Fabrication and optimization of a conducting polymer sensor array using stored grain model volatiles

During storage, grain can experience significant degradation in quality due to a variety of physical, chemical, and biological interactions. Most commonly, these losses are associated with insects or fungi. Continuous monitoring and an ability to differentiate between sources of spoilage are critical for rapid and effective intervention to minimize deterioration or losses. Therefore, there is a keen interest in developing a straightforward, cost-effective, and efficient method for monitoring of stored grain. Sensor arrays are currently used for classifying liquors, perfumes, and the quality of food products by mimicking the mammalian olfactory system. The use of this technology for monitoring of stored grain and identification of the source of spoilage is a new application, which has the potential for broad impact. The main focus of the work described herein is on the fabrication and optimization of a carbon black (CB) polymer sensor array to monitor stored grain model volatiles associated with insect secretions (benzene derivatives) and fungi (aliphatic hydrocarbon derivatives). Various methods of statistical analysis (RSD, PCA, LDA, t test) were used to select polymers for the array that were optimum for distinguishing between important compound classes (quinones, alcohols) and to minimize the sensitivity for other parameters such as humidity. The performance of the developed sensor array was satisfactory to demonstrate identification and separation of stored grain model volatiles at ambient conditions.

High speed silicon electro-optical modulators enhanced via slow light propagation

While current optical communication networks efficiently carry and process huge amounts of digital information over large and medium distances, silicon photonics technology has the capacity to meet the ceaselessly increasing demand for bandwidth via energy efficient, inexpensive and mass producible short range optical interconnects. In this context, handling electrical-to-optical data conversion through compact and high speed electro-optical modulators is of paramount importance. To tackle these challenges, we combine the attractive properties of slow light propagation in a nanostructured periodic waveguide together with a high speed semiconductor pn diode, and demonstrate a highly efficient and mass manufacturable 500 µm-long silicon electro-optical device, exhibiting error free modulation up to 20 Gbit/s. These results, supported by modulation rate capabilities reaching 40 Gbit/s, pave a foreseeable way towards dense, low power and ultra fast integrated networks-on-chip for future chip-scale high performance computing systems.

Dielectric response of particles in flowing media: the effect of shear-induced rotation on the variation in particle polarizability

When particles in liquid suspensions flow through channels and pipes in a laminar fashion, the resulting parabolic velocity profile gives rise to shear, which induces the particles to rotate. If flowing suspensions containing dielectric particles are immersed in an external electric field, the anisotropic polarization induced in rotating nonspherical particles will vary with the orientation of the particle with respect to the external field; what results is an uncertainty in experimental measurements that involve particle polarization. The present study establishes the limits of this uncertainty and shows that departure from spherical symmetry in individual particles can lead to a significant overlap in measurements attempting to discriminate between particle subpopulations in suspensions. For example, the uncertainty in signal amplitude for a population of activated T-lymphocytes can be as high as 20%. Such concerns arise in applications like field-flow fractionation, dielectrophoretic sorting of particles, flow impedance measurements and cytometry, and, most recently, isodielectric separation, all of which are used to separate particles in a flow based on their dielectric response. This paper considers axisymmetric particles as the first departure from the approximation of spherical symmetry, shows how to calculate an estimate of the size of the population overlap, and suggests possible strategies to minimize it.

40 Gb/s silicon photonics modulator for TE and TM polarisations

A key device in future high speed short reach interconnect technology will be the optical modulator. These devices, in silicon, have experienced dramatic improvements over the last 6 years and the modulation bandwidth has increased from a few tens of MHz to over 30 GHz. However, the demands of optical interconnects are significant. Here we describe an approach based on a self-aligned wrap around p-n junction structure embedded in a silicon waveguide that can produce high-speed optical phase modulation, whilst at the same time, capable of a high extinction ratio. An all-silicon optical modulator using a CMOS compatible fabrication process with a data rate of 40 Gb/s and extinction ratio up to approximately 6.5 dB for TE and TM polarisations is demonstrated. This technology is not only compatible with conventional complementary MOS (CMOS) processing, but is also intended to simplify and improve the reliability of, the fabrication process.

High contrast 40Gbit/s optical modulation in silicon

Data interconnects are on the verge of a revolution. Electrical links are increasingly being pushed to their limits with the ever increasing demand for bandwidth. Data transmission in the optical domain is a leading candidate to satisfy this need. The optical modulator is key to most applications and increasing the data rate at which it operates is important for reducing power consumption, increasing channel bandwidth limitations and improving the efficiency of infrastructure usage. In this work silicon based devices of lengths 3.5mm and 1mm operating at 40Gbit/s are demonstrated with extinction ratios of up to 10dB and 3.5dB respectively. The efficiency and optical loss of the phase shifter is 2.7V.cm and 4dB/mm (or 4.5dB/mm including waveguide loss) respectively.

