Tunable ultra-narrow band-gap of anomalous dispersion photonic crystals

We use the transfer-matrix method to research the band structures in one-dimensional photonic crystals composed of anomalous dispersion material ( saturated atomic cesium vapor). Our calculations show that that type of photonic crystal possesses an ultra-narrow photonic band gap and this band gap is tunable when altering the electron population in the atomic ground state of the anomalous dispersion material by the optical pumping method. Copyright (C) EPLA, 2007.

High-spin isomeric structures in exotic odd-odd nuclei: Exploration of the proton drip line and beyond

We investigate the role of two-quasiparticle isomeric states along the proton drip line, using configuration-constrained potential-energy-surface calculations. In contrast to even-even nuclei, odd-odd nuclei can have coexisting low-lying two-quasiparticle states. The low excitation energy and high angular momentum can lead to long-lived isomers. Also, because of the hindrance by spin selection, the probabilities of beta and proton decays from high-spin isomers can be reduced significantly. The present calculations reproduce reasonably well the available data for observed isomers in such nuclei. Unobserved high-spin isomers are predicted, which could be useful for future experimental studies of exotic nuclei at and beyond the proton drip line.

Candidate chiral doublet bands in the odd-odd nucleus Cs-126

The candidate chiral doublet bands recently observed in Cs-126 have been extended to higher spins, several new linking transitions between the two partner members of the chiral doublet bands are observed, and gamma-intensities related to the chiral doublet bands are presented by analyzing the gamma-gamma coincidence data collected earlier at the NORDBALL through the Cd-116(N-14, 4n)Cs-126 reaction at a beam energy of 65 MeV. The intraband B(M1)/B(E2) and interband B(M1)(in)/B(M1)(out) ratios and the energy staggering parameter, S(I), have been deduced for these doublet bands. The results are found to be consistent with the chiral interpretation for the two structures. Furthermore, the observation of chiral doublet bands in Cs-126 together with those in Cs-124, Cs-128, Cs-130, and Cs-132 also indicates that the chiral conditions do not change rapidly with decreasing neutron number in these odd-odd Cesium isotopes.

