No description available.

No description available.

No description available.

We use the positions and velocities of satellites of our galaxy and of other spiral galaxies to determine the radial mass profile of dark matter halos. We combine our measurement of the velocities of five remote Galactic satellites with published observations of the other Galactic satellites to obtain a complete sample of test particles. We then apply statistical techniques and timing arguments to deduce that the mass of the Galaxy is ≳ 1.3 x 10¹²M(⊙) for standard assumptions and that the halo extends beyond 100 kpc Galactocentric distance. We confirm our result by examining the dynamics of other Local Group galaxies. Subsequently, we expand our study to include nearby (1000 km s⁻¹ < ν(R) < 7000 km s⁻¹) Sb-Sc type galaxies. We use multiaperture spectrometers to conduct a survey for satellite galaxies and are able to double the sample of known satellite galaxies (satellites are defined to be at least eight times fainter than the primary) of isolated unbarred late-type spirals. The homogeneity of the primaries allows us to combine observations of satellites of various primaries and analyze the dynamical properties of the ensemble. The characteristics of this satellite sample (number, radial and azimuthal distribution, luminosity function, orbital characteristics, and contamination) are discussed. Finally, new models of the dynamics of satellite galaxies are developed that include the effects of the cosmological evolution of the halos and do not presume that halos are virialized. These models are used to constrain the mass distribution in which the satellite galaxies orbit. We conclude that only model halos with more than 10¹²M(⊙) within a galactocentric radius of 200 kpc are acceptable (90% confidence limit) for orbits of eccentricity < 0.9. The preferred models (60% confidence limit) are of halos with more than 1.6 x 10¹²M(⊙) within 200 kpc. Halos that formed in a universe with Ω = 1 also fall within the preferred range and have ∼ 3 x 10¹²M(⊙) within 200 kpc. In addition, we infer that the satellites’ orbital eccentricities are typically less than 0.9. These results, in conjunction with the results obtained for the halo of our galaxy, constitute convincing evidence for the existence of large (>200 kpc) and massive (> 10¹²M(⊙), M/L > 80) dark matter halos around isolated unbarred late-type spiral galaxies.

In this thesis we use multi-transitional millimeter/submillimeter-wave molecular spectroscopy of CO and CS to determine the state of the molecular gas in the central regions of three starbursts: M82, IC342, and M83. High angular resolution 60 and 100 μm IRAS images provide complementary information about the thermal dust emission in IC342 and M83. Our CO observations reveal the presence of a molecular ring and supernovae driven wind in M82. In IC342 and M83 there is evidence for molecular bars and central rotating cores. The CO and CS line ratio analyses suggest a multicomponenet medium with clouds externally heated by ultraviolet flux from young, massive stars. Excitation temperatures typically range from 20 to 40 K throughout the nuclear regions of the sample galaxies. In M82 the CO and CS optical depths are ∼ 1. Our analysis of ¹²CO indicates that this gas is optically thick toward the centers of IC342 and M83. The molecular gas mass in each galaxy is ∼ 5x10⁷ M(⊙). We derive an average cloud size between 0.1 and 1 pc in the nuclear region of M82 and M83. An average cloud size of 10 pc is found over a comparable region in IC342. From tidal arguments we find that the clouds must have densities greater than 100 to 1000 cm⁻³ to survive. If the clouds are virialized, then the expected individual cloud linewidths are 9, 40, 5 and 27 km/s for M82, IC342, M83 and the Milky Way, respectively. For the clouds to be pressure-bound, inter-cloud pressures > 10x the peak value in the Galactic Center are required. If the magnetic fields are frozen into the gas, an average field strength of 8.5 mG is needed to support the nuclear clouds in each galaxy from collapse. Enhanced IRAS images reveal bright, compact nuclear components in IC342 and M83. HII regions are seen along spiral arms in IC342 and a dusty bar is seen in M83. The similarity between radio continuum maps and the high resolution IRAS maps suggest that infrared emission arises from HII regions. Using an emissivity law of β ∼ 1.5, the derived dust temperatures in the nuclei of IC342 and M83 are essentially the same as the gas excitation temperatures. For this to occur, gas densities of > 10⁴ cm⁻³ are implied. We derive a star-formation efficiency, ∊, of 77, 60, 10 and 2% for M82, M83, IC342, and the Milky Way, respectively. We find evidence that the gas surface density toward the centers of these galaxies is α ∊. We estimate star-formation rates of 16, 6, 2.5, and .06 M(⊙)/yr for M82, M83, IC342 and the Milky Way. The gas depletion timescales are a few million years for M82 and M83 and a few times 10⁷ and 10⁸ years in IC342 and the Milky Way. We find a strong correlation between cloud diameter and star-formation efficiency, with smaller clouds found in galaxies with higher ∊. We conclude these smaller clouds are a by-product and not a causal factor of the starburst phenomenon.

