Two experimental projects involving perovskite manganese oxide compounds are presented. The first involved dielectric and transport studies of the insulator-metal transition as a function of charge-carrier doping in La1-xCaxMnO3 (0 < x < 0.15) bulk samples. The results provide new insight into the role of competing magnetic, lattice and Coulomb energies in determining the insulator-metal transition near x=0.22. The second project involved the growth, structural characterization, and resistive anisotropy of a-axis oriented Nd0.2Sr0.8MnO3 thin films with thicknesses t in the range 10 nm< t < 150 nm. Thicker films develop regular crack arrays which are the origin of a highly anisotropic in-plane electrical resistance. These cracks form parallel to the crystallographic c-axis on films with tensile strain deposited on NdGaO3 (100) and La0.3Sr0.7Al0.65Ta0.35O3 (110) substrates. Films grown under compressive strain on LaAlO3 (110) substrates have no cracks.

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We have investigated the conductance, g, of 1,4-butanedithiol linked Au nanoparticle films as a function of temperature, T, bias potential, V, and applied magnetic field, B. An interesting temperature dependence is observed for non-metallic films with thicknesses just below a critical film thickness: g ~ exp [-(T_0/T)^(1/2)] for 20 K < T < 300 K. We show that this temperature dependence is incompatible with an Efros-Shklovskii "variable range hopping" model, since "hopping distances" are too large to be consistent with tunneling processes, and tend to scale with size of super-clusters of molecularly-linked nanoparticles. We propose a "quasilocalized hopping" model based on competition between single-electron charging of super-clusters and electron backscattering within super-clusters to explain the observed temperature dependence. Various electron scattering time scales are extracted from magnetoconductance data using a modified "weak localization" model. Elastic scattering time scales are comparable to those required for an electron to traverse a nanoparticle, while inelastic and spin-orbit scattering time scales are consistent with those found in studies of conventionally-prepared granular Au films. At interfaces between metallic 1,4-butanedithiol-linked Au nanoparticle films and conventional superconductors, we find that g consistently exhibits peaks, as well as oscillations, that depend simultaneously on both V and B. Such peaks and correlated conductance oscillations are predicted by an enhanced Andreev reflection process due to disorder-driven elastic scattering and electron-hole interference in the nanoparticle film. While oscillations have been predicted by a so-called "reflectionless tunneling" model, they have not been observed at other normal-superconductor interfaces. We speculate that oscillations are observable in this system due to synthetically controlled uniformity of elastic scattering length (i.e., nanoparticle diameter) and a reduced number of current-carrying pathways, especially near the interface. Contrary to predictions of existing "reflectionless tunneling" models, we find that the periods of oscillation in B decrease as T increases. This suggests that the area of interfering pathways increases with T. We propose that this increasing area can be attributed to magnetic field penetration into the superconductor. Conductance data agrees remarkably well with known temperature dependence of penetration depth predicted by BCS theory. Our study shows that this additional region of flux must be considered in experimental and theoretical studies of "reflectionless tunneling", and underscores the utility of molecularly-linked nano\-particle films as a platform for studying charge transport.

We have investigated the conductance, g, of 1,4-butanedithiol linked Au nanoparticle films as a function of temperature, T, bias potential, V, and applied magnetic field, B. An interesting temperature dependence is observed for non-metallic films with thicknesses just below a critical film thickness: g ~ exp [-(T_0/T)^(1/2)] for 20 K < T < 300 K. We show that this temperature dependence is incompatible with an Efros-Shklovskii "variable range hopping" model, since "hopping distances" are too large to be consistent with tunneling processes, and tend to scale with size of super-clusters of molecularly-linked nanoparticles. We propose a "quasilocalized hopping" model based on competition between single-electron charging of super-clusters and electron backscattering within super-clusters to explain the observed temperature dependence. Various electron scattering time scales are extracted from magnetoconductance data using a modified "weak localization" model. Elastic scattering time scales are comparable to those required for an electron to traverse a nanoparticle, while inelastic and spin-orbit scattering time scales are consistent with those found in studies of conventionally-prepared granular Au films. At interfaces between metallic 1,4-butanedithiol-linked Au nanoparticle films and conventional superconductors, we find that g consistently exhibits peaks, as well as oscillations, that depend simultaneously on both V and B. Such peaks and correlated conductance oscillations are predicted by an enhanced Andreev reflection process due to disorder-driven elastic scattering and electron-hole interference in the nanoparticle film. While oscillations have been predicted by a so-called "reflectionless tunneling" model, they have not been observed at other normal-superconductor interfaces. We speculate that oscillations are observable in this system due to synthetically controlled uniformity of elastic scattering length (i.e., nanoparticle diameter) and a reduced number of current-carrying pathways, especially near the interface. Contrary to predictions of existing "reflectionless tunneling" models, we find that the periods of oscillation in B decrease as T increases. This suggests that the area of interfering pathways increases with T. We propose that this increasing area can be attributed to magnetic field penetration into the superconductor. Conductance data agrees remarkably well with known temperature dependence of penetration depth predicted by BCS theory. Our study shows that this additional region of flux must be considered in experimental and theoretical studies of "reflectionless tunneling", and underscores the utility of molecularly-linked nano\-particle films as a platform for studying charge transport.