放射性钚和铯在湖泊中的时空分布特性及近期沉积年代学应用

短半衰期的137Cs具有高放射毒性，而半衰期较长的Pu的化学毒性极强，它们在环境中富集，进而在食物链中迁移，将直接威胁人类健康，国内在Pu和137Cs的分析方法、环境剂量以及湖泊地质等方面已展开了一些研究，但仍处于起步阶段，内容不够系统全面。湖泊和水库是生活饮用水或农用灌溉水源地，与人类生活息息相关，因此研究湖泊中人为放射性核素的污染状况、来源及归宿显得尤为重要；而且湖泊沉积物作为湖泊中大多污染物的最终归宿地，能够有效地保存湖泊区域的污染历史，研究湖泊沉积物有助于认清湖泊污染历史、探明污染机理，为污染现状评价、水质调查及治理提供可靠的基础依据，钚和铯的特殊性质可为环境科学等方面的研究提供关键的沉积年代学基础数据。 本研究在全国范围内选取具有代表性的不同区域分布、湖泊类型、人为扰动状况的湖泊为研究对象，应用基于γ谱的137Cs分析方法和本文建立的针对淡水湖泊沉积物的Pu同位素分析方法，研究了人为放射性核素Pu和137Cs在全国范围内的分布特征、近源传输及在湖泊中的沉积与迁移机理，并探讨了239+240Pu计年方法的有效性。通过上述研究，得到了如下主要结论： 1、建立了基于阴离子交换树脂分离的Pu同位素ICP-SF-MS分析方法，采用AG1-X8树脂分离Pu与杂质元素以及AG MP-1M纯化Pu同位素。高的仪器灵敏度、良好的U去除效率、足够的Pu同位素化学回收率表明该方法能够有效地检测湖泊沉积物样品中的痕量239Pu和240Pu。此外，纯化Pu同位素时，采用HBr洗脱Pu同位素以排除PbCl+对Pu同位素的干扰，因此该方法除了适应239Pu、240Pu分离分析之外，还可为后期分析浓度更低的241Pu提供技术保证。 2、通过分析沉积物岩芯中的239+240Pu沉积通量和137Cs沉积通量、240Pu/239Pu同位素平均比、239+240Pu/137Cs活度平均比及Pu、137Cs在沉积物岩芯中的剖面分布特征发现博斯腾湖有中国核试验基地的人为放射性核素污染，其表现形式为核爆试验产生的可溶性气溶胶颗粒和热核颗粒沉降后再悬浮造成的偶然性污染和源自罗布泊的地表径流引起的普遍性污染。博斯腾湖的Pu同位素结果表明平流层沉降的中国核试验的核碎片的240Pu/239Pu同位素原始比值可能为0.18左右，非常接近全球大气沉降值。苏干湖和双塔水库有源自中国核试验的可溶性气溶胶颗粒经大气沉降后再悬浮造成的人为放射性核素污染，苏干湖中大约有40%左右的137Cs以及27%左右的239+240Pu源自中国核试验，双塔水库中源自中国核试验的239+240Pu和137Cs所占的比例分别为27.1%和30.6%。 3、单一的239+240Pu和137Cs蓄积峰不能完全解析出沉积速率较慢的青海湖是否有源自在罗布泊进行的中国核武器爆炸试验的污染，但1963年全球大气沉降高峰下端的低240Pu/239Pu同位素比值表明青海湖可能有源自始建于1957年的中国原子城的地表径流泄漏或地下渗透泄漏的人为放射性核素污染。 4、西南地区的湖泊中，云南程海部分137Cs可能源于长距离迁移的中国核试验，但明确中国核试验对西南地区的影响还需要中国核试验源Pu和137Cs长距离迁移的信息，如青藏高原湖泊和西川盆地湖泊沉积物中人为放射性核素来源。其它湖泊中人为放射性核素的污染均源于全球大气沉降。 5、火山成因封闭式玛珥湖，在没有人为扰动的条件下，137Cs和239+240Pu主要以微弱的分子扩散迁移，迁移速率不明显，能较好地保持沉积历史；对人为活动比较频繁的浅水湖泊而言，人为活动、强风等恶劣气候以及上层水体和底层水体的交互对流等因素引起的沉积物再悬浮作用加剧了239+240Pu和137Cs主要以分子扩散迁移作用，造成水体寄宿时间短的浅水湖泊中239+240Pu和137Cs的不同步损失，导致239+240Pu和137Cs峰型的无序化。 6、受人为扰动较弱的湖泊中137Cs比活度和239+240Pu比活度成良好的线性相关，表明239+240Pu蓄积峰的信息能够为此类型湖泊沉积物提供有效的近期沉积年代学数据；对受人为扰动比较大的湖泊来说，137Cs和239+240Pu蓄积峰在近期沉积物计年的方面各有优劣，计年数据的可靠性不强；青海湖各沉积物岩芯的沉积物计年结果表明湖泊的沉积物累积率或沉积速度存在区域性差异。

The atom pencil: serial writing in the sub-micrometre domain

The atom pencil we describe here is a versatile tool that writes arbitrary structures by atomic deposition in a serial lithographic process. This device consists of a transversely laser-cooled and collimated cesium atomic beam that passes through a 4-pole atom-flux concentrator and impinges on to micron- and sub-micron-sized apertures. The aperture translates above a fixed substrate and enables the writing of sharp features with sizes down to 280 nm. We have investigated the writing and clogging properties of an atom pencil tip fabricated from silicon oxide pyramids perforated at the tip apex with a sub-micron aperture.

