Molecular chemisorption of N2 on IrO2(110)

We investigated adsorption of N₂ on stoichiometric and O-rich IrO₂(110) surfaces using temperature programmed desorption (TPD) experiments and density functional theory (DFT) calculations. TPD shows that N₂ desorbs predominantly from the stoichiometric-IrO₂(110) surface in a well-defined peak at 270 K for N₂ coverages below about 0.5 ML and that a shoulder centered near 235 K develops in the N₂ TPD traces as the coverage approaches saturation, indicating that adsorbed N₂ molecules destabilize at high N₂ coverages. Experiments of N₂ adsorption onto O-rich IrO₂(110) surfaces provide evidence that N₂ adsorbs exclusively on the coordinatively unsaturated Ir atoms (Ir_cus) of the surface and that pre-adsorbed O-atoms ("on-top" oxygen) stabilize adsorbed N₂ molecules, causing the main N₂ TPD peak to shift toward higher temperature with increasing oxygen coverages. Consistent with prior results, our DFT calculations predict that an N₂ molecule preferentially adsorbs into an upright configuration on an Ir_cus atom of the IrO₂(110) surface and achieves a binding energy of about 100 kJ/mol. The computed binding energy agrees well with our experimental estimate of ∼90 kJ/mol for low N₂ coverages on stoichiometric IrO₂(110). The DFT calculations also quantitatively reproduce the observed stabilization of N₂ by co-adsorption on-top O-atoms and predict the destabilization of N₂ on IrO₂(110) as the N₂ adlayer becomes crowded at high coverages.

Measurements and models of the correlation of redundant spatial coherence measurements for the incoherently scattered field

Sonar systems that exploit correlation for navigation, such as correlation velocity logs and micronavigation for synthetic aperture sonar, often make redundant estimates of the spatial coherence of the scattered field at several spatial lags. Two models for the correlation of these redundant measurements are described. First, an analytical model is derived using the assumption of stationary Gaussian statistics. Next, a numerical model is described that accounts for non-stationary processes present in measurements of seafloor scattering. These models are compared to normal-incidence scattering data collected at Seneca Lake, NY. Both models show good agreement with the measurements when the spatial separation between redundant hydrophone pairs is less than the coherence length. At greater spatial separation, the analytical model diverges from the measurements. This disagreement is explained by a lack of stationarity in the measured data which is captured by the numerical model. Finally, spatial variations in the volume scattering strength of the sediment are identified as a source of the non-stationarity in the measurements.

Retirement Migration Decision Making

This study examines the relative influence of a large number of characteristics of places on the migration decision making of a sample of persons in the age group in which persons will be considering retirement migration. An experimental design is used in which persons judge the desirability of migrating to hypothetical locations that vary in climate, terrain, closeness to family, and a number of other attributes. The findings show the relative importance given to 10 attributes of destinations and the distribution of preferred levels of each attribute when subjects rate the attractiveness of destinations described by multiple attributes.

The influence of peri-conception and first trimester dietary restriction of protein in cattle on meat quality traits of entire male progeny

Primiparous Santa Gertrudis heifers were used to evaluate the effects of gestational dietary protein content on meat quality traits of 20month old bull progeny (n=40). At -60d before AI, heifers were randomly allocated to HIGH or LOW protein diet (HPERI and LPERI). From 24dpc, half of each treatment group changed to an alternative post-conception HIGH or LOW protein diet (HPOST and LPOST). LPERI and LPOST diets resulted in higher shear force of the semitendinosus muscle than HPERI (P=0.053) and HPOST (P=0.003), respectively. Heat-soluble collagen in the semitendinosus muscle was lower (P=0.019) for LPERI than HPERI. Collagen and tenderness of the longissimus muscle were not affected by dam nutrition (P>0.05). Color, pH, sarcomere length, cooking loss, compression values, desmin and troponin-T degradation, fiber type, intramuscular fat and polyunsaturated fatty acid content were not affected by dam nutrition during the peri-conception and first trimester gestational period (P>0.05).

Should recent experiences with CVOTs for oral hypoglycemic drugs allow us to rethink the regulatory paradigm?

In response to a meta-analysis raising significant concerns over the cardiovascular safety of rosiglitazone, the US Food and Drug Administration (FDA) issued a draft guidance directing sponsors of novel diabetes drugs to address cardiovascular risk, including large outcomes trials. Regulatory experience supports that outcomes trials, absent a clear signal of risk, may add reassurance, but also have significant consequences. The FDA should finalize this guidance, taking into account the regulatory experience since 2008.

