Design and comparison of turbo codes under frame‐length and code‐rate constraints

When the performances of error‐correcting codes for space communications are investigated, with the aim to translate them into practical recommendations, comparison among different schemes is usually a very difficult task. As a matter of fact, these comparisons rarely yield general conclusions. On the other hand, most practical space applications impose strong constraints on the code parameters, which have important effects on code selection. In this paper, we show a methodology and several examples of design and comparison, derived under fixed constraints imposed by the system application on the frame‐length and the code‐rate. CCSDS Earth observation missions requiring both large coding gains and high spectral efficiency are considered as a case study. Though referred to this specific space mission framework, the presented study is quite general and applies to many other digital communication systems; e.g. for wireless or wired applications where similar constraints exist but are often not taken in due consideration by the designer of the error‐correcting schemes. Copyright © 2006 John Wiley & Sons, Ltd.     

Micro-Raman spectroscopy study of surface transformations induced by excimer laser irradiation of TiO2

Pressed disks of TiO₂ powder particles (≈1 μm in size) have been irradiated with a pulsed KrF (248 nm) excimer laser source at fluences between 0.1 and 1 J cm⁻². Surface films (1.5–2 μm thick) have been studied by Raman microprobe spectroscopy and atomic force microscopy (AFM). The Raman study reveals a three-layer structure for the irradiated anatase powders. A dark layer of reduced oxide is sandwiched between a top coating of molten/resolidified rutile and an underlying defective, slightly oxygen-deficient mixed-phase of rutile and anatase. AFM measurements indicate that a smooth surface layer coexisting with the initial rough grain morphology gradually appears with increasing fluence. At low fluence, anatase is reduced in a dark film and further transformed into rutile. At intermediate fluence, a shiny coating of resolidified stoichiometric rutile forms on the dark film. It gets thicker as the fluence increases while darkening of the sublayer intensifies up to a maximum of approximately 700 mJ cm⁻². At high fluence, however, melting and re-oxidation (and eventually ablation) prevail over reduction; the whole layer turns into a greyish crust of mostly resolidified rutile in non-ablated regions. A physico-chemical mechanism is proposed to explain the in-depth distribution of the various components as a function of fluence.     

Computing optical flow across multiple scales: An adaptive coarse-to-fine strategy

Single-scale approaches to the determination of the optical flow field from the time-varying brightness pattern assume that spatio-temporal discretization is adequate for representing the patterns and motions in a scene. However, the choice of an appropriate spatial resolution is subject to conflicting, scene-dependent, constraints. In intensity-base methods for recovering optical flow, derivative estimation is more accurate for long wavelengths and slow velocities (with respect to the spatial and temporal discretization steps). On the contrary, short wavelengths and fast motions are required in order to reduce the errors caused by noise in the image acquisition and quantization process.Estimating motion across different spatial scales should ameliorate this problem. However, homogeneous multiscale approaches, such as the standard multigrid algorithm, do not improve this situation, because an optimal velocity estimate at a given spatial scale is likely to be corrupted at a finer scale. We propose an adaptive multiscale method, where the discretization scale is chosen locally according to an estimate of the relative error in the velocity estimation, based on image properties.Results for synthetic and video-acquired images show that our coarse-to-fine method, fully parallel at each scale, provides substantially better estimates of optical flow than do conventional algorithms, while adding little computational cost.     

Microbial Sensory Rhodopsins: Photochemistry and Function

The review covers recent progress on microbial sensory rhodopsins, visual pigment-like retinylidene photoreceptors that function in phototaxis by archaeons, such as Halobacterium salinarium, and by unicellular eukaryotic algae, such as Chlamydomonas reinhardtii. Six demonstrably different sensory rhodopsins are known in halophilic archaea. The best characterized is sensory rhodopsin I (SR-I), a color-sensitive receptor that relays attractant and repellent photosignals to a tightly bound transducer protein HtrI (halobacterial transducer for sensory rhodopsin I). New advances in the mechanism of signal transduction by the SR-I/HtrI complex from molecular-biological and biophysical approaches are summarized. Effects of HtrI on light-induced proton transfers in the receptor are discussed for their possible role in signaling. Current knowledge concerning the growing family of related archaeal sensory rhodopsins is presented. The evidence for a sensory rhodopsin in phototaxis by C. reinhardtii and other unicellular eukaryotic algae is reviewed. The molecular information is more limited than for the archaeal organisms, but the physiological information is rich and complex. Compelling data exist for a single retinal-containing receptor mediating both phototaxis and photophobic responses in C. reinhardtii. From retinal analog studies, the isomeric configuration and ring/chain conformation of the retinal in the receptor appear to be identical to those of the archaeal sensory rhodopsins. Also, photoisomerization from all-trans- to 13-cis-retinal appears to be the trigger for signaling, as in the archaeal pigments. Conflicting early studies suggesting an 11-cis-retinal chromophore and signaling without photoisomerization are analyzed and possible explanations for those reports are suggested. As a general conclusion, the microbial sensory rhodopsins provide an opportunity to explore photochemistry and protein/protein interaction in photosensory transduction in genetically tractable organisms.     