Bioaccumulation Trends of Ten Metals in a Pelagic Food Web of Lake Champlain

Many metals have serious toxic effects when ingested by aquatic organisms, and the process of bioaccumulation intensifies this problem. A better understanding of bioaccumulation trends of anthropogenically introduced metals in freshwater food webs is necessary for the development of effective management strategies to protect aquatic organisms, as well as organisms (including humans) that consume top-predator fish in these food webs. Various fish species representing different trophic levels of a pelagic food chain were sampled from Lake Champlain (VT/NY). Atomic absorption spectrometry (AAS) was used to determine levels of chromium, copper, cobalt, cadmium, lead, zinc, nickel, rubidium, cesium and potassium in the fish samples. Metal concentrations for chromium, cobalt, nickel, cesium, cadmium (<5.0 ppm) and lead (<10.0 ppm) were found to be all below detection limits. Carbon and nitrogen isotopic ratios were analyzed to determine the trophic relationship of each fish species. Stable isotope and AAS metal data were used in tandem to produce linear regressions for each metal against trophic level to assess biomagnification. Both potassium and zinc showed no biomagnification because they are homeostatically regulated essential trace metals. Copper was under the detection limits for all fish species with the exception of the sea lamprey; but showed a significant biodiminution among the invertebrates and lamprey. Rubidium, a rarely studied metal, was shown to increase with trophic level in a marginally significant linear relationship suggesting biomagnification is possible where more trophic levels are sampled.

Stimulated Raman transitions via multiple atomic levels

We consider the stimulated Raman transition between two long-lived states via multiple intermediate states, such as between hyperfine ground states in the alkali-metal atoms. We present a concise treatment of the general, multilevel, off-resonant case, and we show how the lightshift emerges naturally in this approach. We illustrate our results by application to alkali-metal atoms and we make specific reference to cesium. We comment on some artifacts, due solely to the geometrical overlap of states, which are relevant to existing experiments.

Síntese e aplicações catalíticas na funcionalização de alcanos de novos compostos com polioxometalatos e catiões orgânicos

A presente dissertação, que no seu conjunto se propõe apresentar o estudo de oxidação de compostos orgânicos com peróxido de hidrogénio na presença dos aniões do tipo Keggin, mono-substituídos por MnIII e FeIII, sob a forma de sais de tetra-n-butilamónio (TBA) e suportados em matriz de sílica funcionalizada, enquanto vital método de obtenção de importante precursores de síntese orgânica, tem na sua base o trabalho de Doutoramento desenvolvido no Departamento de Química da Universidade de Aveiro. Os compostos preparados e testados em sistema homogéneo foram os sais de TBA dos aniões de Keggin, de fórmula geral [XW11M(H2O)O39]n-, onde X = P, Si ou B e M = MnIII e FeIII. Em sistema heterogéneo foram testados diferentes materiais, que diferem entre si na matriz de sílica. Assim, fez-se a heterogeneização de [PW11Fe(H2O)O39]4- em sílica funcionalizada com catiões de césio e grupos propilamónio; [BW11Fe(H2O)O39]6- e [SiW11Fe(H2O)O39]5- foram imobilizados em sílica contendo grupos aminopropilo e o anião [PW11Mn(H2O)O39]4- foi suportado em sílica quimicamente modificada com grupos alquilamónio. Os substratos orgânicos estudados incluem o 1H-indeno, 1,2-di-hidronaftaleno, etilbenzeno, cumeno, p-cimeno, sec-butilbenzeno, 1- e 2-etilnaftaleno, cis-cicloocteno e ciclooctano. Paralelamente usaram-se alguns outros substratos, quando necessário obter esclarecimentos mecanísticos. A tese assenta numa estrutura composta por 7 capítulos. Na primeira, faz-se uma abordagem aos polioxometalatos e às reacções de oxidação de hidrocarbonetos, com particular destaque no uso de polioxometalatos em catálise oxidativa e também no uso de peróxido de hidrogénio como oxidante. A eficiência catalítica dos aniões de Keggin mono substituídos por MnIII e FeIII, em sistema homogéneo foi avaliada na oxidação de compostos orgânicos característicos, nomeadamente de ciclo-alcenilbenzenos, alquilbenzenos, ciclo-alquilbenzenos e hidrocarbonetos aromáticos policíclicos com H2O2, em acetonitrilo. Os resultados destes estudos encontram-se descritos nos capítulos dois, três e quatro desta tese. Estes compostos mostraram-se catalisadores eficientes e selectivos para a oxidação de alcanos e alcenos. O quinto capítulo da tese prossegue com a síntese, caracterização e eficiência catalítica dos polioxotungstatos referidos anteriormente imobilizados numa matriz de sílica funcionalizada com iões césio (SiO2-Cs), grupos aminopropilo (SiO2–(CH2)3NH2) ou trietilpropilamónio (SiO2-(CH2)3N(Et)3). A actividade catalítica destes compostos foi estudada utilizando o cis-cicloocteno e ciclooctano como substratos padrão. A oxidação de cis-clicoocteno originou o epóxido com 100% de selectividade e o catalisador foi reutilizado durante 4 ciclos com elevada eficiência. No sexto capítulo, são descritas as metodologias experimentais de síntese dos novos compostos, as condições catalíticas, a instrumentação e demais métodos e procedimentos usados. No sétimo e último capítulo, tecem-se as conclusões finais e apresentam-se algumas perspectivas de trabalho futuro utilizando o sistema, POM/H2O2, usado neste trabalho.