Performance of tonpilz transducers with segmented piezoelectric stacks using materials with high electromechanical coupling coefficient

Tonpilz acoustic transducers for use underwater often include a stack of piezoelectric material pieces polarized along the length of the stack and having alternating polarity. The pieces are interspersed with electrodes, bonded together, and electrically connected in parallel. The stack is normally much shorter than a quarter wavelength at the fundamental resonance frequency so that the mechanical behavior of the transducer is not affected by the segmentation. When the transducer bandwidth is less than a half octave, as has conventionally been the case, for example, with lead zirconate titanate (PZT) material, stack segmentation has no significant effect on the mechanical behavior of the device in its normal operating band near the fundamental resonance. However, when a high coupling coefficient material such as lead magnesium niobate-lead titanate (PMN-PT) is used to achieve a wider bandwidth with the tonpilz, the performance difference between a segmented stack and a similar piezoelectric section with electrodes only at the two ends can be significant. This paper investigates the effects of stack segmentation on the performance of wideband underwater tonpilz acoustic transducers. Included is a discussion of a particular tonpilz transducer design using single crystal piezoelectric material with high coupling coefficient compared with a similar design using more traditional PZT ceramics.

Plasmid-like DNAs in the commercially important mushroom genus Agaricus

Two unique plasmid-like DNA components were localized in isolated mitochondria of the commercially important mushroom genus Agaricus: pEM (7.35 ± 0.15 kilobases) and pMPJ (3.65 ± 0.15 kilobases). These DNA moieties were linear; pEM possessed regions of terminal inverted repeated sequences. No homology was detected between pEM or pMPJ DNA and the nuclear or mitochondrial genomes. No homology existed between pEM and pMPJ. This suggests independent replication of pEM and pMPJ. Restriction endonuclease digests indicated that pEM consisted of two components (pEM1 and pEM2) with uniquely different restriction sites and copy number.

Electromechanical nonlinearities and losses in piezoelectric sonar transducer materials

Next-generation sonar projectors rely on piezoelectric single crystals such as lead magnesium niobate-lead titanate to induce mechanical strain and generate ever greater acoustic output, but the performance of these materials under high-power operation is not well understood. As the electrical driving force increases, the linear piezoelectric relationships give way to nonlinear, amplitude-dependent properties. Such behavior is impossible to predict solely from small signal, linear measurements. This work has characterized the behavior of single crystals by examining the dynamic relaxation from initial strain levels of 0.1 to 0.2%. Strain-dependent values of the mechanical quality factor and resonance frequency are reported for single crystals, and these properties are compared with conventional high-power piezoceramics.

Characterization of piezoelectric ceramics and 1-3 composites for high power transducers

The high power characteristics of various piezoelectric ceramics and 1-3 composites were investigated. In contrast to "hard" Pb(Zr,Ti)O(3), modified (Bi(0.5)Na(0.5))TiO(3) based ceramics were found to show a relatively linear electromechanical response under high drive conditions due to their high stability of mechanical quality factor. The effects of high drive field and duty cycle on the behavior of 1-3 composites were analyzed by varying active and passive components. Improved high power characteristics of 1-3 composites were achieved by selection of optimized composite components, with enhanced electromechanical efficiency and thermal stability under high drive conditions.

Modified single crystals for high-power underwater projectors

Underwater electroacoustic projectors using single crystals based on the lead magnesium niobate-lead titanate (PMNT) composition were investigated. The large electromechanical coupling coefficient (k(33) > 0.90) and piezoelectric coefficient (d(33) > 1500 pC/N) of PMNT have been demonstrated to improve transducer bandwidth and source level relative to conventional piezoelectric ceramics. The low mechanical quality factor (Q(M) < 200) and low temperature stability (T(RT) < 95°C) of PMNT, however, limit its utility in high-power, high-duty-cycle applications. Use of modified single crystals was shown to result in transducers which exhibit up to 5 dB improvement in source level over PMNT when operated at resonance. Compared with a PZT4 transducer, these modified crystals offer similar source level and power handling capability at resonance, but the available bandwidth is doubled and a 6 dB improvement in maximum source level is achieved when driven off resonance.

Face shear piezoelectric properties of relaxor-PbTiO(3) single crystals

Poling relaxor-PbTiO(3) single crystals along pseudocubic [011] results in a macroscopic symmetry of mm2, enabling a large face shear d(36) in Zt±45° cut crystals. In order to allow the determination of electrical properties by the resonance method, square samples are required. Using Pb(In(0.5)Nb(0.5))O(3)-Pb(Mg(1∕3)Nb(2∕3))O(3)-PbTiO(3) crystals, piezoelectric d(36) coefficients were determined to be in the range of 2000-2500 pC∕N, with electromechanical coupling factor k(36)∼0.80-0.83. Mechanical quality factor Q∼180 and ultralow frequency constant of ∼500 Hz m were obtained. Together with the wide temperature usage range (up to ∼110 °C) and high ac driving field stability (∼5 kV∕cm), such face shear crystals have a promising potential for ultralow-frequency-transducer applications.

