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GRB030320 is the 5th Gamma-ray burst (GRB) detected by INTEGRAL in the field of view (FoV). It is so far the GRB with the largest off-axis angle with respect to the INTEGRAL pointing direction, near to the edge of the FoV of both main instruments, IBIS and SPI. Nevertheless, it was possible to determine its position and to extract spectra and fluxes. The GRB nature of the event was confirmed by an IPN triangulation. It is a ~ 60 s long GRB with two prominent peaks separated by ~ 35 s. The spectral shape of the GRB is best represented by a single power law with a photon index Gamma ~ 1.7. The peak flux in the 20 - 200 keV band is determined to ~ 5.7 photons cm-2 s-1 and the GRB fluence to 1.1 x 10-5 erg cm-2. Analysing the spectral evolution of the GRB, a ``hard-to-soft'' behaviour emerges. A search for an optical counterpart has been carried out, but none was found., Comment: 5 pages, 3 figures. Accepted for publication in A&AL (INTEGRAL issue)

We investigated the optical properties of 7 clusters of galaxies observed in three colors over the range of absolute magnitudes -24 < M < -12. Our aim is to estimate the Luminosity Function and the total cluster luminosity of our sample in order to have information about the formation and the evolution of galaxies in clusters. In this paper, we present the main points of our analysis and give the formal parameters obtained by fitting the data using the maximum likelihood algorithm. We find consistency between our results and other works in literature confirming the bimodal nature of the luminosity function of cluster galaxies. More important, we find that the relation L_opt/ L_X versus L_X is color dependent: Low X ray Luminosity clusters have a bluer galaxy population., Comment: 22 pages. Accepted for publication on A&A

A doped semiconductor double-quantum-dot molecule is proposed as a qubit realization. The quantum information is encoded in the electron spin, thus benefiting from the long relevant decoherence times; the enhanced flexibility of the molecular structure allows to map the spin degrees of freedom onto the orbital ones and vice versa, and opens the possibility for high-finesse (conditional and unconditional) quantum gates by means of stimulated Raman adiabatic passage., Comment: To appear in Phys. Rev. Lett

We theoretically investigate the Stark shift of the exciton goundstate in two vertically coupled quantum dots as a function of the interdot distance. The coupling is shown to enhance the tuneability of the linear optical properties, including energy and oscillator strength, as well as the exciton polarizability. The coupling regime that maximizes these properties results from the detailed balance between the effects of the single-particle tunneling, of the electric field and of the carrier-carrier interaction. We discuss the relevance of these results to the possible implementation of quantum-information processing based on semiconductor quantum dots: in particular, we suggest the identification of the qubits with the exciton levels in coupled- rather than single-dots.

We present a first-principle investigation of quadruple helix nanowires, consisting of stacked planar hydrogen-bonded guanine tetramers. Our results show that long wires form and are stable in potassium-rich conditions. We present their electronic bandstructure and discuss the interpretation in terms of effective wide-bandgap semiconductors. The microscopic structural and electronic properties of the guanine quadruple helices make them suitable candidates for molecular nanoelectronics., Comment: 7 pages, 3 figures, to be published in Applied Physics Letters (2002)

A way to fully exploit the large collecting area of modern 8-10m class telescopes is high resolution spectroscopy. Many astrophysical problems from planetary science to cosmology benefit from spectroscopic observations at the highest resolution currently achievable and would benefit from even higher resolutions. Indeed in the era of 8-10m class telescopes no longer the telescope collecting area but the size of the beam - which is related to the maximum size in which reflection gratings are manufactured - is what mainly limits the resolution. A resolution-slit product Rphi ~ 40,000 is the maximum currently provided by a beam of 20 cm illuminating the largest grating mosaics. We present a conceptual design for a spectrograph with Rphi ~ 80,000, i.e. twice as large as that of existing instruments. Examples of the possible exploitation of such a high Rphi value, including spectropolarimetry and very high resolution (R ~ 300,000), are discussed in detail. The new concept is illustrated through the specific case of a high resolution spectropolarimeter for the Large Binocular Telescope., Comment: accepted for publication in "Astronomishe Nachrichten"

