A pure S-wave covariant model for the nucleon

Using the manifestly covariant spectator theory, and modeling the nucleon as a system of three constituent quarks with their own electromagnetic structure, we show that all four nucleon electromagnetic form factors can be very well described by a manifestly covariant nucleon wave function with zero orbital angular momentum. Since the concept of wave function depends on the formalism, the conclusions of light-cone theory requiring nonzero angular momentum components are not inconsistent with our results. We also show that our model gives a qualitatively correct description of deep inelastic scattering, unifying the phenomenology at high and low momentum transfer. Finally we review two different definitions of nuclear shape and show that the nucleon is spherical in this model, regardless of how shape is defined.Comment: 20 pages and 10 figures; greatly expanded version with new fits and discussion of DIS; similar to published versio

Experimental constraint on the ρ−\rho - meson form factors in the time--like region

The annihilation reaction $e^++e^-\rightarrow \bar \rho+\rho$ is considered. The constraint on time-like $\rho$-meson form factors from the measurement done by the BaBar collaboration at $\sqrt{s}=10.5$ GeV is analyzed.Comment: 10 pages 3 figure

Millimeter and sub-millimeter atmospheric performance at Dome C combining radiosoundings and ATM synthetic spectra

The reliability of astronomical observations at millimeter and sub-millimeter wavelengths closely depends on a low vertical content of water vapor as well as on high atmospheric emission stability. Although Concordia station at Dome C (Antarctica) enjoys good observing conditions in this atmospheric spectral windows, as shown by preliminary site-testing campaigns at different bands and in, not always, time overlapped periods, a dedicated instrument able to continuously determine atmospheric performance for a wide spectral range is not yet planned. In the absence of such measurements, in this paper we suggest a semi-empirical approach to perform an analysis of atmospheric transmission and emission at Dome C to compare the performance for 7 photometric bands ranging from 100 GHz to 2 THz. Radiosoundings data provided by the Routine Meteorological Observations (RMO) Research Project at Concordia station are corrected by temperature and humidity errors and dry biases and then employed to feed ATM (Atmospheric Transmission at Microwaves) code to generate synthetic spectra in the wide spectral range from 100 GHz to 2 THz. To quantify the atmospheric contribution in millimeter and sub-millimeter observations we are considering several photometric bands in which atmospheric quantities are integrated. The observational capabilities of this site at all the selected spectral bands are analyzed considering monthly averaged transmissions joined to the corresponding fluctuations. Transmission and pwv statistics at Dome C derived by our semi-empirical approach are consistent with previous works. It is evident the decreasing of the performance at high frequencies. We propose to introduce a new parameter to compare the quality of a site at different spectral bands, in terms of high transmission and emission stability, the Site Photometric Quality Factor.Comment: accepted to MNRAS with minor revision

Two-component model for the axial form factor of the nucleon

The axial form factor of the nucleon is studied in a two-component model consisting of a three-quark intrinsic structure surrounded by a meson cloud. The experimental data in the space-like region are well reproduced with a minimal number of parameters. The results are similar to those obtained from a dipole fit up to 1 GeV$^2$, but they surprisingly show a zero between 2 and 3 GeV$^2$. Such behavior, predicted by the present model completely disagrees with the dipole parametrization. The theoretical expression for the form factor is then analytically extrapolated to the time-like region, giving the first predictions in this regime. This kinematical region is especially interesting for present and future colliders.Comment: 12 pages 2 figures Final version to appear in Phys. Rev.

Joint density-functional theory for electronic structure of solvated systems

We introduce a new form of density functional theory for the {\em ab initio} description of electronic systems in contact with a molecular liquid environment. This theory rigorously joins an electron density-functional for the electrons of a solute with a classical density-functional theory for the liquid into a single variational principle for the free energy of the combined system. A simple approximate functional predicts, without any fitting of parameters to solvation data, solvation energies as well as state-of-the-art quantum-chemical cavity approaches, which require such fitting.Comment: Fixed typos and minor updates to tex

Sun-photometric measurements of atmospheric turbidity variations caused by the Pinatubo aerosol cloud in the Himalayan region during the summer periods of 1991 and 1992

