Backward-mode multiwavelength photoacoustic scanner using a planar Fabry-Perot polymer film ultrasound sensor for high-resolution three-dimensional imaging of biological tissues

A multiwavelength backward-mode planar photoacoustic scanner for 3D imaging of soft tissues to depths of several millimeters with a spatial resolution in the tens to hundreds of micrometers range is described. The system comprises a tunable optical parametric oscillator laser system that provides nanosecond laser pulses between 600 and 1200 nm for generating the photoacoustic signals and an optical ultrasound mapping system based upon a Fabry-Perot polymer film sensor for detecting them. The system enables photoacoustic signals to be mapped in 2D over a 50 mm diameter aperture in steps of 10 microm with an optically defined element size of 64 microm. Two sensors were used, one with a 22 microm thick polymer film spacer and the other with a 38 mum thick spacer providing -3 dB acoustic bandwidths of 39 and 22 MHz, respectively. The measured noise equivalent pressure of the 38 microm sensor was 0.21 kPa over a 20 MHz measurement bandwidth. The instrument line-spread function (LSF) was measured as a function of position and the minimum lateral and vertical LSFs found to be 38 and 15 microm, respectively. To demonstrate the ability of the system to provide high-resolution 3D images, a range of absorbing objects were imaged. Among these was a blood vessel phantom that comprised a network of blood filled tubes of diameters ranging from 62 to 300 microm immersed in an optically scattering liquid. In addition, to demonstrate the applicability of the system to spectroscopic imaging, a phantom comprising tubes filled with dyes of different spectral characteristics was imaged at a range of wavelengths. It is considered that this type of instrument may provide a practicable alternative to piezoelectric-based photoacoustic systems for high-resolution structural and functional imaging of the skin microvasculature and other superficial structures.     

Integrative feedback and robustness in a lipid biosynthetic network.

The homeostatic control of membrane lipid composition appears to be of central importance for cell functioning and survival. However, while lipid biosynthetic reaction networks have been mapped in detail, the underlying control architecture which underpins these networks remains elusive. A key problem in determining the control architectures of lipid biosynthetic pathways, and the mechanisms through which control is achieved, is that the compositional complexity of lipid membranes makes it difficult to determine which membrane parameter is under homeostatic control. Recently, we reported that membrane stored elastic energy provides a physical feedback signal which modulates the activity in vitro of CTP:phosphocholine cytidylyltransferase (CCT), an extrinsic membrane enzyme which catalyses a key step in the synthesis of phosphatidylcholine lipids in the Kennedy pathway (Kennedy 1953 J. Am. Chem. Soc. 75, 249-250). We postulate that stored elastic energy may be the main property of membranes that is under homeostatic control. Here we report the results of simulations based on this postulate, which reveal a possible control architecture for lipid biosynthesis networks in vivo.     

Stable iron isotope fractionation between aqueous Fe(II) and hydrous ferric oxide

Despite the ubiquity of poorly crystalline ferric hydrous oxides (HFO, or ferrihydrite) in natural environments, stable Fe isotopic fractionation between HFO and other Fe phases remains unclear. In particular, it has been difficult to determine equilibrium Fe isotope fractionation between aqueous Fe(II) and HFO due to fast transformation of the latter to more stable minerals. Here we used HFO stabilized by the presence of dissolved silica (2.14 mM), or a Si-HFO coprecipitate, to determine an equilibrium Fe(II)-HFO fractionation factor using a three-isotope method. Iron isotope exchange between Fe(II) and HFO was rapid and near complete with the Si-HFO coprecipitate, and rapid but incomplete for HFO in the presence of dissolved silica, the latter case likely reflecting blockage of oxide surface sites by sorbed silica. Equilibrium Fe(II)-HFO (56)Fe/(54)Fe fractionation factors of -3.17 ± 0.08 (2σ)‰ and -2.58 ± 0.14 (2σ)‰ were obtained for HFO plus silica and the Si-HFO coprecipitate, respectively. Structural similarity between ferrihydrite and hematite, as suggested by spectroscopic studies, combined with the minor isotopic effect of dissolved silica, imply that the true equilibrium Fe(II)-HFO (56)Fe/(54)Fe fractionation factor in the absence of silica may be ～-3.2‰. These results provide a critical interpretive context for inferring the stable isotope effects of Fe redox cycling in nature.     