Activated T lymphocytes migrate toward the cathode of DC electric fields in microfluidic devices

Immune cell migration is a fundamental process that enables immunosurveillance and immune responses. Understanding the mechanism of immune cell migration is not only of importance to the biology of cells, but also has high relevance to cell trafficking mediated physiological processes and diseases such as embryogenesis, wound healing, autoimmune diseases and cancers. In addition to the well-known chemical concentration gradient based guiding mechanism (i.e. chemotaxis), recent studies have shown that lymphocytes can respond to applied physiologically relevant direct current (DC) electric fields by migrating toward the cathode of the fields (i.e. electrotaxis) in both in vitro and in vivo settings. In the present study, we employed two microfluidic devices allowing controlled application of electric fields inside the microfluidic channel for quantitative studies of lymphocyte electrotaxis in vitro at the single cell level. The first device is fabricated by soft-lithography and the second device is made in glass with integrated on-chip electrodes. Using both devices, we for the first time showed that anti-CD3/CD28 antibodies activated human blood T cells migrate to the cathode of the applied DC electric field. This finding is consistent with previous electrotaxis studies on other lymphocyte subsets suggesting electrotaxis is a novel guiding mechanism for immune cell migration. Furthermore, the characteristics of electrotaxis and chemotaxis of activated T cells in PDMS microfluidic devices are compared.

Wireless Passive Sensor for Remote pH Monitoring

In this paper we describe a wireless passive pH sensor for high-resolution remote pH monitoring. The sensor is based on a passive LC coil resonator whose resonant frequency is monitored remotely by measuring the change in impedance of an interrogator coil coupled to the sensor coil. The sensor resonator consists of an inductive coil connected in parallel with a voltage dependent capacitor and a pH combination electrode. Change in the electrode potential in response to variations of the pH of the solution changes the capacitance, and therefore the resonant frequency of the sensor. A linear response with a 0.1 pH resolution is achieved over a 4–10 pH dynamic range. The response time of the sensor is demonstrated to be less than 30 s and is limited by the response time of the pH combination electrode. The described sensor technology is suitable for long-term remote pH monitoring in numerous fields such as biomedical sensing, environmental monitoring, industrial and chemical processing, and structural health monitoring.

High speed silicon optical modulator with self aligned fabrication process

With the imminent commercialisation of silicon photonic devices comes the requirement for a fabrication process capable of high yield and device performance repeatability. The precise alignment of the different elements of a device can be a major fabrication challenge for minimising performance variation or even device failure. In this paper a new design of high speed carrier depletion silicon optical modulator is introduced which features the use of a self-aligned fabrication process to form the pn junction. Experimental results are presented from an initial fabrication run, which has demonstrated a 6 dB modulation depth at 10 Gbit/s from a 3.5 m long device.

Field enhanced charge carrier reconfiguration in electronic and ionic coupled dynamic polymer resistive memory

Dynamic resistive memory devices based on a conjugated polymer composite (PPy(0)DBS(-)Li(+) (PPy: polypyrrole; DBS(-): dodecylbenzenesulfonate)), with field-driven ion migration, have been demonstrated. In this work the dynamics of these systems has been investigated and it has been concluded that increasing the applied field can dramatically increase the rate at which information can be 'written' into these devices. A conductance model using space charge limited current coupled with an electric field induced ion reconfiguration has been successfully utilized to interpret the experimentally observed transient conducting behaviors. The memory devices use the rising and falling transient current states for the storage of digital states. The magnitude of these transient currents is controlled by the magnitude and width of the write/read pulse. For the 500 nm length devices used in this work an increase in 'write' potential from 2.5 to 5.5 V decreased the time required to create a transient conductance state that can be converted into the digital signal by 50 times. This work suggests that the scaling of these devices will be favorable and that 'write' times for the conjugated polymer composite memory devices will decrease rapidly as ion driving fields increase with decreasing device size.

