The first project investigated the reasons for why grafted polyelectrolye brushes have smaller friction coefficients than grafted neutral polymer brushes. The flexible neutral polymer brush is treated as a bead-spring model, and the polyelectrolyte brush is treated the same way except that each bead is charged and there are counterions present to neutralize the charge. We investigated the friction coefficient, monomer density, and brush penetration for the two kinds of brushes with both... ]]> Yangpeng Ou http://iris.lib.neu.edu/physics_diss/37 http://iris.lib.neu.edu/physics_diss/37 Thu, 13 Jun 2013 08:52:42 PDT This main focus of the work is on controlling the growth morphology in GaN and related nanowires. Two key results are presented: (1) demonstration of GaN nanowire growth in a newly discovered `serrated' morphology and (2) demonstration of Mn-doped, GaMnN nanowires by a new method. In (1) it is shown that simply by controlling the type of catalyst, size of the catalyst and the initial ratio of the precursor materials, GaN nanowire growth in a highly periodic serrated morphology can be obtained. Unlike regular non-serrated wires which grow in the non-polar [1010] direction, growth of the serrated wires is in... ]]> Zheng Ma http://iris.lib.neu.edu/physics_diss/36 http://iris.lib.neu.edu/physics_diss/36 Wed, 05 Jun 2013 13:08:00 PDT Most technological functional and structural materials consist of an assembly of small crystal grains of different orientation, which can vary in size from a few nanometers to several hundred microns. The physical properties of "polycrystalline materials'' are strongly influenced by the complex interfaces between grains that break the translational order of the crystal. Grain boundaries (GBs) exhibit equilibrium structures that can greatly vary in their degree of ordering depending on the relative orientation of the two grains, temperature, and atomic species. They can also move (migrate) in different ways in response to different external driving forces such as GB curvature... ]]> Ari Joel Adland http://iris.lib.neu.edu/physics_diss/35 http://iris.lib.neu.edu/physics_diss/35 Mon, 03 Jun 2013 09:23:28 PDT Single molecule force spectroscopy is a powerful method that explores the DNA interaction properties of proteins involved in a wide range of fundamental biological processes such as DNA replication, transcription, and repair. We use optical tweezers to capture and stretch a single DNA molecule in the presence of proteins that bind DNA and alter its mechanical properties. We quantitatively characterize the DNA binding mechanisms of proteins in order to provide a detailed understanding of their function. In this work, we focus on proteins involved in replication of Escherichia coli (E. coli), endogenous eukaryotic retrotransposons Ty3 and LINE-1, and human immunodeficiency... ]]> Kathy Rajni Chaurasiya http://iris.lib.neu.edu/physics_diss/34 http://iris.lib.neu.edu/physics_diss/34 Mon, 06 May 2013 08:35:41 PDT In the last ten years important breakthroughs in the understanding of the topology of complexity have been made in the framework of network science. Indeed it has been found that many networks belong to the universality classes called small-world networks or scale-free networks. Moreover it was found that the complex architecture of real world networks strongly affects the critical phenomena defined on these structures. Nevertheless the main focus of the research has been the characterization of single and static networks.

