We present a systematic methodology to functionalize magnetic nanoparticles through surface-initiated atom-transfer radical polymerization (ATRP). The magnetite nanoparticles are prepared according to the method proposed by Sun et al. (2004), which leads to a monodisperse population of ~ 6 nm particles stabilized by oleic acid. The functionalization of the nanoparticles has been performed by transforming particles into macro-initiators for the ATRP, and to achieve this two different routes have been explored. The first one is the ligand-exchange method, which consists of replacing some oleic acid molecules adsorbed on the particle surface with molecules that act as an initiator for ATRP. The second method consists in using the addition reaction of bromine to the oleic acid double bond, which turns the oleic acid itself into an initiator for the ATRP. We have then grown polymer brushes of a variety of acrylic polymers on the particles, including polyisopropylacrylamide and polyacrylic acid. The nanoparticles so functionalized are water soluble and show responsive behavior: either temperature responsive behavior when polyisopropylacrylamide is grown from the surface or PH responsive in the case of polyacrylic acid. This methodology has potential applications in the control of clustering of magnetic nanoparticles. / Singapore-MIT Alliance (SMA)

Thesis (M.Sc.)--Memorial University of Newfoundland, 2005. / Bibliography: leaves 81-83.

Resonant states are multiply excited states in atoms and ions that have enough energy to decay by emitting an electron. The ability to emit an electron and the strong electron correlation (which is extra strong in negative ions) makes these states both interesting and challenging from a theoretical point of view. The main contribution in this thesis is a method, which combines the use of B splines and complex rotation, to solve the three-electron Schrödinger equation treating all three electrons equally. It is used to calculate doubly excited and triply excited states of 4S symmetry with even parity in He-. For the doubly excited states there are experimental and theoretical data to compare with. For the triply excited states there is only theoretical data available and only for one of the resonances. The agreement is in general good. For the triply excited state there is a significant and interesting difference in the width between our calculation and another method. A cause for this deviation is suggested. The method is also used to find a resonant state of 4S symmetry with odd parity in H2-. This state, in this extremely negative system, has been predicted by two earlier calculations but is highly controversial. Several other studies presented here focus on two-electron systems. In one, the effect of the splitting of the degenerate H(n=2) thresholds in H-, on the resonant states converging to this threshold, is studied. If a completely degenerate threshold is assumed an infinite series of states is expected to converge to the threshold. Here states of 1P symmetry and odd parity are examined, and it is found that the relativistic and radiative splitting of the threshold causes the series to end after only three resonant states. Since the independent particle model completely fails for doubly excited states, several schemes of alternative quantum numbers have been suggested. We investigate the so called DESB (Doubly Excited Symmetry Basis) quantum numbers in several calculations. For the doubly excited states of He- mentioned above we investigate one resonance and find that it cannot be assigned DESB quantum numbers unambiguously. We also investigate these quantum numbers for states of 1S even parity in He. We find two types of mixing of DESB states in the doubly excited states calculated. We also show that the amount of mixing of DESB quantum numbers can be inferred from the value of the cosine of the inter-electronic angle. In a study on Li- the calculated cosine values are used to identify doubly excited states measured in a photodetachment experiment. In particular a resonant state that violates a propensity rule is found.

This thesis reports experimental observations of electric fields using Rydberg atoms, including dc field measurements near the surface of an atom chip, and demonstration of measurement techniques for ac fields far from the surface. Associated theoretical results are also presented, including Monte Carlo simulations of the decoherence of Rydberg states in electric field noise as well as an analytical calculation of the statistics of dc electric field inhomogeneity near polycrystalline metal surfaces. DC electric fields were measured near the heterogeneous metal and dielectric surface of an atom chip using optical spectroscopy on cold atoms released from the trapping potential. The fields were attributed to charges accumulating in the dielectric gaps between the wires on the chip surface. The field magnitude and direction depend on the details of the dc biasing of the chip wires, suggesting that fields may be minimized with appropriate biasing. Techniques to measure ac electric fields were demonstrated far from the chip surface, using the decay of a coherent superposition of two Rydberg states of cold atoms. We have used the decay of coherent Rabi oscillations to place some bounds on the magnitude and frequency dependence of ac field noise. The rate of decoherence of a superposition of two Rydberg states was calculated with Monte Carlo simulations. The states were assumed to have quadratic Stark shifts and the power spectrum of the electric field noise was assumed to have a power-law dependence of the form 1/f^κ. The decay is exponential at long times for both free evolution of the superposition and and Hahn spin-echo sequences with a π refocusing pulse applied to eliminate the effects of low-frequency field noise. This decay time may be used to calculate the magnitude of the field noise if κ is known. The dc field inhomogeneity near polycrystalline metal surfaces due to patch potentials on the surface has been calculated, and the rms field scales with distance to the surface as 1/z^2. For typical evaporated metal surfaces the magnitude of the rms field is comparable to the image field of an elementary charge near the surface.

En learning study om grundskoleelevers förklaring av vattenkokning och fasövergången har gjorts. Utifrån tidigare forskning har några delar av materians beskaffenhet och kokning av vatten valts ut och använts för att designa ett förtest som hjälper till att kartlägga elevernas tidigare kunskap. Alla elevers svar har analyserats och jämförts med varandra i likheter och skillnader. Några kritiska aspekter av lärandeobjektet valdes och en lektion som belyser de kritiska aspekterna av lärandeobjektet planerades. Genomförandet av lektionen filmades med fokus på att belysa kritiska aspekterna och filmen transkriberades för att studera samtalen under lektionen. Ett eftertest gjordes och resultatet av eftertestet analyserades och jämfördes med resultatet av elevernas svar på förtestet. Utfallet av studien har använts för att på en vetenskaplig grund designa en ny lektion som främjar lärandet.

