Control of an underactuated-slender-hull unmanned underwater vehicle using Port-Hamiltonian theory

This paper presents a control design for tracking of attitude and speed of an underactuated slender-hull unmanned underwater vehicle (UUV). The control design is based on Port-Hamiltonian theory. The target dynamics (desired dynamic response) is shaped with particular attention to the target mass matrix so that the influence of the unactuated dynamics on the controlled system is suppressed. This results in achievable dynamics independent of uncontrolled states. Throughout the design, insight of the physical phenomena involved is used to propose the desired target dynamics. The performance of the design is demonstrated through simulation with a high-fidelity model.

Local dispersion and damage of Corymbia citriodora subsp. variegata (Myrtaceae) regrowth by eriophyid mites (Acari: Eriophyoidea).

Eriophyid mites (Acari: Eriophyoidea: Eriophyidae: Rhombacus sp. and Acalox ptychocarpi Keifer) are recently-emerged pests of commercial eucalypt plantations in subtropical Australia. They cause severe blistering, necrosis and leaf loss to Corymbia citriodora subsp. variegata (F. Muell.) K.D. Hill & L.A.S. Johnson, one of the region's most important hardwood plantation species. In this study we examine the progression, incidence and severity of these damage symptoms. We also measure within-branch colonisation by mites to identify dispersive stages, and estimate the relative abundance of the two co-occurring species. Rhombacus sp., an undescribed species, was numerically dominant, accounting for over 90% of all adult mites. Adults were the dispersive stage, moving mostly within branches, but 12% of recruitment onto new leaves occurred on previously uninfested branches. Damage incidence and severity were correlated, while older leaves had more damage than younger leaves. "Patch-type" damage was less frequent but was associated with higher mite numbers and damage scores than "spot-type" damage, while leaf discoloration symptoms related mostly to leaf age.

Crystal structure and conformation of the cyclic dipeptide cyclo-(L-histidyl-L-aspartyl) trihydrate

The crystal structure of cyclo-(L-histidyl-L-aspartyl) trihydrate has been determined by x-ray diffraction techniques, and refined to a final R index of 0.056 for 1601 reflections. The molecule is in a folded conformation, with the imidazole ring facing the diketopiperazine ring. However, since the diketopiperazine ring is essentially planar, the interaction between the two rings is not as intimate as in those cyclic dipeptides in which the diketopiperazine ring is in a boat conformation with the side chain occupying an axial, or flagpole, site. Planarity of the diketopiperazine ring may be dictated by steric interactions between the imidazole ring and the aspartyl side chain. The molecule is a zwitterion, a proton having been transferred from the carboxyl group of the aspartyl side chain to the imidazole ring.

Venous thromboembolism during pregnancy and the impact of thrombophilia in pregnancy complications

Venous thromboembolism (VTE) is the greatest single cause of maternal mortality in pregnant women in developed countries. Pregnancy is a hypercoagulable state and brings about an enhanced risk of deep venous thrombosis (DVT) in otherwise healthy women. Traditionally, unfractionated heparin (UFH) has been used for treatment of DVT during pregnancy. We showed in our observational study that low molecular weight heparin (LMWH) is as effective and safe as UFH in the treatment of DVT during pregnancy. Although DVT during pregnancy is often massive, increasing the risk of developing long-term consequences, namely post-thrombotic syndrome (PTS), only 11% of all patients had confirmed PTS 3 4 years after DVT. In our studies the prevalence of PTS was not dependent on treatment (UFH vs LMWH). Low molecular weight heparin is more easily administered, few laboratory controls are required and the hospital stay is shorter, factors that lower the costs of treatment. Cervical insufficiency is defined as repeated very preterm delivery during the second or early third trimester. Infection is a well-known risk factor of preterm delivery. We found overpresentation of thrombophilic mutations (FV Leiden, prothrombin G20210A)among 42 patients with cervical insufficiency compared with controls (OR 6.7, CI 2.7 18.4). Thus, thrombophilia might be a risk factor of cervical insufficiency possibly explained by interaction of coagulation and inflammation processes. The presence of antiphospholipid (aPL) antibodies increases the risk for recurrent miscarriage (RM). Annexins are proteins which all bind to anionic phospholipids (PLs) preventing clotting on vascular phospholipid surfaces. Plasma concentrations of circulating annexin IV and V were investigated in 77 pregnancies at the beginning of pregnancy among women with a history of RM, and in connection to their aPL antibody status. Control group consisted unselected pregnant patients (n=25) without history of adverse pregnancy outcome. Plasma levels of annexin V were significantly higher at the beginning (≤5th week) of pregnancy in women with aPL antibodies compared with those without aPL antibodies (P=0.03). Levels of circulating annexin V were also higher at the 6th (P= 0.01) and 8th week of pregnancy in subjects with aPL antibodies (P=0.01). Results support the hypothesis that aPL could displace annexin from anionic phospholipid surfaces of syncytiotrophoblasts (STBs) and may exert procoagulant activities on the surfaces of STBs Recurrent miscarriage (RM) has been suggested to be caused by mutations in genes coding for various coagulation factors resulting in thrombophilia. In the last study of my thesis were investigated the prevalence of thrombomodulin (TM) and endothelial protein C receptor polymorphism EPCR among 40 couples and six women suffering RM. This study showed that mutations in the TM or EPCR genes are not a major cause of RM in Finnish patients.