A microwave interferometric system for simultaneous actuation and detection of single biological cells

In biomedical applications ranging from the study of pathogen invasion to drug efficacy assays, there is a growing need to develop minimally invasive techniques for single-cell analysis. This has inspired researchers to develop optical, electrical, microelectromechanical and microfluidic devices for exploring phenomena at the single-cell level. In this work, we demonstrate an electrical approach for single-cell analysis wherein a 1.6 GHz microwave interferometer detects the capacitance changes (DeltaC) produced by single cells flowing past a coplanar interdigitated electrode pair. The experimental and simulated capacitance changes generated by yeast cells are in close agreement. By using the capacitance changes of uniform polystyrene spheres (diameter = 5.7 microm) for calibration purposes, we demonstrate a 0.65 aF sensitivity in a 10 ms response time. Using an RC circuit, a low frequency sinusoidal potential is simultaneously superimposed on the electrode pair to generate a dielectrophoretic force that translates cells. Specifically, when yeast cells suspended in a solution of 90 ppm NaCl in deionized water are exposed to 10 kHz and 3 MHz potentials (ranging from 1-3 V(pp)), they experience negative and positive dielectrophoresis, respectively. The corresponding changes in cell elevation above the interdigitated electrodes are detected using the asymmetry of the capacitance signature produced by the cell. Cell elevation changes can be detected in less than 80 ms. The minimum detectable change in elevation is estimated to be 0.22 microm. This approach will have applications in rapid single-cell dielectrophoretic analysis, and may also prove useful in conjunction with impedance spectroscopy.

Comment on "Fundamentals of pair diffusion in kinematic simulations of turbulence"

Osborne et al [Phys. Rev. E 74, 036309 (2006)] suggested that our conclusions on the ability of kinematic simulation to represent the t(3) Richardson law [Thomson and Devenish, J. Fluid Mech. 526, 277 (2005)] were an artifact of our choice of time step. Here we repeat some of the simulations with a small fixed time step, enabling us to confirm that our previous study was not compromised by the variable time step used.

Microwave frequency sensor for detection of biological cells in microfluidic channels

We present details of an apparatus for capacitive detection of biomaterials in microfluidic channels operating at microwave frequencies where dielectric effects due to interfacial polarization are minimal. A circuit model is presented, which can be used to adapt this detection system for use in other microfluidic applications and to identify ones where it would not be suitable. The detection system is based on a microwave coupled transmission line resonator integrated into an interferometer. At 1.5 GHz the system is capable of detecting changes in capacitance of 650 zF with a 50 Hz bandwidth. This system is well suited to the detection of biomaterials in a variety of suspending fluids, including phosphate-buffered saline. Applications involving both model particles (polystyrene microspheres) and living cells-baker's yeast (Saccharomyces cerevisiae) and Chinese hamster ovary cells-are presented.

Free carrier lifetime modification for silicon waveguide based devices

We investigate the effect of silicon ion irradiation on free carrier lifetime in silicon waveguides, and thus its ability to reduce the density of two-photon-absorption (TPA) generated free carriers. Our experimental results show that free carrier lifetime can be reduced significantly by silicon ion implantation. Associated excess optical absorption from the implanted ions can be reduced to an acceptable level if irradiation energy and dose are correctly chosen. Simulations of Raman scattering suggest that net gain can be achieved in certain cases without the need for an integrated diode in reverse bias to remove the photo-generated free carriers.

Microfluidic electromanipulation with capacitive detection for the mechanical analysis of cells

The mechanical behavior of cells offers insight into many aspects of their properties. We propose an approach to the mechanical analysis of cells that uses a combination of electromanipulation for stimulus and capacitance for sensing. To demonstrate this approach, polystyrene spheres and yeast cells flowing in a 25 mumx100 mum microfluidic channel were detected by a perpendicular pair of gold thin film electrodes in the channel, spaced 25 mum apart. The presence of cells was detected by capacitance changes between the gold electrodes. The capacitance sensor was a resonant coaxial radio frequency cavity (2.3 GHz) coupled to the electrodes. The presence of yeast cells (Saccharomyces cerevisiae) and polystyrene spheres resulted in capacitance changes of approximately 10 and 100 attoFarad (aF), respectively, with an achieved capacitance resolution of less than 2 aF in a 30 Hz bandwidth. The resolution is better than previously reported in the literature, and the capacitance changes are in agreement with values estimated by finite element simulations. Yeast cells were trapped using dielectrophoretic forces by applying a 3 V signal at 1 MHz between the electrodes. After trapping, the cells were displaced using amplitude and frequency modulated voltages to produce modulated dielectrophoretic forces. Repetitive displacement and relaxation of these cells was observed using both capacitance and video microscopy.