We present high resolution Halpha rotation curves of 4 late-type dwarf galaxies and 2 low surface brightness galaxies (LSB) for which accurate HI rotation curves are available from the literature. Observations are carried out at Telescopio Nazionale Galileo (TNG). For LSB F583-1 an innovative dispersing element was used, the Volume Phase Holographic (VPH) with a dispersion of about 0.35 A/pxl. We find good agreement between the Halpha data and the HI observations and conclude that the HI data for these galaxies suffer very little from beam smearing. We show that the optical rotation curves of these dark matter dominated galaxies are best fitted by the Burkert profile. In the centers of galaxies, where the N-body simulations predict cuspy cores and fast rising rotation curves, our data seem to be in better agreement with the presence of soft cores., Comment: Accepted for Publication in ApJ with minor changes required

Several assemblies of guanine molecules are investigated by means of first-principle calculations. Such structures include stacked and hydrogen-bonded dimers, as well as vertical columns and planar ribbons, respectively, obtained by periodically replicating the dimers. Our results are in good agreement with experimental data for isolated molecules, isolated dimers, and periodic ribbons. For stacked dimers and columns, the stability is affected by the relative charge distribution of the pi orbitals in adjacent guanine molecules. pi-pi coupling in some stacked columns induces dispersive energy bands, while no dispersion is identified in the planar ribbons along the connections of hydrogen bonds. The implications for different materials comprised of guanine aggregates are discussed. The bandstructure of dispersive configurations may justify a contribution of band transport (Bloch type) in the conduction mechanism of deoxyguanosine fibres, while in DNA-like configurations band transport should be negligible., Comment: 21 pages, 6 figures, 3 tables, to be published in Phys. Rev. B

We present a first principle study about the stability and the electronic properties of a new biomolecular solid-state material, obtained by the self-assembling of guanine (G) molecules. We consider hydrogen-bonded planar ribbons in isolated and stacked configurations. These aggregates present electronic properties similar to inorganic wide-bandgap semiconductors. The formation of Bloch-type orbitals is observed along the stacking direction, while it is negligible in the ribbon plane. Global band-like conduction may be affected by a dipole-field which spontaneously arises along the ribbon axis. Our results indicate that G-ribbon assemblies are promising materials for biomolecular nanodevices, consistently with recent experimental results., Comment: 7 pages, 3 figures, to be published in Physica E

We present high spatial resolution H\alpha rotation curves of late-type dwarf and LSB galaxies. From our analysis we find good agreement between our H\alpha data and the HI observations taken from the literature, concluding that the HI rotation curves for these galaxies suffer very little from beam smearing. A preliminary analysis of our data rules out the CDM model in the inner regions of these galaxies., Comment: Contribution to "Tracing Cosmic Evolution with Galaxy Clusters" (Sesto 2001), ASP Conference Series

We briefly describe the main features of the Brera Multi-Wavelet (BMW) survey of serendipitous X-ray clusters, based on the still unexploited ROSAT-HRI archival observations. Cluster candidates are selected from the general BMW catalogue of 20,000 sources based exclusively on their X-ray extension. Contrary to common wisdom, a clever selection of the HRI energy channels allows us to significantly reduce the background noise, thus greatly improving the ability to detect low surface-brightness sources as clusters. The resulting sample of ~250 candidates shows a very good sky coverage down to a flux \~3x10^-14 erg/s/cm^2 ([0.5-2.0] keV band), i.e comparable to existing PSPC-based deep survey, with a particularly interesting area of ~100 sq.deg. around fluxes ~10^-13 erg/s/cm^2, i.e. where highly-luminous, rare systems at z~0.6-1 can be detected. At the same time, the superior angular resolution of the instrument should avoid biases against intrinsically small systems, while easing the identification process (e.g. by spotting blends and AGN contaminants). While about 20% of the candidates are already identified with groups/clusters at z<0.3 on the DSS2 images, we have started a deep CCD imaging campaign to observe all sources associated to "blank fields". First results from these observations reveal a distant (z>0.5) bonafide cluster counterpart for ~80% of the targets., Comment: 3 pages, 2 figures; to appear in Proc. of the ESO/ECF/STSCI workshop on "Deep Fields", Garching Oct 2000, (Publ: Springer)