Non local scale effects on ultrasonic wave characteristics nanorods

In this paper, the nonlocal elasticity theory has been incorporated into classical Euler-Bernoulli rod model to capture unique features of the nanorods under the umbrella of continuum mechanics theory. The strong effect of the nonlocal scale has been obtained which leads to substantially different wave behaviors of nanorods from those of macroscopic rods. Nonlocal Euler-Bernoulli bar model is developed for nanorods. Explicit expressions are derived for wavenumbers and wave speeds of nanorods. The analysis shows that the wave characteristics are highly over estimated by the classical rod model, which ignores the effect of small-length scale. The studies also shows that the nonlocal scale parameter introduces certain band gap region in axial wave mode where no wave propagation occurs. This is manifested in the spectrum cures as the region where the wavenumber tends to infinite (or wave speed tends to zero). The results can provide useful guidance for the study and design of the next generation of nanodevices that make use of the wave propagation properties of single-walled carbon nanotubes. (C) 2010 Elsevier B.V. All rights reserved.

Steady-State Stability of Current Mode Active-Clamp ZVS DC-DC Converters

Active-clamp dc-dc converters are pulsewidth-modulated converters having two switches featuring zero-voltage switching at frequencies beyond 100 kHz. Generalized equivalent circuits valid for steady-state and dynamic performance have been proposed for the family of active-clamp converters. The active-clamp converter is analyzed for its dynamic behavior under current control in this paper. The steady-state stability analysis is presented. On account of the lossless damping inherent in the active-clamp converters, it appears that the stability region in the current-controlled active-clamp converters get extended for duty ratios, a little greater than 0.5, unlike in conventional hard-switched converters. The conventional graphical approach fails to assess the stability of current-controlled active-clamp converters due to the coupling between the filter inductor current and resonant inductor current. An analysis that takes into account the presence of the resonant elements is presented to establish the condition for stability. This method correctly predicts the stability of the current-controlled active-clamp converters. A simple expression for the maximum duty cycle for subharmonic free operation is obtained. The results are verified experimentally.

Sosiaalisen elämän persoonallis-onttinen luonne : Tutkielma Lutherin alkutilaopista