Cooperative effect in the radiation process has been studied in for more than half a century. It is important in the sense of both basic physics and applied science. In this work, we study the dynamics of the cooperative spontaneous emission from an ensemble of N atoms which is uniformly excited by absorbing a single photon. We reveal that there are two different regimes in which the system exhibits totally different behaviors. One of them is the superradiance type of behavior: the system decays much quicker than single atom decay, with a decay rate proportional to N(λ/R)2, where N is the atom numbers, R is the size of the atom cloud, and λ is the wavelength. We call it Markovian regime because the sytem does not persist memory effect. The other regime is called non-Markovian regime and the system oscillates with effective Rabi oscillation frequency while slowly decaying with a rate proportional to the photon escaping rate. The effective Rabi oscillation is a new type of dynamics which analogs well known Cavity QED behavior. Particularly in the Markovian regime, we study the system dynamics as a manybody eigenfunction and eigenvalue problem. For a dense cloud, we find analytical solutions for the eigenstates and corresponding eigenvalues, which can help to generally describe the system dynamics for any initial conditions in this regime. One of the applications is in atom microscopy. We propose a scheme to measure the distance between two atoms/molecules beyond diffraction limit. It covers the whole range from half the wavelength to sub-nanometers, utilizing both the atom localization technique and the collective frequency shift effect due to the cooperative effect in the radiation of the two atoms. Another application that we propose is to generate Coherent XUV radiation using Raman-type superradaince. We prove that intense short pulses of XUV radiation can be produced by Raman type superradiance from an ensemble of atoms/ions driven by visible or IR laser pulses.

Using the resonant two-photon ionization (R2PI) and mass analyzed threshold ionization (MATI) spectroscopic techniques, we have recorded the vibrationally resolved spectra of p-bromoaniline in the S1 and cationic ground state. The band origin of the S1

Under the conditions of transfer hydrogenation employing ortho-cyclometallated iridium C,O-benzoate catalysts, selective silylallylation and CF₃-allylation were developed. In both cases, high levels of catalyst-directed enantioselectivity and diastereoselectivity were observed. Column chromatography was then tested as a new protocol to purify the iridium precatalyst; this single component precatalyst was proved to be more efficient to promote carbonyl crotylation reactions, both diastereo- and enantioselectivity were increased. Then, double asymmetric crotylation of 1,3-diols to deliver (pseudo-)C₂-symmetric adducts with exceptional level of enantioselectivity was devised. Implementation of this methodology and other hydrogenative C-C bond formations proved to be effective means for the preparation of two known polypropionate natural product fragments of C19-C25 of scytophycin C, C19-C27 of rifamycin S and the total synthesis of 6-deoxyerythronolide B. / text

In this dissertation I present theory and experimental results obtained in the Jones research group at the University of Arizona investigating the feasibility of neutral Hg as a candidate for an atomic clock. This investigation includes laser-cooling and trapping of several neutral Hg isotopes as well as spectroscopy of the 6¹S₀ - 6³P₀ doubly forbidden clock transition in neutral Hg¹⁹⁹. We demonstrate precision spectroscopy of the ground state cooling/trapping transition of neutral mercury at 254 nm using an optically pumped semiconductor laser (OPSL). This demonstration exhibits the utility of optically pumped semiconductor lasers (OPSLs) in the field of precision atomic spectroscopy. The OPSL lases at 1015 nm and is frequency quadrupled to provide the trapping light for the ground state cooling transition. We get up to 1.5 W single-frequency output power having a linewidth of < 10 kHz in the IR with active feedback. We frequency quadruple the OPSL in two external cavity stages to produce up to 120 mW of deep-UV light at 253.7 nm. I give a detailed characterization of the construction and implementation of the neutral Hg vapor cell magneto-optical trap (MOT). The trap can be loaded in as quickly as 75 ms at background vapor pressures below 10⁻⁸ torr. At reduced background pressure (< 10⁻¹⁰ torr) the loading time approaches 2 sec. We describe construction and stabilization of a laser resonant with the Hg¹⁹⁹ clock transition and the methods employed to find and perform the experimentally delicate spectroscopy of the clock transition. We present experimental results and analysis for our initial spectroscopy of the 6¹S₀- 6³P₀ clock transition in the Hg¹⁹⁹ isotope of neutral mercury.

Atomic polarizability plays an essential role in topics ranging from van der Waals interactions, state lifetimes, and indices of refraction, to next generation atomic clocks and atomic parity non-conservation experiments. Polarizability measurements, such as the ones described in this thesis, provide valuable input to these subjects and serve as benchmark tests for sophisticated atomic structure calculations. We measured the static polarizability of potassium and rubidium with record precision and 0.5% uncertainty using a Mach-Zehnder atom interferometer with an electric-field gradient. To support future precision measurements of polarizability, we developed a new atom beam velocity measurement technique called phase choppers. Using phase choppers, we demonstrated measurements of mean atom beam velocity with an uncertainty of 0.1%. We also developed a new way to probe atomic structure: a measurement of a zero-crossing of the dynamic polarizability of potassium, known as a magic-zero wavelength. We measured the first magic-zero wavelength of potassium with 1.5 pm uncertainty and established a new benchmark measurement for the ratio of the D1 and D2 line strengths. Finally, we propose the use of a resonant photoionization detector for measurements of strontium polarizability, and the use of contrast interferometry for measurements of alkali dimer tensor polarizabilities.