By use of magneto-photoluminescence spectroscopy we demonstrate bias controlled single-electron charging of a single quantum dot. Neutral, single, and double charged excitons are identified in the optical spectra. At high magnetic fields one Zeeman component of the single charged exciton is found to be quenched, which is attributed to the competing effects of tunneling and spin-flip processes. Our experimental data are in good agreement with theoretical model calculations for situations where the spatial extent of the hole wave functions is smaller as compared to the electron wave functions., Comment: to be published in Physical Review B (rapid communication)

After the completion of the catalogue built with ESO key program (REFLEX), we are beginning to explore the multiband optical characteristics of a subsample of those clusters selected in a statistically independent way. We have already observed in B, V, R, 9 of the about 50 clusters of the subsample, with 0.15 \le z \le 0.18. More time has been allocated by ESO for our project in March 2001. We will therefore be able to compare X-ray and optical morphologies and luminosities and, thanks to the large field of view of the WFI instrument, assess the luminosity function and the color segregation in the cluster on a robust statistical basis. In this poster we present the project, the technical problems we are facing in the reduction phase, and show the first preliminary results, which seem very encouraging., Comment: 7 pages, 11 figures, Poster for in the Proceedings of the Colloque IAP "Constructing the Universe with clusters of galaxies", Paris, France, 4-8 July 2000, B/W version. A full color figures version of the paper at: http://golem.merate.mi.astro.it/emilio/wfi/stateofwork.html

We investigate theoretically the spatial dependence of the linear absorption spectra of single and coupled semiconductor quantum dots, where the strong three-dimensional quantum confinement leads to an overall enhancement of Coulomb interaction and, in turn, to a pronounced renormalization of the excitonic properties. We show that -because of such Coulomb correlations and the spatial interference of the exciton wavefunctions- unexpected spectral features appear whose intensity depends on spatial resolution in a highly non-monotonic way when the spatial resolution is comparable with the excitonic Bohr radius. We finally discuss how the optical near-field properties of double quantum dots are affected by their coupling., Comment: To appear in Phys. Rev. B. Figures (two in colors) embedded

We present a theoretical approach to calculate the {\it local} absorption spectrum of excitons confined in a semiconductor nanostructure. Using the density-matrix formalism, we derive a microscopic expression for the non-local susceptibility, both in the linear and non-linear regimes, which includes a three-dimensional description of electronic quantum states and their Coulomb interaction. The knowledge of the non-local susceptibility allows us to calculate a properly defined local absorbed power, that depends on the electro-magnetic field distribution. We report on explicit calculations of the local linear response of excitons confined in single and coupled T-shaped quantum wires with realistic geometry and composition. We show that significant interference effects in the interacting electron-hole wavefunction induce new features in the space-resolved optical spectra, particularly in coupled nanostructures. When the spatial extension of the electromagnetic field is comparable to the exciton Bohr radius, Coulomb effects on the local spectra must be taken into account for a correct assignment of the observed features., Comment: To appear in Phys. Rev. B. Figures (1 in colors) embedded

We report on a new class of hybrid electronic devices based on a DNA nucleoside (deoxyguanosine lipophilic derivative) whose assembled polymeric ribbons interconnect a submicron metallic gate. The device exhibits large conductivity at room temperature, rectifying behaviour and strong current-voltage hysteresis. The transport mechanism through the molecules is investigated by comparing films with different self-assembling morphology. We found that the main transport mechanism is connected to pi-pi interactions between guanosine molecules in adjacent ribbons, consistently with the results of our first-principles calculations., Comment: Submitted to Phys. Rev. Lett