Optical fiber refractometer using narrowband cladding-mode resonance shifts

Short-period fiber Bragg gratings with weakly tilted grating planes generate multiple strong resonances in transmission. Our experimental results show that the wavelength separation between selected resonances allows the measurement of the refractive index of the medium surrounding the fiber for values between 1.25 and 1.44 with an accuracy approaching 1x10(-4). The sensor element is 10 mm long and made from standard single-mode telecommunication grade optical fiber by ultraviolet light irradiation through a phase mask.

Expression of Bcl-x, Bcl-2, Bax, and Bak in endarterectomy and atherectomy specimens

The regulation of apoptosis in atherosclerosis is not completely defined. The aim of this study was to determine the expression of Bcl-2, Bcl-x, Bax, and Bak in relation to apoptosis in advanced atherosclerotic lesions. In atherectomy (15), endarterectomy (10), and control non-atherosclerotic segments of renal (2) and of coronary and carotid (5) arteries, the extent of apoptosis was determined using TdT dUTP nick end labelling (TUNEL) and nuclear morphology (karyorrhexis/pyknosis) and expression of apoptosis regulators by immunohistochemistry and western blot analysis on paraffin-embedded material. In all specimens, the atherosclerotic involvement was advanced: grade V (n=18) and grade VI (n=7). The apoptotic index was high (mean 30%) in advanced lesions compared with controls (<2%) and smooth muscle cells (SMCs) were the predominant cell type undergoing apoptosis. In all TUNEL-positive apoptotic cells, Bax and Bak were present, while Bcl-x was absent. Bcl-2 was absent in a majority of these cells, but occasional TUNEL-positive cells expressed Bcl-2. In non-apoptotic cells, Bcl-x was present and western blot detected only the long isoform, Bcl-xL, from the plaques. In conclusion, increased Bax and Bak coupled with lack/paucity of Bcl-2 and Bcl-xL are associated with SMC apoptosis in advanced lesions. Bcl-xL in non-apoptotic cells appears to contribute to prolonged cell survival.

Medtronic Mosaic porcine bioprosthesis: midterm investigational trial results

BACKGROUND

The midterm clinical and hemodynamic performance of the Medtronic Mosaic porcine bioprosthesis was evaluated in a regulatory trial.

METHODS

In nine Canadian centers, 802 bioprostheses (560 aortic and 242 mitral) were implanted between September 1994 and April 1999 in patients with a mean age of 70 years.

RESULTS

Survival for aortic valve replacement at 4 years was 84.4%+/-3.1%. Freedom from valve-related or unexplained death was 95.6%+/-1.9%; structural valve deterioration, 100.0%; reoperation, 96.2%+/-1.7%; major thromboembolism, 96.1%+/-1.8%; and major antithrombotic-related hemorrhage, 96.4%+/-1.7%. Echocardiographic derived mean systolic gradient was 13.4 mm Hg at 4 years with an indexed effective orifice area of 0.7 to 0.8 cm2/m2. A significant decrease in left ventricular mass was shown over time in all valve sizes. Survival for mitral valve replacement at 4 years was 79.2%+/-6.8%. Freedom from valve-related or unexplained death was 96.5%+/-3.4%; structural valve deterioration, 100%; reoperation, 97.0%+/-3.2%; major thromboembolism, 95.7%+/-3.8%; and major antithrombotic-related hemorrhage, 95.0%+/-4.2%. Echocardiographically measured averaged mean diastolic gradient was 4.5 mm Hg.

CONCLUSIONS

The Medtronic Mosaic bioprosthesis is safe and effective in both the aortic and mitral positions. The valve has low gradients in both positions and excellent left ventricular mass regression in the patients with aortic valve replacement.

Impedance-matched absorbers for finite-difference parabolic equation algorithms

In this paper, a perfectly matched layer (PML) absorber, recently introduced into the electromagnetic propagation literature by Berenger [J. Comput. Phys. 114, 185-200 (1994)], is adapted for use with both paraxial and wide-angle acoustic parabolic equations (PEs). Our procedure incorporates an imaginary component into the transverse coordinate that mimics the introduction of a fictitious absorber on the edge of the computational grid. Use of such an impedance-matched layer can significantly reduce spurious reflections compared to physical absorbing layer methods and thus allows a smaller number of boundary points to be employed in PE calculations. Numerical results obtained with several higher-order propagator approximations confirm that such impedance-matched absorbers efficiently eliminate reflections.

Medtronic mosaic porcine bioprosthesis satisfactory early clinical performance

BACKGROUND

The Medtronic (Minneapolis, MN) Mosaic porcine bioprosthesis is an investigational prosthesis which incorporates zero-pressure fixation, aortic root predilation, low profile stent, and alpha oleic acid antimineralization treatment.

