Phase diagram of electrostatically doped SrTiO3.

Electric double layer transistor configurations have been employed to electrostatically dope single crystals of insulating SrTiO(3). Here we report on the results of such doping over broad ranges of temperature and carrier concentration employing an ionic liquid as the gate dielectric. The surprising results are, with increasing carrier concentration, an apparent carrier-density dependent conductor-insulator transition, a regime of the anomalous Hall effect, suggesting magnetic ordering, and finally the appearance of superconductivity. The possible appearance of magnetic order near the boundary between the insulating and superconducting regimes is reminiscent of effects associated with quantum critical behavior in some complex compounds.

Magnetic-field-induced superconducting state in Zn nanowires driven in the normal state by an electric current.

Four-terminal resistance measurements have been carried out on Zn nanowires formed using electron-beam lithography. When driven resistive by current, these wires reenter the superconducting state upon application of small magnetic fields. The data are qualitatively different from those of previous experiments on superconducting nanowires, which revealed either negative magnetoresistance near T_{c} or high-magnetic-field-enhanced critical currents.

Salmonella produces an O-antigen capsule regulated by AgfD and important for environmental persistence.

In this study, we show that Salmonella produces an O-antigen capsule coregulated with the fimbria- and cellulose-associated extracellular matrix. Structural analysis of purified Salmonella extracellular polysaccharides yielded predominantly a repeating oligosaccharide unit similar to that of Salmonella enterica serovar Enteritidis lipopolysaccharide O antigen with some modifications. Putative carbohydrate transport and regulatory operons important for capsule assembly and translocation, designated yihU-yshA and yihVW, were identified by screening a random transposon library with immune serum generated to the capsule. The absence of capsule was confirmed by generating various isogenic Deltayih mutants, where yihQ and yihO were shown to be important in capsule assembly and translocation. Luciferase-based expression studies showed that AgfD regulates the yih operons in coordination with extracellular matrix genes coding for thin aggregative fimbriae and cellulose. Although the capsule did not appear to be important for multicellular behavior, we demonstrate that it was important for survival during desiccation stress. Since the yih genes are conserved in salmonellae and the O-antigen capsule was important for environmental persistence, the formation of this surface structure may represent a conserved survival strategy.

The phylogeny of the Schistosomatidae based on three genes with emphasis on the interrelationships of Schistosoma Weinland, 1858.

Schistosomes are digenean flukes, parasitic of birds, mammals and crocodiles. The family Schistosomatidae contains species of considerable medical and veterinary importance, which cause the disease schistosomiasis. Previous studies, both morphological and molecular, which have provided a good deal of information on the phylogenetics of this group, have been limited in the number of species investigated or the type or extent of molecular data used. This paper presents the most comprehensive phylogeny to date, based on the sequences of 3 genes, complete ribosomal small subunit rRNA and large ribosomal subunit rRNA, and mitochondrial cytochrome oxidase 1, sequenced from 30 taxa including at least 1 representative from 10 of the 13 known genera of the Schistosomatidae and 17 of the 20 recognized Schistosoma species. The phylogeny is examined using morphological characters, intermediate and definitive host associations and biogeography. Theories as to the origins and spread of Schistosoma are also explored. The principal findings are that Ornithobilharzia and Austrobilharzia form a sister group to the Schistosoma; mammalian schistosomes appear paraphyletic and 2 Trichobilharzia species, T. ocellata and T. szidati, seem to be synonymous. The position of Orientobilharzia within the Schistosoma is confirmed, as is an Asian origin for the Schistosoma, followed by subsequent dispersal through India and Africa.

Phylogenetic and biogeographical relationships among some holarctic frog lung flukes (Digenea: Haematoloechidae).

A phylogenetic study of 8 North American and European species of frog lung flukes belonging to Haematoloechus was conducted using approximately 850 to 1,000 bases of the intemal transcribed spacer region (ITS 1 + 5.8S + ITS 2) and 1,250 bases of the large subunit (LSU) of the nuclear ribosomal DNA. Adequate phylogenetic resolution could not be obtained from 5.8S or ITS 2 data. Analysis of ITS 1 data produced 2 equally parsimonious trees that differed only in the position of Haematoloechus breviplexus relative to H. medioplexus and H. varioplexus. Single, identical trees were produced by analysis of both LSU sequence data and a data set comprised of all ITS and LSU data. All trees demonstrated 3 distinct evolutionary lineages within the Holarctic Haematoloechus examined. The results confirmed the taxonomic validity of H. abbreviatus and demonstrated that the presence or absence of extracecal uterine loops is not a character meaningful to the recognition of evolutionary lineages or differentiation of genera. Examination of ITS sequence data revealed almost no intraspecific variation within 5 species of Haematoloechus and demonstrated an approximately 150-base indel common to the North American H. longiplexus and the European H. asper. Two of 3 clades revealed by the phylogenetic analyses are comprised of both European and North American species, indicating that lineages of Haematoloechus arose before the breakup of Laurasia and radiated after Eurasia and North America split. Within each of 3 evolutionary lineages, members share similar patterns of arthropod host specificity distinct from patterns found in the other lineages. This suggests that second intermediate host specificity may be a trait that has been conserved through evolutionary time.