I prepared Ag/Pd and Cu/Pd superlattices using both sputtering and molecular beam epitaxy. For the Ag/Pd (t(Ag):t(Pd) = 1:1) superlattices, I observed two distinctive behaviors in the structural coherence length ξ as a function of modulation wavelength Λ. Using Brillouin light scattering (BLS) I observed a 50% enhancement of the shear elastic constant c₅₅ and a 16% increase of c₁₁ with decreasing Λ. Annealing study showed that a high structural order of the films in the growth direction was strongly correlated to the increase of c₅₅. For the 3:1 and 1:3 Ag/Pd samples, I also observed a monotonic increase of the Rayleigh velocity υ(R) (or c₅₅) with decreasing Λ and similar behavior in the structural coherence length to the 1:1 samples. In conclusion, the recrystallization of the alloy and the formation of extended interfaces by intermixing at the Ag-Pd interfaces are responsible for a large enhancement of c₅₅. Using BLS for the Cu/Pd superlattices, I observed a 24% decrease of c₅₅ as Λ was decreased to ∼30-40 Å, followed by a rapid increase for smaller Λ. The observed homogeneous strain in the growth direction showed a strong relationship with c₅₅. The strain was localized at the interface and the Cu/Pd films were in compressive stress for Λ < 38 Å. In conclusion, a localized strain at the interfaces in Cu/Pd is related to the softening in c₅₅. The measurements of in-plane lattice spacing d[220] indicated a structural transformation of the films at Λ = 14 Å from an incoherent to a coherent structure. However, the in-plane strain did not show any relationship with the softening of c₅₅. For single crystalline Cu/Pd superlattices, well-defined RHEED streaks showed incommensurate growth of Cu(111) on Pd(111) layer. The measured shear elastic constant c₅₅ showed a 26% decrease with respect to the largest Λ film with a peak at Λ ≃ 40 Å. Unlike the sputtered films, while c₅₅ decreases by 26% with decreasing Λ, the Cu/Pd films show no change in d(avg)[111] for Λ > 40 Å. I observed no in-plane anisotropies in υ(R) as predicted from theory for single crystal films.

Structural, magnetic, and magneto-optical properties of Co/Pd and Co/Pd/Cu superlattices, ultra-thin Co films and MnSb alloys have been studied. The superlattices and Co films were grown by molecular beam epitaxy (MBE) while the MnSb alloy films were made by sputtering techniques. Several x-ray diffraction techniques were used to analyze the physical structure of the superlattices and alloys. Magnetometry techniques were used to determine some of the room temperature and temperature dependent magnetic properties of the films. In situ and ex situ measurements of the magneto-optical properties of the ultra-thin Co films and alloys also were made.