Recently, temporal networks and interacting networks have attracted large interest. Indeed many networks are interacting or formed by a multilayer... ]]> Kun Zhao http://iris.lib.neu.edu/physics_diss/33 http://iris.lib.neu.edu/physics_diss/33 Wed, 16 Jan 2013 09:25:43 PST Current major topics in condensed matter physics mostly focus on the investigation of materials having exotic quantum phases. For instance, Z₂ topological insulators have novel quantum states, which are distinct from ordinary band insulators. Recent developments show that these nontrivial topological phases may provide a platform for creating new types of quasiparticles in real materials, such as Majorana fermions. In correlated systems, high-T_c superconducting cuprates are complicated due to the richness of their phase diagram. Surprisingly, the discovery of iron pnictides demonstrates that high-T_c superconductivity related phenomena are not unique to copper oxide compounds. Many people believe that the better... ]]> Yung Jui Wang http://iris.lib.neu.edu/physics_diss/32 http://iris.lib.neu.edu/physics_diss/32 Fri, 21 Dec 2012 11:45:51 PST In this thesis, we focus on the massive superstring states. Starting from a short review on the first massive level open string states in ten dimensions, we investigate the four-dimensional physical open string states under N=4,2,1 compactifications. We find these physical states split into certain supermultiplets by working out explicitly their supersymmetry transformations. We then focus on the universal states which are common to all compactifications, their scattering amplitudes are the most appealing and important for these scattering processes could generate model-independent stringy signals which could be tested at the Large Hadron Collider if the fundamental string mass scale is... ]]> Wan-Zhe Feng http://iris.lib.neu.edu/physics_diss/31 http://iris.lib.neu.edu/physics_diss/31 Mon, 19 Nov 2012 12:37:34 PST Phase-field modeling has emerged as a powerful method to model interface evolution in various contexts. In this thesis, we use this general formulation to model materials interfaces in three distinct, yet related, problems. In the first problem, we characterize both analytically and numerically short-range forces between spatially diffuse interfaces in multi-phase-field models of polycrystalline materials. The results show that forces are always attractive for traditional models where each phase-field represents the phase fraction of a given grain. The implication of these results for understanding grain-boundary premelting are discussed. In the second problem, we present a phase-field model of nanowire growth... ]]> Nan Wang http://iris.lib.neu.edu/physics_diss/30 http://iris.lib.neu.edu/physics_diss/30 Wed, 20 Jun 2012 06:26:11 PDT Studies of small molecule-DNA interactions are essential for developing new drugs for challenging diseases like cancer and HIV. The main idea behind developing these molecules is to target and inhibit the reproduction of the tumor cells and infected cells. We mechanically manipulate single DNA molecule using optical tweezers to investigate two molecules that have complex and multiple binding modes. Mononuclear ruthenium complexes have been extensively studied as a test for rational drug design. Potential drug candidates should have high affinity to DNA and slow dissociation kinetics. To achieve this, motifs of the ruthenium complexes are altered. Our collaborators designed a... ]]> Thayaparan Paramanathan http://iris.lib.neu.edu/physics_diss/29 http://iris.lib.neu.edu/physics_diss/29 Wed, 28 Mar 2012 07:32:11 PDT Quantum channels are functions that map density matrices to density matrices. They can be used to describe a vast array of system environment interactions for quantum mechanical systems. The focus in quantum information theory lies on the study of the information content -- the quantum entropy -- of input and output system. The property of how much information a channel can convey is called capacity. When two quantum channels are combined they act on a bigger, possibly entangled state in parallel. The effects of entanglement on the capacity of a pair of channels have been widely studied. Still, recent work... ]]> David K. Moser Entropy Force and energy http://iris.lib.neu.edu/physics_diss/28 http://iris.lib.neu.edu/physics_diss/28 Thu, 08 Mar 2012 05:23:41 PST Spectroscopies resolved highly in momentum, energy and/or spatial dimensions are playing an important role in unraveling key properties of wide classes of novel materials. However, spectroscopies do not usually provide a direct map of the underlying electronic spectrum, but act as a complex `filter' to produce a `mapping' of the underlying energy levels, Fermi surfaces (FSs) and excitation spectra. The connection between the electronic spectrum and the measured spectra is described as a generalized `matrix element effect'. The nature of the matrix element involved differs greatly between different spectroscopies. For example, in angle-resolved photoemission (ARPES) an incoming photon knocks out... ]]> Susmita Basak Spectrum analysis http://iris.lib.neu.edu/physics_diss/27 http://iris.lib.neu.edu/physics_diss/27 Wed, 07 Mar 2012 09:04:15 PST The discovery of the Metal-Insulator Transition at B = 0 in strongly correlated two-dimensional electron systems with low disorder has lead to investigations into related phenomena in this regime of signicant electron-electron interactions. Diverging spin susceptibility has been observed in parallel magnetic fields which was traced to an enhancement of the effective mass (albeit to values only up to 4 times band mass of electrons in Si) at low electron densities corresponding to strong electron-electron interactions. Below a certain density n close to the critical density of the MIT, the electron spins are spontaneously polarized which is interpreted as a... ]]> Anish Mokashi Electron transport Thermoelectricity http://iris.lib.neu.edu/physics_diss/26 http://iris.lib.neu.edu/physics_diss/26 Tue, 29 Nov 2011 10:00:26 PST In past decades revolutionary developments took place in many aspects of science. One of the leading developments is in the field of material science where there is great interest in developing new materials for various applications. Massive number of applications will change the entire life of mankind on earth and in space. Nanomaterials science is considered the pioneer in this new era.

