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Papers by david santiago

Polymers, 2019

New thermosets from a triglycidyl eugenol derivative (3EPOEU) as a renewable epoxy monomer were o... more New thermosets from a triglycidyl eugenol derivative (3EPOEU) as a renewable epoxy monomer were obtained by an epoxy-amine curing process. A commercially-available Jeffamine® and isophorone diamine, both obtained from renewable resources, were used as crosslinking agents, and the materials obtained were compared with those obtained from a standard diglycidylether of bisphenol A (DGEBA). The evolution of the curing process was studied by differential scanning calorimetry and the materials obtained were characterized by means of calorimetry, thermogravimetry, thermodynamomechanical analysis, stress–strain tests and microindentation. 3EPOEU formulations were slightly less reactive, and the thermosets obtained showed higher Tgs than those prepared from DGEBA, since they had higher crosslinking density than formulations with DGEBA because of the more compact structure and higher functionality of the eugenol derivative. 3EPOEU thermosets showed good thermal stability and mechanical proper...

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Physics Letters A, 2002

A set of new exact analytical General Relativity (GR) solutions with time-dependent and spatially... more A set of new exact analytical General Relativity (GR) solutions with time-dependent and spatially inhomogeneous quintessence demonstrate 1) a static non-empty spacetime with a horizon-type singular surface; 2) time-dependent spatially homogeneous 'spheres' which are completely different in geometry from the Friedmann isotropic models; 3) infinitely strong anti-gravity at a 'true' singularity where the density is infinitely large. It is also found that 4) the GR solutions allow for an extreme 'density-free' form of energy that can generate regular space-time geometries.

Physical Review Letters, 2006

EVIDENCIA Conocimiento (Saber) Desempeño (Hacer) Producto (resultado) El estudiante es capaz de i... more EVIDENCIA Conocimiento (Saber) Desempeño (Hacer) Producto (resultado) El estudiante es capaz de identificar la clasificación documental que le permite manejar un archivo empresarial según la legislación vigente El estudiante selecciona la técnica de estudio adecuada a su aprendizaje El estudiante presenta el desarrollo de un cuestionario y una evaluación escrita permiten mejorar su proceso más apropiada de acuerdo con los comparativo, mapa conceptual, resumen, etc) de aprendizaje. conocimientos y saberes. de acuerdo con lo solicitado por el maestro.

IEEE Transactions on Ultrasonics, Ferroelectrics and Frequency Control, 1995

Page 1. 812 IEEE TRANSACTIONS ON ULTRASONICS, FERROELECTRICS, AND FREQUENCY CONTROL, VOL. 42, NO.... more Page 1. 812 IEEE TRANSACTIONS ON ULTRASONICS, FERROELECTRICS, AND FREQUENCY CONTROL, VOL. 42, NO. 5, SEPTEMBER 1995 Temperature-Compensated Sapphire Resonator for Ultra-Stable Oscillator Capability at Temperatures Above 77 K ...

Arxiv preprint cond-mat/0403746, 2004

We review the nature of superfluid ground states and the universality of their properties with em... more We review the nature of superfluid ground states and the universality of their properties with emphasis to Bose Einstein Condensate systems in atomic physics. We then study the superfluid Mott transition in such systems. We find that there could be two types of Mott transitions and phases. One of them was described long ago and corresponds to suppression of Josephson tunneling within superfluids sitting at each well. On the other hand, the conditions of optical lattice BEC experiments are such that either the coherence length is longer than the interwell separation, or there is too small a number of bosons per well. This vitiates the existence of a superfluid order parameter within a well, and therefore of Josephson tunneling between wells. Under such conditions, there is a transition to a Mott phase which corresponds to suppression of individual boson tunneling among wells. This last transition is in general discontinuous and can happen for incommensurate values of bosons per site. If the coherence length is small enough and the number of bosons per site large enough, the transition studied in the earlier work will happen.

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We here consider a generalization of the Klein-Gordon scalar wave equation which involves a singl... more We here consider a generalization of the Klein-Gordon scalar wave equation which involves a single arbitrary function. The quantization may be viewed as allowingh to be a function of the momentum or wave vector rather than a constant. The generalized theory is most easily viewed in the wave vector space analog of the Lagrangian. We need no reference to spacetime. In the generalized theory the de Broglie relation between wave vector and momentum is generalized, as are the canonical commutation relations and the uncertainty principle. The generalized uncertainty principle obtained is the same as has been derived from string theory, or by a general consideration of gravitational effects during the quantum measurement process. The propagator of the scalar field is also generalized, and an illustrative example is given in which it factors into the usual propagator times a "propagator form factor."

ACM Transactions on Quantum Computing

As the size and complexity of a quantum computer increases, quantum bit (qubit) characterization ... more As the size and complexity of a quantum computer increases, quantum bit (qubit) characterization and gate optimization become complex and time-consuming tasks. Current calibration techniques require complicated and verbose measurements to tune up qubits and gates, which cannot easily expand to the large-scale quantum systems. We develop a concise and automatic calibration protocol to characterize qubits and optimize gates using QubiC , which is an open source FPGA (field-programmable gate array)-based control and measurement system for superconducting quantum information processors. We propose multi-dimensional loss-based optimization of single-qubit gates and full XY-plane measurement method for the two-qubit CNOT gate calibration. We demonstrate the QubiC automatic calibration protocols are capable of delivering high-fidelity gates on the state-of-the-art transmon-type processor operating at the Advanced Quantum Testbed at Lawrence Berkeley National Laboratory. The single-qubit an...