We initiated a large project aimed to estimate the Luminosity Function of galaxies in clusters and to evaluate its relation to cluster morphology. With this paper we deem necessary to outline the general procedures of the data reduction and details of the data analysis. The cluster sample includes the brightest southern ROSAT all-sky survey clusters with z < 0.1. These have been observed in three colours g, r, i, and mapped up to a few core radii using a mosaic of CCD frames. E/S0 galaxies in the cluster core are singled out both by morphology (for the brightest galaxies), and by colour. The details of the data reduction procedure are illustrated via the analysis of the cluster Abell 496, which has been used as a pilot cluster for the whole program. The related photometric catalogue consists of 2355 objects. The limiting magnitudes (the reference Surface Brightness is given in parenthesis) in the various colours are respectively g(25.5) = 24.14, r(25.5) = 24.46, i(25.0) = 23.75$. These correspond to the limiting absolute magnitudes -12.28, -11.96 and -12.67 (H_0=50 km/sec/Mpc)., Comment: 17 pages, 19 ps figures, aa.cls

We study coupled semiconductor quantum dots theoretically through a generalized Hubbard approach, where intra- and inter-dot Coulomb Correlation, as well as tunneling effects are described on the basis of realistic electron wavefunctions. We find that the ground-state configuration of vertically-coupled double dots undergoes non-trivial quantum transitions as a function of the inter-dot distance d; at intermediate values of d we predict a new phase that should be observable in the addition spectra and in the magnetization changes., Comment: RevTeX, 4 pages, 4 ps figures, to appear in Solid State Communications

We present a theoretical analysis of the effect of dielectric confinement on the Coulomb interaction in dielectrically modulated quantum structures. We discuss the implications of the strong enhancement of the electron-hole and electron-electron coupling for two specific examples: (i) GaAs-based quantum wires with remote oxide barriers, where combined quantum and dielectric confinements are predicted to lead to room temperature exciton binding, and (ii) semiconductor quantum dots in colloidal environments, where the many-body ground states and the addition spectra are predicted to be drastically altered by the dielectric environment., Comment: Proc. of the EP2DS - 13 conference, written in ReVTeX, three figure embedded

A theoretical description of local absorption is proposed in order to investigate spectral variations on a length scale comparable with the extension of the relevant quantum states. A general formulation is derived within the density-matrix formalism including Coulomb correlation, and applied to the prototypical case of coupled quantum wires. The results show that excitonic effects may have a crucial impact on the local absorption with implications for the spatial resolution and the interpretation of near-field optical spectra., Comment: To appear in Phys. Rev. Lett. - 11 pages, 3 PostScript figures (1 figure in colors) embedded. Uses RevTex, and psfig styles

We propose a new type of hybrid systems formed by conventional semiconductor nanostructures with the addition of remote insulating layers, where the electron-hole interaction is enhanced by combining quantum and dielectric confinement over different length scales. Due to the polarization charges induced by the dielectric mismatch at the semiconductor/insulator interfaces, we show that the exciton binding energy can be more than doubled. For conventional III-V quantum wires such remote dielectric confinement allows exciton binding at room temperature., Comment: 4 pages, 3 PostScript figures embedded, best printed in color. Uses RevTex, multicol, and psfig styles. To appear in Phys. Rev. Lett

We review the effects of Coulomb correlation on the linear and non-linear optical properties of semiconductor quantum wires, with emphasis on recent results for the bound excitonic states. Our theoretical approach is based on generalized semiconductor Bloch equations, and allows full three-dimensional multisubband description of electron-hole correlation for arbitrary confinement profiles. In particular, we consider V- and T-shaped structures for which significant experimental advances were obtained recently. Above band gap, a very general result obtained by this approach is that electron-hole Coulomb correlation removes the inverse-square-root single-particle singularity in the optical spectra at band edge, in agreement with previous reports from purely one-dimensional models. Strong correlation effects on transitions in the continuum are found to persist also at high densities of photoexcited carriers. Below bandgap, we find that the same potential- (Coulomb) to kinetic-energy ratio holds for quite different wire cross sections and compositions. As a consequence, we identify a shape- and barrier-independent parameter that governs a universal scaling law for exciton binding energy with size. Previous indications that the shape of the wire cross-section may have important effects on exciton binding are discussed in the light of the present results., Comment: Proc. OECS-5 Conference, G\"ottingen, 1997 (To appear in Phys. Stat. Sol. (b))