Titania nanotube is considered a very important material due to its promising applications in many fields ranging from energy harvesting to sensors and photocatalytic applications. Electrochemical anodization method is used to fabricate titania nanotube arrays, this method is... ]]> Mohamed AbdElmoula Nanotubes http://iris.lib.neu.edu/physics_diss/25 http://iris.lib.neu.edu/physics_diss/25 Thu, 13 Oct 2011 09:43:10 PDT This thesis is about metamaterials and its application in negative refraction, slow light and transformation optics. Metamaterials have properties not available in nature and are typically man-made. They have exciting applications such as invisible cloaking, modulators, band-pass filters, perfect lenses, subwavelength resolution, beam compressors, slow-light devices and so on. We demonstrated one-dimensional, two-dimensional photonic crystals negative lenses, prisms, flat lens theoretically and experimentally at both microwave and optical frequency. We roposed a new mechanism on surface grating to realize negative refraction in photonics crystals. This approach can be used to image large and/or far way objects. We studied the slow... ]]> Yongjian Huang Metamaterials Photonic crystals Negative refraction Optics http://iris.lib.neu.edu/physics_diss/24 http://iris.lib.neu.edu/physics_diss/24 Mon, 03 Oct 2011 06:51:15 PDT In this thesis, polymer and biopolymer structure and dynamics were studied with scanning probe microscopy and computational simulation. In part 1, chapters 1-4, an image charge model was employed to simulate the effect of local dielectric response in electric force microscopy (EFM) of a glass polymer film. Local dielectric spectroscopy of the PVAC films was studied with both simulation and EFM experiments. Part 2, chapters 5-12, scanning probe microscopy or atomic force microscopy (AFM) techniques and computational simulations were applied to study DNA flexibility enhancement by HMGB proteins. The study relies on a large amount of statistical works. HMGB protein... ]]> Jingyun Zhang Scanning probe microscopy Polymers Biopolymers http://iris.lib.neu.edu/physics_diss/23 http://iris.lib.neu.edu/physics_diss/23 Fri, 01 Jul 2011 07:22:21 PDT Presented is a series of analyses which are central to the search for a low-mass Higgs boson. A search for ZZ production in the $ZZ \rightarrow \ell^\minus\ell^\plus v\bar{v}$ channel is introduced then the successful combination of this analysis with with the $ZZ \ell^\plus\ell^\minus\ell\prime^\plus\ell\prime^\minus$ search to produce the first observation of the ZZ process at a hadron collider is then detailed. The final analysis presented is the search for the Higgs in the $ZH \rightarrow v\bar{v} b\bar{b}$ channel and the interpretation as a $ZZ \rightarrow v\bar{v} b\bar{b}$ search in order to validate the techniques. Common themes are discussed, such as multivariate... ]]> Gabriel Facini Higgs bosons Neutrinos http://iris.lib.neu.edu/physics_diss/22 http://iris.lib.neu.edu/physics_diss/22 Tue, 24 May 2011 12:51:42 PDT The Large Hadron Collider (LHC) has recently turned on and started collecting invaluable physics data. The particle physics community is eager to see which of the recent beyond the Standard Model theories will be discovered at the LHC. Supersymmetry is one of the strongest candidate for the physics beyond the Standard Model. In this thesis, first, we study the possibilities of discovering supersymmetry at the LHC running at 7 TeV center of mass energy and carry out a reach analysis within the mSUGRA parameter space. We generate nonuniversal mSUGRA benchmark models with nonuniversilities in the gaugino sector which satisfy all... ]]> Ismet Baris Altunkaynak Large Hadron Collider (France and Switzerland) String models http://iris.lib.neu.edu/physics_diss/21 http://iris.lib.neu.edu/physics_diss/21 Thu, 28 Apr 2011 12:10:26 PDT We have applied first-principles calculations to investigate the topological insulator state of half-Heusler materials and the momentum density for overdoped cuprates. The specific topics addressed in this thesis are as follows.