Polymers, 2020

A series of bio-based epoxy shape-memory thermosetting polymers were synthesized starting from a ... more A series of bio-based epoxy shape-memory thermosetting polymers were synthesized starting from a triglycidyl phloroglucinol (3EPOPh) and trimethylolpropane triglycidyl ether (TPTE) as epoxy monomers and a polyetheramine (JEF) as crosslinking agent. The evolution of the curing process was studied by differential scanning calorimetry (DSC) and the materials obtained were characterized by means of DSC, thermogravimetric analysis (TGA), dynamic mechanical analysis (DMA), stress-strain tests, and microindentation. Shape-memory properties were evaluated under free and totally constrained conditions. All results were compared with an industrial epoxy thermoset prepared from standard diglycidyl ether of Bisphenol A (DGEBA). Results revealed that materials prepared from 3EPOPh were more reactive and showed a tighter network with higher crosslinking density and glass transition temperatures than the prepared from DGEBA. The partial substitution of 3EPOPh by TPTE as epoxy comonomer caused an i...

Physics Letters B, 2000

We discuss a recent provocative suggestion by Amelino-Camelia and others that classical spacetime... more We discuss a recent provocative suggestion by Amelino-Camelia and others that classical spacetime may break down into "quantum foam" on distance scales many orders of magnitude larger than the Planck length, leading to effects which could be detected using large gravitational wave interferometers. This suggestion is based on a quantum uncertainty limit obtained by Wigner using a quantum clock in a gedanken timing experiment. Wigner's limit, however, is based on two unrealistic and unneccessary assumptions: that the clock is free to move, and that it does not interact with the environment. Removing either of these assumptions makes the uncertainty limit invalid, and removes the basis for Amelino-Camelia's suggestion.

Physics Letters A, 2000

We give a complete description of the asymptotic behavior of a Friedmann-Robertson-Walker Univers... more We give a complete description of the asymptotic behavior of a Friedmann-Robertson-Walker Universe with "normal" matter and a minimally coupled scalar field. We classify the conditions under which the Universe is or is not accelerating. In particular, we show that only two types of large time behavior exist: an exponential regime, and a subexponential expansion with the logarithmic derivative of the scale factor tending to zero. In the case of the subexponetial expansion the Universe accelerates when the scalar field energy density is dominant and the potential behaves in a specified manner, or if matter violates the strong energy condition ρ + 3p > 0. When the expansion is exponential the Universe accelerates, and the scalar field energy density is dominant. We find that for the Big Bang to occur at zero scale factor, the equation of state of matter needs to satisfy certain restrictions at large densities. Similarly, a never ending expansion of the Universe constrains the equation of state at small matter densities.

Physical Review D, 1998

We study the asymptotic behavior at late times of Friedmann-Robertson-Walker (uniform density) co... more We study the asymptotic behavior at late times of Friedmann-Robertson-Walker (uniform density) cosmological models within scalar-tensor theories of gravity. Particularly, we analyze the late time behavior in the present (matter dominated) epoch of the universe. The result of Damour and Nordtvedt that for a massless scalar in a flat cosmology the Universe evolves towards a state indistinguishable from general relativity is generalized. We first study a massless scalar field in an open universe. It is found that, while the universe tends to approach a state with less scalar contribution to gravity, the attractor mechanism is not effective enough to drive the theory towards a final state indistinguishable from general relativity. For the self-interacting case it is found that the scalar field potential dominates the late time behavior. In

IEEE International Frequency Control Symposium, 1995

We report on improved stability in a whispering gallery sapphire resonator for which the dominant... more We report on improved stability in a whispering gallery sapphire resonator for which the dominant WGHnll microwave mode family shows frequency-stable, compensated operation for temperatures above 77 K. Several modifications during the past year have led to significant improvements in performance. Current tests with improved thermal stability provide Allan Deviation of frequency of 2.6-4·10-13 for measurement times of 1⩽τ⩽100 seconds.