METHODS

From September 1994 to August 1996, 289 patients (mean age 70 years, range, 28 to 88 years) had 227 (78.5%) aortic valve replacements and 62 (21.5%) mitral valve replacements. Concomitant procedures were performed in 61.2% (139) of aortic valve replacements and 54.8% (34) of mitral valve replacements. Of the aortic valve replacement group 70 (30.8%) were in the 61 to 70 age group and 134 (59.0%) were 71 years or older. Of the mitral valve replacements, 23 (37.1%) were 61 to 70 years and 30 (48.4%) 71 years or older.

RESULTS

The early mortality, overall, was 4.2% (12 of 289); for aortic valve replacement it was 4.0% (9) and for mitral valve replacement it was 4.8% (3). The late mortality for aortic valve replacement was 2.6% per patient-year (3 events, 1.3% of total) and for mitral valve replacement it was 3.3% per patient-year (one event, 1.6% of total). The reoperative rate for aortic valve replacement was 3.0% per patient-year (4), while there were no mitral valve replacement reoperations. The freedom from major thromboembolism was 97.3%+/-1.6% for aortic valve replacement and 94.7%+/-3.0% for mitral valve replacement at 1 to 1.5 years. The freedom from reoperation was 96.7%+/-1.7% for aortic valve replacement; there was no reoperation for mitral valve replacement. There were no cases of structural valve deterioration. In the aortic position the mean systolic gradient was low, approximately 11 mm Hg, across all sizes (range 8 to 12 mm Hg at 3 months and 10 to 13 mm Hg at 12 months). In the mitral position the mean diastolic gradient was approximately 5 mm Hg (range, 2 to 6 mm Hg) for all sizes 25 to 31 mm at the early and 1 year follow-up echocardiographic assessment.

CONCLUSIONS

The early clinical performance and in vivo hemodynamics are encouraging.

High-resolution zero-dispersion wavelength mapping in single-mode fiber

We present a new noninvasive technique for measuring the spatial variation of the zero-dispersion wavelength (lambda(0)) in single-mode fibers. This technique uses low-power continuous-wave lasers and is simple to implement. When applying this technique to dispersion-shifted fibers, we can resolve subnanometer fluctuations in lambda(0) with a potential spatial resolution of better than 100 m. We also discuss and show the limits of this and other techniques that arise from polarization-mode dispersion in the fibers.

Dependence of global temperatures on atmospheric CO2 and solar irradiance

Changes in global average temperatures and of the seasonal cycle are strongly coupled to the concentration of atmospheric CO2. I estimate transfer functions from changes in atmospheric CO2 and from changes in solar irradiance to hemispheric temperatures that have been corrected for the effects of precession. They show that changes from CO2 over the last century are about three times larger than those from changes in solar irradiance. The increase in global average temperature during the last century is at least 20 times the SD of the residual temperature series left when the effects of CO2 and changes in solar irradiance are subtracted.

Deep hypothermic low flow cardiopulmonary bypass in small dogs

OBJECTIVE

To evaluate the feasibility of and morbidity and mortality associated with cardiopulmonary bypass (CPB) using deep hypothermia and low flow perfusion in adult dogs weighing less than 10 kg.

STUDY DESIGN

Prospective, descriptive study.

ANIMALS

Two groups of three dogs underwent CPB. Group 1 dogs underwent deep hypothermia (15 to 18 degrees C), 45 minutes of low perfusion flow (20 mL/kg/min) and 1 hour of aortic cross clamp time. In group 2, ultrafiltration of perfusate before discontinuation of bypass was added to the standard treatment. Complete blood counts, serum biochemistry, urine output, ejection fraction, and cardiac output were monitored before and for 7 days after surgery.

RESULTS

All dogs were successfully weaned from bypass. Four of six dogs survived, three without major complications. One dog developed and recovered from septic pleuritis. Two dogs died or were euthanatized after surgery because of respiratory or gastrointestinal complications. Minor complications included anemia, hypoproteinemia, and electrolyte disturbances. Transfusion requirements and edema formation were reduced by ultrafiltration.

CONCLUSIONS

The observations in this study support the feasibility of low flow hypothermic CPB. Meticulous tissue handling, precise equipment, ultrafiltration, and aggressive postoperative potassium supplementation are recommended for smaller patients.

CLINICAL RELEVANCE

Increased sensitivity to adverse sequelae of CPB may be associated with small patient size. Further evaluation is necessary before routine clinical application of low flow hypothermic CPB in this patient population.