Superfluidity in the interior-gap states

We investigate superfluidity in the interior-gap states proposed by Liu and Wilczek. At weak coupling, we find the {\em gapless} interior-gap state unstable in physically accessible regimes of the parameter space, where the superfluid density is shown to be always negative. We therefore conclude that the spatially-uniform interior-gap phase is extremely unstable unless it is fully gapped; in this case, however, the state is rather similar to conventional BCS states.Comment: To appear in Physical Review

Climate change impacts on plant phenology: Grapevine (vitis vinifera) bud break in wintertime in southern italy

The effects of global warming on plants are not limited to the exacerbation of summer stresses; they could also induce dormancy dysfunctions. In January 2020, a bud break was observed in an old poly-varietal vineyard. Meteorological data elaboration of the 1951–2020 period confirmed the general climatic warming of the area and highlighted the particular high temperatures of the last winter. Phenological records appeared to be significantly correlated to wood hydration and starch reserve consumption, demonstrating a systemic response of the plant to the warm conditions. The eight cultivars, identified by single-nucleotide polymorphism (SNP) profiles and ampelographic description, grown in this vineyard showed different behaviors. Among them, the neglected Sprino, Baresana, Bianco Palmento, and Uva Gerusalemme, as well as the interspecific hybrid Seyve Villard 12.375, appeared to be the most interesting. Among the adaptation strategies to climate changes, the cultivar selection should be considered a priority, as it reduces the inputs required for the plant management over the entire life cycle of the vineyard. Hot Mediterranean areas, such as Salento, are a battlefront against the climate change impacts, and, thus, they represent a precious source of biodiversity for viticulture

The Red Sequence of High-Redshift Clusters: a Comparison with Cosmological Galaxy Formation Models

We compare the results from a semi-analytic model of galaxy formation with spectro-photometric observations of distant galaxy clusters observed in the range 0.8< z< 1.3. We investigate the properties of their red sequence (RS) galaxies and compare them with those of the field at the same redshift. In our model we find that i) a well-defined, narrow RS is obtained already by z= 1.2; this is found to be more populated than the field RS, analogously to what observed and predicted at z=0; ii) the predicted U-V rest-frame colors and scatter of the cluster RS at z=1.2 have average values of 1 and 0.15 respectively, with a cluster-to-cluster variance of 0.2 and 0.06, respectively. The scatter of the RS of cluster galaxies is around 5 times smaller than the corresponding field value; iii) when the RS galaxies are considered, the mass growth histories of field and cluster galaxies at z=1.2 are similar, with 90 % of the stellar mass of RS galaxies at z=1.2 already formed at cosmic times t=2.5 Gyr, and 50 % at t=1 Gyr; v) the predicted distribution of stellar ages of RS galaxies at z=1.2 peaks at 3.7 Gyr for both cluster and field populations; however, for the latter the distribution is significantly skewed toward lower ages. When compared with observations, the above findings show an overall consistency, although the average value 0.07 of the observed cluster RS scatter (U-V colors) at z=1.2 is smaller than the corresponding model central value. We discuss the physical origin and the significance of the above results in the framework of cosmological galaxy formation.Comment: 14 pages, accepted for publication in ApJ. Updated one referenc

Pauli Blocking of Collisions in a Quantum Degenerate Atomic Fermi Gas

We have produced an interacting quantum degenerate Fermi gas of atoms composed of two spin-states of magnetically trapped $^{40}$K. The relative Fermi energies are adjusted by controlling the population in each spin-state. Measurements of the thermodynamics reveal the resulting imbalance in the mean energy per particle between the two species, which is as large as a factor of 1.4 at our lowest temperature. This imbalance of energy comes from a suppression of collisions between atoms in the gas due to the Pauli exclusion principle. Through measurements of the thermal relaxation rate we have directly observed this Pauli blocking as a factor of two reduction in the effective collision cross-section in the quantum degenerate regime.Comment: 11 pages, 4 figure

Resonant control of elastic collisions in an optically trapped Fermi gas of atoms

We have loaded an ultracold gas of fermionic atoms into a far off resonance optical dipole trap and precisely controlled the spin composition of the trapped gas. We have measured a magnetic-field Feshbach resonance between atoms in the two lowest energy spin-states, |9/2, -9/2> and |9/2, -7/2>. The resonance peaks at a magnetic field of 201.5 plus or minus 1.4 G and has a width of 8.0 plus or minus 1.1 G. Using this resonance we have changed the elastic collision cross section in the gas by nearly 3 orders of magnitude.Comment: 4 pages, 3 figure