Finding ‘Good Friday’ An explorative study into the sedimentary structures left from the Good Friday tsunami

Senior thesis written for Oceanography 444

Adenovirus-based exogenous gene expression in mammalian cells

Thesis (Ph.D.)--Brock University, 2010.

Condensation of helium in nanoscopic alkali wedges at zero temperature

We present a complete calculation of the structure of liquid 4He confined to a concave nanoscopic wedge, as a function of the opening angle of the walls. This is achieved within a finite-range density functional formalism. The results here presented, restricted to alkali metal substrates, illustrate the change in meniscus shape from rather broad to narrow wedges on weak and strong alkali adsorbers, and we relate this change to the wetting behavior of helium on the corresponding planar substrate. As the wedge angle is varied, we find a sequence of stable states that, in the case of cesium, undergo one filling and one emptying transition at large and small openings, respectively. A computationally unambiguous criterion to determine the contact angle of 4He on cesium is also proposed.

Helices, chirality and interpenetration: the versatility and remarkable interconversion of silver-copper cyanide frameworks

The structural transformations between cesium silver-copper cyanides under modest conditions, both in solution and in the solid state, are described. Three new cesium silver(I) copper(I) cyanides with three-dimensional (3-D) framework structures were prepared as single crystals from a one-pot reaction initially heated under hydrothermal conditions. The first product to appear, Cs3Ag2Cu3(CN)(8) (I), when left in contact with the supernatant produced CsAgCu(CN)(3) (II) and CsAgCu(CN)(3)center dot 1/3H(2)O (III) over a few months via a series of thermodynamically controlled cascade reactions. Crystals of the hydrate (III) can be dehydrated to polycrystalline CsAgCu(CN)(3) (II) on heating at 100 degrees C in a remarkable solid-state transformation involving substantial breaking and reconnection of metal-cyanide linkages. Astonishingly, the conversion between the two known polymorphs of CsAg2Cu(CN)(4), which also involves a major change in connectivity and topology, occurs at 180 degrees C as a single-crystal to single-crystal transformation. Structural features of note in these materials include the presence of helical copper-cyanide chains in (I) and (II), which in the latter compound produce a chiral material. In (II) and (III), the silver-copper cyanide networks are both self- and interpenetrating, features also seen in the known polymorphs of CsAg2Cu(CN)(4).

Three-boson recombination at ultralow temperatures

The effects of trimer continuum resonances are considered in the three-body recombination rate of a Bose system at finite energies for large and negative two-body scattering lengths (a). The thermal average of the rate allows to apply our formula to Bose gases at ultra-low temperatures. We found a good quantitative description of the experimental three-body recombination length of cesium atoms to deeply bound molecules up to 500 nK. Consistent with the experimental data, the increase of the temperature moves the resonance peak of the three-body recombination rate to lower values of vertical bar a vertical bar exhibiting a saturation behavior. (C) 2006 Elsevier B.V. All rights reserved.

Four-fermion contact interactions at one-loop and the new atomic parity violation results.

We investigate the possibility that four-fermion contact interactions give rise to the observed deviation from the Standard Model prediction for the weak charge of cesium, through one-loop contributions. We show that the presence of loops involving the third generation quarks can explain such deviation.

Preparation of different basic Si-MCM-41 catalysts and application in the Knoevenagel and Claisen-Schmidt condensation reactions

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)