On the distributed construction of a collision-free schedule in multi-hop packet radio networks

This paper introduces a protocol that distributively constructs a collision-free schedule for multi-hop packet radio networks in the presence of hidden terminals. As a preliminary step, each wireless station computes the schedule length after gathering information about the number of flows in its neighbourhood. Then, a combination of deterministic and random backoffs are used to reach a collision-free schedule. A deterministic backoff is used after successful transmissions and a random backoff is used otherwise. It is explained that the short acknowledgement control packets can easily result in channel time fragmentation and, to avoid this, the use of link layer delayed acknowledgements is advocated and implemented. The performance results show that a collision-free protocol easily outperforms a collision-prone protocol such as Aloha. The time that is required for the network to converge to a collision-free schedule is assessed by means of simulation.     

From concept to application. A new phase change material for thermal protection at -11 °C

Molecular Alloys as Phase Change Materials (MAPCM) offer opportunities in the fields of energy storage and thermal protection, where the classic Phase Change Materials (PCM) don't exist or they are difficult to find. The MAPCM's are thermo-adjustable materials by means of their composition. The present paper is on the design of a MAPCM to be used for thermal protection at –11 °C. We show how fundamental studies are helpful to choose the right composition that is able to work at the temperature required for an application. Several molecular alloys among n-alkanes were elaborated and characterized. Finally, a multicomponent molecular alloy is proposed and tested in a double wall prototype, for thermal protection of ice cream or other kinds of product around –11 °C. As result, we propose a prototype that it is effective for more than 4 hours and 30 minutes in an external environmental temperature of 20 °C. Electronic Publication     

Handover defects: comparison of construction and post-handover housing defects

Although inspections occur during construction or at handover, customers do not normally participate. This situation creates a gap between the quality perceived by both contractors and customers. An analysis of 52 552 handover defects in 2179 flats in Spain is presented which identified their nature, the building element and trade where these defects are located. These results are compared with previous studies that analysed defects detected during the construction stage and those that remain after handing over the building to the client. The research reveals that structural defects are resolved during construction due to existing quality standards. However, other aesthetic and functional defects remain and/or arise at handover. Some defects are not resolved until customers complain after they first occupy the dwelling. Many functional defects arise due to the lack of involvement of end users in the early project stages.     

Sorption of selenium(IV) and selenium(VI) onto natural iron oxides: goethite and hematite

Selenium is a toxic element with a relatively high mobility in the natural waters. Iron oxy-hydroxides might play an important role in the migration of this element as well as on its removal from contaminated water. In this work we study the interaction of Se(IV), and Se(VI) with natural iron oxides hematite and goethite through two series of batch experiments at room temperature. In the first series, sorption as a function of initial selenium concentration is studied and the results have been fitted with Langmuir isotherms. In a second series of experiments, sorption is studied as a function of pH, being the main trend an increase of the sorption at acidic pH. The variation of the sorption with pH has been modelled with a triple layer surface complexation model and using the FITEQL program. The experimental data have been modelled considering for the Se(IV) the formation of the FeOSe(O)O(-) complex onto the hematite surface, and a mixture of FeOSe(O)O(-), and FeOSe(O)OH onto the goethite surface. For Se(VI) the surface complex considered is FeOH(2)(+)-SeO(4)(2-) on both goethite and hematite.     

Electroflottation et desinfection simultanee d'eaux residuaires urbaines

This reports presents the results of a simultaneous electroflotation and disinfection sewage treatment, after chemical coagulation and flocculation and in the presence of chloride ions at various concentrations. Theoretical studies had shown that anodic oxidation of chloride ions gives hyperchlorites (for pH 7.5) together with (if sufficient potential is provided) oxygen. A dynamic study was thus achieved. It appeared that for a given chloride concentration the chlorine production linearly increases with the current density and depends on the organic load (COD) and oxidation potential of the effluent (Figs 6, 7 and 8). The performances of the process were studied in the continuous mode on a small pilot plant, after treatment of the effluent with ferric chloride and an organic polymer (Fig. 2). In all experiments current density and chloride concentration were raised (respectively 100, 200, 300 A m⁻² and from 300 to 3000 mg l⁻¹). The results obtained showed that solid-liquid separation was improved over static clarification for 2 h (Table 3) and the disinfection efficiency was equal or better than that obtained with gaseous chlorine (Table 4, Fig. 9). For example at a 900 mg l⁻¹ chloride concentration the three current density used give treated water containing less than 10³/100 ml total coliforms (initial concentration 4.7 · 10⁷/100 ml). These results have direct applications to the design of electroflotation units where a better plug flow should be sought. Moreover this process produces highly concentrated sludges. The utilization of ATP (Adenosine Triphosphate) as an indicator of the viability of a biomass showed that the process is applicable to activated sludges with recycling. The experimental conditions required for this application are still uncertain and require further study.     

