Pedro Amaral

An improved low-voltage low-power CMOS comparator to be used in high-speed pipeline ADCs

This paper presents an improved low-voltage low-power CMOS comparator suitable for high-speed pipeline ADCs. Simulated results of the proposed circuit in a 0.35 /spl mu/m standard CMOS technology operating at supply voltages within the range of 1.0-1.5 V show that this comparator achieves low offset, reduced kickback noise, high mean-time to failure and exhibits low-power dissipation at very high-speed operation.

Chronic arthritis leads to disturbances in the bone collagen network

IntroductionIn this study we used a mice model of chronic arthritis to evaluate if bone fragility induced by chronic inflammation is associated with an imbalance in bone turnover and also a disorganization of the bone type I collagen network.MethodsSerum, vertebrae and femur bones were collected from eight-month-old polyarthritis SKG mice and controls. Strength of the femoral bones was evaluated using three-point bending tests and density was assessed with a pycnometer. Bone turnover markers carboxy-terminal collagen cross-linking telopeptides (CTX-I) and amino-terminal propeptide of type I procollagen (PINP) were measured in serum. The organization and density of bone collagen were analyzed in vertebrae using second-harmonic generation (SHG) imaging with a two-photon microscope and trabecular bone microstructure was assessed by scanning electron microscope (SEM).ResultsFemoral bones of SKG mice revealed increased fragility expressed by deterioration of mechanical properties, namely altered stiffness (P = 0.007) and reduced strength (P = 0.006), when compared to controls. Accordingly, inter-trabecular distance and trabecular thickness as observed by SEM were reduced in SKG mice. PINP was significantly higher in arthritic mice (9.18 ± 3.21 ng/ml) when compared to controls (1.71 ± 0.53 ng/ml, P < 0.001). Bone resorption marker CTX-I was 9.67 ± 3.18 ng/ml in arthritic SKG mice compared to 6.23 ± 4.11 ng/ml in controls (P = 0.176). The forward-to-backward signal ratio measured by SHG was higher in SKG animals, reflecting disorganized matrix and loose collagen structure, compared to controls.ConclusionsWe have shown for the first time that chronic arthritis by itself impairs bone matrix architecture, probably due to disturbed bone remodeling and increased collagen turnover. This effect might predispose patients to bone fragility fractures.

Weibull statistical analysis of flexure breaking performance for alumina ceramic disks sintered by solar radiation heating

Densified alumina ceramic disk specimens were prepared through sintering compacted alumina powders by concentrated solar beam in inert Ar gas atmosphere and their flexure breaking behaviour was evaluated by the ring-on-ring jig test under application of equibiaxial stress. Slope m of Weibull plot for MOR (modulus of rupture) values of these specimens was comparable to that of the reference alumina disk specimens prepared by sintering in an electric furnace under comparable conditions (1600°C for 30 min) whereas mean MOR level of the former was slightly lower than that of the latter. Thus, the failure mechanism of the specimens sintered by solar radiation heating and that of the specimens sintered in the electric furnace were concluded to be practically indistinguishable. This evidence guarantees that alumina ceramic sintered bodies, with quality comparable to those obtained through traditional sintering process, can be prepared by solar heating in spite of quite fast rate of heating and cooling realised in the solar furnace.

Fracture toughness of solar-sintered WC with Co additive

A tungsten carbide (WC) cylinder specimen containing 10 mass% Co sintering aid was prepared under concentrated solar radiation (measured maximum temperature no higher than 1500 °C) in dynamic primary vacuum and its fracture toughness was evaluated by Vickers indentation method. In spite of very fast rates of heating and cooling applied in the solar-sintering process, fracture toughness of the prepared WC cylinder specimen was comparable to that of WC sintered piece prepared through a conventional industrial process in electric furnace under a slow heating and cooling condition. Present results together with the previously reported results for solar-sintered alumina ceramic disk appear to suggest the promising possibility of using solar radiation heating for manufacturing sintered ceramic components.

Photochemical Effects in Carbide Synthesis of d-group Transition Metals (Ti, Zr; V, Nb, Ta; Cr, Mo, W) in a Solar Furnace at PSA (Plataforma Solar de Almerı́a)

During the course of our recent series of solar carbide and carbonitride synthesis work During the course of our recent series of solar carbide and carbonitride synthesis work for d-group transition elements (Ti,Zr;V,Nb,Ta;Cr,Mo,W), we detected several intriguing evidences apparently indicative of involvement of photochemical effects in some reactions under solar radiation. 1) Acceleration of graphitization of amorphous carbon during carburization of W under solar radiation. 2) Promoted formation of high remperature mono-carbide phase of Mo under solar radiation at a temperature lower than the one indicated in equilibrium phase diagram. 3) Formation of sub-carbide Ta 2 C besides mono-carbide TaC in the carburization of Ta with amorphous carbon under solar radiation. Only mono-carbide TaC formed by the carburization of Ta with graphite under solar radiation in accordance with the equilibrium phase diogram. These features were already published individually elsewhere. This article is the brief summary of the reported facts in our earlier publications. Although the results so-far-obtained are rather primitive and our earlier publications. Although the results so-far-obtained are rather primitive and still lacking quantitative characterization, there seems to be no doubt that solar materials processing would open new routes for unique products which cannot be prepared through traditional industrial manufacturing processes.

