Packet Delay in UAV Wireless Networks Under Non-saturated Traffic and Channel Fading Conditions

In this paper, we conduct a statistical analysis for the packet delay in a wireless network of unmanned aerial vehicles (UAVs) under non-saturated traffic and channel fading conditions. Each UAV runs the distributed coordination function of IEEE 802.11 at the medium access control layer, and all UAVs are one-hop neighbors. A pair of UAVs can communicate over the lossy wireless channel of a fixed data rate. A non-saturated traffic condition is used. By modeling each node UAV as a standard queueing system (i.e., $M/M/1$ or $M/G/1$ queue), we derive the mean packet delay under the non-saturated traffic condition. Numerical and simulation results show that the mean packet delay derived based on $M/M/1$ queue is accurate for UAV wireless networks under the non-saturated traffic condition and with an independent packet error rate. It is observed that the mean packet delay increases with either the number of UAVs in the network or the packet generation rate. More important, existing results in the literature, based on the saturated traffic condition (i.e., packets are always supplied for transmission), tend to overestimate by a large amount the mean packet delay for networks with non-saturated traffic. In the second part of this paper, we apply simulation data to analysis of the probability distribution function of the packet delay when the packet error rate equals zero. Using a distribution fitting tool, we observe that the packet delay can be well approximated by the sum of a deterministic delay, which corresponds to the time period during which the UAV senses the medium and is able to perform a successful transmission, and a random delay, which follows a Gamma distribution function.     

Splice loss measurement using local launch and detect

This paper reports a new method for measuring absolute splice loss using a local launch and detect technique. The theory of the procedure and the calibration routine are described. Results with single-mode fiber splices are presented and compared with the cutback measurements.     

Control system design for VSC transmission

This paper investigates a suitable control system for a DC transmission system based on voltage source converters (VSC). Each of the two VSC converters has two control inputs and the four control channels on a VSC transmission system offer potential for a versatile control. However, the main challenge is the dynamic interaction among the control loops. It is proposed in this study that the overall system stability and good robustness should be achieved with two high-gain feedback loops, one at each converter. Eigenvalue and robustness analysis with MATLAB software shows that the best fast feedback signals are inverter DC voltage and rectifier AC voltage q component. The slow controller consists of three PI controllers that regulate: rectifier AC voltage, inverter AC voltage and the DC power. The VSC transmission control under fault conditions is achieved with a separate controller that takes over system control for fault-level currents. The fault controller regulates the local DC currents at each converter. The proposed controller is tested using PSCAD/EMTDC for a wide range of small-signal step inputs and the design performance is confirmed. The design is also tested for typical fault scenarios on AC and DC side to verify the fault controller operation.     

Bronchiolitis obliterans organising pneumonia. A report of 11 cases and a review of the literature

The clinical syndrome "Bronchiolitis Obliterans Organising Pneumonia" (BOOP) has to be considered in patients with a flu-like illness since some weeks, fine crackles, and on chest X-ray bilateral patchy infiltrates. There is no response to antibiotics. BOOP is essentially idiopathic, but associations to other conditions exist. Lung function is often restrictive; biochemistry is not pathognomonic. BAL shows a mixed cellular pattern. The gold standard for pathologic diagnosis is open or thoracoscopic lung biopsy. However, a BOOP pattern or reaction is often seen on histologic specimens without the clinical-radiologic features of the BOOP-entity. Therapy consists of corticosteroids, which have to be prescribed for a long time at a rather high dose. Recurrence is frequent, but prognosis is good. Evolution to respiratory insufficiency and death is rare and may occur in rapidly progressive BOOP. This study reports on 11 cases (6 males/5 females) of clinical-pathological BOOP-syndrome (mean age 58 yrs, range 17-73 yrs), with an unexpectedly high mortality rate of 36% (4 cases). The disease was idiopathic in 7, and was associated with intake of amiodarone (in 1), with past Mycoplasma pneumonia (in 1) and with connective tissue disease (in 2). There was a history of a flu-like syndrome, cough and dyspnea of a mean duration of 4 months (range 1 week to 8 months). Lung function was mostly restrictive or/and obstructive with a diffusing capacity ranging between 47 and 95% predicted; there was hypoxia in about half of the patients. Chest X-ray and computed tomography (CT) scan showed a patchy consolidation with linear opacities (unilateral in 4 patients, bilateral in 5) and/or a ground glass pattern (in 4 patients), and a focal pseudo-tumoral lesion (in 1). Bronchoalveolar lavage showed a variable pattern of mixed, or eosinophilic or neutrophilic alveolitis. Histologic diagnosis was based on open lung biopsy (in 3), on thoracoscopic biopsy (in 2), on transbronchial biopsy (in 2), on wedge resection of the nodular lesion (in 1) and on postmortem lung biopsy (in 3). One patient recovered spontaneously, 1 remained cured after resection of the focal lesion, 7 were treated with 16-125 mg methylprednisolone (of whom 3 had a temporary flare-up during tapering the corticosteroids and 2 died after 1 and 3 months due to infectious complications), 2 died due to rapidly progressive BOOP.     

Multiport-readout frame-transfer 5 megapixel CCD imaging system for TEM applications

A multiport-readout, frame-transfer charge-coupled device (CCD) digital imaging system has been successfully developed and tested for intermediate-high-voltage electron microscopy (IVEM) applications up to 400 keV. The system employs a back-thinned CCD with 2560 x 1960 pixels and a pixel size of 24 microm x 24 microm. In the current implementation, four of the eight on-chip readout ports are used in parallel each operating at a pixel rate of 1- or 2-MHz so that the entire CCD array can be read out in as short as 0.6 s. The frame-transfer readout functions as an electronic shutter which permits the rapid transfer of charges in the active pixels to four masked buffers where the charges are readout and digitized while the active area of the CCD is integrating the next frame. With a thin film-based phosphor screen and a high-performance lens relay, the system has a conversion factor of 2.1 digital units per incident electron at 400 keV, and a modulation transfer function value of 14% at the Nyquist frequency.     

Effect of fire on composite long span truss floor systems

Much research has been and is currently being done to try and accurately recreate the effects of fire on structures including the effects of redistribution within the structure and the associated changes in load carrying mechanisms. This work has mostly focussed upon the most common and simplest structural forms currently used. As such most of the research to date tends to involve Universal Beam and Universal Column sections in a grid formation with spans of 6-9 m. This paper reports on an investigation of the effects of heating on a long span truss floor system. The ABAQUS finite element package is used to model the structure including fully non-linear behaviour and thermal expansion effects. Different boundary conditions and heating regimes are investigated to understand the response of the truss members to fire. The effects of heating on the lateral restraint available from the slender floor systems to a column have also been studied. The results and analysis indicate that composite truss flooring systems may not fail suddenly. Individual member buckling seems to be a much more gradual occurrence linked to material failure and expansion based geometry change rather than sudden “failure”.     

Mass transfer from bubbles in cocurrent flow

An experimental study has been made of liquid phase mass transfer from bubbles travelling cocurrently with liquid in a horizontal pipe. A simple model of the process based on streams of spherical bubbles has been developed and solved in the form of fractional absorption as a function of dimensionless groups. The derivation of and results obtained from this model are presented and explained. Experimental absorption rates measured in turbulent liquid flow over very wide ranges of bubble frequencies support the predictions of this model. A very effective bubble-frequency counter has also been developed capable of counts as high as 1600/min.