In vivo quantification of response to treatment in patients with multiple myeloma by <Superscript>1</Superscript>H magnetic resonance spectroscopy of bone marrow

Object Magnetic resonance imaging (MRI) is the gold standard non-invasive technique to detect malignant disease in the bone marrow. Proton magnetic resonance spectroscopy (MRS) can be performed as a quick adjunct to routine spinal MRI. We performed proton MRS to patients with multiple myeloma (MM) at diagnosis and after treatment to investigate the possible correlation of MRS data with response to therapy. Patients and methods Twenty-one patients with newly diagnosed MM underwent combined MRI/MRS explorations of a transverse center section in the fifth lumbar vertebral body. MRS was acquired with STEAM and 40 ms TE. Areas of unsuppressed water and lipid resonances were used to calculate the lipid-to-water ratio (LWR). Results No association was detected between initial LWRs and the clinical characteristics of patients. Post treatment MRS was available in 16 patients of whom 11 (69%) presented an LWR increase, this included all complete responders (8/8, 100%, P = 0.012). A post-treatment LWR value equal to or larger than one is proposed as a non-invasive marker of complete response to treatment. Conclusion Only patients responding to treatment presented a significant increase in bone marrow LWR after therapy. MRS may provide an adequate quantification of response to chemotherapy in patients with MM.     

A Module for BiST of CMOS RF Receivers

A module to perform a built-in self-test in CMOS RF receivers is presented. The module is associated with a test strategy consisting of measuring the main performance parameters of the single building blocks individually. Circuitry overhead, however, is kept low by using some blocks as part of the test set-up and reusing them. The test overhead has also been reduced by replacing direct determination of performance parameters with their estimation. The test methodology has been applied to a mixer in the first down conversion stage of a GSM receiver, estimating its conversion gain, 1dB compression and third-order interception points. Using the output of the IF amplifier as the only testing point, the rms errors in the estimation of the above mentioned parameters are 1.5, 3.0 and 2.7%, respectively.

Revisiting the pallet loading problem using a discrete event system approach to minimise logistic costs

This paper presents a new challenging modelling approach to support different heuristics to tackle the pallet loading problem (PLP). A discrete event system model to tackle the PLP is specified using the coloured Petri net formalism in order to integrate the model with the industrial context in which the PLP must be solved. New events can be formalised in the model to implement different heuristics to consider the upstream (production) and downstream (transport) influence of the palletising activity in the logistic flow. A state space analysis is performed to evaluate the different solutions to fit the maximum number of boxes on a rectangular pallet, supporting the inherent box diversity (heterogeneous palletising problems) of present production and distribution logistic systems. The heuristics implemented show that acceptable occupancy results can be obtained without requiring the exhaustive evaluation of the different feasible combination. The results demonstrate that it outperforms other approaches which have been suggested for this type of problem. Potentially useful extensions of the work are discussed.     

An experimental investigation of distortional buckling of steel storage rack columns

An experimental investigation on the behavior of steel storage rack columns subjected to compression is presented. Members of different lengths are tested, but special attention is focused on the behavior of the specimens having lengths that make them subject to distortional buckling. This mode of buckling can be observed in moderately long specimens; namely, longer than the stub columns used for the determination of the local buckling strength, but short enough to avoid the effects of global buckling. The deformation experienced by these specimens is measured, and it is observed that there is a range of member lengths where the failure mode is a combination of distortional buckling and global buckling modes. Furthermore, it is verified that, although the effect of the interaction between these modes on the member strength is not large, the accuracy of the current design procedures improves if it is considered in the calculations.