Ultra-slow atomic beam generation by velocity selective resonance

We describe a method to generate an ultra-slow atomic beam by velocity selective resonance (VSR). A VSR experiment on a metastable helium beam in a magnetic field is presented and the results show that the transverse velocity of the defected beam can be cooled and precisely controlled to less than the recoil velocity, depending on the magnitude of the magnetic field. We extend this idea to a cold atomic cloud to produce an ultra-slow Rb-87 beam that can be used as a source of an atomic fountain clock or a space clock.

Stopping power of gases for heavy ions

Pulse-height and time-of-flight methods have been used to measure the electronic stopping cross sections for projectiles of ¹²C, ¹⁶O, ¹⁹F, ²³Na, ²⁴Mg, and ²⁷Al, slowing in helium, neon, argon, krypton, and xenon. The ion energies were in the range 185 keV ≤ E ≤ 2560 keV.

A semiempirical calculation of the electronic stopping cross section for projectiles with atomic numbers between 6 and 13 passing through the inert gases has been performed using a modification of the Firsov model. Using Hartree-Slater-Fock orbitals, and summing over the losses for the individual charge states of the projectiles, good agreement has been obtained with the experimental data. The main features of the stopping cross section seen in the data, such as the Z₁ oscillation and the variation of the velocity dependence on Z₁ and Z₂, are present in the calculation. The inclusion of a modified form of the Bethe-Bloch formula as an additional term allows the increase of the velocity dependence for projectile velocities above v_o to be reproduced in the calculation.

Infared observations of H II regions

Spectral data are presented, giving intensities of the Brackett ɤ (B₇) line at six positions in M 42 and of the Brackett ten through fourteen (B₁₀-B₁₄) lines plus the He 4d³D-3p³p⁰ line at three positions in M 42. Observations of the Brackett ɤ line are also given for the planetary nebulae NGC 7027 and IC 418. Brackett gamma is shown to exhibit an anomalous satellite line in NGC 7027. Broadband data are presented, giving intensities at effective wavelengths of 1.25 μ, 1.65 μ, 2.2 μ, 3.5 μ and 4.8 μ for three positions in M 42.

Comparisons with visual and radio data as well as 12 micron and 20 micron data are used to derive reddening, electron temperatures, and electron densities for M 42 and the two planetaries, as well as a helium abundance for M 42. A representative electron temperature of 8400°K ± 1000°K, an electron density of 1.5 ±0.1 x 10³ cm^-3 and a He/H number density ratio of 0.10 +0.10/-0.05 are derived for the central region of M 42. The electron temperature is found to increase slightly with distance from the Trapezium.

M 42 is shown to emit in excess of the predicted recombination radiation throughout the entire infrared spectrum. The variations in the excess with wavelength and with position are analyzed to determine which of several physical processes may be operating. The longer wavelength infrared excess is shown to be dominated by dust emission, while the shorter wavelength infrared excess is caused by dust scattering. The dust is shown to be larger than the average interstellar particle. A new feature of the Orion red star ORS-1 is found in that it appears to have a reflection nebula around it.

Neutron-neutron scattering parameters from the ^3He(d,t)2p and ^3H(d,^3He)2n reactions

The energy spectra of tritons and Helium-3 nuclei from the reactions ³He(d,t)2p, ³H(d,³He)2n, ³He(d,³He)pn, and ³H(d,t)pn were measured between 6° and 20° at a bombarding energy of 10.9 MeV. An upper limit of 5 μb/sr. was obtained for producing a bound di-neutron at 6° and 7.5°. The ³He(d,t)2p and ³H(d,³He)2n data, together with previous measurements at higher energies, have been used to investigate whether one can unambiguously extract information on the two-nucleon system from these three-body final state reactions. As an aid to these theoretical investigations, Born approximation calculations were made employing realistic nucleon-nucleon potentials and an antisymmetrized final state wave function for the five-particle system. These calculations reproduce many of the features observed in the experimental data and indicate that the role of exchange processes cannot be ignored. The results show that previous attempts to obtain information on the neutron-neutron scattering length from the ³H(d,³He)2n reaction may have seriously overestimated the precision that could be attained.

