Microwave Spectroscopy

Contains reports on five research projects.United States Army Signal Corps (Contract DA36-039-sc-74895

Coherent Signal Amplification in Bistable Nanomechanical Oscillators by Stochastic Resonance

Stochastic resonance is a counter-intuitive concept[1,2], ; the addition of noise to a noisy system induces coherent amplification of its response. First suggested as a mechanism for the cyclic recurrence of ice ages, stochastic resonance has been seen in a wide variety of macroscopic physical systems: bistable ring lasers[3], SQUIDs[4,5], magnetoelastic ribbons[6], and neurophysiological systems such as the receptors in crickets[7] and crayfish[8]. Although it is fundamentally important as a mechanism of coherent signal amplification, stochastic resonance is yet to be observed in nanoscale systems. Here we report the observation of stochastic resonance in bistable nanomechanical silicon oscillators, which can play an important role in the realization of controllable high-speed nanomechanical memory cells. Our nanomechanical systems were excited into a dynamic bistable state and modulated in order to induce controllable switching; the addition of white noise showed a marked amplification of the signal strength. Stochastic resonance in nanomechanical systems paves the way for exploring macroscopic quantum coherence and tunneling, and controlling nanoscale quantum systems for their eventual use as robust quantum logic devices.Comment: 18 pages, 4 figure

Microwave Spectroscopy

Contains reports on seven research projects.United States Army Signal Corps (Contract DA36-039-sc-74895

Anxiety and Depression Correlates at Age 10 in Children Born Extremely Preterm

Objective:Anxiety and depression rates are known to be elevated in prematurely-born children and adolescents. This prospective study examines demographic, academic, and physical health correlates of anxiety and depression symptoms in a sample of 10-year-old children who were born extremely preterm. Methods:Participants were 889 (51.2% male; 62.3% White) children who were born <28weeks gestation. Child and family demographic data were collected at birth. When the children were 10, parents (n=871) and teachers (n=640) rated the level of anxiety and depression in children through the Child Symptom Inventory-4. Child academic functioning was assessed via the Wechsler Individual Achievement Test-III. Parents completed questionnaires about child academic functioning and physical health issues. Data analyses were conducted with multivariate linear modeling. Results:Level of prematurity was significantly related to both parent and teacher reports of anxiety. Public health insurance and individualized education program (IEP) status were associated with both parent and teacher reports of depression. Hispanic ethnicity, public insurance, IEP status, and asthma were significantly associated with both parent-reported anxiety and depression. Gross motor impairment was associated with parent-reported anxiety and teacher-reported depression. Child obesity was associated with teacher reports of anxiety, while male sex was significantly related to teacher reports of depression. Conclusion:This pattern of findings may suggest hypotheses for future research on models of the development and persistence of anxiety and depression within this particularly vulnerable group of children

Microwave Spectroscopy

Contains reports on seven research projects.United States Army Signal Corps (Contract DA36-039-sc-74895

Neutral and Cationic Rare Earth Metal Alkyl and Benzyl Compounds with the 1,4,6-Trimethyl-6-pyrrolidin-1-yl-1,4-diazepane Ligand and Their Performance in the Catalytic Hydroamination/Cyclization of Aminoalkenes

A new neutral tridentate 1,4,6-trimethyl-6-pyrrolidin-1-yl-1,4-diazepane (L) was prepared. Reacting L with trialkyls M(CH2SiMe3)3(THF)2 (M = Sc, Y) and tribenzyls M(CH2Ph)3(THF)3 (M = Sc, La) yielded trialkyl complexes (L)M(CH2SiMe3)3 (M = Sc, 1; M = Y, 2) and tribenzyl complexes (L)M(CH2Ph)3 (M = Sc, 3; M = La, 4). Complexes 1 and 2 can be converted to their corresponding ionic compounds [(L)M(CH2SiMe3)2(THF)][B(C6H5)4] (M = Sc, Y) by reaction with [PhNMe2H][B(C6H5)4] in THF. Complexes 3 and 4 can be converted to cationic species [(L)M(CH2Ph)2]+ by reaction with [PhNMe2H][B(C6F5)4] in C6D5Br in the absence of THF. The neutral complexes 1-4 and their cationic derivatives were studied as catalysts for the hydroamination/cyclization of 2,2-diphenylpent-4-en-1-amine and N-methylpent-4-en-1-amine reference substrates and compared with ligand-free Sc, Y, and La neutral and cationic catalysts. The most effective catalysts in the series were the cationic L-yttrium catalyst (for 2,2-diphenylpent-4-en-1-amine) and the cationic lanthanum systems (for N-methylpent-4-en-1-amine). For the La catalysts, evidence was obtained for release of L from the metal during catalysis.

Assessing Positive Child Health among Individuals Born Extremely Preterm

OBJECTIVE: To assess the development of a Positive Child Health Index (PCHI) based on 11 adverse outcomes and evaluate the association of PCHI with quality of life (QoL) scores in a preterm cohort. STUDY DESIGN: A total of 889 children enrolled in the Extremely Low Gestational Age Newborn (ELGAN) study in 2002-2004 were followed up at 10 years of age. A parent/caregiver completed questionnaires for child QoL, asthma, visual or hearing impairment, gross motor function impairment, epilepsy, attention deficit/hyperactivity disorder, anxiety, and depression. The child was assessed for cognitive impairment, autism, and obesity. PCHI scores were computed and linear regression models were used to evaluate the relationship between QoL categories (psychosocial, physical, emotional, social, school, and total) and the PCHI (dichotomized and coded as a multilevel categorical predictor) and to assess sex differences. RESULTS: Among ELGAN children, higher PCHI scores were associated with higher reported QoL scores for all QoL categories. Children with no disorders and a PCHI of 100% had Pediatric Quality of Life Inventory total scores that were 11 points higher than children with 1 or more adverse outcomes (PCHI of <100%). Boys had lower QoL scores for the total, psychosocial, social, and school categories. CONCLUSIONS: Positive child health assessed using a quantitative PCHI was associated with QoL across the ELGAN cohort at school age. In the current study, the PCHI encompassed 11 outcomes assessed in ELGANs. Future research could include an enhanced panel of child health outcomes to support the use of PCHI as an indicator of positive child health

Understanding positive child health

In response to the commentary, we would like to thank the authors for their interest and thoughtful comments