Assembling single cells to create a stack: The case of a 100 W microtubular anode-supported solid oxide fuel cell stack

Microtubular solid oxide fuel cell systems have many desirable characteristics compared with their planar counterparts; however, there are many obstacles and difficulties that must be met to achieve a successful and economically viable manufacturing process and stack design. Anode-supported tubes provide an excellent platform for individual cells. They allow for a thin electrolyte layer, which helps to minimize polarization losses, to be applied to the outside of the tube, thus avoiding the difficulty of coating the inside of an electrolyte or cathode-supported tubes, or the stack design problem of having a fuel chamber if the anode is on the outside of the tube. This article describes the fabrication of a traditional (Ni-YSZ) anode tube via extrusion of a plastic mass through a die of the required dimensions. The anode tubes were dried before firing, and tests were performed on the tubes to determine the effects of prefiring temperature on porosity. The porous tubes had a vacuum applied to the inside while being submerged in aqueous electrolyte slurry. Various parameters were examined, including vacuum pressure, submergence time, and drying conditions, and were studied using microscopy. Cathode coatings (based on both doped lanthanum manganite and doped lanthanum cobaltite) were applied using a brush-painting technique, and were optimized as a function of paint consistency, drying conditions, and firing temperatures. The finished tubes were then stacked in an array to provide the specific current/voltage requirements, using a brazing technique. This article will describe the output characteristics of a single cell and a small stack (of 100 W designed power output). This paper was presented at the ASM Materials Solutions Conference & Show held October 18–21, 2004 in Columbus, OH.     

Blind-ending branch of bifid ureter: apropos of a case

The Authors report on a case of blind-ending ureter. A young woman (29 years old) underwent surgery because of recurrent urinary tract infections and left loin pain. The operation consisted in a radical resection of the blind branch together with Coen's operation for the coexistence of vesicoureteral reflux. Authors' goal was to review the international Literature on this rare pathology pointing out their opinion on the existing terminology which is still far from being clear and definite.     

Rhythms of temperature selection and body temperature are out of phase in the golden hamster.

Body temperature, locomotor activity, and thermoregulatory behavior of freely moving golden hamsters maintained in a spatial thermocline were measured over several weeks. The thermoregulatory behavior of temperature selection exhibited a robust daily rhythm 180° out of phase with the rhythms of body temperature and locomotor activity. However, the parameters of the body temperature rhythm (rhythmicity, mean level, and amplitude) were not significantly affected by the thermoregulatory behavior. Although the observed phase difference between the rhythms of temperature selection and body temperature might suggest that thermoregulatory behavior is modulated to oppose (rather than to defend) the rhythm of body temperature, the absence of effect of temperature selection on the parameters of the body temperature rhythm fails to reveal the physiological significance of such opposition. Further studies are necessary to establish the physiological significance of the rhythm of temperature selection. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

A formal approach for checking security properties in SecSpaces

SecSpaces is a Linda-like coordination model whose aim is to provide a support for secure coordination in Open System applications. Substantially it provides a methodology to restrict the access to the objects stored in the shared dataspace. In this paper we introduce a formal language for representing systems interacting via SecSpaces primitives and its operational semantics. Moreover in this context we consider a notion of observational equivalence, namely testing equivalence. In order to evaluate the adequacy of the model for limiting the access to the shared dataspace, we present some examples of interaction protocols that can be used to obtain some security properties (e.g., authentication or privacy of a datum).