I. Numerical solution of exact pair equations. II. Numerical solution of first-order pair equations

Part I

Numerical solutions to the S-limit equations for the helium ground state and excited triplet state and the hydride ion ground state are obtained with the second and fourth difference approximations. The results for the ground states are superior to previously reported values. The coupled equations resulting from the partial wave expansion of the exact helium atom wavefunction were solved giving accurate S-, P-, D-, F-, and G-limits. The G-limit is -2.90351 a.u. compared to the exact value of the energy of -2.90372 a.u.

Part II

The pair functions which determine the exact first-order wavefunction for the ground state of the three-electron atom are found with the matrix finite difference method. The second- and third-order energies for the (1s1s)¹S, (1s2s)³S, and (1s2s)¹S states of the two-electron atom are presented along with contour and perspective plots of the pair functions. The total energy for the three-electron atom with a nuclear charge Z is found to be E(Z) = -1.125•Z² +1.022805•Z-0.408138-0.025515•(1/Z)+O(1/Z²)a.u.

The reduced-alpha-width of the lowest 1¯ state of ^(16)O

Cross sections for the reaction ¹²C(α,γ)¹⁶O have been measured for a range of center-of-mass alpha particle energies extending from 1.72 MeV to 2.94 MeV. Two 8"x5" NaI (Tℓ) crystals were used to detect gamma rays; time-of-flight technique was employed to suppress cosmic ray background and background due to neutrons arising mainly from the ¹³C(α,n)¹⁶O reaction. Angular distributions were measured at center-of-mass alpha energies of 2.18, 2.42, 2.56 and 2.83 MeV. Upper limits were placed on the amount of radiation cascading through the 6.92 or 7.12-MeV states in ¹⁶O. By means of theoretical fits to the measured electric dipole component of the total cross section, in which interference between the 1¯ states in ¹⁶O at 7.12 MeV and at 9.60 MeV is taken into account, it is possible to extract the dimensionless, reduced-alpha-width of the 7.12-MeV state in ¹⁶O. A three-level R-matrix parameterization of the data yields the width Θ_α,F² = 0.14^+0.10_-0.08. A "hybrid" R-matrix-optical-model parameterization yields Θ_α,F² = 0.11^+0.11_-0.07. This quantity is of crucial importance in determining the abundances of ¹²C and ¹⁶O at the end of helium burning in stars.

An experimental study of a stellar neutron source: ^(13)C(α, n)^(16)O

Described in this thesis are measurements made of the thick-target neutron yield from the reaction ¹³C(α, n)¹⁶O. The yield was determined for laboratory bombarding energies between 0.475 and 0.700 MeV, using a stilbene crystal neutron detector and pulse-shape discrimination to eliminate gamma rays. Stellar temperatures between 2.5 and 4.5 x 10^{8 o}K are involved in this energy region. From the neutron yield was extracted the astrophysical cross-section factor S(E), which was found to fit a linear function: S(E) = [(5.48 ± 1.77) + (12.05 ± 3.91)E] x 10⁵ MeV-barns, center-of-mass system. The stellar rate of the ¹³C(α, n)¹⁶O reaction if calculated, and discussed with reference to helium burning and neutron production in the core of a giant star.

Results are also presented of measurements carried out on the reaction ⁹Be(α, n)¹²C, taken with a thin Be target. The bombarding energy-range covered was from 0.340 to 0.680 MeV, with excitation curves for the ground- and first excited-state neutrons being reported. Some angular distributions were also measured. Resonances were found at bombarding energies of E_LAB = 0.520 MeV (E_CM = 0.360 MeV, Γ ~ 55 keV CM, ωγ = 3.79 eV CM) and E_LAB = 0.600 MeV (E_CM = 0.415 MeV, Γ ˂ 4 keV CM, ωγ = 0.88 eV CM). The astrophysical rate of the ⁹Be(α, n)¹²C reaction due to these resonances is calculated.

Determination of electronic energy levels of molecules by 90° low energy electron scattering

A review of the theory of electron scattering indicates that low incident beam energies and large scattering angles are the favorable conditions for the observation of optically forbidden transitions in atoms and molecules.

An apparatus capable of yielding electron impact spectra at 90° with incident electron beam energies between 30 and 50 electron volts is described. The resolution of the instrument is about 1 electron volt.