Recent Developments on High Curie Temperature PIN-PMN-PT Ferroelectric Crystals

Pb(In(0.5)Nb(0.5))O(3)-Pb(Mg(1/3)Nb(2/3))O(3)-PbTiO(3) (PIN-PMN-PT) ferroelectric crystals attracted extensive attentions in last couple years, due to their higher usage temperatures range (> 30°C) and coercive fields (~5kV/cm), meanwhile maintaining similar electromechanical couplings (k(33)> 90%) and piezoelectric coefficients (d(33)~1500pC/N), when compared to their binary counterpart Pb(Mg(1/3)Nb(2/3))O(3)-PbTiO(3). In this article, we reviewed recent developments on the PIN-PMN-PT single crystals, including the Bridgman crystal growth, dielectric, electromechanical, piezoelectric and ferroelectric behaviors as function of temperature and dc bias. Mechanical quality factor Q was studied as function of orientation and phase. Of particular interest is the dynamic strain, which related to the Q and d(33), was found to be improved when compared to binary system, exhibiting the potential usage of PIN-PMN-PT in high power application. Furthermore, PIN-PMN-PT crystals exhibit improved thickness dependent properties, due to their small domain size, being on the order of 1μm. Finally, the manganese acceptor dopant in the ternary crystals was investigated and discussed briefly in this paper.

Material selection for acoustic radiators that are light and stiff

The headmass is a key element in tonpilz transducer design. As an acoustic radiator, a successful headmass must be built from a material that is both light and stiff. To assess the suitability of ceramics for this application, the authors used the mechanical properties of candidate materials to perform a theoretical comparison based on the flexural behavior of square plates. Although not a comprehensive metric for identifying the best headmass materials, the headmass flexure may be usefully employed as a first-level selection criteria. A software routine based on thin plate and thick plate theory was created to evaluate the flexural behavior in candidate materials.

Polarization Fatigue in Pb(In(0.5)Nb(0.5))O(3)-Pb(Mg(1/3)Nb(2/3))O(3)-PbTiO(3) Single Crystals

Electric fatigue tests have been conducted on pure and manganese modified Pb(In(0.5)Nb(0.5))O(3)-Pb(Mg(1/3)Nb(2/3))O(3)-PbTiO(3) (PIN-PMN-PT) single crystals along different crystallographic directions. Polarization degradation was observed to suddenly occur above 50-100 bipolar cycles in <110> oriented samples, while <001> oriented samples exhibited almost fatigue free characteristics. The fatigue behavior was investigated as a function of orientation, magnitude of the electric field and manganese dopant. It was found that <001> oriented PIN-PMN-PT crystals were fatigue free, due to its small domain size, being on the order of 1µm. The <110> direction exhibited a strong electrical fatigue behavior due to mechanical degradation. Micro/macro cracks were developed in fatigued <110> oriented single crystals. Fatigue and cracks were the results of strong anisotropic piezoelectric stress and non-180° domain switching, which completely locked the non-180° domains. Furthermore, manganese modified PIN-PMN-PT crystals were found to show improved fatigue behavior due to its enhanced coercive field.

Conjugative DNA metabolism in Gram-negative bacteria

Bacterial conjugation in Gram-negative bacteria is triggered by a signal that connects the relaxosome to the coupling protein (T4CP) and transferosome, a type IV secretion system. The relaxosome, a nucleoprotein complex formed at the origin of transfer (oriT), consists of a relaxase, directed to the nic site by auxiliary DNA-binding proteins. The nic site undergoes cleavage and religation during vegetative growth, but this is converted to a cleavage and unwinding reaction when a competent mating pair has formed. Here, we review the biochemistry of relaxosomes and ponder some of the remaining questions about the nature of the signal that begins the process.

Comparison of the properties of tonpilz transducers fabricated with 001 fiber-textured lead magnesium niobate-lead titanate ceramic and single crystals

Tonpilz transducers are fabricated from 001 fiber-textured 0.72Pb(Mg(1/3)Nb(2/3))O(3)-0.28PbTiO(3) (PMN-28PT) ceramics, obtained by the templated grain growth process, and PMN-28PT ceramic and Bridgman grown single crystals of the same composition. In-water characterization of single element transducers shows higher source levels, higher in-water coupling, and more usable bandwidth for the 81 vol % textured PMN-28PT device than for the ceramic PMN-28PT element. The 81 vol % textured PMN-28PT tonpilz element measured under large signals shows linearity in sound pressure levels up to 0.23 MV/m drive field but undergoes a phase transition due to a lowered transition temperature from the SrTiO(3) template particles. Although the textured ceramic performs well in this application, it could be further improved with compositional tailoring to raise the transition temperature and better processing to improve the texture quality. With these improvements textured piezoelectric ceramics will be viable options for medical ultrasound, actuators, and sonar applications because of their ease of processing, compositional homogeneity, and potentially lower cost than single crystal.

