Applications of an exact counting formula in the Bousso-Polchinski Landscape

The Bousso-Polchinski (BP) Landscape is a proposal for solving the Cosmological Constant Problem. The solution requires counting the states in a very thin shell in flux space. We find an exact formula for this counting problem which has two simple asymptotic regime one of them being the method of counting low $\Lambda$ states given originally by Bousso and Polchinski. We finally give some applications of the extended formula: a robust property of the Landscape which can be identified with an effective occupation number, an estimator for the minimum cosmological constant and a possible influence on the KKLT stabilization mechanism.Comment: 43 pages, 11 figures, 2 appendices. We have added a new section (3.4) on the influence of the fraction of non-vanishing fluxes in the KKLT mechanism. Other minor changes also mad

Determination of Transverse Density Structuring from Propagating MHD Waves in the Solar Atmosphere

We present a Bayesian seismology inversion technique for propagating magnetohydrodynamic (MHD) transverse waves observed in coronal waveguides. The technique uses theoretical predictions for the spatial damping of propagating kink waves in transversely inhomogeneous coronal waveguides. It combines wave amplitude damping length scales along the waveguide with theoretical results for resonantly damped propagating kink waves to infer the plasma density variation across the oscillating structures. Provided the spatial dependence of the velocity amplitude along the propagation direction is measured and the existence of two different damping regimes is identified, the technique would enable us to fully constrain the transverse density structuring, providing estimates for the density contrast and its transverse inhomogeneity length scale

Height variation of the vector magnetic field in solar spicules

Proving the magnetic configuration of solar spicules has hitherto been difficult due to the lack of spatial resolution and image stability during off-limb ground-based observations. We report spectropolarimetric observations of spicules taken in the He I 1083 nm spectral region with the Tenerife Infrared Polarimeter II at the German Vacuum Tower Telescope of the Observatorio del Teide (Tenerife; Canary Islands; Spain). The data provide the variation with geometrical height of the Stokes I, Q, U, and V profiles whose encoded information allows the determination of the magnetic field vector by means of the HAZEL inversion code. The inferred results show that the average magnetic field strength at the base of solar spicules is about 80 gauss and then it decreases rapidly with height to about 30 gauss at a height of 3000 km above the visible solar surface. Moreover, the magnetic field vector is close to vertical at the base of the chromosphere and has mid inclinations (about 50 degree) above 2 Mm height.Comment: Published in ApJ Letter

Spatial deconvolution of spectropolarimetric data: an application to quiet Sun magnetic elements

Observations of the Sun from the Earth are always limited by the presence of the atmosphere, which strongly disturbs the images. A solution to this problem is to place the telescopes in space satellites, which produce observations without any (or limited) atmospheric aberrations. However, even though the images from space are not affected by atmospheric seeing, the optical properties of the instruments still limit the observations. In the case of diffraction limited observations, the PSF establishes the maximum allowed spatial resolution, defined as the distance between two nearby structures that can be properly distinguished. In addition, the shape of the PSF induce a dispersion of the light from different parts of the image, leading to what is commonly termed as stray light or dispersed light. This effect produces that light observed in a spatial location at the focal plane is a combination of the light emitted in the object at relatively distant spatial locations. We aim to correct the effect produced by the telescope's PSF using a deconvolution method, and we decided to apply the code on Hinode/SP quiet Sun observations. We analyze the validity of the deconvolution process with noisy data and we infer the physical properties of quiet Sun magnetic elements after the deconvolution process.Comment: 14 pages, 9 figure

How different Fermi surface maps emerge in photoemission from Bi2212

We report angle-resolved photoemission spectra (ARPES) from the Fermi energy ($E_F$) over a large area of the ($k_x,k_y$) plane using 21.2 eV and 32 eV photons in two distinct polarizations from an optimally doped single crystal of Bi$_2$Sr$_2$CaCu$_2$O$_{8+\delta}$ (Bi2212), together with extensive first-principles simulations of the ARPES intensities. The results display a wide-ranging level of accord between theory and experiment and clarify how myriad Fermi surface (FS) maps emerge in ARPES under various experimental conditions. The energy and polarization dependences of the ARPES matrix element help disentangle primary contributions to the spectrum due to the pristine lattice from those arising from modulations of the underlying tetragonal symmetry and provide a route for separating closely placed FS sheets in low dimensional materials.Comment: submitted to PR

Analysis of Quiet-Sun Internetwork Magnetic Fields Based on Linear Polarization Signals

We present results from the analysis of Fe I 630 nm measurements of the quiet Sun taken with the spectropolarimeter of the Hinode satellite. Two data sets with noise levels of 1.2{\times}10-3 and 3{\times}10-4 are employed. We determine the distribution of field strengths and inclinations by inverting the two observations with a Milne-Eddington model atmosphere. The inversions show a predominance of weak, highly inclined fields. By means of several tests we conclude that these properties cannot be attributed to photon noise effects. To obtain the most accurate results, we focus on the 27.4% of the pixels in the second data set that have linear polarization amplitudes larger than 4.5 times the noise level. The vector magnetic field derived for these pixels is very precise because both circular and linear polarization signals are used simultaneously. The inferred field strength, inclination, and filling factor distributions agree with previous results, supporting the idea that internetwork fields are weak and very inclined, at least in about one quarter of the area occupied by the internetwork. These properties differ from those of network fields. The average magnetic flux density and the mean field strength derived from the 27.4% of the field of view with clear linear polarization signals are 16.3 Mx cm-2 and 220 G, respectively. The ratio between the average horizontal and vertical components of the field is approximately 3.1. The internetwork fields do not follow an isotropic distribution of orientations.Comment: To appear in APJ, Vol 749, 201

Extracció amb CO2 supercrític. I. Una alternativa als dissolvents per a l'obtenció d'extractes naturals dels aliments

La tècnica d'extracció amb fluids supercrítics a la indústria alimentària i amb CO2 com a dissolvent està plenament establerta, sobretot en processos de descafeïnat de cafè i te, extracció de llúpol, extracció d'aromes i sabors d'espècies i herbes aromàtiques i separació del colesterol de la mantega, la carn i el rovell de l'ou. L'ESC és una tècnica de separació respectuosa amb el medi ambient i pot substituir progressivament molts dels processos d'extracció duts a terme amb uns dissolvents orgànics, que són en general potencialment tòxics, inflamables i tenen un preu elevat. L'ESC presenta un futur encoratjador en processos d'extracció i separació de principis actius de productes naturals pels seus avantatges. Aquesta primera part correspon a les bases teòriques de la nova tècnica d'extracció. En una segona part es presentaran les aplicacions industrials. Aquest article correspon a un resum adaptat d'un treball més complet que ha estat publicat en un review al Food Science and Technology International (octubre 2002), i constitueix el capítol 5 del llibre sobre tecnologies emergents (gener 2003).The extraction technique in the food industry by using supercritical fluids, and with CO2 as solvent, is widely established, especially in caffeine removing from coffee and tea, in the extraction of hops, flavours and fragrances from spices and aromatic herbs, as well as in the separation of cholesterol from butter, meat and egg-yolk. The ESC is an environmental friendly technique and is able to substitute progressively a lot of extraction processes based on organic solvents, which are usually potentially toxic, flammable and expensive.Due to their advantages, ESC shows an encouraging future in the processes of extraction and separation of the active substances in natural products. The present article is an abstracts from the complete job that has been published as a review in FSTI (October 2002) and corresponds to chapter 5 of the book on emergent technologies (January 2003)