Toward an understanding of aging in plutonium from direct measurements of stored energy

ABSTRACT

We present here the first direct measurement of the radiation-damage-induced energy stored in δ-phase plutonium. The primary mode of radioactive decay of ²³⁹Pu occurs with a time constant of τ=1.1?×?10¹²?s. Each decay imparts about 85?keV of recoil energy to the uranium byproduct, 5.2?Mev to the alpha particle, and a spectrum of mostly low energy gamma rays with the most probable at 51?keV [1]. Most of the decay energy is converted immediately to heat, releasing about 1.9?mW/g. However, some thermally-recoverable energy remains trapped. Reported here are measurements of that stored energy using differential scanning calorimetry (DSC) applied to ²³⁹Pu-2.0 at.%Ga δ-phase alloy. Retained energy of ～2 J/g saturates at about 5 months and is unchanged after 30 years. The magnitude of the stored energy agrees with a short-bond defect model that that we present here. This model treats radiation damage as a Pu impurity with shortened bond lengths. It explains the change in known properties with age and predicts that density increases with age, contrary to current thinking. The short-bond impurities proposed are expected to act like other impurities, affecting strength, phase transitions, grain boundaries and other metallurgical properties.     

Investigation of the interaction of He and D in FeBSi alloy

He and H can be produced by nuclear reaction. In addition, energetic particles of He and T and D, which are isotopes of H, in the plasma of fusion reactor induce the damage in the surface of materials, such as erosion, sputtering and blistering. To investigate the interaction of He and D, amorphous and crystalline FeBSi alloys were irradiated by He or D₂ or He?+?D₂ ions with 5?keV. The results of thermal desorption indicated that more He atoms were trapped in both the amorphous and crystalline alloy irradiated by He ions than D atoms in those alloys irradiated by D₂ ions. Although He and D atoms were trapped in FeBSi alloy irradiated by He?+?D₂ ions, desorption peaks of D₂ and He were separated. Absorption of D in an amorphous alloy was influenced by the presence of He; however, absorption of He was independent of D₂ irradiation in both alloys.     

药物成瘾诱导相关大脑核团功能和行为改变的DNA甲基化机制

药物成瘾会导致相关神经环路的结构和功能长期改变.大量新的研究证据表明,在DNA序列不变的情况下,药物成瘾可通过影响不同亚型DNA甲基转移酶(DNMTs)的表达,使脑内多个相关核团发生DNA甲基化以及基因表达的改变,进而导致神经元功能的可塑性变化.因此,DNA甲基化被视作导致成瘾行为长期存在的可能机制之一.结合近几年来的重要发现,本文将重点讨论相关脑区的DNA甲基化在成瘾行为发生发展过程中的作用,以及成瘾药物影响DNA甲基化水平的可能机制,并试图提出可深入的研究展望.     

骨髓捐献人中途拒捐的民事责任探析——基于信赖保护的视角

基于捐献行为的公益性、单务性和人身性,各国法律赋予捐献人任意撤销权,但是出于对捐献人允诺的信赖而改变自身处境的接受人利益也应该得到保护.从信赖保护的视角出发,在血型高分辨检测之前,捐献人一旦签订了捐献协议,即负有保护接受人信赖利益的义务,捐献人虽然有权中途拒捐,但应当承担信赖赔偿责任.     

The effects of stress on dna repair capacity

Abstract

Research has shown that lymphocytes of high-distress patients have reduced DNA repair relative to that of low-distress patients and healthy controls. Furthermore, deficits in repair are associated with an increased risk of cancer. Using and academic stress model, we hypothesized that students would exhibit lower levels of Nucleotide Excision Repair (NER) during a stressful exam period when compared to a lower stress period. Participants were 19 healthy graduate level students. NER was measured in lymphocytes using the unscheduled DNA synthesis (UDS) assay with slide autoradiography. Contrary to prediction, mean values for NER significantly increased during the higher stress period relative to the lower stress period controlling for background differences in repair. Furthermore, lymphocytes had significantly increased repair of endogenous damage during the higher stress period. Stress appears to directly increase DNA repair. Additionally, stress may increase DNA repair indirectly by increasing damage to DNA.     