Electromechanical characterization of [Formula: see text] crystals as a function of crystallographic orientation and temperature

Relaxor based [Formula: see text] ternary single crystals (PIN-PMN-PT) were reported to have broader temperature usage range [Formula: see text] and comparable piezoelectric properties to [Formula: see text] (PMNT) crystals. In this work, the orientation dependent dielectric, piezoelectric and electromechanical properties for PIN-PMN-PT crystals were investigated along [Formula: see text] and [Formula: see text] directions. The electromechanical couplings [Formula: see text] and [Formula: see text] for [Formula: see text] poled crystals were found to be 0.91 and 0.91, respectively, with piezoelectric coefficients [Formula: see text] and [Formula: see text] on the order of 925 and -1420 pC/N. Of particular significance was the mechanical quality factor [Formula: see text] for [Formula: see text] oriented crystals, which was found to be [Formula: see text], much higher than the [Formula: see text] values of [Formula: see text] oriented relaxor-PT crystals [Formula: see text]. The temperature dependence of the piezoelectric properties exhibited good temperature stability up to their ferroelectric phase transition [Formula: see text], indicating [Formula: see text] and [Formula: see text] oriented PIN-PMN-PT are promising materials for transducer applications, with the latter for high power resonant devices where low loss (high [Formula: see text]) was required.

Crystallographic dependence of loss in domain engineered relaxor-PT single crystals

Domain engineered 001 oriented relaxor-PbTiO(3) ferroelectric crystals exhibit high electromechanical properties and low mechanical Q values, analogous to "soft" piezoelectric ceramics. However, their characteristic low dielectric loss (</=0.5%) and strain-electric field hysteresis are reflective of "hard" piezoelectric materials. In this work, the electromechanical behavior of relaxor-PT crystals was investigated as a function of crystallographic orientations. It was found that the electrical and mechanical losses in crystals depends on the specific engineered domain configuration, with high Q observed for the 110 orientation. The high Q, together with high electromechanical coupling ( approximately 0.9) for 110 oriented relaxor-PT crystals, make them promising candidates for resonant based high power transducer applications.

The R1162 relaxase/primase contains two, type IV transport signals that require the small plasmid protein MobB

The relaxase of the plasmid R1162 is a large protein essential for conjugative transfer and containing two different and physically separate catalytic activities. The N-terminal half cleaves one of the DNA strands at the origin of transfer (oriT) and becomes covalently linked to the 5' terminal phosphate; the C-terminal half is a primase essential for initiation of plasmid vegetative replication. We show here that the two parts of the protein are independently transported by the type IV pathway. Part of the domain containing the catalytic activity, as well as an adjacent region, is required in each case, but the required regions do not physically overlap. Both transport systems contribute to the overall frequency of conjugative transfer. MobB is a small protein, encoded within mobA but in a different reading frame, that stabilizes the relaxase at oriT. MobB is required for efficient type IV transport of both the complete relaxase and its two, separate functional halves. MobB inserts into the membrane and could thus stabilize the association between the relaxase and the type IV transfer apparatus.

Rectangular cymbal arrays for improved ultrasonic transdermal insulin delivery

Circular cymbal ultrasound arrays have been shown to be effective in delivering therapeutic levels of insulin in rats, rabbits, and pigs. To improve delivery efficiency, a rectangular cymbal design was desired in order to achieve a broader spatial intensity field without increasing the size of the device or the spatial-peak temporal-peak intensity (I(SPTP)). With a similar intensity (50 mWcm(2)), the goal was to determine if the 3x1 rectangular cymbal array could perform significantly better than the 3x3 circular array for glucose reduction in hyperglycemic rabbits. Rabbit experiments were performed using three groups: nonsonicated control (n=3), ultrasound exposure using a circular cymbal array (n=3), and ultrasound exposure using a rectangular cymbal array (n=3). Rabbits were anesthetized and a water tight reservoir that held the insulin was fastened on the rabbit's thigh. At the beginning of the experiment and every 15 min for 90 min, the blood glucose level was determined. For comparison between individual rabbits, the absolute level is normalized by subtracting out the baseline in order to arrive at the change in glucose level. For the control group, the normalized glucose level increased (more hyperglycemic) to +80.0+/-28.8 mgdl (mean+/-SEM). Using the circular array, the glucose level decreased to -146.7+/-17.8 mgdl at 90 min. However, using the rectangular cymbal array, the glucose decreased faster and to a level of -200.8+/-5.9 mgdl after 90 min. These results indicated the feasibility of the rectangular cymbal array as an improved device for drug delivery.