A quantitative analysis of carrier-carrier scattering for electron-hole semiconductor plasmas is presented. Material parameters appropriate for GaAs are used for all calculations. Calculations are performed using the Boltzmann equation for carrier-carrier scattering. Screening of the Coulomb potential is treated in the fully-dynamical random phase approximation. Results are shown for roomtemperature near-equilibrium and far-from-equilibrium plasmas. Also, the equilibrium zero momentum scattering rates are calculated as a function of temperature (T = 10K to T = 1000K) and density (n = 10¹⁵ cm⁻³ to n = 10¹⁹ cm⁻³). Ultrafast scattering rates (on the order of 10 fs) are found to result for a carrier distribution with vacant low-momentum states. These rates are shown to be associated with the undamping of the acoustic plasmon which influences the scattering through screening of the Coulomb potential. Further analysis of plasmon undamping is presented, showing the conditions necessary for undamping of the acoustic mode. Results from a separate set of calculations, showing the time-evolution of the Wigner distribution for a semiconductor quantum wire, are shown. These numerical calculations were performed using the collisionless quantum Boltzmann equation for the case of a lightly-damped plasmon and an unstable growing plasma mode. Comparison is made with results predicted by the linear theory (Lindhard). Results showing the effects of increasing the field strength beyond the linear regime are also presented.

This thesis investigates the carrier and gain dynamics of semiconductor quantum dots in the strong quantum confinement regime (i.e. the dot radius is smaller than the bulk excitonic Bohr radius). The materials under investigation are InP and CdSe. We can summarize our findings as follows: For the first time, the quantum confined ground state in InP quantum dots has been observed at room temperature by femtosecond spectral holeburning. This is the first confirmation of the observation of a strongly confined quantum dot made of III-V semiconductor materials. In CdSe quantum dots with a radius of half the bulk exciton Bohr radius, the carrier and gain dynamics have been investigated. The predicted phonon bottleneck, which should slow down carrier relaxation up to nanoseconds, has not been found. The carrier relaxation rates are rather on the order of 1 eV/ps. Gain has been found for the first time in strongly confined quantum dots. The existence of gain was proven by spectral holeburning in the gain region. The gain buildup and decay dynamics have been studied on a femtosecond and picosecond timescale. A multi-level model including biexcitons accounts for the gain formation. The model has been confirmed by three-beam spectral holeburning experiments and femtosecond pump-probe experiments with circularly polarized light. Some quantum dots did not show gain under high optical excitation but instead exhibited photodarkening. The carrier separation and localization dynamics of this photodarkening process has been studied on a femtosecond timescale. For the first time, the shift of the bleaching towards lower energy during the localization process could be observed on a femtosecond timescale. Finally, pulse propagation in bulk CdSe at multiple Pi-pulses has been studied. For the first time, strong evidence for the observation of self induced transparency in semiconductors has been found. Also, optical precursors, probably of nonlinear nature, have been found.

Large-scale neutrino telescopes will be powerful tools to observe multitude of mysterious phenomena happening in the Universe. The dark matter puzzle is listed as one of them. In this study, indirect detection of dark matter via neutrino signals is presented. The upward muon, the contained muon and the hadronic shower fluxes are calculated, assuming annihilation/decay of the dark matter in the core of the astrophysical objects and in the Galactic center. Direct neutrino production and secondary neutrino production from the decay of Standard Model particles produced in the annihilation/decay of dark matter are studied. The results are contrasted to the ones previously obtained in the literature, illustrating the importance of properly treating muon propagation and energy loss for the upward muon flux. The dependence of the dark matter signals on the density profile, the dark matter mass and the detector threshold are discussed. Different dark matter models (gravitino, Kaluza-Klein and leptophilic) which can account for recent observations of some indirect searches are analyzed regarding their detection in the kilometer size neutrino detectors in the near future. Muon and shower rates and the minimum observation times in order to reach 2σ detection significance are evaluated, with the result suggesting that the optimum cone half angles chosen about the Galactic center are about 10° (50°) for the muon (shower) events. A detailed analysis shows that for the annihilating dark matter models such as the leptophilic and Kaluza-Klein models, upward and contained muon as well as showers yield promising signals for dark matter detection in just a few years of observation, whereas for decaying dark matter models, the same observation times can only be reached with showers. The analytical results for the final fluxes are also obtained as well as parametric forms for the muon and shower fluxes for the dark matter models considered in this study.