PATERNITY BETWEEN LAW AND BIOLOGY: THE RECONSTRUCTION OF THE ISLAMIC LAW OF PATERNITY IN THE WAKE OF DNA TESTING

Abstract: The discovery of DNA paternity tests has stirred a debate concerning the definition of paternity and whether the grounds for such a definition are legal or biological. According to the classical rules of Islamic law, paternity is established and negated on the basis of a valid marriage. Modern biomedical technology raises the question of whether paternity tests can be the sole basis for paternity, even independently of marriage. Although on the surface this technology seems to challenge the authority of Islamic law in this area, the paper argues that classical Islamic rulings pertaining to paternity issues continue to hold higher authority even in cases of conflict with modern technology‐based alternatives. Through closer analysis, the paper traces the emergence of a differentiation in the function of DNA tests between identity and paternity verification. While the former is accepted without reservation, the latter is approved only when it does not violate the rulings of Islamic law.     

Aquinas's Opposition to Killing the Innocent and its Distinctiveness within the Christian just War Tradition

This essay argues that Aquinas's position regarding the killing of innocent people differs significantly from other representatives of the Christian just war tradition. While his predecessors, notably Augustine, as well as his successors, from Cajetan and Vitoria onward, affirm the legitimacy of causing the death of innocents in a just war in cases of necessity, Aquinas holds that causing the death of innocents in a foreseeable manner, whether intentionally or indirectly, is never justified. Even an otherwise legitimate act of just war cannot legitimate causing the death of innocent people, as this can never advance the common good. This stance also contrasts sharply with much modern and contemporary double effect theorizing in relation to jus in bello. In this regard, Aquinas's position, shaped decisively by his biblical and theological commitments, may point the way towards an ethical orientation beyond the typical divisions of “pacifism” and “just war.”     

Cities and the real world

It is generally recognized that modern cities pose many problems for their inhabitants and contribute to environmental damage. However, neither planners nor scientists give adequate consideration to cities’ place in the evolutionary process and the planet's ecological system. By recognizing these connections and natural laws, planning would become more realistic, and meaningful progress could be made in solving serious social and environmental problems. Some basic problems influencing urban form are discussed, and a schematic example of how we might approach the planning of urban settlements is presented.     

Leveraging epigenetics to examine differences in developmental trajectories of social attention: A proof-of-principle study of DNA methylation in infants with older siblings with autism

Preliminary evidence suggests that changes in DNA methylation, a widely studied epigenetic mechanism, contribute to the etiology of Autism Spectrum Disorder (ASD). However, data is primarily derived from post-mortem brain samples or peripheral tissue from adults. Deep-phenotyped longitudinal infant cohorts are essential to understand how epigenetic modifications relate to early developmental trajectories and emergence of ASD symptoms. We present a proof-of-principle study designed to evaluate the potential of prospective epigenetic studies of infant siblings of children with ASD.Illumina genome-wide 450 K DNA methylation data from buccal swabs was generated for 63 male infants at multiple time-points from 8 months to 2 years of age (total N = 107 samples). 11 of those infants received a diagnosis of ASD at 3 years. We conducted a series of analyses to characterize DNA methylation signatures associated with categorical outcome and neurocognitive measures from parent-report questionnaire, eye-tracking and electro-encephalography.Effects observed across the entire genome (epigenome-wide association analyses) suggest that collecting DNA methylation samples within infant-sibling designs allows for the detection of meaningful signals with smaller sample sizes than previously estimated. Mapping networks of co-methylated probes associated with neural correlates of social attention implicated enrichment of pathways involved in brain development. Longitudinal modelling found covariation between phenotypic traits and DNA methylation levels in the proximity of genes previously associated with cognitive development, although larger samples and more complete datasets are needed to obtain generalizable results.In conclusion, assessment of DNA methylation profiles at multiple time-points in infant-sibling designs is a promising avenue to comprehend developmental origins and mechanisms of ASD.