Regulatory Considerations for Determining Postmarketing Study Commitments

Postmarketing Study Commitments (PMCs) are, most commonly, agreements made by pharmaceutical companies at the time of an FDA approval to perform a study or studies to elucidate further characteristics of the drug under consideration. The role of PMCs in drug regulation has come under considerable scrutiny in recent years, particularly as discussions of drug safety have intensified. Although these agreed-upon PMCs are described in FDA regulations, such PMCs are not sought by FDA with every approval, and completion of the agreed-upon studies is not a requirement for the drug's sponsor (there are required PMCs under certain regulatory provisions and these are discussed below). Requests by FDA at the time of regulatory approval for studies under PMCs have been a common practice for many years. When made, PMCs are described in the approval letters and are therefore publicly available. Concerns over whether PMCs were being duly performed, reported, and reviewed by FDA were addressed in the FDA Modernization Act of 1997, which required more detailed reporting by manufactures on their progress in meeting the PMCs and required FDA to report certain information publicly.

The structure of the minimal relaxase domain of MobA at 2.1 A resolution

The plasmid R1162 encodes proteins that enable its conjugative mobilization between bacterial cells. It can transfer between many different species and is one of the most promiscuous of the mobilizable plasmids. The plasmid-encoded protein MobA, which has both nicking and priming activities on single-stranded DNA, is essential for mobilization. The nicking, or relaxase, activity has been localized to the 186 residue N-terminal domain, called minMobA. We present here the 2.1 A X-ray structure of minMobA. The fold is similar to that seen for two other relaxases, TraI and TrwC. The similarity in fold, and action, suggests these enzymes are evolutionary homologs, despite the lack of any significant amino acid similarity. MinMobA has a well- defined target DNA called oriT. The active site metal is observed near Tyr25, which is known to form a phosphotyrosine adduct with the substrate. A model of the oriT substrate complexed with minMobA has been made, based on observed substrate binding to TrwC and TraI. The model is consistent with observations of substrate base specificity, and provides a rationalization for elements of the likely enzyme mechanism.

Fabrication and characterization of micromachined high-frequency tonpilz transducers derived by PZT thick films

Miniaturized tonpilz transducers are potentially useful for ultrasonic imaging in the 10 to 100 MHz frequency range due to their higher efficiency and output capabilities. In this work, 4 to 10-microm thick piezoelectric thin films were used as the active element in the construction of miniaturized tonpilz structures. The tonpilz stack consisted of silver/lead zirconate titanate (PZT)/lanthanum nickelate (LaNiO3)/silicon on insulator (SOI) substrates. First, conductive LaNiO3 thin films, approximately 300 nm in thickness, were grown on SOI substrates by a metalorganic decomposition (MOD) method. The room temperature resistivity of the LaNiO3 was 6.5 x 10(-6) omega x m. Randomly oriented PZT (52/48) films up to 7-microm thick were then deposited using a sol-gel process on the LaNiO3-coated SOI substrates. The PZT films with LaNiO3 bottom electrodes showed good dielectric and ferroelectric properties. The relative dielectric permittivity (at 1 kHz) was about 1030. The remanent polarization of PZT films was larger than 26 microC/cm2. The effective transverse piezoelectric e31,f coefficient of PZT thick films was about -6.5 C/m2 when poled at -75 kV/cm for 15 minutes at room temperature. Enhanced piezoelectric properties were obtained on poling the PZT films at higher temperatures. A silver layer about 40-microm thick was prepared by silver powder dispersed in epoxy and deposited onto the PZT film to form the tail mass of the tonpilz structure. The top layers of this wafer were subsequently diced with a saw, and the structure was bonded to a second wafer. The original silicon carrier wafer was polished and etched using a Xenon difluoride (XeF2) etching system. The resulting structures showed good piezoelectric activity. This process flow should enable integration of the piezoelectric elements with drive/receive electronics.

Molecular handcuffing of the relaxosome at the origin of conjugative transfer of the plasmid R1162

The assembly of plasmid-encoded proteins at a unique site (oriT) on the plasmid R1162, to form a complex called the relaxosome, is required for conjugative transfer of the plasmid and for negative regulation of neighboring promoters. Two-dimensional chloroquine gel electrophoresis was used to show that oriTs are physically coupled at the relaxosome. This interaction requires all the relaxosome proteins, which are assembled into a structure resulting in a decrease in the average linking number of the plasmid DNA in the cell. Molecules with higher superhelical densities are preferentially selected for assembly of the relaxosome. Genetic data obtained earlier indicate that the molecular coupling reported here is a 'handcuffing' reaction that contributes to the regulation of adjacent plasmid promoters. However, although these promoters affect the expression of the genes for replication, plasmid copy-control is regulated independently. This is the first time 'handcuffing' has been observed at an oriT, and its possible significance for transfer is discussed.

Relaxed specificity of the R1162 nickase: a model for evolution of a system for conjugative mobilization of plasmids

The primary DNA processing protein for conjugative mobilization of the plasmid R1162 is the transesterase MobA, which acts at a unique site on the plasmid, the origin of transfer (oriT). Both MobA and oriT are members of a large family of related elements that are widely distributed among bacteria. Each oriT consists of a highly conserved core and an adjacent region that is required for binding by its cognate MobA. The sequence of the adjacent region is important in determining the specificity of the interaction between the Mob protein and the oriT DNA. However, the R1162 MobA is active on the oriT of pSC101, another naturally occurring plasmid. We show here that MobA can recognize oriTs having different sequences in the adjacent region and, with varying frequencies, can cleave these oriTs at the correct position within the core. Along with the structure of the oriTs themselves, these characteristics suggest a model for the evolution of this group of transfer systems.

