Three-Phase Three Level, Soft Switched, Phase Shifted PWM DC–DC Converter for High Power Applications

A new three-phase, three-level dc to dc phase shifted pulsewidth modulation (PWM) converter is proposed for high power and high input voltage applications. Output voltage is controlled by incorporating phase shift PWM. Clocked gate signals of each leg are phase shifted by 2pi/3 from each other. Major features of the converter include: (1) outer two switches of each leg are turned on and off as zero voltage switching, (2) inner two switches of each leg are turned on and off as zero current switching, and (3) this is achieved without involving any extra passive or active components. The secondary side of the converter is of center tapped full-wave current tripler type. This results in an increase of ripple frequency by a factor of six, leading to a significant reduction in size of the output filter. In order to obtain behavioral and performance characteristics of the proposed converter topology, detailed analytical and simulation studies are carried out. Finally the viability of the scheme is confirmed through detailed experimental studies on a laboratory prototype developed for the purpose.     

Effect of comparator offset on the linearity of charge sharing ADCs

The charge-sharing (CS) switching scheme appeared recently as an alternative to the charge-redistribution (CR) ADC for moderate-resolution low-power applications. One advantage of the CS is that it requires less demanding reference and input buffers. On the other hand, the CS ADC is very sensitive to the comparator offset, because the latter is translated into non-linearity on the ADC transfer curve. This paper examines the mechanism that causes this non-linearity and proposes a closed-form expression for the maximum effective resolution that a CS ADC may achieve in the presence of comparator offset. Finally, the model is verified with behavioral simulations.     

Multidimensional, mapping-based complex wavelet transforms.

Although the discrete wavelet transform (DWT) is a powerful tool for signal and image processing, it has three serious disadvantages: shift sensitivity, poor directionality, and lack of phase information. To overcome these disadvantages, we introduce multidimensional, mapping-based, complex wavelet transforms that consist of a mapping onto a complex function space followed by a DWT of the complex mapping. Unlike other popular transforms that also mitigate DWT shortcomings, the decoupled implementation of our transforms has two important advantages. First, the controllable redundancy of the mapping stage offers a balance between degree of shift sensitivity and transform redundancy. This allows us to create a directional, nonredundant, complex wavelet transform with potential benefits for image coding systems. To the best of our knowledge, no other complex wavelet transform is simultaneously directional and nonredundant. The second advantage of our approach is the flexibility to use any DWT in the transform implementation. As an example, we exploit this flexibility to create the complex double-density DWT: a shift-insensitive, directional, complex wavelet transform with a low redundancy of (3M - 1)/(2M - 1) in M dimensions. No other transform achieves all these properties at a lower redundancy, to the best of our knowledge. By exploiting the advantages of our multidimensional, mapping-based complex wavelet transforms in seismic signal-processing applications, we have demonstrated state-of-the-art results.     

Approaches to deductive object-oriented databases

The paper is concerned with the problem of combining deductive and object-oriented features to produce a deductive object-oriented database system which is comparable to those currently available under the relational view of data modelling not only in its functionality but also in the techniques employed in its construction and use. Under this assumption, the kinds of issues that have to be tackled for a similar research strategy to produce comparable results are highlighted. The authors motivate their terms of comparison, characterize three broad approaches to deductive object-oriented databases and introduce the notion of language convergence to help in the characterization of some shortcomings that have been perceived in them. Three proposals that have come to light in the past three years are looked into in some detail, in so far as they exemplify some of the positions in the space of choices defined. The main contribution of the paper is towards a characterization of the language convergence property of deductive database languages which has a key role in addressing critiques of the deductive and object-oriented database research enterprise. A basic familiarity with notions from deductive databases and from object-oriented databases is assumed.     

Safeguarding ad hoc networks with a self-organized membership control system

One of the key challenges for ad hoc networks is providing distributed membership control. This paper introduces a self-organized mechanism to control user access to ad hoc networks without requiring any infrastructure or a central administration entity. Our mechanism authenticates and monitors nodes with a structure that we call controller set, which is robust to the dynamic network membership. We develop analytical models for evaluating the proposal and validate them through simulations. The analysis shows that the proposed scheme is robust even to collusion attacks and provides availability up to 90% better than proposals based on threshold cryptography. The performance improvement arises mostly from the controller sets capability to recover after network partitions and from the identification and exclusion of malicious nodes.     

Natural killing and antibody-dependent cytotoxicity by lymphocyte subpopulations in young and aging humans

Natural killer (NK) and antibody-dependent cellular cytotoxicity (ADCC) were examined in the peripheral blood lymphocytes and their major subpopulations from young and aging subjects. Monocyte-depleted unseparated lymphocyte-mediated NK activity (against cells of K-562) and ADCC (against IgG-coated chicken erythrocytes) were comparable between young and aging subjects. Similarly no significant difference was observed in T cell-mediated NK and ADCC and non-T cell-mediated ADCC between young and aging subjects. Non-T cell-mediated NK activity, however, was significantly (P less than 0.025) greater in aging humans compared to that of young subjects. When the data were analyzed according to gender, T cell-mediated ADCC in aging males was significantly (P less than 0.05) greater than that found in young males. No significant difference was observed between T-cell ADCC among young and aging females. T cell-mediated NK was comparable among young and aging males and young and aging females. Non-T cell-mediated NK as well as ADCC activity was significantly (P[ less than 0.025 or less than 0.05) greater in aging males compared to that in young males. Both non-T-cell NK and ADCC were comparable among young and aging females. This study demonstrates an increase in NK and ADCC activity in aging subjects that is primarily shared by males and not by females. No correlation was observed between the proportion of T gamma cells and T-cell NK or ADCC activity.     

