment security. They make it clear that attachment security can be stable from infancy through early adulthood and that change in attachment security is meaningfully related to changes in the family environment. The task now is to better understand the roles of cross-age consistency in caregiver behavior and the structure of mental representations of early experience in stability and change.

Correlation of systemic and developmental toxicities with chemical component classes of refinery streams.

Refinery streams are complex mixtures, but of a relatively few homologous series of hydrocarbons (paraffins, olefins, naphthenics, and aromatics). Studies were performed to determine if systemic and developmental toxicity were related to the presence and levels of certain classes of refinery stream components. We have performed systemic toxicology studies in the rat on 13 refinery streams: Clarified Slurry Oil, Coker Light Gas Oil, Distillate Aromatic Extract, Heavy Atmospheric Gas Oil, Heavy Coker Gas Oil (from three refineries), Heavy Vacuum Gas Oil, Light Catalytically Cracked Naphtha, Light Cycle Oil, Syntower Bottoms, Vacuum Tower Overhead, and Visbreaker Gas Oil. Rats were exposed via repeated dermal administration (daily) at several dose levels. Developmental toxicology studies were performed on these same streams with the following exceptions: only two Heavy Coker Gas Oils were tested and Visbreaker Gas Oil was not tested. End points for systemic toxicity (13-week) studies included skin irritation, body and organ weights, hematology, and serum chemistry; for developmental toxicity studies some of these same end points (excluding hematology) were considered, but they also included resorption and fetal body weight. In general, toxicity was correlated with concentrations of polycyclic aromatic compounds (PAC) composed of 3, 4, 5, 6, and/or 7 rings (decreased thymus weight, increased liver weight, aberrant hematology and serum chemistry, increased incidence of resorption, decreased fetal body weight), PAC containing nonbasic nitrogen heteroatoms (increased mortality, decreased body weight, decreased thymus weight, increased liver weight, decreased hemoglobin content and hematocrit level, decreased fetal body weight), and/or PAC containing sulfur heteroatoms (decreased red blood cell and platelet counts, increased sorbitol dehydrogenase.)(ABSTRACT TRUNCATED AT 250 WORDS)

Systemic toxicity of dermally applied crude oils in rats.

Two crude oils, differing in viscosity (V) and nitrogen (N) and sulfur (S) content, were evaluated for systemic toxicity. In the Crude I (low V, low N, low S) study, the material was applied to the clipped backs of rats at dose levels of 0, 30, 125, and 500 mg/kg. In the Crude II (high V, high N, moderate S) study, the oil was applied similarly at the same dose levels. The crude oils were applied for 13 wk, 5 d/wk. Exposure sites were not occluded. Mean body weight gain (wk 1-14) was significantly reduced in male rats exposed to Crude II; body weight gain of all other animals was not adversely affected by treatment. An increase in absolute (A) and relative (R) liver weights and a decrease in A and R thymus weights were observed in male and female rats exposed to Crude II at 500 mg/kg; only liver weights (A and R) were adversely affected in male and female rats exposed to Crude I. In general, there was no consistent pattern of toxicity for serum chemistry endpoints; however, more parameters were adversely affected in Crude II-exposed female rats than in the other exposed groups. A consistent pattern of toxicity for hematology endpoints was observed among male rats exposed to Crude I and male and female rats exposed to Crude II. Parameters affected included: Crudes I and II, red blood cell count, hemoglobin, and hematocrit; Crude II, platelet count. Microscopic evaluation of tissues revealed the following treatment-related findings: Crude I, treated skin, thymus, and thyroid; Crude II, bone marrow, treated skin, thymus, and thyroid. The LOEL (lowest observable effect level) for skin irritation and systemic toxicity (based on marginal effects on the thyroid) for both crude oils was 30 mg/kg; effects were more numerous and more pronounced in animals exposed to Crude II. Systemic effects are probably related to concentrations of polycyclic aromatic compounds (PAC) found in crude oil.

Developmental toxicity of dermally applied crude oils in rats.

Two crude oils, differing in viscosity (V) and nitrogen (N) and sulfur (S) content, were evaluated for pre- and postnatal developmental toxicity. In Crude I (low V, low N, low S) studies, the material was applied neat to the clipped backs of pregnant rats at dose levels of 0, 125, 500, 1000 (postnatal only), and 2000 (prenatal only) mg/kg. In Crude II (high V, high N, moderate S) studies, the oil was applied similarly but at dose levels of 0, 30, 125, and 500 mg/kg. Rats were exposed to the crude oils on gestation days (GD) 0-19; application sites were not covered. "Prenatal" rats were killed on GD 20. "Postnatal" rats were allowed to deliver naturally; surviving dams and litters were killed 3-4 wk postpartum. Both crude oils produced maternal and developmental toxicity. Adverse fetal effects included increased in utero death, decreased body weight, and reduced ossification of skeletal elements. Parturition was delayed in Crude II dams at 500 mg/kg. The 4-d viability index was decreased in all Crude II-exposed groups. Pup body weights were decreased by each oil, but at the high dose only. Prenatal effects are probably related to polynuclear aromatic compounds (PAC) found in petroleum. The cause(s) of delayed parturition and postnatal toxicity have not been determined.