Thermal inactivation of Escherichia coli O157:H7, Salmonella, and Listeria monocytogenes in breaded pork patties

ABSTRACT:  Decimal reduction times ( D -values) and thermal resistance constants ( z -values) for 3 foodborne pathogenic bacteria in formulated ready-to-eat breaded pork patties were determined with thermal inactivation studies. Meat samples, inoculated with Escherichia coli O157:H7, Salmonella , and Listeria monocytogenes cultures or uninoculated controls, were packaged in sterile bags, immersed in circulated water bath, and held at 55, 57.5, 60, 62.5, 65, 67.5, and 70 °C for different durations of time. The D - and z -values were determined by using a linear regression model. Average calculated D -values for E. coli O157:H7, Salmonella , and L . monocytogenes at a temperature range of 55 to 70 °C were 32.11 to 0.08 min, 69.48 to 0.29 min, and 150.46 to 0.43 min, respectively. Calculated z -values for E. coli O157:H7, Salmonella , and L. monocytogenes were 5.4, 6.2, and 5.9 °C, respectively. The results of this study will be useful to food processors to validate thermal lethality of the studied foodborne pathogens in ready-to-eat breaded pork patties.     

Strained Interface Defects in Silicon Nanocrystals

The surface of silicon nanocrystals embedded in an oxide matrix can contain numerous interface defects. These defects strongly affect the nanocrystals’ photoluminescence efficiency and optical absorption. Dangling‐bond defects are nearly eliminated by H₂ passivation, thus decreasing absorption below the quantum‐confined bandgap and enhancing PL efficiency by an order of magnitude. However, there remain numerous other defects seen in absorption by photothermal deflection spectroscopy; these defects cause non‐radiative recombination that limits the PL efficiency to <15%. Using atomistic pseudopotential simulations, we attribute these defects to two specific types of distorted bonds: Si‐Si and bridging Si‐O‐Si bonds between two Si atoms at the nanocrystal surface.     

Hyporheic exchange and fulvic acid redox reactions in an Alpine stream/wetland ecosystem, Colorado Front Range

The influence of hyporheic zone interactions on the redox state of fulvic acids and other redox active species was investigated in an alpine stream and adjacent wetland, which is a more reducing environment. A tracer injection experiment using bromide (Br-) was conducted in the stream system. Simulations with a transport model showed that rates of exchange between the stream and hyporheic zone were rapid (alpha approximately 10(-3) s(-1)). Parallel factor analysis of fluorescence spectra was used to quantifythe redox state of dissolved fulvic acids. The rate coefficient for oxidation of reduced fulvic acids (lambda = 6.5 x 10(-3) s(-1)) in the stream indicates that electron-transfer reactions occur over short time scales. The rate coefficients for decay of ammonium (lambda = 1.2 x 10(-3) s(-1)) and production of nitrate (lambda = -1.0 x 10(-3) s(-1)) were opposite in sign but almost equal in magnitude. Our results suggest that fulvic acids are involved in rapid electron-transfer processes in and near the stream channel and may be important in determining ecological energy flow at the catchment scale.     

Early alliance, alliance ruptures, and symptom change in a nonrandomized trial of cognitive therapy for avoidant and obsessive-compulsive personality disorders.

Participants were 30 adult outpatients diagnosed with avoidant personality disorder or obsessive-compulsive personality disorder who enrolled in an open trial of cognitive therapy for personality disorders. Treatment consisted of up to 52 weekly sessions. Symptom evaluations were conducted at intake, at Sessions 17 and 34, and at the last session. Alliance variables were patients' first alliance rating and "rupture-repair" episodes, which are disruptions in the therapeutic relationship that can provide corrective experiences and facilitate change. Stronger early alliances and rupture-repair episodes predicted more improvement in symptoms of personality disorder and depression. This work points to potentially important areas to target in treatment development for these personality disorders. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Glass Surface Layer Density by Neutron Depth Profiling

Several lithium-disilicate ( Li₂O∙2SiO₂ ) glass samples were synthesized, polished and subjected to static leach tests for varying periods of time in an HCl solution (pH 4) at 90°C. The presence of an alteration layer on the leached specimens was independently confirmed using infrared spectroscopy. These samples were then analyzed with neutron depth profiling (NDP), and for all exposure times between 1 and 20 h, a leached layer was detected by NDP. The residual concentration of ⁶Li in the alteration layer was observed to be approximately 10% of the bulk glass value. The 7.5 h and 17.5 h samples were cross-sectioned using focused ion beam milling, and the thickness of the alteration layer on the samples was measured directly using scanning electron microscopy to be 9.8 and 22.9 μm, respectively. The areal density of the gel layers — determined by deconvolution of the NDP spectra — was coupled with the SEM measurement to give densities of 1.46 ± 0.08 g/cm³ for the 7.5 h specimen and 1.46 ± 0.05 g/cm³ for the 17.5 h specimen. This preliminary work shows that NDP can be used to determine the average density of gel layers formed owing to leaching of alkali-silicate glass.