Collective excitations of a trapped degenerate Fermi gas

We evaluate the small-amplitude excitations of a spin-polarized vapour of Fermi atoms confined inside a harmonic trap. The dispersion law $\omega=\omega_{f}[l+4n(n+l+2)/3]^{1/2}$ is obtained for the vapour in the collisional regime inside a spherical trap of frequency $\omega_{f}$, with $n$ the number of radial nodes and $l$ the orbital angular momentum. The low-energy excitations are also treated in the case of an axially symmetric harmonic confinement. The collisionless regime is discussed with main reference to a Landau-Boltzmann equation for the Wigner distribution function: this equation is solved within a variational approach allowing an account for non-linearities. A comparative discussion of the eigenmodes of oscillation for confined Fermi and Bose vapours is presented in an Appendix.Comment: 14 pages, no figures, accepted for publication in Eur.Phys.Jour.

Miscibility in a degenerate fermionic mixture induced by linear coupling

We consider a one-dimensional mean-field-hydrodynamic model of a two-component degenerate Fermi gas in an external trap, each component representing a spin state of the same atom. We demonstrate that the interconversion between them (linear coupling), imposed by a resonant electromagnetic wave, transforms the immiscible binary gas into a miscible state, if the coupling constant, $\kappa$, exceeds a critical value, $\kappa _{\mathrm{cr}}$. The effect is predicted in a variational approximation, and confirmed by numerical solutions. Unlike the recently studied model of a binary BEC with the linear coupling, the components in the immiscible phase of the binary fermion mixture never fill two separated domains with a wall between them, but rather form anti-locked ($\pi$ -phase-shifted) density waves. Another difference from the bosonic mixture is spontaneous breaking of symmetry between the two components in terms of numbers of atoms in them, $N_{1}$ and $N_{2}$. The latter effect is characterized by the parameter $\nu \equiv (N_{1}-N_{2})/(N_{1}+N_{2})$ (only $N_{1}+N_{2}$ is a conserved quantity), the onset of miscibility at $\kappa \geq \kappa_{\mathrm{cr}}$ meaning a transition to $\nu \equiv 0$. At $\kappa <\kappa_{\mathrm{cr}}$, $\nu$ features damped oscillations as a function of $\kappa$. We also briefly consider an asymmetric model, with a chemical-potential difference between the two components.Comment: 9 pages, 12 figures, PRA (in press

Static Properties of Trapped Bose-Fermi Mixed Condensate of Alkali Atoms

Static properties of a bose-fermi mixture of trapped potassium atoms are studied in terms of coupled Gross-Pitaevskii and Thomas-Fermi equations for both repulsive and attractive bose-fermi interatomic potentials. Qualitative estimates are given for solutions of the coupled equations, and the parameter regions are obtained analytically for the boson-density profile change and for the boson/fermion phase separation. Especially, the parameter ratio $R_{int}$ is found that discriminates the region of the large boson-profile change. These estimates are applied for numerical results for the potassium atoms and checked their consistency. It is suggested that a small fraction of fermions could be trapped without an external potential for the system with an attractive boson-fermion interaction.Comment: 8 pages,5 figure

Two-component repulsive Fermi gases with population imbalance in elongated harmonic traps

We study the two-component repulsive Fermi gas with imbalanced populations in one dimension. Starting from the Bethe Ansatz solution we calculate analytically the phase diagram for the homogeneous system. We show that three phases appear: the balanced phase, the fully polarised phase and the partially polarised phase. By means of the local density approximation and the equation of state for the homogeneous system we calculate the density profile for the harmonically confined case. We show that a two-shell structure appears: at the center of the cloud we find the partially polarised phase and at the edges the fully polarised one. The radii of the inner and outer shells are calculated for different values of the polarisation and the coupling strength. We calculate the dependence of the magnetisation on the polarisation for different values of the coupling strength and we show that the susceptibility is always finite.Comment: 6 pages, 3 figures. Published versio

Subextensive singularity in the 2D ±J\pm J Ising spin glass

The statistics of low energy states of the 2D Ising spin glass with +1 and -1 bonds are studied for $L \times L$ square lattices with $L \le 48$, and $p$ = 0.5, where $p$ is the fraction of negative bonds, using periodic and/or antiperiodic boundary conditions. The behavior of the density of states near the ground state energy is analyzed as a function of $L$, in order to obtain the low temperature behavior of the model. For large finite $L$ there is a range of $T$ in which the heat capacity is proportional to $T^{5.33 \pm 0.12}$. The range of $T$ in which this behavior occurs scales slowly to $T = 0$ as $L$ increases. Similar results are found for $p$ = 0.25. Our results indicate that this model probably obeys the ordinary hyperscaling relation $d \nu = 2 - \alpha$, even though $T_c = 0$. The existence of the subextensive behavior is attributed to long-range correlations between zero-energy domain walls, and evidence of such correlations is presented.Comment: 13 pages, 7 figures; final version, to appear in J. Stat. Phy

Holistic model-based monitoring of the human health status in an urban environment system: pilot study in Verona city, Italy

