Hyperuniformity and its Generalizations

Disordered many-particle hyperuniform systems are exotic amorphous states characterized by anomalous suppression of large-scale density fluctuations. Here we substantially broaden the hyperuniformity concept along four different directions. This includes generalizations to treat fluctuations in the interfacial area in heterogeneous media and surface-area driven evolving microstructures, random scalar fields, divergence-free random vector fields, as well as statistically anisotropic many-particle systems and two-phase media. Interfacial-area fluctuations play a major role in characterizing the microstructure of two-phase systems , physical properties that intimately depend on the geometry of the interface, and evolving two-phase microstructures that depend on interfacial energies (e.g., spinodal decomposition). In the instances of divergence-free random vector fields and statistically anisotropic structures, we show that the standard definition of hyperuniformity must be generalized such that it accounts for the dependence of the relevant spectral functions on the direction in which the origin in Fourier space (nonanalyticities at the origin). Using this analysis, we place some well-known energy spectra from the theory of isotropic turbulence in the context of this generalization of hyperuniformity. We show that there exist many-particle ground-state configurations in which directional hyperuniformity imparts exotic anisotropic physical properties (e.g., elastic, optical and acoustic characteristics) to these states of matter. Such tunablity could have technological relevance for manipulating light and sound waves in ways heretofore not thought possible. We show that disordered many-particle systems that respond to external fields (e.g., magnetic and electric fields) are a natural class of materials to look for directional hyperuniformity.Comment: In pres

Ultra-Wideband Secure Communications and Direct RF Sampling Transceivers

Larger wireless device bandwidth results in new capabilities in terms of higher data rates and security. The 5G evolution is focus on exploiting larger bandwidths for higher though-puts. Interference and co-existence issues can also be addressed by the larger bandwidth in the 5G and 6G evolution. This dissertation introduces of a novel Ultra-wideband (UWB) Code Division Multiple Access (CDMA) technique to exploit the largest bandwidth available in the upcoming wireless connectivity scenarios. The dissertation addresses interference immunity, secure communication at the physical layer and longer distance communication due to increased receiver sensitivity. The dissertation presents the design, workflow, simulations, hardware prototypes and experimental measurements to demonstrate the benefits of wideband Code-Division-Multiple-Access. Specifically, a description of each of the hardware and software stages is presented along with simulations of different scenarios using a test-bench and open-field measurements. The measurements provided experimental validation carried out to demonstrate the interference mitigation capabilities. In addition, Direct RF sampling techniques are employed to handle the larger bandwidth and avoid analog components. Additionally, a transmit and receive chain is designed and implemented at 28 GHz to provide a proof-of-concept for future 5G applications. The proposed wideband transceiver is also used to demonstrate higher accuracy direction finding, as much as 10 times improvement

Beamforming design and power control for spectrum sharing systems

In order to provide wireless services for the current demand of high data rate mobile applications, more spectrally efficient systems are needed. As a matter of fact, the current wireless systems are limited by a frequency splitting spectrum management which in one hand minimizes the multiuser interference but; on the other hand, it precludes the use of wider bandwidth signals. As a more aggressive frequency reuse is targeted (ideally, all transmitters might eventually share the same frequency band), the use of multiple antennas for interference reliving, jointly with a smart power allocation is compulsory. In addition, novel spectrum management regulatory policies are required for ensuring a peaceful coexistence between adjacent spectrum sharing networks and for promoting their development. The aim of this dissertation is provide a beamforming and power allocation design for these novel spectrum sharing systems which are meant to exponentially increase the spectral efficiency of the systems. A mathematical framework based on multicriteria optimization for analyzing the beamforming design is provided which serves as a fundamental tool for describing the state-of-the-art studies in multiantenna interference networks. Indeed, the achievable rates are described and several ways of computing the Pareto rate region of MISO interference channel (i.e. the communication model that represents the spectrum sharing network when the transmitters use multiple antennas) are studied. Nevertheless, as the system designer aims to work in a single efficient rate point, the sum-rate optimal beamforming design is studied. Curiously, it results that under some realistic assumptions on both the desired and interference power levels, the obtained beamformer is the reciprocal version of a known receiving one and it optimizes a notion of antenna directivity for multiuser communications. Neverthelss, it is important to remark that the higher transmit power is used, the more interference dominated is the medium, not only within the wireless network, but also to eventually adjacent networks that might suffer from inter-network interference. In order to cope with this problem, a spectrum licensing system is revisited, namely time-area-spectrum license. Under this spectrum management mechanism, a license holder is able to radiate signals under a certain portion of time, within a concrete area and in a given band. Moreover, the amount of signal strength within the area is constraint by a certain value. Since controlling the signal power levels in a given area is cumbersome, we propose to restrict the receive power as an estimation of the overall accumulated signal strength. Therefore, the optimal transmit beamformers and power allocations are studied. Concretely, the achievable rates are derived and an operational working point is envisaged. In addition, a suboptimal yet low computationally complex and decentralized beamforming design is presented and it shows a good performance in front of other decentralized designs