Selection of plasmid molecules for conjugative transfer and replacement strand synthesis in the donor

Plasmid selection and strand replacement synthesis in donor cells during conjugative transfer was examined by a procedure involving electroporation of test plasmid DNA, containing a base pair mismatch, into donor cells prior to mating. Multiple copies of the plasmid were transferred from a donor cell that allowed vegetative replication of the plasmid. Under conditions non-permissive for vegetative replication, there were further rounds of transfer after a lag period. Strand replacement in the donor did not depend solely on the initiation mechanism for vegetative replication, indicating a conjugation-specific mechanism was also available. The lag period between first and second rounds of transfer argues against the transfer of multiple copies into recipients by the spooling of copies generated on a master molecule by rolling-circle replication.

Transducer design for a portable ultrasound enhanced transdermal drug-delivery system

For application in a portable transdermal drug-delivery system, novel transducers have been designed to enhance insulin transmission across skin using ultrasound. Previous research has shown transdermal delivery of insulin across skin using commercial sonicators operating at 20 kHz with intensities ranging from 12.5 to 225 mW/cm2. The goal of this research was to design and construct a small, lightweight transducer or array that could operate with a similar frequency and intensity range as a commercial sonicator used in previous transdermal ultrasound insulin experiments, but without the weight and mass of a sonicator probe. To obtain this intensity range, a cymbal transducer design was chosen because of its light, compact structure and low resonance frequency in water. To increase the spatial ultrasound field for drug delivery across skin, two arrays, each comprising of four cymbal transducers, were constructed. The first array, designated the standard array, used four cymbals transducer elements in parallel. A second array (named the stack array) used four cymbal transducers that used stacked piezoelectric discs to drive the titanium flextensional caps. Under similar driving conditions, the standard array produced intensities comparable to those achieved using a commercial sonicator.

MobA, the DNA strand transferase of plasmid R1162: the minimal domain required for DNA processing at the origin of transfer

MobA is a DNA strand transferase encoded by the plasmid R1162 and required for plasmid DNA processing during conjugal transfer. The smallest active fragment was identified using phage display and partial enzymatic digestion of the purified protein. This fragment, consisting of approximately the first 184 amino acids, is able to bind and cleave its normal DNA substrate, the origin of transfer (oriT). Smaller fragments having one of these activities were not obtained. An active intermediate consisting of MobA linked to DNA was isolated and used to show that a single molecule of MobA is sufficient to carry out all of the DNA processing steps during transfer. These results, along with those obtained earlier, point to a single large, active site in MobA that makes several different contacts along the oriT DNA strand.

Design, fabrication, and evaluation of high frequency, single-element transducers incorporating different materials

The performance of high frequency, single-element transducers depends greatly on the mechanical and electrical properties of the piezoelectric materials used. This study compares the design and performance of transducers incorporating different materials. The materials investigated include 1-3 lead zirconate titanate (PZT) fiber composite, lead titanate (PbTiO3) ceramic, poly(vinylidene fluoride) (PVDF) film, and lithium niobate (LiNbO3) single crystal. All transducers were constructed with a 3-mm aperture size and an f-number between 2 and 3. Backing and matching materials were selected based on design goals and fabrication limitations. A simplified coaxial cable tuning method was employed to match the transducer impedance to 50 ohms for the PZT fiber composite and PbTiO3 ceramic transducers. Transducers were tested for two-way loss and -6 dB bandwidth using the pulse/echo response from a flat quartz target. Two-way loss varied from 21 to 46 dB, and bandwidths measured were in the range from 47 to 118%. In vitro ultrasonic backscatter microscope (UBM) images of an excised human eye were obtained for each device and used to compare imaging performance. Both press-focusing and application of a lens proved to be useful beam focusing methods for high frequency. Under equal gain schemes, the LiNbO3 and PbTiO3 transducers provided better image contrast than the other materials.

Internal Transcribed Spacer Sequence-Based Phylogeny and Polymerase Chain Reaction-Restriction Fragment Length Polymorphism Differentiation of Tilletia walkeri and T. indica

ABSTRACT A polymerase chain reaction-restriction fragment length polymorphism assay to distinguish Tilleita walkeri, a rye grass bunt fungus that occurs in the southeastern United States and Oregon, from T. indica, the Karnal bunt fungus, is described. The internal transcribed spacer (ITS) region of the ribosomal DNA repeat unit was amplified and sequenced for isolates of T. indica, T. walkeri, T. horrida, and a number of other taxa in the genus Tilletia. A unique restriction digest site in the ITS1 region of T. walkeri was identified that distinguishes it from the other taxa in the genus. Phylogenetic analysis of the taxa based on ITS sequence data revealed a close relationship between T. indica and T. walkeri, but more distant relationships between these two species and other morphologically similar taxa.