Schistosoma mansoni and Biomphalaria: past history and future trends.

Schistosoma mansoni is one of the most abundant infectious agents of humankind. Its widespread distribution is permitted by the broad geographic range of susceptible species of the freshwater snail genus Biomphalaria that serve as obligatory hosts for its larval stages. Molecular phylogenetic studies suggest that Schistosoma originated in Asia, and that a pulmonate-transmitted progenitor colonized Africa and gave rise to both terminal-spined and lateral-spined egg species groups, the latter containing S. mansoni. Schistosoma mansoni likely appeared only after the trans-Atlantic dispersal of Biomphalaria from the Neotropics to Africa, an event that, based on the present African fossil record, occurred only 2-5 million years ago. This parasite became abundant in tropical Africa and then entered the New World with the slave trade. It prospered in the Neotropics because a remarkably susceptible and productive host, B. glabrata, was widely distributed there. Indeed, a snail similar to B. glabrata may have given rise to the African species of Biomphalaria. Schistosoma mansoni has since spread into other Neotropical Biomphalaria species and mammalian hosts. The distribution of S. mansoni is in a state of flux. In Egypt, S. mansoni has nearly completely replaced S. haematobium in the Nile Delta, and has spread to other regions of the country. A susceptible host snail, B. straminea, has been introduced into Asia and there is evidence of S. mansoni transmission in Nepal. Dam and barrage construction has lead to an epidemic of S. mansoni in Senegal, and the parasite continues its spread in Brazil. Because of competition with introduced aquatic species and environmental changes, B. glabrata and consequently S. mansoni have become less abundant on the Caribbean islands. Control of S. mansoni using praziquantel and oxamniquine has reduced global prevalence but control is difficult to sustain, and S. mansoni can develop tolerance/resistance to praziquantel, raising concerns about its future efficacy. Because of legitimate environmental concerns, snail control is unlikely to be an option in future control efforts. Global warming will impact the distribution of Biomphalaria and S. mansoni, but the magnitude and nature of the effects are poorly understood.

Evolutionary relationships among the Schistosomatidae (Platyhelminthes:Digenea) and an Asian origin for Schistosoma.

Schistosome blood flukes parasitize birds, mammals, and crocodilians and are responsible for causing one of the great neglected diseases of humanity, schistosomiasis. A phylogenetic study of 10 schistosome genera using approximately 1,100 bases of the large subunit of the nuclear ribosomal gene complex revealed 2 major clades. One clade is entirely mammalian and includes the genera Schistosoma and Orientobilharzia. A close examination of relationships in this group suggests that the medically important Schistosoma arose in Asia and not in Africa as generally presumed and is paraphyletic. The second clade is primarily avian, consisting of 6 genera of exclusively avian parasites and 2 genera of North American mammal flukes. These results indicate a secondary host capture of mammals on the North American continent. This study provides little evidence concerning the ancestral molluscan or vertebrate schistosome host but does demonstrate that host switching has been an important feature of schistosome evolution. Evidence also indicates that the reduced sexual dimorphism characteristic of some avian schistosomes is derived evolutionarily.

Evolutionary constraints on population structure: the parasites of Fundulus zebrinus (Pisces:Cyprinodontidae) in the South Platte River of Nebraska.

Population and community descriptor values (parasites per host, prevalence per parasite species, variance/mean ratios, species density, and diversity indices) for the 7-species parasite community of 61 relatively homogeneous samples of Fundulus zebrinus (Pisces: Cyprinodontidae) in the South Platte River of Nebraska, U.S.A., taken over a 14-yr period, are reported. South Platte River streamflow fluctuates over 2 orders of magnitude on several time scales-monthly, annually, and over multiple year wet-dry cycles. Relatively homogeneous sampling of a single host species with several parasite species provided a system that allowed assessment of the contribution of evolved parasite life cycles to population structure in an everchanging environment. No significant negative species-to-species associations were observed. Species abundance, order of abundance, and diversity were affected most strongly by streamflow, with high water reducing prevalence and abundance of larval trematode parasites. Each parasite species had its characteristic long- and short-term patterns of variation in population descriptor values, with mostly long-term stability superimposed on sometimes extreme short-term fluctuations of descriptor values. The differences in these characteristic patterns were considered products primarily of the evolved life cycle traits and transmission mechanisms operating in the common fluctuating environment. The parasite community as a whole showed resilience, returning to preperturbation diversity following extended periods of high water.

Behavioral basis of second intermediate host specificity among four species of Haematoloechus (Digenea: Haematoloechidae).