Carbide formation of Va-group metals (V, Nb and Ta) in a solar furnace

Abstract In our recent series of solar carbide synthesis for Si and d-group transition metals (Ti, Zr; Cr, Mo, W) using graphite (G) or amorphous carbon (aC) as carburising medium, we observed some evidences indicative of involvement of photochemical effects in the reaction process. For example, (1) graphitisation of aC was accelerated during carburisation of W under solar radiation; (2) high-temperature mono-carbide phase of Mo (α-MoC1−x) formed at a temperature appreciably lower than the lower-threshold temperature of the stability range of the α-MoC1−x phase given in the available equilibrium phase diagram for Mo–C system. In this work, we investigated solar carburisation reactions for Va-group metals (V, Nb, Ta) in Ar or N2 gas environment. For this group of metals, only carbide phases formed even in N2 atmosphere without forming carbonitride like the cases with VIa-group metals (Cr, Mo, W). For carburisation of Ta with aC in Ar, an unexpected formation of sub-carbide Ta2C besides mono-carbide TaC took place, while Ta2C phase did not form through carburisation of Ta with aC in N2 or carburisation of Ta with G in either Ar or N2 atmosphere. No graphitisation promotion for aC was detected during the carburisation of none of the Va-group elements.

A Comparison between X-Ray Diffraction and Petrography Techniques Used to Determine the Mineralogical Composition of Granite and Comparable Hard Rocks

Petrography and X-ray diffraction techniques are used in this work to determine the mineralogical composition of a granite, a gabbro and a quartzite. The experimental difficulties and the results obtained by both methods are described and discussed. The semi-quantitative procedure of XRD analysis used in this work allows an estimate of the relative mineral phase composition of each type of rock. Petrography was found to be crucial in terms of textural analysis.

Machine Learning in Software Defined Networks: Data collection and traffic classification

Software Defined Networks (SDNs) provides a separation between the control plane and the forwarding plane of networks. The software implementation of the control plane and the built in data collection mechanisms of the OpenFlow protocol promise to be excellent tools to implement Machine Learning (ML) network control applications. A first step in that direction is to understand the type of data that can be collected in SDNs and how information can be learned from that data. In this work we describe a simple architecture deployed in an enterprise network that gathers traffic data using the OpenFlow protocol. We present the data-sets that can be obtained and show how several ML techniques can be applied to it for traffic classification. The results indicate that high accuracy classification can be obtained with the data-sets using supervised learning.

SIDSP: Simple Inter-Domain QoS Signaling Protocol

This paper presents a study on a scalable inter-domain signaling protocol to provide quality of service to the Internet. The protocol uses a hard-state approach and separates data forwarding procedures, control procedures, and resource allocation procedures. Current solutions adopt a soft-state label switching approach where border routers are responsible for maintaining resource accounting and the paths next-hop information for every aggregated flow. Due to the Internets almost hierarchical structure, the routers at the core can become a bottleneck to the systems overall scalability. Our protocol, SIDSP, reduces the core routers complexity by transferring most of the state data to the peripheral routers. This is accomplished by the usage of source routing for the flows. As a hard-state approach, it does not require periodical refreshing messages. However it puts more pressure on state coherence and state stabilization algorithms. SIDSPs performance was tested using ns-2 simulations, and was compared to BGRPs performance.

Multipath policy routing using destination based hop-by-hop forwarding

Algebra has made the tasks of defining routing algorithms and proving their correct operation very clear. However, current results in the modelling of multipath policy routing protocols only prove correct behaviour for models that exhibit a strict decrease in the preference of a path with every added link. This is very rigid for multipath routing. For instance it does not allow a link attribute to dominate the entire path classification or having equivalent paths with similar policy but a different number of links. This paper starts by defining the fundamental sufficient conditions for the correct operation of a multipath policy routing protocol with independent destination based hop-by-hop forwarding. We then study the sufficient properties that the protocol model should exhibit so that those conditions are met. We prove that correct operation is possible without the strict increase in preference, provided that the policies applied to links forming circuits in the network graph are restricted. We derive two conditions on the policies applied in the circuits of a network graph that assure correct behaviour and can serve as a tool in the design process.