Tämän tutkimuksen tehtävänä oli selvittää, ovatko sosiaaliset järjestykset Martti Lutherin (1483-1546) mukaan Jumalan erityisesti asettamia. Johdannossa luotiin katsaus moderniin Luther-tutkimukseen. Aikaisemmassa tutkimuksessa havaittiin vallitsevan erimielisyyttä siitä, ovatko sosiaaliset järjestykset Jumalan erityisesti asettamia luomisjärjestyksiä (Schöpfungsordnungen), vai ovatko ne Jumalasta vain välillisesti riippuvaisia, järjen vapaasti muutettavissa olevia sosiaalisen elämän muotoja. Lutherin mukaan ihmisen elämälle on luonteenomaista osallisuus kolmesta sosiaalisesta järjestyksestä. Liittyen keskiaikaiseen käsitykseen Luther puhuu kirkon (ecclesia), perheen (oeconomia) ja yhteiskunnan (politia) järjestyksistä, joista kaksi edellistä olivat olemassa jo alkutilassa. Yhteiskunta sai alkunsa vasta syntiinlankeemuksen jälkeen. Tässä tutkimuksessa ihmisen sosiaalisen elämän tarkastelu rajattiin koskemaan alkutilan sosiaalisia järjestyksiä. Tutkimus suoritettiin kaksiosaisesti. Ensimmäisessä pääjaksossa selvitettiin, minkälainen ontologinen luonne ihmisen sosiaalisella elämällä on. Luther ymmärtää teologian tehtävän kaksiosaisesti Jumalan ja ihmisen tuntemiseksi (cognitio Dei et hominis). Teologia ja erityisesti Raamattu sisältävät Lutherin mukaan luonnon kaikkia aspekteja koskevaa tietoa. Tästä syystä immanenttiin todellisuuteen kuuluvien sosiaalisten järjestysten rajaaminen teologisen tiedon ulkopuolelle ei ole perusteltua. Karl Hollin Luther-tulkinnan tavoin tutkimuksessa havaittiin, että ihmisen ja Jumalan suhde perustuu tahdonyhteyteen, josta seuraa ihmisessä Jumalan sana vaikutuksesta syntyvä usko. Tahdonyhteyden johdosta ihminen tulee osalliseksi Jumalan persoonallisista ominaisuuksista siten, että Jumalan mielenliikkeet heijastuvat ihmisen psyykkisiin ominaisuuksiin. Erityisesti tahdon ja järjen alueilla tapahtuvaa partisipaatiota jumalalliseen luontoon voidaan luonnehtia persoonallis-onttiseksi. Persoonallis-onttinen partisipaatio vaikuttaa sekä ihmisen yksilölliseen elämäntodellisuuteen Jumalan kuvana (imago Dei) että yhteisölliseen elämäntodellisuuteen sosiaalisissa järjestyksissä. Toisessa pääjaksossa havaittiin, että kirkko ja perhe ovat Jumalan erityisillä asetussanoilla perustamia sosiaalisia järjestyksiä, joita voidaan kutsua luomisjärjestyksiksi. Sosiaalisina järjestyksinä kirkko ja perhe eivät kuulu Jumalan inhimilliselle järjelle antaman valtuutuksen (mandatum Dei) piiriin. Saman luonteiseen Jumalan käskyyn (mandatum) perustuva kirkko on järjestys (institutio), joka antaa Jumalan sanan voimalla ihmisen "juopuneelle" mielelle muodon (forma). Kirkko ylläpitää ihmisen persoonallis-onttista partisipaatiota sakramentin ja saarnan välityksellä. Jumalanpalveluksesta Jumala puhuttelee ihmistä inhimillisellä kielellä, antaen muodon sekä ihmisen uskolle että immanentit elämänalueet käsittävälle ulkoiselle kuuliaisuudelle. Sosiaaliset normit syntyvät, kun Jumala puhuttelee ihmistä kirkossa. Perheen havaittiin olevan Jumalan asettama sosiaalinen järjestys (institutio), jonka piiriin kuuluvat miehen ja naisen välisen avioliiton lisäksi taloudellinen toiminta ja kasvatus. Avioliitto on luonteeltaan pyhä ja Jumalan käskyyn perustuva. Perhe mahdollistaa ihmisen lisääntymisen, antaen ulkoiselle työlle ja lasten kasvatukselle sosiaalisen struktuurin. Perheen piiriin kuuluva elämä on riippuvainen kirkosta, sillä jumalanpalveluksen ja saarnaviran välittämä Jumalan sana antaa perheessä tapahtuvalle ulkoiselle kuuliaisuudelle muodon. Perhe on riippuvainen persoonallis-onttisesta partisipaatiosta. Tämä ilmenee myös siten, että langenneessa tilassa perhettä koskeva tieto on riippuvainen teologiasta.