Hemodialysis followed by continuous hemofiltration for treatment of lithium intoxication in children

Hemodialysis is the usual recommended treatment for severe lithium intoxication; however, rebound of lithium levels may require repeated hemodialysis treatments. We proposed that the addition of continuous hemofiltration after hemodialysis would prevent rebound by providing ongoing clearance of lithium. We report two pediatric patients with lithium intoxication treated by hemodialysis followed by continuous venovenous hemofiltration with dialysis (CVVHD). Both patients were symptomatic at presentation and had initial lithium levels more than three times the usual therapeutic range. Hemodialysis followed by CVVHD resulted in rapid resolution of symptoms, followed by continuous clearance of lithium without requiring repeated hemodialysis sessions. Both patients had return of normal mental status during CVVHD treatment, and neither patient experienced complications of hemodialysis or CVVHD. Total duration of treatment with hemodialysis followed by CVVHD was 34.5 hours for the first patient and 26 hours for the second patient. We conclude that hemodialysis followed by CVVHD is a safe and effective approach to the management of lithium intoxication in children.

Recognition of oriT for DNA processing at termination of a round of conjugal transfer

Conjugal transfer of plasmid DNA is terminated when the transferred strand, linearized at the 38 base-pair origin of transfer (oriT), is recircularized. For the plasmid R1162, it is the protein MobA, covalently linked to the linear strand, that rejoins the ends by a reversible transesterification reaction. We have identified from those oligonucleotides with a partially degenerate oriT base sequence, subpopulations bound by MobA that undergo transesterification, and support efficient termination of conjugal transfer. Two domains of oriT, a ten base-pair inverted repeat and an adjacent TAA, are required for tight binding by the protein, whereas the location of the dinucleotide YG determines the site of strand cleavage. The results indicate that capture of MobA by oriT, and subsequent processing of the DNA for termination, are determined by different sequence motifs within this locus.

Nonpulmonary organ failure and outcome in children treated with high-frequency oscillatory ventilation

PURPOSE

The purpose of this study was to quantitate the contribution of nonpulmonary organ failure to mortality of patients treated with high-frequency oscillatory ventilation (HFOV) and to determine which gas-exchange differences are associated with improvement on HFOV.

MATERIALS AND METHODS

Charts of all patients treated with HFOV in our pediatric intensive care unit from January 1992 until January 1997 were retrospectively reviewed.

RESULTS

Sixty-six patients were treated and 21 patients improved during HFOV (group 1); 45 patients did not improve (group 2). Seventeen patients (26%) had isolated respiratory failure and their mortality was 12%. Percentages of patients with 2, and 3 or more organ failure were 45%, 29%, and their mortality was significantly higher, 67% and 95%, respectively. Patients with primary respiratory failure demonstrated a significantly greater risk of improvement on HFOV (RR ratio of 2.5, 95% CI 1.5 to 4.2). There was a significantly greater proportion of patients with primary cardiac failure who did not improve on HFOV compared with all other patients. Oxygenation index significantly improved over the first 72 hours for both groups, but then significantly worsened over the next 48 hours in group 2 but not in group 1.

CONCLUSION

Patients with nonpulmonary organ failure were significantly less likely to improve on HFOV and had a significantly higher mortality than patients with isolated respiratory failure. Children who do not improve on HFOV appear to reach a plateau in oxygenation indices after 3 days of HFOV.

Methanol poisoning

AIMS

This study examines clinical experience with methanol poisoning during a one-year period.

METHODS

All admissions with the diagnosis of suspected methanol toxicity were analysed and the current guidelines for the management of this problem were reviewed.

RESULTS

Twenty-four subjects were identified. Most had a history of chronic use of methylated spirits. Four died before admission to hospital and the other 20 patients had 26 admissions to hospital and form the basis for this report. Four patients died in the Intensive Care Unit. In total 11 patients were admitted to the Intensive Care Unit. Seven patients received haemodialysis. There was no correlation between the methanol level and the outcome. The strongest predictor of death or a poor outcome was a blood pH < 7.0. Some patients, in spite of potentially lethal methanol levels of up to 160 mmol/L, did not develop signs of toxicity.

CONCLUSIONS

The overall mortality was high and ethanol was given to most of the patients for up to several days. Some patients did not show any toxicity and some of those were not given ethanol. It is recommended that chronic meths drinkers, who are not acidaemic and are generally well, do not require ethanol treatment. Only the complete removal of methanol from methylated spirits will reduce the morbidity of this condition.

