A Film Fabrication Process on Transparent Substrate using Mask Projection Micro-Stereolithography

In this study, a Mask Projection Micro-Stereolithography (MPµSLA) process with the ability to cure a film of various thicknesses on transparent substrates is presented. Incident radiation, patterned by a dynamic mask, passes through a transparent substrate to cure photopolymer resin layers that grow progressively from the substrate surface. When compared to existing Stereolithography techniques, this technique eliminates the necessity of recoating, reducing process time and improving accuracy. A film of varying thicknesses can be fabricated on flat or curved transparent substrates. Models of the optical system and resin cure are developed and reported. An existing MPµSLA process planning method is being extended to account for radiation transmission through a substrate. The models are verified using experiments.Mechanical Engineerin

Intermediate-Term Risk of Stroke Following Cardiac Procedures in a Nationally Representative Data Set.

BACKGROUND: Studies on stroke risk following cardiac procedures addressed only perioperative and long-term risk following limited higher-risk procedures, were poorly generalizable, and often failed to stratify by stroke type. We calculated stroke risk in the intermediate risk period following cardiac procedures compared with common noncardiac surgeries and medical admissions. METHODS AND RESULTS: The Nationwide Readmissions Database contains readmission data for 49% of US admissions in 2013. We compared age-adjusted stroke readmission rates up to 90 days postdischarge. We used Cox regression to calculate hazard ratios, up to 1 year, of stroke risk comparing transcatheter aortic valve replacement versus surgical aortic valve replacement and coronary artery bypass graft versus percutaneous coronary intervention. Procedures and diagnoses were identified by International Classification of Disease, Ninth Revision, Clinical Modification codes. After cardiac procedures, 90-day ischemic stroke readmission rate was highest after transcatheter aortic valve replacement (2.05%); 90-day hemorrhagic stroke rate was highest after left ventricular assist device placement (0.09%). The hazard ratio for ischemic stroke after transcatheter aortic valve replacement, compared with surgical aortic valve replacement, in fully adjusted Cox models was 1.86 (95% confidence interval, 1.12-3.08; P=0.016) and 6.17 (95% confidence interval, 1.97-19.33; P=0.0018) for hemorrhagic stroke. There was no difference between coronary artery bypass graft and percutaneous coronary intervention. CONCLUSIONS: We demonstrated elevated readmission rates for ischemic and hemorrhagic stroke in the intermediate 30-, 60-, and 90-day risk periods following common cardiac procedures. Furthermore, we found an elevated risk of stroke after transcatheter aortic valve replacement compared with surgical aortic valve replacement up to 1 year

A recurrent neural network with ever changing synapses

A recurrent neural network with noisy input is studied analytically, on the basis of a Discrete Time Master Equation. The latter is derived from a biologically realizable learning rule for the weights of the connections. In a numerical study it is found that the fixed points of the dynamics of the net are time dependent, implying that the representation in the brain of a fixed piece of information (e.g., a word to be recognized) is not fixed in time.Comment: 17 pages, LaTeX, 4 figure

Quantum Field Theory for the Three-Body Constrained Lattice Bose Gas -- Part I: Formal Developments

We develop a quantum field theoretical framework to analytically study the three-body constrained Bose-Hubbard model beyond mean field and non-interacting spin wave approximations. It is based on an exact mapping of the constrained model to a theory with two coupled bosonic degrees of freedom with polynomial interactions, which have a natural interpretation as single particles and two-particle states. The procedure can be seen as a proper quantization of the Gutzwiller mean field theory. The theory is conveniently evaluated in the framework of the quantum effective action, for which the usual symmetry principles are now supplemented with a ``constraint principle'' operative on short distances. We test the theory via investigation of scattering properties of few particles in the limit of vanishing density, and we address the complementary problem in the limit of maximum filling, where the low lying excitations are holes and di-holes on top of the constraint induced insulator. This is the first of a sequence of two papers. The application of the formalism to the many-body problem, which can be realized with atoms in optical lattices with strong three-body loss, is performed in a related work [14].Comment: 21 pages, 5 figure

Role of fluctuations in membrane models: thermal versus non-thermal

We study the comparative importance of thermal to non-thermal fluctuations for membrane-based models in the linear regime. Our results, both in 1+1 and 2+1 dimensions, suggest that non-thermal fluctuations dominate thermal ones only when the relaxation time $\tau$ is large. For moderate to small values of $\tau$, the dynamics is defined by a competition between these two forces. The results are expected to act as a quantitative benchmark for biological modelling in systems involving cytoskeletal and other non-thermal fluctuations.Comment: 4 pages, 1 figur

