排序方式: 共有50条查询结果,搜索用时 15 毫秒
1.
Bonnie Jeanne Baty Leslie Cohen Lorna Phelps Marcy C. Speer Pamela Stengel Lori Williamson-Kruse 《Journal of genetic counseling》1996,5(3):139-145
Considerable scientific evidence demonstrates the reduction in risk for neural tube defects (NTDs) associated with maternal preconceptional folic acid supplementation. The National Society of Genetic Counselors (NSGC) endorses the U.S. Public Health Service recommendations for folic acid supplementation at the 0.4 mg level for women in the general population and at the 4.0 mg level for women at high or increased risk for NTD pregnancies for at least 4 weeks prior to active pursuit of conception. We encourage targeted educational efforts and surveillance to assess results of this dietary supplementation. The NSGC further urges the Food and Drug Administration to fortify staple foodstuffs with folic acid for a population-based approach to minimize the number of NTD births. 相似文献
2.
Ann Streissguth 《Journal of clinical psychology in medical settings》2007,14(2):81-101
Before alcohol was generally known to cause birth defects, NIAAA in 1974 began funding a population-based Seattle study on
alcohol use and pregnancy outcome. Women receiving prenatal care by mid-pregnancy were recruited (N = 1,529) and interviewed at home. Approximately 500 offspring exposed to a range of alcohol levels were examined on 11 occasions
between day 1 and 25 years. Neuropsychological and neurobehavioral performance measures are correlated with prenatal alcohol
dose, without substantial confounding by socio-demographic or rearing conditions, smoking, nutrition, or other drugs. Deficits
in attention, arithmetic skill, spatial-visual memory, and IQ, as well as increased alcohol problems and psychiatric disorders
are among offspring outcomes correlated at several ages with maternal drinking during and before pregnancy recognition. Findings
are not confined to women who believed they had alcohol problems. Not all exposed offspring appear affected. 相似文献
3.
Perumalsamy Kiruthika 《Philosophical Magazine Letters》2015,95(3):138-144
Interdiffusion study is conducted in the Ni-rich part of the β-Ni(Pt)Al phase following the pseudo-binary approach. Interdiffusion coefficients over the whole composition range considered in this study increases with increase in Pt content, which is in line with the theoretical study predicting the decrease in vacancy formation and migration energy because of Pt addition. The trend of change in diffusion coefficient with the increase in Ni and Pt contents indicates that Pt preferably replaces Ni antisites. 相似文献
4.
ABSTRACTUsing a two-step focused ion beam irradiation process, tilted InSb nanostructures have been fabricated using a off-normal angle of irradiation. In the first step, a well-focused ion beam was used to irradiate the surface of the structure to achieve top-down sputtering. In the second step, the ion beam was used to irradiate the entire surface to promote bottom-up nanostructure growth through the migration of ion-beam-induced interstitial atoms. The formation of a nanostructure with a 46° tilt and an aspect ratio of 0.5 was achieved using ion beam irradiation at an angle of 45° in both steps of the process. The 2% concentration of point defects obtained by changing the volume of the nanostructure before and after irradiation contributed to the growth of the structure. The results showed that many point defects did not recombine, and survived to contribute toward the growth of the wall structure. 相似文献
5.
M. Massazza G. Riontino A. Dupasquier R. Ferragut A. Somoza P. Folegati 《Philosophical Magazine Letters》2013,93(9):495-502
Secondary ageing, that is microstructural evolution occurring at room temperature after short heating at temperatures above the metastable phase boundary of Guinier-Preston zones, has been studied for an Al-Cu-Mg alloy with a high Cu-to-Mg ratio. Combined data from positron annihilation spectroscopy, Vickers microhardness measurements and differential scanning calorimetry show that, on secondary ageing after 5 or 7min at 190°C, firstly, hardening takes place at a rate nine to 16 times slower than natural age hardening; secondly, vacancies slowly released by Cu-rich aggregates formed during the heat treatment at 190°C promote further formation of solute aggregates, with a time-dependent chemical composition; thirdly, the thermal stability of the structures formed during secondary ageing increases with increasing dwell time at room temperature; and, fourthly, solute aggregates formed at 190°C undergo a structural reorganization and possibly a change in the composition, leading to species with a different thermal stability. The slow release of vacancies from Cu-rich aggregates is proposed as one of the limiting factors of the hardening rate. 相似文献
6.