Impact spectra of thirteen molecules have been obtained. Known forbidden transitions to the helium 2³S, the hydrogen b³Ʃ⁺_u, the nitrogen A³Ʃ⁺_u, B³π_g, a’π_g, and C³π_u, the carbon monoxide a³π, the ethylene ᾶ³B_1u, and the benzene ᾶ³B_1u states from the corresponding ground states have been observed.

In addition, singlet-triplet vertical transitions in acetylene, propyne, propadiene, norbornadiene and quadricyclene, peaking at 5.9, 5.9, 4.5, 3.8, and 4.0 ev (±0.2 ev), respectively, have been observed and assigned for the first time.

Caracterização química de fases cristalográficas e física dos cimentos MTA Fillapex, AH Plus, Sealer 26 e Endofill

O objetivo desta pesquisa consiste em analisar através da caracterização química de fases cristalinas a composição e estrutura; e com a caracterização física a densidade, porosidade e área superficial dos seguintes cimentos endodônticos: MTA Fillapex, AH Plus, Sealer 26 e o Endofill. Para tal, foram realizadas análises dos cimentos antes da manipulação (pó e pastas) e depois da manipulação (corpos de prova). Empregando-se as técnicas de caracterização química: DRX e FRX e como técnicas de caracterização física: Picnometria de Hélio, a porosimetria de mercúrio, distribuição granulométrica e área superficial pela metodologia de BET. A caracterização química detalhou a composição dos cimentos sendo compatível com a descrição do fabricante e forneceu a quantificação das suas fases. A caracterização física mostrou que o MTA Fillapex apresentou os melhores resultados: a menor porosidade, o menor volume médio e o menor diâmetro do poro, o Sealer 26 dentre os cimentos resinosos apresentou o pior resultado, o Endofill mostrou-se melhor que o Sealer 26 tendo a maior densidade, o menor diâmetro das partículas, a distribuição granulométrica mais homogênea comparando-se a este. Os cimentos a base de resina mostraram um diâmetro do poro menor que o Endofill. Estes resultados podem estar ligados diretamente aos requisitos de um material obturador ideal. A metodologia utilizada produziu um detalhamento das características químicas e físicas dos cimentos estudados, mostrando um caminho para novas pesquisas na área.

微晶玻璃在大功率脉冲氙灯封接中的应用

：为提高大功率脉冲氙灯的封接强度，将微晶玻璃作为封接材料引入到氙灯封接应用中. 以 Bi2O3,ZnO,Al2O3,MgO,CaCO3,SiO2,BaO,H3BO3,P2O5,Na2O 为原料，通过高温熔融制备了大功率脉冲氙灯封接 用微晶玻璃样品. 测试了样品的热膨胀系数,并通过差热分析(Differential Thermal Analysis，DTA)对脉冲氙灯 微晶玻璃的封接温度进行了讨论，用X 射线衍射(X-ray diffraction ，XRD)表征了封接玻璃，并进行了分析. 将 制得的样品磨成玻璃粉末，制成膏剂状玻璃焊料，对大功率脉冲氙灯进行封接，得到大功率脉冲氙灯的微晶 玻璃封接件. 通过氦质谱检漏仪检测，1#、2#、4#封接件气密性良好，达到10-6 Pa.

Kontrapultsazio-baloi uhin-forma errealistak sortzeko tresna.

[EN]In this project has been developed a tool which synthesizes realistic waveforms produced by the intra-aortic balloon pump. In addition the following waveforms have also been synthesized: arterial blood pressure (ABP) waveform, the four variations produced due to timing errors of the balloon and the waveform of the helium gas rapidly shuttling in and out of the balloon chamber. All waveforms are synthesized in synchrony with the balloon's inflation/deflation cycles. A database composed of annotated ECG (Electrocardiogram) normal sinus rhythm records has also been created during the project. In order to facilitate the work, two graphical user interfaces were developed. The first interface allows the selection of the ECG records, which were latter annotated using the second interface. Starting from the newly created annotated database, the different waveforms, mentioned above, were synthesized. In this document, in view of the synthesized waveforms, it can be concluded that the obtained results are satisfactory.

