Hubbard model as an approximation to the entanglement in nanostructures

We investigate how well the one-dimensional Hubbard model describes the entanglement of particles trapped in a string of quantum wells. We calculate the average single-site entanglement for two particles interacting via a contact interaction and consider the effect of varying the interaction strength and the interwell distance. We compare the results with the ones obtained within the one-dimensional Hubbard model with on-site interaction. We suggest an upper bound for the average single-site entanglement for two electrons in M wells and discuss analytical limits for very large repulsive and attractive interactions. We investigate how the interplay between interaction and potential shape in the quantum-well system dictates the position and size of the entanglement maxima and the agreement with the theoretical limits. Finally, we calculate the spatial entanglement for the quantum-well system and compare it to its average single-site entanglement

Massive Cosmologies

We explore the cosmological solutions of a recently proposed extension of General Relativity with a Lorentz-invariant mass term. We show that the same constraint that removes the Boulware-Deser ghost in this theory also prohibits the existence of homogeneous and isotropic cosmological solutions. Nevertheless, within domains of the size of inverse graviton mass we find approximately homogeneous and isotropic solutions that can well describe the past and present of the Universe. At energy densities above a certain crossover value, these solutions approximate the standard FRW evolution with great accuracy. As the Universe evolves and density drops below the crossover value the inhomogeneities become more and more pronounced. In the low density regime each domain of the size of the inverse graviton mass has essentially non-FRW cosmology. This scenario imposes an upper bound on the graviton mass, which we roughly estimate to be an order of magnitude below the present-day value of the Hubble parameter. The bound becomes especially restrictive if one utilizes an exact self-accelerated solution that this theory offers. Although the above are robust predictions of massive gravity with an explicit mass term, we point out that if the mass parameter emerges from some additional scalar field condensation, the constraint no longer forbids the homogeneous and isotropic cosmologies. In the latter case, there will exist an extra light scalar field at cosmological scales, which is screened by the Vainshtein mechanism at shorter distances.Comment: 21 page

Continuum elasticity theory of edge excitations in a two-dimensional electron liquid with finite range interactions

We make use of continuum elasticity theory to investigate the collective modes that propagate along the edge of a two-dimensional electron liquid or crystal in a magnetic field. An exact solution of the equations of motion is obtained with the following simplifying assumptions: (i) The system is {\it macroscopically} homogeneous and isotropic in the half-plane delimited by the edge (ii) The electron-electron interaction is of finite range due to screening by external electrodes (iii) The system is nearly incompressible. At sufficiently small wave vector $q$ we find a universal dispersion curve $\omega \sim q$ independent of the shear modulus. At larger wave vectors the dispersion can change its form in a manner dependent on the comparison of various length scales. We obtain analytical formulas for the dispersion and damping of the modes in various physical regimes.Comment: 3 figure

Low Power Analog Design in Scaled Technologies

In this paper an overview on the main issues in analog IC design in scaled CMOS technology is presented. Decreasing the length of MOS channel and the gate oxide has led to undoubted advantages in terms of chip area, speed and power consumption (mainly exploited in the digital parts). Besides, some drawbacks are introduced in term of power leakage and reliability. Moreover, the scaled technology lower supply voltage requirement has led analog designers to find new circuital solution to guarantee the required performance

Stima della pericolosità sismica in termini di intensità macrosismica in Italia: due metodologie di calcolo a confronto

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PSR J1016-5857: a young radio pulsar with possible supernova remnant, X-ray, and gamma-ray associations

We report the discovery of a young and energetic pulsar in the Parkes multibeam survey of the Galactic plane. PSR J1016-5857 has a rotation period of 107 ms and period derivative of 8e-14, implying a characteristic age of 21 kyr and spin-down luminosity of 2.6e36 erg/s. The pulsar is located just outside, and possibly interacting with, the shell supernova remnant G284.3-1.8. Archival X-ray data show a source near the pulsar position which is consistent with emission from a pulsar wind nebula. The pulsar is also located inside the error box of the unidentified EGRET source 3EG J1013-5915, for which it represents a plausible counterpart.Comment: 5 pages, 3 included figures, accepted for publication by ApJ Letter