Introduction. In recent decades the global health paradigm gained an increasing systemic characterization. The ecosystem health theory states that a healthy ecosystem, whether natural or artificial, significantly contributes to the good health status of the human population. Methods. The present study describes an interdisciplinary monitoring model that retrospectively analyzes the intersection between the urban environment and citizens. The model analyzes both the biophysical and the anthropic subsystems through the application of landscape ecology and environmental quality indexes along with human health indicators. Particularly, ecological quality of landscape pattern, atmospheric pollution, outdoor noise levels and local health indicators were assessed. Verona municipality was chosen as study area to test the preliminary efficiency of the model. Territory was split into two superimposed layers of land units, which were further geo-referentiated with Geographical Information System (GIS) technology. Interdependence of any of the analyzed traits was further investigated with Fisher exact test. Results. Landscape composition was assessed and an Average Ecological Quality (AEQ) score assigned to each land unit. A direct proportionality emerged for concentrations of considered air pollutants and traffic levels: a spatial model for the atmospheric pollution was drawn. A map depicting the distribution of traffic- related noise levels was also drawn. From chosen indicators, a quality class score was assigned to every minor and major land unit. Age-standardised rates about hospitalizations for the municipal population and specific rates for the over-65s/1000 inhabitants were calculated. Quality class assignement for each health indicator was graphically rendered. After direct standardisation of rates for the population sample, data were compared with two reference populations, the Regional population and the Local Socio-sanitary Unit (ULSS20) population. Standardised hospitalization rates for the whole municipal population always resulted lower than the ULSS20 rates, except for auditory pathologies. It was notable that rates of hospitalizations for cancerous diseases for Verona municipal population were four times and two times lower than the ULSS20 and the Regional population ones, respectively. Contingency table were made for the health main indicator (specific rates for the over 65s/1000 inhabitants) and the environmental quality key factors of landscape ecological quality, outdoor noise level and air pollution. H0 of independence was rejected for respiratory pathologies and air pollution and for the triad cardiocirculatory pathologies, air pollution and landscape ecological quality at (? = 0.05). Fisher exact test confirmed the non-independence of cardiocirculatory diseases and biophysical environment and the analogous association for respiratory pathologies when comparison was made with global environmental quality index. Discussion. The first testing of the model suggests some possible elements of implementation and integration which could further enhance it. Among them, the subjective investigation of the health status assumes a primary role. On the whole the monitoring model seems to effectively represent the real complexity of the urban environment systems and should be regarded as an important contribution to the new way of health research

Temperature Chaos in Two-Dimensional Ising Spin Glasses with Binary Couplings: a Further Case for Universality

We study temperature chaos in a two-dimensional Ising spin glass with random quenched bimodal couplings, by an exact computation of the partition functions on large systems. We study two temperature correlators from the total free energy and from the domain wall free energy: in the second case we detect a chaotic behavior. We determine and discuss the chaos exponent and the fractal dimension of the domain walls.Comment: 5 pages, 6 postscript figures; added reference

Introduction: Knowledge, Power, and the “Settler Colonial Turn” in Palestine Studies

This is the author accepted manuscript. The final version is available from Taylor & Francis via the DOI in this recordThis special issue presents essays on the topic of settler colonialism in Palestine, covering conceptual and empirical, historical and contemporary, as well as literary, legal and political aspects of the debate. All essays examine the validity and applicability of the settler colonial paradigm to the context of Palestine (West Bank, Gaza Strip, East Jerusalem, and the 1948 territories). They approach this paradigm as a powerful means to challenge and disarticulate established historiographies and narratives, and, as such, engage with settler colonialism as a structure (Wolfe 1999, 2006), but also with the various forms of resistance and decolonization that aim at undoing this structure

Measurement of the two-photon absorption cross-section of liquid argon with a time projection chamber

This paper reports on laser-induced multiphoton ionization at 266 nm of liquid argon in a time projection chamber (LAr TPC) detector. The electron signal produced by the laser beam is a formidable tool for the calibration and monitoring of next-generation large-mass LAr TPCs. The detector that we designed and tested allowed us to measure the two-photon absorption cross-section of LAr with unprecedented accuracy and precision: sigma_ex=(1.24\pm 0.10stat \pm 0.30syst) 10^{-56} cm^4s{-1}.Comment: 15 pages, 9 figure

Finite-Size Scaling in the Energy-Entropy Plane for the 2D +- J Ising Spin Glass

For $L \times L$ square lattices with $L \le 20$ the 2D Ising spin glass with +1 and -1 bonds is found to have a strong correlation between the energy and the entropy of its ground states. A fit to the data gives the result that each additional broken bond in the ground state of a particular sample of random bonds increases the ground state degeneracy by approximately a factor of 10/3. For $x = 0.5$ (where $x$ is the fraction of negative bonds), over this range of $L$, the characteristic entropy defined by the energy-entropy correlation scales with size as $L^{1.78(2)}$. Anomalous scaling is not found for the characteristic energy, which essentially scales as $L^2$. When $x= 0.25$, a crossover to $L^2$ scaling of the entropy is seen near $L = 12$. The results found here suggest a natural mechanism for the unusual behavior of the low temperature specific heat of this model, and illustrate the dangers of extrapolating from small $L$.Comment: 9 pages, two-column format; to appear in J. Statistical Physic