Digestão nitro-sulfúrica de fígado de peixe Mugil liza em forno de micro-ondas com radiação focalizada para determinar elementos de interesse ambiental por ICPMS

O presente estudo propõe uma metodologia para dissolução de tecidos biológicos em sistema de micro-ondas com radiação focalizada e posterior análise elementar por espectrometria de massas com plasma acoplado indutivamente (ICPMS). Foram determinados os elementos arsênio (As), cádmio (Cd), cobre (Cu), chumbo (Pb), níquel (Ni), vanádio (V) e zinco (Zn). A matriz nitro-peroxo-sulfúrica foi comparada com outra sem o ácido sulfúrico e apresentou melhor padrão de recuperação (acima de 90%) na quantificação dos elementos certificados no material de referência TORT-2. As interferências causadas pela presença do ácido sulfúrico na matriz digestora foram contornadas com o uso da célula de reação/colisão com gás hélio (He) e adição deste ácido na composição da curva de quantificação. O ganho analítico proporcionado pelo método de digestão em matriz sulfúrica, em sistema não pressurizado, baseia-se no incremento da temperatura reacional e na degradação completa da matéria orgânica. As digestões tradicionalmente realizadas para quantificação por ICPMS, compostas unicamente de ácido nítrico (HNO3) e peróxido de hidrogênio (H2O2), não apresentam a mesma eficiência na degradação da matéria orgânica em sistemas abertos. Por fim, este método foi aplicado satisfatoriamente em amostras de tecido hepático de peixe Mugil liza (tainha), comprovando sua eficiência em monitorar a bioacumulação, utilizando-se da sensibilidade da técnica multielementar de ICPMS

Low field electron emission from nanoclustered carbon grown by cathodic arc

Nanocluster carbon films grown using a cathodic arc process at room temperature in the presence of background gases such as helium are found to be good electron emitters. The variation in the surface morphology and the corresponding emission characteristics of the films with change in helium partial pressure (5×10-4 to 50 Torr) during film growth are reported. The effect of helium partial pressure on clustering was studied for films grown at nitrogen partial pressures of 10-4 and 10-3 Torr. The surface morphology of the films varied from smooth through clusters (with sizes 50-200 nm) to fibrous films. The threshold field varied from 1 to 10 V/μm for an emission current density 1 μA/cm2.

Hydrogenated amorphous silicon and silicon nitride deposited at less than 100° C by ECR-PECVD for thin film transistors

A systematic study has been made of the growth of both hydrogenated amorphous silicon (a-Si:H) and silicon nitride (a-SiN) by electron cyclotron resonance plasma enhanced chemical vapour deposition (ECR-PECVD). In the case of a-SiN, helium and nitrogen gas is injected into the system such that it passes through the resonance zone. These highly ionised gases provide sufficient energy to ionise the silane gas, which is injected further downstream. It is demonstrated that a gas phase reaction occurs between the silane and nitrogen species. It is control of the ratio of silane to nitrogen in the plasma which is critical for the production of stoichiometric a-SiN. Material has been produced at 80°C with a Si:N ratio of 1:1.3 a breakdown strength of ∼6 MV cm-1 and resistivity of > 1014 Ω cm. In the case of a-Si:H, helium and hydrogen gas is injected into the ECR zone and silane is injected downstream. It is shown that control of the gas phase reactions is critical in this process also. a-Si:H has been deposited at 80 °C with a dark conductivity of 10-11 Ω-1 cm-1 and a photosensitivity of justbelowl 4×104. Such materials are suitable for use in thin film transistors on plastic substrates.

Recent developments of the Laser-assisted Cold Spray process and deposit characterisation

Laser-assisted Cold Spray (LCS) is a new coating and fabrication process which combines the supersonic powder beam found in Cold Spray (CS) with laser heating of the deposition zone. LCS retains the advantages of CS; solid-state deposition, high build rate and the ability to deposit onto a range of substrates, while reducing operating costs by removing the need to use gas heating and helium as the process gas. Recent improvements in powder delivery and laser energy coupling to workpiece have been undertaken to improve deposition efficiency (DE) and build rate, while real-time temperature logging allows greater management of deposition conditions and deposit characteristics.