Chemical Physics Letters, 1991

8a. NAME O; FUNDING/SPONSORING oBc OFFICE SYMBOL 9. PROCUREMENT INSTRUMENT IDENTIFICATION %.UMBER... more 8a. NAME O; FUNDING/SPONSORING oBc OFFICE SYMBOL 9. PROCUREMENT INSTRUMENT IDENTIFICATION %.UMBER ORGANIZATON (if N epGcable) Office of Naval Research Grant N00014-89-J-1829 BC. ADDRESS (City,. State. and ZIP Code) 10 SOURCE OF FUNDING NUMBERS

Arxiv preprint cond-mat/0312417, 2003

We study inter-well coherent quantum tunneling of Bose-Einstein condensates (BEC's) in optical la... more We study inter-well coherent quantum tunneling of Bose-Einstein condensates (BEC's) in optical lattices. Irrespective of whether the BEC is a superfluid in the whole lattice, it may or may not be a superfluid within each well of the lattice depending on whether the ratio of the well kinetic energy to the interaction energy is small or large. When the bosons in each well are superfluid, we have Josephson tunneling among the wells driven by the phase difference between the superfluids in the different wells. For typical lattice parameters the Josephson tunneling rate will be somewhat enhanced from the naive estimate of (tunneling energy scale)/. Whether it is enhanced or not will depend on lattice parameters, but it can never be zero. When the bosons in each well are not superfluid, there is coherent quantum tunneling of essentially free bosons between the wells. This tunneling is proportional to the boson number difference between the wells.

Arxiv preprint cond-mat/ …, 2003

Recently a new phenomenological Hamiltonian was introduced to describe the superconducting cuprat... more Recently a new phenomenological Hamiltonian was introduced to describe the superconducting cuprates in which correlations and on-site Coulomb repulsion are introduced by partial Gutzwiller projection. This Gossamer Hamiltonian has an exact ground state and differs from the t-J and Hubbard Hamiltonians in possessing a powerful attractive interaction among electrons responsible for Cooper pairing in a d-wave channel. It is a faithful description for a superconductor with strong on-site electronic repulsion. The supercodnucting tunnelling gap remains intact and despite onsite repulsion. Near half-filling the Gossamer superconductor with strong repulsion has suppresed photoemission intensities and superfluid density, is unstable toward an antiferromagnetic insulator and posseses an incipient Mott-Hubbard gap. The Gossamer technique can be applied to metallic ground states thus possibly serving as an apt description of strongly correlated metals. Such a Gossamer metallic phase, just as the Gossamer superconducting one, becomes arbitrarily hard to differentiate from an insulator as one turns the Coulomb correlations up near half-filling. Both the metallic and superconducting states undergo a quantum phase transition to an antiferromagnetic insulator as one increases the on-site Coulomb repulsion. In the Gossamer model we reach the critical point at half-filling by fully projecting double occupancy. Such a critical point might be the Anderson Resonating Valence bond state.

Arxiv preprint cond-mat/0606386, 2006

The Nèel magnetization of 2+1 D antiferromagnets is composed of quark-like spin 1/2 constituents,... more The Nèel magnetization of 2+1 D antiferromagnets is composed of quark-like spin 1/2 constituents, the spinons, as follows from the CP 1 mapping. These quark spinons are confined in both the Nèel ordered phase and quantum paramagnetic phases. The confinement in the quantum paramagnetic phase is understood as arising from quantum tunneling events, instantons or hedgehog monopole events. In the present article, we study the approach to the quantum critical point, where the quantum paramagnetic phase ceases to exist. We find that irrespective of the intrinsic spin of the antiferromagnet, instanton events disappear at the deconfined critical point because instanton tunelling becomes infinitely costly and have zero probability at the quantum critical point. Berry phase terms relevant to the paramagnetic phase vanish at the quantum critical point, but make the confinement length scale diverge more strongly for half-integer spins, next strongest for odd integer spins, and weakest for even integer spins. There is an emergent photon at the deconfined critical point, but the "semimetallic" nature of critical spinons screens such photon making it irrelevant to long distance physics and the deconfined spinons are strictly free particles. A unique prediction of having critical free spinons is an anomalous exponent η for the susceptibility exactly equal to one. Experimentally measurable response functions are calculated from the deconfined spinon criticality.

Nuclear Physics B, 2007

It has been proposed that there are new degrees of freedom intrinsic to quantum critical points t... more It has been proposed that there are new degrees of freedom intrinsic to quantum critical points that contribute to quantum critical physics. We study 2+1 D antiferromagnets in order to explore possible new quantum critical physics arising from nontrivial topological effects. We show that skyrmion excitations are stable at criticality and have nonzero probability at arbitrarily low temperatures. To include quantum critical skyrmion effects, we find a class of exact solutions composed of skyrmion and antiskyrmion superpositions, which we call topolons. We include the topolons in the partition function and renormalize by integrating out small size topolons and short wavelength spin waves. We obtain a correlation length critical exponent ν = 0.9297 and anomalous dimension η = 0.3381.

General Relativity and Gravitation, 2014

We study the Schwarzschild and Reissner-Nordström black hole thermodynamics using the simplest fo... more We study the Schwarzschild and Reissner-Nordström black hole thermodynamics using the simplest form of the generalized uncertainty principle (GUP) proposed in the literature. The expressions for the mass-temperature relation, heat capacity and entropy are obtained in both cases from which the critical and remnant masses are computed. Our results are exact and reveal that these masses are identical and larger than the so called singular mass for which the thermodynamics quantities become ill-defined. The expression for the entropy reveals the well known area theorem in terms of the horizon area in both cases upto leading order corrections from GUP. The area theorem written in terms of a new variable which can be interpreted as the reduced horizon area arises only when the computation is carried out to the next higher order correction from GUP.