We propose that the recently realized T-shaped semiconductor quantum wires (T-wires) could be exploited as three-terminal quantum interference devices. T-wires are formed by intersecting two quantum wells (QWs). By use of a scattering matrix approach and the Landauer-B\"uttiker theory, we calculate the conductance for ballistic transport in the parent QWs and across the wire region as a function of the injection energy. We show that different conductance profiles can be selected by tailoring the widths of the QWs and/or combining more wires on the scale of the Fermi wavelength. Finally, we discuss the possibility of obtaining spin-dependent conductance of ballistic holes in the same structures., Comment: To appear in the 09/15/97 issue of Appl. Phys. Lett. (9 pages in REVTEX + 2 figures in postscript)

The scaling of exciton binding energy in semiconductor quantum wires is investigated theoretically through a non-variational, fully three-dimensional approach for a wide set of realistic state-of-the-art structures. We find that in the strong confinement limit the same potential-to-kinetic energy ratio holds for quite different wire cross-sections and compositions. As a consequence, a universal (shape- and composition-independent) parameter can be identified that governs the scaling of the binding energy with size. Previous indications that the shape of the wire cross-section may have important effects on exciton binding are discussed in the light of the present results., Comment: To appear in Phys. Rev. Lett. (12 pages + 2 figures in postscript)

We present a theoretical investigation of the electronic and optical properties of V- and T-shaped quantum wires. Valence band mixing as well as realistic sample geometries are fully included through an accurate and efficient approach that is described here in detail. We investigate the resulting valence band structure, which shows some significant peculiarities, such as an anomalously large spin splitting in the lowest heavy hole subband of T-shaped wires. For both classes of wires we obtain good agreement between calculated optical absorption and recent experimental spectra, and we demonstrate that the analysis of optical anisotropy can be used as an effective tool to extract information on valence states, usually very difficult to obtain otherwise., Comment: To appear in Phys. Rev. B (32 pages + 11 figures in postscript)

We present a combined theoretical and experimental study of the anisotropy in the optical absorption of V-shaped quantum wires. By means of realistic band structure calculations for these structures, we show that detailed information on the heavy- and light-hole states can be singled out from the anisotropy spectra {\em independently of the electron confinement}, thus allowing accurate valence band spectroscopy., Comment: To be published in Appl. Phys. Lett. (8 pages in REVTeX, two postscipt figures)

We present deep CCD surface photometry in the Gunn g, r, i system and spectroscopy of the cD galaxy at the centre of the cluster A3284 at z = 0.15. The brightness profile of the galaxy has been tracked up to 40 arcsec (142 kpc) from the centre, and down to 26 mag/arcsec^2. The core and halo components in the galaxy have been singled out deriving geometrical parameters of the fitting isophotes as well as magnitudes and colours. The spectral properties of the galaxy core indicate a stellar population super metal-rich with [Fe/H] = +0.5. The cD halo is clearly dominant at 45 kpc from the galactic centre and has exceedingly red colours (g-r = 1.03, g-i = 1.82), about 0.7 mag redder than the core g-i. A match with the models for evolutionary population synthesis by Buzzoni (1989) show that the halo is consistent with a population of unevolved M-dwarf stars lower than 0.7 M_\odot. The M/L ratio in B for the halo is estimated to range between 50 and 200 implying a total mass for the cD galaxy of 1.6-3.1~10^{13} M_\odot and a total B luminosity of 6.0~10^{11} L_\odot., Comment: 6 pages with 5 figures, uuencoded poscript file, accepted by A&A, e-mail: molinari@astmim.mi.astro.it