Novel structures for multiple hydrogen atoms trapped at a monovacancy are discussed. Using atomistic simulations based on semiempirical interatomic potentials and density functional theory, we find low-energy configurations for four, five, and six hydrogen atoms around a monovacancy different than those that have been previously studied in the literature. The energetics of hydrogen binding are compared to results, both theoretical and experimental, previously published in the literature. We argue that up to four hydrogen atoms may be exothermically bound to monovacancy. 相似文献
7.
Samiran Hazarika 《Philosophical Magazine Letters》2016,96(4):157-164
We report on the manifestation and interconnected photoluminescence and electron paramagnetic resonance responses in gadolinium oxide (Gd2O3) nanorods subjected to 80 MeV carbon ion irradiation. On increasing the irradiation fluence between 1 × 1011 and 3 × 1012 ions/cm2, the emission associated with neutral oxygen vacancies (VOx), positioned at ~350 nm, undergoes a steady increase compared to that associated with singly charged vacancies (VO+), located at ~414 nm. The enhancement of spin–spin relaxation time (τss) is ascribed to a substantial changeover from VO+ to VOx defects with irradiation, the former being recognized as the major contributor to paramagnetic centres. Interconnected luminescence and spin–spin relaxation could provide insight for making advanced nanophosphors and spin valve elements. 相似文献
8.
Agostinho Almeida 《Studia Logica》2009,91(2):171-199
This work is part of a wider investigation into lattice-structured algebras and associated dual representations obtained via the methodology of canonical extensions. To this end, here we study lattices, not necessarily distributive, with negation operations.We consider equational classes of lattices equipped with a negation operation ¬ which is dually self-adjoint (the pair (¬,¬) is a Galois connection) and other axioms are added so as to give classes of lattices in which the negation is De Morgan, orthonegation, antilogism, pseudocomplementation or weak pseudocomplementation. These classes are shown to be canonical and dual relational structures are given in a generalized Kripke-style. The fact that the negation is dually self-adjoint plays an important role here, as it implies that it sends arbitrary joins to meets and that will allow us to define the dual structures in a uniform way.Among these classes, all but one—that of lattices with a negation which is an antilogism—were previously studied by W. Dzik, E. Or?owska and C. van Alten using Urquhart duality.In some cases in which a given axiom does not imply that negation is dually self-adjoint, canonicity is proven with the weaker assumption of antitonicity of the negation. 相似文献
9.
出生缺陷儿的救治决策不仅是新生儿科医生和患儿家长面临的难题,也是无法回避的社会问题。除了医学科学上的可行性外,出生缺陷儿的救治决策是否合乎伦理也十分重要。阐述了出生缺陷儿的处置困境的现实来源和相关伦理学理论,回顾了国内外的相关法律法规及存在的问题,并结合国外经验启示和具体案例,探讨出生缺陷儿的处置决策的主体、原则和方案。同时,针对建立更加全面的社会机制、法律法规提出建议,以供未来的临床实践参考。 相似文献
10.
通过光固化氢氧化钙垫底后Dyract复合体修复和直接用Fuji II玻璃离子水门汀分别修复牙颈部深度楔状缺损,临床观察6个月~24个月。对二者的治疗效果进行研究分析,认为玻璃离子水门汀直接修复深度楔状缺损治疗效果优于以光固化氢氧化钙垫底用Dyract复合体修复,Fuji II玻璃离子水门汀直接充填是一种较理想的修复深度楔状缺损技术。 相似文献