Measurements of direct solar irradiance were taken episodically on two days of September 1990 and regularly in the summer periods from July to October 1991 and from mid-July to mid-August 1992 at the Pyramid Laboratory (5050 m a.m.s.l.) situated at the foot of Mt. Everest (Nepal), using two examples of the Volz multispectral sunphotometer, model A. These sun-photometric measurements were analysed in terms of the Bouguer-Lambert-Beer law in order to determine the values of aerosol optical thickness at the three sun-photometric window-wavelengths. Examining these spectral series in terms of the well-known Ångström formula, the best-fit values of turbidity parameters a and b were calculated with great accuracy. From the measurements taken in September 1990, we found values of the aerosol optical thickness in good agreement with the mean values of the background aerosol optical depth measured at the Mauna Loa Observatory (Hawaii) during the four-year period from 1988 to 1991. The spectral values of the aerosol optical thickness determined during the summer of 1991 show that the mean daily values of parameter b increased abruptly from about 0.06 to more than 0.16 from July 26 to 28, 1991, and then varied between 0.09 and 0.16 during the rest of the measurement period. Simultaneously, parameter a was found to decrease from more than 1.25 to 0.39 towards the end of July and to vary between 0.40 and 0.78 during September. These large variations of both atmospheric turbidity parameters have been attributed to the growth of the aerosol particles and to the consequent changes in the size distribution curve of the Pinatubo aerosol particles. Analysing the variations of the stratospheric aerosol optical depth in terms of particle polydispersions consisting of a linear combination of a background aerosol monomodal model and a bimodal model representing the Pinatubo fresh aerosol particle size distribution, the vertical mass loading of stratospheric aerosol particles was estimated to vary between 0.037 and 0.047 g m22 from July 24 to 27 and to increase to values ranging between 0.048 and 0.074 g m22 during the rest of summer 1991, presenting a mean value of (0.063 6 0.009) g m22 for the two-month period. The measurements taken in summer 1992 show that parameter b ranged between 0.08 and 0.12, while parameter a was found to vary between 0.23 and 0.73. The stratospheric aerosol depth values were analysed through a best-fit procedure based on a linear combination of a background model of small aerosol particles and a trimodal model consisting of aged volcanic aerosol particles. Following this procedure, the vertical mass loading of Pinatubo aerosol particles was found to vary between 0.043 and 0.057 g m22 during summer 1992, the mean value being evaluated as equal to (0.047 6 0.004) g m22

Macroscopic dynamics of the fusion process

A macroscopic dynamical model has been used to calculate fusion cross sections for a wide number of systems ranging from 16O + 27Al to 40Ar + 165Ho. This model takes into account the reorganization of the densities and the nucleon exchanges. The possible reaction mechanisms after capture of the system into the pocket of the interaction potential are discussed Two processes contribute to fusion : compound nucleus formation and fast fission phenomenon. The calculated fusion cross sections are in overall agreement with the data

Turbulence underneath the big calm? The micro-evidence behind Italian productivity dynamics

Italy ranked last in terms of manufacturing productivity growth according to OECD estimates over the last decade, with a flat, if not declining, trend. In this work we investigate the underlying firm-level dynamics of enterprises on the basis of a database developed by the Italian Statistical Office (ISTAT) covering the period 1989–2004 and containing information on more than 100,000 firms. Over this period not only have the indicators of the central tendency of the distribution of labor productivity not significantly changed, but also the whole sectoral distributions have remained relatively stable over time, with their support at least not shrinking, or even possibly widening, over time. This is even more surprising if one takes into consideration the “Euro” shock that occurred during the period investigated. On the contrary, we observe that inter-decile differences in productivity have been increasing. Further, heterogeneous firms’ characteristics (i.e. export activity and innovation) seem to have contributed to boosting such intra-industry differences. Given such wide heterogeneities we resort to quantile regressions to identify the impact of a set of regressors at different levels of the conditional distribution of labor productivity. One phenomenon that we observe is what we call a tendency toward “neo-dualism” involving the co-existence of a small group of dynamic firms with a bigger ensemble of much less technologically progressive ones