”FDT” Violation in Proteins

abstract: Bio-molecules and proteins are building blocks of life as is known, and understanding their dynamics and functions are necessary to better understand life and improve its quality. While ergodicity and fluctuation dissipation theorem (FDT) are fundamental and crucial concepts regarding study of dynamics of systems in equilibrium, biological function is not possible in equilibrium. In this work, dynamical and orientational structural crossovers in low-temperature glycerol are investigated. A sudden and notable increase in the orientational Kirk- wood factor and the dielectric constant is observed, which appears in the same range of temperatures that dynamic crossover of translational and rotational dynamics oc- cur. Theory and electrochemistry of cytochrome c is also investigated. The seeming discrepancy in reorganization energies of protein electron transfer produced by atom- istic simulations and those reported by protein electrochemistry (which are smaller) is resolved. It is proposed in this thesis that ergodicity breaking results in an effective reorganization energy (0.57 eV) consistent with experiment. Ergodicity breaking also affects the iron displacement in heme proteins. A model for dynamical transition of atomic displacements in proteins is provided. Different temperatures for rotational and translational crossovers of water molecules are re- ported, which all are ergodicity breaking transitions depending on the corresponding observation windows. The comparison with Mössbauer spectroscopy is presented. Biological function at low temperatures and its termination is also investigated in this research. Here, it is proposed that ergodicity breaking gives rise to the violation of the FDT, and this violation is maintained in the entire range of physiological temperatures for cytochrome c. Below the crossover temperature, the protein returns to the FDT, which leads to a sudden jump in the activation barrier for electron itransfer. Finally the interaction of charges in dielectric materials is discussed. It is shown that the potential of mean force between ions in polar liquids becomes oscillatory at short distances.Dissertation/ThesisDoctoral Dissertation Physics 201

Innovative patternable materials for micro- and nano- fabrication

The research activity of this thesis is focused on the development and optimization of new directly patternable organically modified TiO2, Al2O3 and ZrO2 based sol-gel materials whose peculiar characteristics and performances were optimized and exploited for the final specific application. In particular, the main strategy that lies at the basis of all the thesis work is the combination of top down and- bottom up approach for the final device realization. In fact, special attention has been set to materials design and synthesis (bottom up) and subsequently to the micro- and nano- fabrication of patterns on the corresponding film surface with different lithographic techniques (top down) in order to achieve the required properties, according to the final application. As it concerns the bottom up approach, the sol-gel has been assumed as the main synthetic method since, by mixing different organic-inorganic precursors, new materials with unique properties and microstructures can be created. In fact, by using organically modified precursors (such as trimethoxyphenylsilane, 3-glycidoxypropyltrimethoxysilane, 3-(Trimethoxysilyl)propyl methacrylate) or organic monomers it was possible to produce hybrid materials with the organic and inorganic components intimately mixed at a molecular scale, with the twofold effect of obtaining new properties and conferring them the patternability. Moreover, the addition of tetrafunctional precursors (Titanium isopropoxide, Zirconium butoxide, Aluminum-tri-sec-butoxide) allowed to increase the reticulation degree, taking part to the inorganic network formation, to improve the material mechanical properties (such as scratch, abrasion, plasma etching resistance) and to confer particular characteristics to the final materials, i.e. to modulate the refractive index. On the other hand, as it regards the top down approach, different lithographic techniques (photolithography, X-ray lithography, electron beam lithography and nanoimprint lithography) have been exploited in the realization of high refractive index patterns, high selective etching masks features, adaptive-optics devices and stamps for microinjection moulding directly with the synthesized materials. The structural and chemical changes induced inside the material by the interactions with the source used in the lithographic process have been deeply investigated in order to optimize both the synthesis of the best sol-gel systems and the final lithographic procedures. In conclusion the development of all the above mentioned advanced materials and innovative processing was pushed by the main target of improving, simplifying and decreasing costs and time of the overall micro- and nano- fabrication process in order to obtain better final features quality, with respect to traditional lithographic procedures