Cercarial behavior patterns were examined in 4 species of frog lung flukes (Haematoloechus spp.). Cercariae of Haematoloechus complexus, Haematoloechus medioplexus, Haematoloechus longiplexus, and Haematoloechus varioplexus were exposed to 3 species of experimental arthropods and an inanimate control. The number of cercariae attached to an experimental host at 5 min postexposure was recorded. Haematoloechus longiplexus and H. complexus cercariae attached to experimental hosts at higher rates than cercariae of H. medioplexus and H. varioplexus. Cercariae of H. longiplexus attached to experimental hosts in approximately the same numbers as H. complexus, but H. longiplexus penetrated only damselfly naiads, and only at the base of the zygopteran caudal gills. Cercariae of H. complexus, a second intermediate host generalist, were able to penetrate and enter several arthropod species at the intersegmental membranes. Haematoloechus medioplexus and H. varioplexus are restricted to development in dragonfly naiads and cercariae rarely attached to and never penetrated experimental hosts. These behavioral patterns dictate the range of hosts suitable for metacercarial development of H. complexus, H. longiplexus, H. medioplexus, and H. varioplexus. The evolution of disparate patterns of behavior among the cercariae of these 4 congeners has directly affected subsequent patterns of transmission to the definitive host.

Active control of vibration using a neural network.

Feedforward control of sound and vibration using a neural network-based control system is considered, with the aim being to derive an architecture/algorithm combination which is capable of supplanting the commonly used finite impulse response filter/filtered-x least mean square (LMS) linear arrangement for certain nonlinear problems. An adaptive algorithm is derived which enables stable adaptation of the neural controller for this purpose, while providing the capacity to maintain causality within the control scheme. The algorithm is shown to be simply a generalization of the linear filtered-x LMS algorithm. Experiments are undertaken which demonstrate the utility of the proposed arrangement, showing that it performs as well as a linear control system for a linear control problem and better for a nonlinear control problem. The experiments also lead to the conclusion that more work is required to improve the predictability and consistency of the performance before the neural network controller becomes a practical alternative to the current linear feedforward systems.

Second intermediate host-specificity of Haematoloechus complexus and Haematoloechus medioplexus (Digenea: Haematoloechidae).

Second intermediate host-specificity was examined for 2 species of the frog lung fluke genus Haematolechus. Nine species of freshwater arthropods were exposed to cercariae of H. complexus and H. medioplexus. Metacercariae of H. complexus developed in all arthropod species used. Metacercariae of H. medioplexus developed only in anisopteran odonate naiads. This difference in host utilization may have epizootiological implications. The potential development of H. complexus in a greater number of arthropods than H. medioplexus may increase the chances of ingestion of H. complexus by an anuran host. The range of arthropods parasitized by H. complexus indicates that host-specificity of the metacercarial stage of this fluke is not restricted by the phylogeny of aquatic arthropods.

Trematode community structure in the pulmonate snail Physa gyrina.

Trematode community structure was examined in the pulmonate snail Physa gyrina over a 12-mo period. A total of 1,181 snails was collected from Charlie's Pond, North Carolina, and was found to be parasitized by 6 trematode species. Infracommunities were relatively species rich when compared to previous studies, with 18.4% of infected snails having multi-species infections. Halipegus eccentricus was found in 88.4% of multiple infections, usually with 1 of 2 other autogenic, egg-transmitted species (Haematoloechus complexus and Glypthelmins quieta). Neither negative interspecific interactions nor a dominance hierarchy were apparent among the trematodes. These factors, along with high snail vagility and the temporal heterogeneity of infective stages in the environment, are suggested to have contributed to the high number of multiple infections. Halipegus eccentricus was also the most prevalent parasite throughout the study, occurring in nearly 50% of all snails during May, June, and July. Apparent parasite-induced host mortality caused by this trematode species contributed to increasing species diversity in larger snails. The component community was also affected by the continuous recruitment of new snails into the host population and by changes in the number of infective stages present over time.

Active noise control in ducts: some physical insights.

The mechanisms of active noise control in a duct are examined. Acoustical measurements are used to determine directly the acoustic power flow associated with both primary and secondary sources as a function of secondary to primary source strength ratio and volume velocity relative phase angles. A complete analytical model is also developed which allows calculation of individual source power flows and total downstream power flow as a function of source strengths and relative phase angles for finite size sources. It is evaluated for monopole and dual secondary source arrangements, but can be extended easily to any number of secondary sources. The model considers a finite size primary source in the plane of the duct cross section and evaluates the effect that the secondary sources have on the primary source power output. Measurements of individual source output powers and total downstream acoustic powers agree well with theoretical predictions. It is demonstrated that, for the monopole system, sound attenuation is achieved primarily by suppression of the primary source acoustic power output, with a little remaining power being absorbed by the secondary source. For the dual secondary source system, it is shown that the power is primarily absorbed by the secondary sources, but that, at phase and amplitude values slightly different to optimum, noise reduction is achieved by a combination of energy absorption and primary source power suppression. The analysis also demonstrates the dependence of the achievable noise reduction on secondary source size and location with respect to the primary source.