Compressive behavior and fracture features of rubber bearing glass-epoxy composites exposed to aqueous media

Epoxy systems containing HTBN rubber material and reinforced with E-glass fibres, exposed to a fixed time duration in three separate media were subjected to compressive mode of deformation. The yield stress and fractographic features noted on the compression failed samples are reported in this work. The experiment reveals that the seawater exposed sample exhibits a drop in strength compared to dry (unexposed) sample. This kind of drop is maintained if the media is changed from seawater to distilled water. When HCl is included in seawater. the experiment shows a small rise in strength value. These changes have been attributed to various factors like medium ingress into samples assisting interface failure, the larger-sized Cl- influencing the extent of diffusion of medium into system and finally their participation in the deformation phenomena. The fractographic features reveal interface separations that show either scattered debris or a cleaner surface or display a whitish-coated matrix region depending on whether the tests are done on unexposed samples or on ones following the immersion in the media.

Multi-agent Search using Voronoi partitions

This paper addresses the problem of multiagent search in an unknown environment. The agents are autonomous in nature and are equipped with necessary sensors to carry out the search operation. The uncertainty, or lack of information about the search area is known a priori as a probability density function. The agents are deployed in an optimal way so as to maximize the one step uncertainty reduction. The agents continue to deploy themselves and reduce uncertainty till the uncertainty density is reduced over the search space below a minimum acceptable level. It has been shown, using LaSalle’s invariance principle, that a distributed control law which moves each of the agents towards the centroid of its Voronoi partition, modified by the sensor range leads to single step optimal deployment. This principle is now used to devise search trajectories for the agents. The simulations were carried out in 2D space with saturation on speeds of the agents. The results show that the control strategy per step indeed moves the agents to the respective centroid and the algorithm reduces the uncertainty distribution to the required level within a few steps.

Optimal Hop Distance and Power Control for a Single Cell, Dense, Ad Hoc Wireless Network

We consider a dense, ad hoc wireless network, confined to a small region. The wireless network is operated as a single cell, i.e., only one successful transmission is supported at a time. Data packets are sent between source-destination pairs by multihop relaying. We assume that nodes self-organize into a multihop network such that all hops are of length d meters, where d is a design parameter. There is a contention-based multiaccess scheme, and it is assumed that every node always has data to send, either originated from it or a transit packet (saturation assumption). In this scenario, we seek to maximize a measure of the transport capacity of the network (measured in bit-meters per second) over power controls (in a fading environment) and over the hop distance d, subject to an average power constraint. We first motivate that for a dense collection of nodes confined to a small region, single cell operation is efficient for single user decoding transceivers. Then, operating the dense ad hoc wireless network (described above) as a single cell, we study the hop length and power control that maximizes the transport capacity for a given network power constraint. More specifically, for a fading channel and for a fixed transmission time strategy (akin to the IEEE 802.11 TXOP), we find that there exists an intrinsic aggregate bit rate (Theta(opt) bits per second, depending on the contention mechanism and the channel fading characteristics) carried by the network, when operating at the optimal hop length and power control. The optimal transport capacity is of the form d(opt)((P) over bar (t)) x Theta(opt) with d(opt) scaling as (P) over bar (t) (1/eta), where (P) over bar (t) is the available time average transmit power and eta is the path loss exponent. Under certain conditions on the fading distribution, we then provide a simple characterization of the optimal operating point. Simulation results are provided comparing the performance of the optimal strategy derived here with some simple strategies for operating the network.

Phase Field Simulation of Equiaxed Microstructure Formation during Semi-solid Processing of A380 Al Alloy

A phase field modelling approach is implemented in the present study towards simulation of microstructure evolution during cooling slope semi solid slurry generation process of A380 Aluminium alloy. First, experiments are performed to evaluate the number of seeds required within the simulation domain to simulate near spherical microstructure formation, occurs during cooling slope processing of the melt. Subsequently, microstructure evolution is studied employing a phase field method. Simulations are performed to understand the effect of cooling rate on the slurry microstructure. Encouraging results are obtained from the simulation studies which are validated by experimental observations. The results obtained from mesoscopic phase field simulations are grain size, grain density, degree of sphericity of the evolving primary Al phase and the amount of solid fraction present within the slurry at different time frames. Effect of grain refinement also has been studied with an aim of improving the slurry microstructure further. Insight into the process has been obtained from the numerical findings, which are found to be useful for process control.