Stabilized jellium model and structural relaxation effects on the fragmentation energies of ionized silver clusters

Using the stabilized jellium model in two schemes of `relaxed' and `rigid', we have calculated the dissociation energies and the fission barrier heights for the binary fragmentations of singly-ionized and doubly-ionized Ag clusters. In the calculations, we have assumed spherical geometries for the clusters. Comparison of the fragmentation energies in the two schemes show differences which are significant in some cases. This result reveals the advantages of the relaxed SJM over the rigid SJM in dynamical processes such as fragmentation. Comparing the relaxed SJM results and axperimental data on fragmentation energies, it is possible to predict the sizes of the clusters just before their fragmentations.Comment: 9 pages, 12 JPG figure

Volume change of bulk metals and metal clusters due to spin-polarization

The stabilized jellium model (SJM) provides us a method to calculate the volume changes of different simple metals as a function of the spin polarization, $\zeta$, of the delocalized valence electrons. Our calculations show that for bulk metals, the equilibrium Wigner-Seitz (WS) radius, $\bar r_s(\zeta)$, is always a n increasing function of the polarization i.e., the volume of a bulk metal always increases as $\zeta$ increases, and the rate of increasing is higher for higher electron density metals. Using the SJM along with the local spin density approximation, we have also calculated the equilibrium WS radius, $\bar r_s(N,\zeta)$, of spherical jellium clusters, at which the pressure on the cluster with given numbers of total electrons, $N$, and their spin configuration $\zeta$ vanishes. Our calculations f or Cs, Na, and Al clusters show that $\bar r_s(N,\zeta)$ as a function of $\zeta$ behaves differently depending on whether $N$ corresponds to a closed-shell or an open-shell cluster. For a closed-shell cluster, it is an increasing function of $\zeta$ over the whole range $0\le\zeta\le 1$, whereas in open-shell clusters it has a decreasing behavior over the range $0\le\zeta\le\zeta_0$, where $\zeta_0$ is a polarization that the cluster has a configuration consistent with Hund's first rule. The resu lts show that for all neutral clusters with ground state spin configuration, $\zeta_0$, the inequality $\bar r_s(N,\zeta_0)\le\bar r_s(0)$ always holds (self-compression) but, at some polarization $\zeta_1>\zeta_0$, the inequality changes the direction (self-expansion). However, the inequality $\bar r_s(N,\zeta)\le\bar r_s(\zeta)$ always holds and the equality is achieved in the limit $N\to\infty$.Comment: 7 pages, RevTex, 10 figure

Exponential Distributions in a Mechanical Model for Earthquakes

We study statistical distributions in a mechanical model for an earthquake fault introduced by Burridge and Knopoff [R. Burridge and L. Knopoff, {\sl Bull. Seismol. Soc. Am.} {\bf 57}, 341 (1967)]. Our investigations on the size (moment), time duration and number of blocks involved in an event show that exponential distributions are found in a given range of the paramenter space. This occurs when the two kinds of springs present in the model have the same, or approximately the same, value for the elastic constants. Exponential distributions have also been seen recently in an experimental system to model earthquake-like dynamics [M. A. Rubio and J. Galeano, {\sl Phys. Rev. E} {\bf 50}, 1000 (1994)].Comment: 11 pages, uuencoded (submitted to Phys. Rev. E

VLC Based Guidance System to Be Used by Mobile Users Inside Large Buildings

The main goal of this paper is a Visible Light Communication (VLC) based guidance system to be used by mobile users inside large buildings. This system is composed of several transmitters (ceiling luminaries), which transmit map information and path guidance messages. Mobile devices, with VLC support, decode the information. A mesh cellular hybrid structure is proposed. The luminaires, via VLC, deliver their geographic position and specific information to the users, making them available for whatever use they request. The communication protocol, coding/decoding techniques, and error control are examined. Bidirectional communication is implemented and the best route to navigate through venue calculated. We propose several guidance services and multi-person cooperative localization. By analyzing the results, it became clear that the system not only provides self-location, but also the capability to determine the direction of travel and to interact with information received in order to optimize the route towards a static or dynamic destination.publishersversionpublishe

HerMES: Lyman Break Galaxies Individually Detected at 0.7 ≤ z ≤ 2.0 in GOODS-N with Herschel/SPIRE

As part of the Herschel Multi-tiered Extragalactic Survey we have investigated the rest-frame far-infrared (FIR) properties of a sample of more than 4800 Lyman break galaxies (LBGs) in the Great Observatories Origins Deep Survey North field. Most LBGs are not detected individually, but we do detect a sub-sample of 12 objects at 0.7 2.5. The UV-to-FIR spectral energy distributions of the objects detected in the rest-frame FIR are investigated using the code CIGALE to estimate physical parameters. We find that LBGs detected by SPIRE are high-mass, luminous infrared galaxies. It appears that LBGs are located in a triangle-shaped region in the A_(FUV) versus log L_(FUV) = 0 diagram limited by A_(FUV) = 0 at the bottom and by a diagonal following the temporal evolution of the most massive galaxies from the bottom right to the top left of the diagram. This upper envelop can be used as upper limits for the UV dust attenuation as a function of L_(FUV). The limits of this region are well explained using a closed-box model, where the chemical evolution of galaxies produces metals, which in turn lead to higher dust attenuation when the galaxies age

SEMICONDUCTOR DEVICE FOR DETECTION OF FRET SIGNALS

The transducer consists on a semiconductor device based on two stacked-i-n  heterostructures, that were designed to detect the emissions of the fluorescence resonance energy transfer between fluorophores in the cyan (470 nm) and yellow (588 nm) range of the spectrum. This research represents a preliminary study on the use of such wavelength sensitive devices as photodetectors for this kind of application. The device was characterized through optoelectronic measurements concerning spectral response measurements under different electrical and optical biasing conditions. To simulate the FRET pairs a chromatic time dependent combination of cyan and yellow wavelengths was applied to the device. The generated photocurrent was measured under reverse and forward bias to readout the output photocurrent signal. Different wavelength biasing light was also superimposed. Results show that under reverse bias the photocurrent signal presents four separate levels each one assigned to the different wavelength combinations of the FRET pairs. If a blue background is superimposed the yellow channel is enhanced and the cyan suppressed while under red irradiation the opposite behavior occurs. So under suitable biasing light the transducer is able to detect separately the cyan and yellow fluorescence pairs. An electrical model, supported by a numerical simulation supports the transduction mechanism of the device