Interaction effects on 2D fermions with random hopping

We study the effects of generic short-ranged interactions on a system of 2D Dirac fermions subject to a special kind of static disorder, often referred to as ``chiral.'' The non-interacting system is a member of the disorder class BDI [M. R. Zirnbauer, J. Math. Phys. 37, 4986 (1996)]. It emerges, for example, as a low-energy description of a time-reversal invariant tight-binding model of spinless fermions on a honeycomb lattice, subject to random hopping, and possessing particle-hole symmetry. It is known that, in the absence of interactions, this disordered system is special in that it does not localize in 2D, but possesses extended states and a finite conductivity at zero energy, as well as a strongly divergent low-energy density of states. In the context of the hopping model, the short-range interactions that we consider are particle-hole symmetric density-density interactions. Using a perturbative one-loop renormalization group analysis, we show that the same mechanism responsible for the divergence of the density of states in the non-interacting system leads to an instability, in which the interactions are driven strongly relevant by the disorder. This result should be contrasted with the limit of clean Dirac fermions in 2D, which is stable against the inclusion of weak short-ranged interactions. Our work suggests a novel mechanism wherein a clean system, initially insensitive to interaction effects, can be made unstable to interactions upon the inclusion of weak static disorder.Comment: 16 pages, 10 figures; References added, figures enlarged; to be published in Phys. Rev.

Conductance of quantum wires: a numerical study of the effects of an impurity and interactions

We use the non-equilibrium Green's function formalism along with a self-consistent Hartree-Fock approximation to numerically study the effects of a single impurity and interactions between the electrons (with and without spin) on the conductance of a quantum wire. We study how the conductance varies with the wire length, the temperature, and the strength of the impurity and interactions. The dependence of the conductance on the wire length and temperature is found to be in rough agreement with the results obtained from a renormalization group analysis based on the Hartree-Fock approximation. For the spin-1/2 model with a repulsive on-site interaction or the spinless model with an attractive nearest neighbor interaction, we find that the conductance increases with increasing wire length or decreasing temperature. This can be qualitatively explained using the Born approximation in scattering theory. For a strong impurity, the conductance is significantly different for a repulsive and an attractive impurity; this is due to the existence of a bound state in the latter case. In general, the large density deviations at short distances have an appreciable effect on the conductance which is not captured by the renormalization group analysis.Comment: Revtex, 15 pages including 21 figures; all the numerical calculations have been re-done with a Fermi wavenumber of pi/10; this is the version published in Phys Rev

Sine-Gordon Field Theory for the Kosterlitz-Thouless Transitions on Fluctuating Membranes

In the preceding paper, we derived Coulomb-gas and sine-Gordon Hamiltonians to describe the Kosterlitz-Thouless transition on a fluctuating surface. These Hamiltonians contain couplings to Gaussian curvature not found in a rigid flat surface. In this paper, we derive renormalization-group recursion relations for the sine-Gordon model using field-theoretic techniques developed to study flat space problems.Comment: REVTEX, 14 pages with 6 postscript figures compressed using uufiles. Accepted for publication in Phys. Rev.

Effect of long range connections on an infinite randomness fixed point associated with the quantum phase transitions in a transverse Ising model

We study the effect of long-range connections on the infinite-randomness fixed point associated with the quantum phase transitions in a transverse Ising model (TIM). The TIM resides on a long-range connected lattice where any two sites at a distance r are connected with a non-random ferromagnetic bond with a probability that falls algebraically with the distance between the sites as 1/r^{d+\sigma}. The interplay of the fluctuations due to dilutions together with the quantum fluctuations due to the transverse field leads to an interesting critical behaviour. The exponents at the critical fixed point (which is an infinite randomness fixed point (IRFP)) are related to the classical "long-range" percolation exponents. The most interesting observation is that the gap exponent \psi is exactly obtained for all values of \sigma and d. Exponents depend on the range parameter \sigma and show a crossover to short-range values when \sigma >= 2 -\eta_{SR} where \eta_{SR} is the anomalous dimension for the conventional percolation problem. Long-range connections are also found to tune the strength of the Griffiths phase.Comment: 5 pages, 1 figure, To appear in Phys. Rev.

Evidence of magnetic mechanism for cuprate superconductivity

A proper understanding of the mechanism for cuprate superconductivity can emerge only by comparing materials in which physical parameters vary one at a time. Here we present a variety of bulk, resonance, and scattering measurements on the (Ca_xLa_{1-x})(Ba_{1.75-x}La_{0.25+x})Cu_3O_y high temperature superconductors, in which this can be done. We determine the superconducting, Neel, glass, and pseudopage critical temperatures. In addition, we clarify which physical parameter varies, and, equally important, which does not, with each chemical modification. This allows us to demonstrate that a single energy scale, set by the superexchange interaction J, controls all the critical temperatures of the system. J, in-turn, is determined by the in plane Cu-O-Cu buckling angle.Comment: 17 pages, 13 figure