Preserving Film Preservation in the Digital Era

This paper explores the current controversies surrounding film preservation in the digital era. Questions address the benefits of new technologies and the potential sacrifices to a film\u27s authenticity and designation as a valued historical, social, and cultural artifact. Issues examined include film\u27s frail format, archives\u27s financial and storage limitations, the concept of the original film, and how current digitization methods affect each of these areas. This paper addresses the recent restorations of two particular films—Fritz Lang\u27s Metropolis (1927) and Alfred Hitchcock\u27s Vertigo (1958)—and concludes that digital technologies are not stable enough to replace traditional preservation methods, but they can greatly increase exposure to lesser-known films and support the general preservation of film

Non-Commutative Geometry and the Strong Force

The restrictions imposed on the strong force in the `non-commutative standard model' are examined. It is concluded that given the framework of non-commutative geometry and assuming the electroweak sector of the standard model many details of the strong force can be explained including its vectorial nature.Comment: 7 pages, LATEX (minor grammatical changes

Nagaoka ferromagnetism in the two-dimensional infinite-U Hubbard model

We present different numerical calculations based on variational quantum Monte Carlo simulations supporting a ferromagnetic ground-state for finite and small hole densities in the two-dimensional infinite-$U$ Hubbard model. Moreover, by studying the energies of different total spin sectors, these calculations strongly suggest that the paramagnetic phase is unstable against a phase with a partial polarization for large hole densities $\delta \sim 0.40$ with evidence for a second-order transition to the paramagnetic large doping phase.Comment: 4 page

Quantum Phase Transition in Coupled Spin Ladders

The ground state of an array of coupled, spin-half, antiferromagnetic ladders is studied using spin-wave theory, exact diagonalization (up to 36 sites) and quantum Monte Carlo techniques (up to 256 sites). Our results clearly indicate the occurrence of a zero-temperature phase transition between a N\'eel ordered and a non-magnetic phase at a finite value of the inter-ladder coupling ($\alpha_c\simeq0.3$). This transition is marked by remarkable changes in the structure of the excitation spectrum.Comment: 4 pages, 6 postscript figures, to appear in Physical Review

From magnetism to one-dimensional spin liquid in the anisotropic triangular lattice

We investigate the anisotropic triangular lattice that interpolates from decoupled one-dimensional chains to the isotropic triangular lattice and has been suggested to be relevant for various quasi-two-dimensional materials, such as Cs$_2$CuCl$_4$ or $\kappa$-(ET)$_2$Cu$_2$(CN)$_3$, an organic material that shows intriguing magnetic properties. We obtain an excellent accuracy by means of a novel representation for the resonating valence bond wave function with both singlet and triplet pairing. This approach allows us to establish that the magnetic order is rapidly destroyed away from the pure triangular lattice and incommensurate spin correlations are short range. A non-magnetic spin liquid naturally emerges in a wide range of the phase diagram, with strong one-dimensional character. The relevance of the triplet pairing for $\kappa$-(ET)$_2$Cu$_2$(CN)$_3$ is also discussed.Comment: 4+epsilon pages, 6 figure

Spin-12\frac{1}{2} Heisenberg J1J_1-J2J_2 antiferromagnet on the kagome lattice

We report variational Monte Carlo calculations for the spin-$\frac{1}{2}$ Heisenberg model on the kagome lattice in the presence of both nearest-neighbor $J_1$ and next-nearest-neighbor $J_2$ antiferromagnetic superexchange couplings. Our approach is based upon Gutzwiller projected fermionic states that represent a flexible tool to describe quantum spin liquids with different properties (e.g., gapless and gapped). We show that, on finite clusters, a gapped $\mathbb{Z}_{2}$ spin liquid can be stabilized in the presence of a finite $J_2$ superexchange, with a substantial energy gain with respect to the gapless $U(1)$ Dirac spin liquid. However, this energy gain vanishes in the thermodynamic limit, implying that, at least within this approach, the $U(1)$ Dirac spin liquid remains stable in a relatively large region of the phase diagram. For $J_2/J_1 \gtrsim 0.3$, we find that a magnetically ordered state with ${\bf q}={\bf 0}$ overcomes the magnetically disordered wave functions, suggesting the end of the putative gapless spin-liquid phase.Comment: 6 pages, 4 figures. Published versio