Combining Raman and infrared spectroscopy as a powerful tool for the structural elucidation of cyclodextrin-based polymeric hydrogels

A detailed experimental and theoretical vibrational analysis of hydrogels of b-cyclodextrin nanosponges (b-CDNS), obtained by polymerization of b-cyclodextrin (b-CD) with the cross-linking agent ethylenediaminetetraacetic acid (EDTA), is reported here. Thorough structural characterization is achieved by exploiting the complementary selection rules of FTIR-ATR and Raman spectroscopies and by supporting the spectral assignments by DFT calculations of the spectral profiles. The combined analysis of the FTIR-ATR spectra of the polymers hydrated with H2O and D2O allowed us to isolate the HOH bending of water molecules not involved in symmetrical, tetrahedral environments. The analysis of the HOH bending mode was carried out as a function of temperature, showing the existence of a supercooled state of the water molecules. The highest level of cooperativity of the hydrogen bond scheme was reached at a value of the b-CD/EDTA molar ratio n = 6. Finally, the connectivity pattern of ‘‘uncoupled’’ water molecules bound to the nanosponge backbone was found to be weakened by increasing T. The temperature above which the population of non-tetracoordinated water molecules becomes predominant turned out to be independent of the parameter n

Discovery of Five Binary Radio Pulsars

We report on five binary pulsars discovered in the Parkes multibeam Galactic plane survey. All of the pulsars are old, with characteristic ages 1-11 Gyr, and have relatively small inferred magnetic fields, 5-90e8 G. The orbital periods range from 1.3 to 15 days. As a group these objects differ from the usual low-mass binary pulsars (LMBPs): their spin periods of 9-88 ms are relatively long; their companion masses, 0.2-1.1 Msun, are, in at least some cases, suggestive of CO or more massive white dwarfs; and some of the orbital eccentricities, 1e-5 < e < 0.002, are unexpectedly large. We argue that these observed characteristics reflect binary evolution that is significantly different from that of LMBPs. We also note that intermediate-mass binary pulsars apparently have a smaller scale-height than LMBPs.Comment: 5 pages, 4 embedded EPS figs, accepted for publication by ApJ Letter

Discovery of a Young Radio Pulsar in a Relativistic Binary Orbit

We report on the discovery of PSR J1141-6545, a radio pulsar in an eccentric, relativistic 5-hr binary orbit. The pulsar shows no evidence for being recycled, having pulse period P = 394 ms, characteristic age tau_c = 1.4 x 10^6 yr, and inferred surface magnetic dipole field strength B = 1.3 x 10^12 G. From the mass function and measured rate of periastron advance, we determine the total mass in the system to be (2.300 +/- 0.012) solar masses, assuming that the periastron advance is purely relativistic. Under the same assumption, we constrain the pulsar's mass to be M_p < 1.348 solar masses and the companion's mass to be M_c > 0.968 solar masses (both 99% confidence). Given the total system mass and the distribution of measured neutron star masses, the companion is probably a massive white dwarf which formed prior to the birth of the pulsar. Optical observations can test this hypothesis.Comment: 18 pages, 4 figures, Accepted for Publication in Ap

A confirmation of agreement of different approaches for scalar gauge-invariant metric perturbations during inflation

We revisit an extension of the well-known formalism for gauge-invariant scalar metric fluctuations, to study the spectrums for both, the inflaton and gauge invariant (scalar) metric fluctuations in the framework of a single field inflationary model where the quasi-exponential expansion is driven by an inflation which is minimally coupled to gravity. The proposal here examined is valid also for fluctuations with large amplitude, but for cosmological scales, where vector and tensor perturbations can be neglected and the fluid is irrotacional.Comment: Version accepted in EPJC with new title. 11 pages, no figure