Wireless Sensor Networks (WSNs) are ad-hoc wireless networks for small form-factor embedded nodes with limited memory, processing and energy resources. Certain applications, like industrial automation and real-time process monitoring requires time synchronized reliable network protocol. Current work for WSNs provides either time synchronized with low reliability (WirelessHART) or reliable network without time synchronization (Collection Tree Protocol). The Collection Tree Protocol (CTP) provides the reliability from 94.7% to 99.9% for CSMA-CA based MAC layer. This paper addresses channel hopping, a class of frequency diverse communication protocol in which subsequent packets are sent over different frequency channels. Channel hopping combats external interference and persistent multipath fading, two of the main causes of failure along a communication link. Channel hopping technique leads to a high reliable and efficient protocol which is specified by HART Communication Foundation and named as WirelessHART. WirelessHART Data-Link layer designed based on TDMA and CSMA-CA mechanism. By implementing the CTP over WirelessHART Data-Link layer, the reliability of the network protocol can be improved compare to actual CTP standard implementation. This thesis describes the design and implementation of Collection Tree Protocol over WirelessHART Data-Link layer. The implementation is done using TinyOS, nesC programming language using Crossbow TelosB CC2420 radio chip nodes. The results and experiments show the evaluation of the system prototype.

Two global optimization methods are proposed in this thesis. They are the multicanonical basin hopping (MUBH) method and the basin paving (BP) method. <br /><br /> The MUBH method combines the basin hopping (BH) method, which can be used to efficiently map out an energy landscape associated with local minima, with the multicanonical Monte Carlo (MUCA) method, which encourages the system to move out of energy traps during the computation. It is found to be more efficient than the original BH method when applied to the Lennard-Jones systems containing 150-185 particles. <br /><br /> The asynchronous multicanonical basin hopping (AMUBH) method, a parallelization of the MUBH method, is also implemented using the message passing interface (MPI) to take advantage of the full usage of multiprocessors in either a homogeneous or a heterogeneous computational environment. AMUBH, MUBH and BH are used together to find the global minimum structures for Co nanoclusters with system size <em>N</em>&le;200. <br /><br /> The BP method is based on the BH method and the idea of the energy landscape paving (ELP) strategy. In comparison with the acceptance scheme of the ELP method, moving towards the low energy region is enhanced and no low energy configuration may be missed during the simulation. The applications to both the pentapeptide Met-enkephalin and the villin subdomain HP-36 locate new configurations having energies lower than those determined previously. <br /><br /> The MUBH, BP and BH methods are further employed to search for the global minimum structures of several proteins/peptides using the ECEPP/2 and ECEPP/3 force fields. These two force fields may produce global minima with different structures. The present study indicates that the global minimum determination from ECEPP/3 prefers helical structures. Also discussed in this thesis is the effect of the environment on the formation of beta hairpins.

The structural and electronic properties of small tungsten nanoparticles Wn (n=2-16) were investigated by density functional theory (DFT) calculation. For the W10 nanoparticle, ten lowest-energy structures were first obtained by basin-hopping method (BH) and ten by big-bang method (BB) with the tight-binding many-body potential for bulk tungsten material. These fifty structures were further optimized by the DFT calculation in order to find the better parameters of tight-binding potential adquately for W nanoparticles. With these modified parameters of tight-binding potentials, several lowest-energy W nanoparticles of different sizes can be obtained by BH and BB methods and then further refined by DFT calculation. According to the values of binding energy and second-order energy difference, it reveals that the structure W12 has a relatively higher stability than those of other sizes. The vertical ionization potential (VIP), adiabatic electron affinity (AEA) and HOMO-LUMO Gap are also discussed for W nanoparticles of different sizes.