The Possible z=0.83 Precursors of z=0 M* Early-type Cluster Galaxies

We examine the distribution of stellar masses of galaxies in MS 1054-03 and RX J0152.7-1357, two X-ray selected clusters of galaxies at z=0.83. Our stellar mass estimates, from spectral energy distribution fitting, reproduce the dynamical masses as measured from velocity dispersions and half-light radii with a scatter of 0.2 dex in the mass for early-type galaxies. When we restrict our sample of members to high stellar masses, > 1e11.1 Msun (M* in the Schechter mass function for cluster galaxies), we find that the fraction of early-type galaxies is 79 +/- 6% at z=0.83 and 87 +/- 6% at z=0.023 for the Coma cluster, consistent with no evolution. Previous work with luminosity-selected samples finds that the early-type fraction in rich clusters declines from =~80% at z=0 to =~60% at z=0.8. The observed evolution in the early-type fraction from luminosity-selected samples must predominately occur among sub-M* galaxies. As M* for field and group galaxies, especially late-types, is below M* for clusters galaxies, infall could explain most of the recent early-type fraction growth. Future surveys could determine the morphological distributions of lower mass systems which will confirm or refute this explanation.Comment: 5 pages in emulate ApJ format with three color figures. Accepted for publication in ApJ Letters, v642n2. Updated to correct grammatical and typographic errors found by the journa

Cooper Pairing in Ultracold K-40 Using Feshbach Resonances

We point out that the fermionic isotope K-40 is a likely candidate for the formation of Cooper pairs in an ultracold atomic gas. Specifically, in an optical trap that simultaneously traps the spin states |9/2,-9/2> and |9/2,-7/2>, there exists a broad magnetic field Feshbach resonance at B = 196 gauss that can provide the required strong attractive interaction between atoms. An additional resonance, at B = 191 gauss, could generate p-wave pairing between identical |9/2,-7/2> atoms. A Cooper-paired degenerate Fermi gas could thus be constructed with existing ultracold atom technology.Comment: 4 pages, 2 figs, submitted to Phys. Rev.

Deriving the bulk properties of solar wind electrons observed by Solar Orbiter: A preliminary study of electron plasma thermodynamics

We demonstrate the calculation of solar wind electron bulk parameters from recent observations by Solar Wind Analyser Electron Analyser System on board Solar Orbiter. We use our methods to derive the electron bulk parameters in a time interval of a few hours. We attempt a preliminary examination of the polytropic behavior of the electrons by analyzing the derived electron density and temperature. Moreover, we discuss the challenges in analyzing the observations due to the spacecraft charging and photo-electron contamination in the energy range < 10 eV. Aims: We derive bulk parameters of thermal solar wind electrons by analyzing Solar Orbiter observations and we investigate if there is any typical polytropic model that applies to the electron density and temperature fluctuations. Methods: We use the appropriate transformations to convert the observations to velocity distribution functions in the instrument frame. We then derive the electron bulk parameters by a) calculating the statistical moments of the constructed velocity distribution functions and b) by fitting the constructed distributions with analytical expressions. We firstly test our methods by applying them to an artificial data-set, which we produce by using the forward modeling technique. Results: The forward model validates the analysis techniques which we use to derive the electron bulk parameters. The calculation of the statistical moments and the fitting method determines bulk parameters that are identical within uncertainty to the input parameters we use to simulate the plasma electrons in the first place. An application of our analysis technique to the data reveals a nearly isothermal electron "core". The results are affected by the spacecraft potential and the photo-electron contamination, which we need to characterize in detail in future analyses

Rapid sympathetic cooling to Fermi degeneracy on a chip

Neutral fermions present new opportunities for testing many-body condensed matter systems, realizing precision atom interferometry, producing ultra-cold molecules, and investigating fundamental forces. However, since their first observation, quantum degenerate Fermi gases (DFGs) have continued to be challenging to produce, and have been realized in only a handful of laboratories. In this Letter, we report the production of a DFG using a simple apparatus based on a microfabricated magnetic trap. Similar approaches applied to Bose-Einstein Condensation (BEC) of 87Rb have accelerated evaporative cooling and eliminated the need for multiple vacuum chambers. We demonstrate sympathetic cooling for the first time in a microtrap, and cool 40K to Fermi degeneracy in just six seconds -- faster than has been possible in conventional magnetic traps. To understand our sympathetic cooling trajectory, we measure the temperature dependence of the 40K-87Rb cross-section and observe its Ramsauer-Townsend reduction.Comment: 5 pages, 4 figures (v3: new collision data, improved atom number calibration, revised text, improved figures.

Excess energy of an ultracold Fermi gas in a trapped geometry

We have analytically explored finite size and interparticle interaction corrections to the average energy of a harmonically trapped Fermi gas below and above the Fermi temperature, and have obtained a better fitting for the excess energy reported by DeMarco and Jin [Science $\textbf{285}$, 1703 (1999)]. We have presented a perturbative calculation within a mean field approximation.Comment: 8 pages, 4 figures; Accepted in European Physical Journal