Cymbal array: a broad band sound projector

A prototype 3 x 3 planar cymbal transducer array was built and tested. The array has a radiating area of 5.5 cm x 5.5 cm and a thickness of less than 8 mm. The measured transmitting voltage response was above 134 dB re 1 microPa/V @ 1 m and flat over the frequency range of 16 and 100 kHz. Array interaction was analyzed using an equivalent circuit model. The array interaction leads to variations in radiation resistance and velocity of the transducers in the array according to their surroundings in the array. The effect is enhanced overall efficiency and a flat response.

A United States regulator's perspective on the ongoing chlorofluorocarbon transition

The Food and Drug Administration (FDA) put in place a general ban on the use of chlorofluorocarbons for the products it regulates (medical devices, drugs, and foods) in 1978, exempting those products where chlorofluorocarbon use was determined to be essential for the public health. In the intervening years, as the international commitment to a full transition away from all chlorofluorocarbon use took shape under the Montreal Protocol, the FDA has worked with industry to facilitate the development and testing of alternative technologies and products for inhalation drug products. As these alternative products begin to move from testing through the approval process and into marketing, the FDA is working collaboratively with the Environmental Protection Agency, other governmental agencies, and nongovernmental stakeholders to develop a transition policy for the United States. The transition policy for metered dose inhalers must be one that achieves the dual aims of first protecting the patients who rely on these vital medical products, while also achieving the public health need of protecting the ozone layer. As a part of developing such a transition strategy, the FDA published an advance notice of proposed rulemaking (ANPRM) in March 1997. The ANPRM proposed mechanisms by which the FDA could determine when chlorofluorocarbon use in a drug product could no longer be considered essential. The ANPRM resulted in a large amount of valuable public debate and input. The FDA is now working to incorporate the knowledge gained from these public comments as it continues the rule-making process.

Stabilization of the relaxosome and stimulation of conjugal transfer are genetically distinct functions of the R1162 protein MobB

MobB is a small protein encoded by the broad-host-range plasmid R1162 and required for efficient mobilization of its DNA during conjugation. The protein was shown previously to stabilize the relaxosome, the complex of plasmid DNA and mobilization proteins at the origin of transfer (oriT). We have generated in-frame mobB deletions that specifically inactivate the stabilizing effect of MobB while still allowing a high rate of transfer. Thus, MobB has two genetically distinct functions in transfer. The effect of another deletion, extending into mobA, indicates that both functions require a specific region of MobA protein that is distinct from the nicking-ligating domain. The mobB mutations that specifically affected stability also resulted in poor growth of cells, due to increased transcription from the promoters adjacent to oriT. The effects of the mutations could be suppressed not only by full-length MobB provided in trans, as expected, but also by additional copies of oriT, cloned in pBR322. In addition, in the presence of MobA both the full-length and truncated forms of MobB stimulated recombination between oriT-containing plasmids. We propose a model in which MobB regulates expression of plasmid genes by altering the stability of the relaxosome, in a manner that involves the coupling of plasmid molecules.

An audit of the assessment and management of adults admitted to Christchurch Hospital with community acquired pneumonia

AIMS

To audit the management of adult patients admitted with community acquired pneumonia including the standards of clinical assessment, use of modified British Thoracic Society prognostic criteria and antibiotic therapy.

METHODS

A prospective, 16 week, study of consecutive patients admitted to Christchurch Hospital with community acquired pneumonia.

RESULTS

Ninety-six patients met the inclusion criteria. The median age was 70 years. A pathogen was identified in 28 (26%) patients. Forty two patients fulfilled the modified British Thoracic Society criteria for severe disease and all 9 deaths occurred in that subgroup. The management guidelines were followed without exception in only 15% of cases. Documentation of the prognostic criteria was often incomplete and therefore only 33% of those patients with severe disease were correctly identified. Seventy one percent of those with severe disease were treated with only one antibiotic and there was significant delay in administering the first dose in 44% of cases. A follow up chest radiograph was performed in 43 (51%) of those discharged.

CONCLUSIONS

There was poor compliance with the management guidelines. There was a lack of awareness of the severity criteria leading to inadequate treatment in many cases. Further educational initiatives are indicated.

Acquisition of resistance genes by the IncQ plasmid R1162 is limited by its high copy number and lack of a partitioning mechanism

R1162 is a representative member of the broad-host-range IncQ group of multicopy plasmids. Lower-copy-number derivatives of R1162 were constructed in vitro and shown to be unstable, indicating that partitioning of plasmid copies at cell division is due to random distribution and not to an active partitioning mechanism. However, the normal copy number of R1162 reduces cell fitness during growth in broth and favors the emergence of unstable, lower-copy-number variants. As a result, plasmid-borne antibiotic resistance genes active at a low copy number eventually result in plasmid loss during periods of no selection. We argue that the maintenance of R1162 in a population requires a gene that is selected only at high levels. This reduces the potential for acquiring genes from other R factors and could explain the limited variety of antibiotic resistance genes contained by naturally occurring IncQ plasmids.