Neonatal lensectomy and intraocular lens implantation: effects in rhesus monkeys

PURPOSE: To compare the effects of a lensectomy with and without intraocular lens (IOL) implantation on a neonatal rhesus monkey eye. METHODS: A lensectomy and anterior vitrectomy was performed on 75 monkeys during the first 16 days of life; 21 of these monkeys also had an IOL implanted into the posterior chamber. The eyes were examined at regular intervals using biomicroscopy, applanation tonometry, and ophthalmoscopy. RESULTS: The pseudophakic monkeys were studied until they were 92.5 +/- 5.8 weeks of age and the aphakic monkeys until they were 80.4 +/- 5.7 weeks of age. Pupillary membranes (100% versus 55.5%; P < 0.01) and lens regeneration into the pupillary aperture (28.6% versus 5.6%; P = 0.02) occurred more often in the pseudophakic than the aphakic eyes. As a result, the pseudophakic eyes required more reoperations than the aphakic eyes to keep the visual axis clear (P < 0.01). There was not a significant difference in the incidence of ocular hypertension between the pseudophakic and aphakic eyes (9.5% versus 12.7%; P = 0.34). Pupillary capture of the IOL optic occurred in 52% and haptic breakage in 33% of the pseudophakic eyes. All of the eyes with broken haptics had a prominent Soemmerring's ring varying in maximum thickness from 0.6 to 2 mm. Nine of the haptics from the seven eyes with broken IOLs had eroded into the iris, two into the ciliary body, and one into the anterior chamber. CONCLUSIONS: Implanting an IOL into a neonatal monkey eye after a lensectomy and anterior vitrectomy increases the likelihood of a reoperation being necessary. Haptics frequently erode into the iris and ciliary body and may break because of stress placed on the optic-haptic junction by forward movement of the IOL.     

Evaluation of Vulnerability to Extreme Climatic Events in the Brazilian Amazonia: Methodological Proposal to the Rio Acre Basin

The southern border of the Brazilian Amazon is one of the most sensitive areas to deforestation in Brazil. In addition to problems related to changes in land use, new issues are emerging, including climate change and its negative effects on the regional hydrological cycle. In recent years considerable research has been undertaken focusing on climate change and its effects on Amazon Biodiversity, carbon cycle, fire incidence and even on regional water resources, but there is very little research linking territorial planning and public policies to prospective planning scenarios and climate change and the necessary adaptation or mitigation actions to address climate vulnerability. This study examines issues pertaining to social, economic and environmental vulnerability, including new challenges posed by climate change. Examples of environmental problems related to climate dynamics of the Rio Acre Basin are floods and dry periods such as the major drought of 2005 and the 2009 flood. The use of methodology for integrated assessment of vulnerability to river basins in Amazon Region constitutes a valuable instrument for territorial planning, since it takes into account both the challenges of poverty and the environmental fragility, as well the possible aggravations of extreme climatic events in the future.     

Phase behavior of binary mixtures of styrene/acrylonitrile copolymers and aliphatic polyesters

The phase behavior of binary mixtures of copolymers containing varying amounts of styrene and acrylonitrile (SAN) with a large range of aliphatic polyesters was examined. Miscibility was observed over a limited range of AN contents of the SANs, for each polyester, while similarly for each SAN, miscibility was only observed over a limited range of polyester molecular structures. Thermodynamic interaction parameters for the miscible blends were obtained by analysis of the depression of the polyester melting point. A binary interaction model was used to correlate the data and six group interaction parameters were deduced by subdividing the polyester and SAN copolymer repeating units in three different ways. It is concluded that there is a strong repulsion between the segmental units within the polyesters and within the SAN copolymers, which is an important factor in the observed phase behavior.     

Blends containing polymers of epichlorohydrin and ethylene oxide. Part I: Polymethacrylates

The phase behavior of blends of various polymethacrylates with poly(epichlorohydrin) (PECH); poly(ethylene oxide) (PEO); and a copolymer of epichlorohydrin and ethylene oxide [P(ECH/EO)], was examined using differential scanning calorimetery (DSC), dynamic mechanical properties, and optical indications of phase separation on heating, namely lower critical solution temperature (LCST) behavior. Poly(methyl methacrylate) (PMMA), was shown to be miscible with PECH, PEO, and P(ECH/EO), while only PECH was found miscible with the higher polymethacrylates: poly(ethyl methacrylate), poly(n-propyl methacrylate), poly(n-butyl methacrylate), and poly(cyclohexyl methacrylate). However, even PECH was found to be only partially miscible with poly(isopropyl methacrylate). In many cases, unusually broad glass transitions were observed by DSC for blends which are believed to be the result of equilibrium composition fluctuations. All mixtures showed LCST behavior and based on this and excess volume measurements, to the extent possible, qualitative conclusions were made concerning the relative strength of the interactions among the various blend pairs. For PECH, it appears that the interaction with polymethacrylates decreases with increasing size of the alkyl pendant group, with poly(cyclohexyl methacrylate) being a possible exception. The interaction with PMMA is apparently about the same for PECH and PEO, but somewhat less for P(ECH/EO). The latter is consistent with an intrachain attraction of ECH and EO believed to exist. The reasons for similar interactions of PEO and PECH with PMMA are not understood; however, it is clear that the chlorine moiety of PECH is needed for miscibility with higher polymethacrylates.