In this study, we used the molecular statics, molecular dynamics, and density function theory to investigate structural, electronic, and mechanical properties of ultra-thin silica nanowires. There are two parts in this study. In the first part, we used basin-hopping method to get different diameters of silica nanowires, nemed 2MR, 2MR-2O, 3MR-3O, 4MR-4O, 5MR-5O, 4MR-3f, 4MR-4f, and 4MR-5f. The various silica nanowires were optimized by density function theory to obtain the projected density of states, Mulliken charge, and electronic density difference, and we also compared this results to £\-quartz. In the second part, the molecular dynamics simulations were performed to investigate deformation behavior of silica nanowires under axial tensile loading at 10K. The Young¡¦s modulus increases when the diameter decreases. We also used angular correlation function to study the mechanical properties and variation of structures.

With the progress of technology, large capacity and scalable are required for the future. Recent years, the physical limit is approached and a next-generation memory is needed in the future. In addition, non- volatile memory occupies more than 96% in the memory market, and RRAM has great advantages such as simple structure, high scalable, low operation voltage, high operation speed, high endurance and retention. That is the reason RRAM is the candidate in the next generation. In this experiment, multi-sputtering was used to deposit Zr:SiO 2 and Pt on TiN bottom electrode. The sandwich structure was metal/insulator/metal (MIM). With the different dielectric constant material, a different electrical field will be produced. And then I-V measurement and materials analysis were used to investigate the characteristic of the RRAM. At first, a forming process is required to the RRAM. The device was swept from negative to positive voltage and obtained the conduction mechanism from curve fitting. The different dielectric constant materials were used to fabricate the RRAM. High and low dielectric materials were HfO 2 and BN, respectively. The electric field distribution is centralized in low dielectric material so the electrons will drift to the direction of electric field. Hence, the Vset will be centralized and more stable. We also fabricated a Zr:SiO 2 /C:SiO 2 RRAM as an high K and low K material. The current fitting results that a hopping conduction occurs in low resistive state (LRS) and high resistive state (HRS). Both from Raman spectrum and FT-IR spectrum, a graphene oxide was existed in the C:SiO 2 thin film. While the filament was form, the tip of the filament will approach the graphene oxide because of the point effect. Hence, the resistance switching will happen in the grapheme oxide and set voltage will be more stable and lower the operated current. Next, an ICP treatment was used in order to "burn" the carbon in SiO 2 . The purpose is to make an extremely low K material and ignore the effect of the existence of carbon. From the FT-IR spectrum, the carbon signals were disappeared after the ICP oxygen plasma treatment. In the I-V fitting diagram, space char limit results in the high voltage region. The electrical field simulation was an auxiliary tool which shows a strong electrical field occurs in the extremely low K area. While the electrons flow through the conduction path, they will be confined in the porous area. The operation current will decrease because of the limited conduction area.

The allocation of frequency spectrum by the FCC for Ultra Wideband (UWB) communications in the 3.1-10.6 GHz has paved the path for very high data rate Gb/s wireless communications. Frequency synthesis in these communication systems involves great challenges such as high frequency and wideband operation in addition to stringent requirements on frequency hopping time and coexistence with other wireless standards. This research proposes frequency generation schemes for such radio systems and their integrated implementations in silicon based technologies. Special emphasis is placed on efficient frequency planning and other system level considerations for building compact and practical systems for carrier frequency generation in an integrated UWB radio. This work proposes a frequency band plan for multiband OFDM based UWB radios in the 3.1-10.6 GHz range. Based on this frequency plan, two 11-band frequency synthesizers are designed, implemented and tested making them one of the first frequency synthesizers for UWB covering 78% of the licensed spectrum. The circuits are implemented in 0.25µm SiGe BiCMOS and the architectures are based on a single VCO at a fixed frequency followed by an array of dividers, multiplexers and single sideband (SSB) mixers to generate the 11 required bands in quadrature with fast hopping in much less than 9.5 ns. One of the synthesizers is integrated and tested as part of a 3-10 GHz packaged receiver. It draws 80 mA current from a 2.5 V supply and occupies an area of 2.25 mm2. Finally, an architecture for a UWB synthesizer is proposed that is based on a single multiband quadrature VCO, a programmable integer divider with 50% duty cycle and a single sideband mixer. A frequency band plan is proposed that greatly relaxes the tuning range requirement of the multiband VCO and leads to a very digitally intensive architecture for wideband frequency synthesis suitable for implementation in deep submicron CMOS processes. A design in 130nm CMOS occupies less than 1 mm2 while consuming 90 mW. This architecture provides an efficient solution in terms of area and power consumption with very low complexity.