Solidly Mounted Resonators with Carbon Nanotube Electrodes for Biosensing Applications

The work reported here shows a direct experimental comparison of the sensitivities of AlN solidly mounted resonators (SMR)-based biosensors fabricated with standard metal electrodes and with carbon nanotube electrodes. SMRs resonating at frequencies around 1.75 GHz have been fabricated, some devices using a thin film of multi-wall carbon nanotubes (CNTs) as the top electrode material and some identical devices using a chromium/gold electrode. Protein solutions with different concentrations were loaded on the top of the resonators and their responses to mass-load from physically adsorbed coatings were investigated. Results show that resonators using CNTs as the top electrode material exhibited higher frequency change for a given load due to the higher active surface area of a thin film of interconnecting CNTs compared to that of a metal thin film electrode and hence exhibited greater mass loading sensitivity. It is therefore concluded that the use of CNT electrodes on resonators for their use as gravimetric biosensors is viable and worthwhile.

Multiple Frequency Solidly Mounted BAW Filters

This paper reports the simultaneous fabrication of Receive and Transmit Bulk Acoustic Wave filters for the WCDMA standard on the same die. Both filters are based on Solidly Mounted Resonators using a common Bragg mirror, but with each having a specific piezoelectric film thickness. Electrical measurements reveal that the process steps required to provide the two different piezoelectric film thicknesses on the same die does not impact the electrical performances of resonators and filters and that this approach could thus be generalised to more than two filters.

Tiled Projector Displays Correction for Dark Scenes in Railway Simulators

Tiled projector displays are a common choice for training simulators, where a high resolution output image is required. They are cheap for the resolution that they can reach and can be configured in many different ways. Nevertheless, such kinds of displays require geometric and color correction so that the composite image looks seamless. Display correction is an even bigger challenge when the projected images include dark scenes combined with brighter scenes. This is usually a problem for railway simulators when the train is positioned inside a tunnel and the black offset effect becomes noticeable. In this paper, a method for fast photometric and geometric correction of tiled display systems where dark and bright scenes are combined is presented. The image correction is carried out in two steps. First, geometric alignment and overlapping areas attenuation for brighter scenes is applied. Second, in the event of being inside a tunnel, the brightness of the scene is increased in certain areas using light sources in order to create the impression of darkness but minimizing the effect of the black offset

PDR with a foot-mounted IMU and ramp detection

The localization of persons in indoor environments is nowadays an open problem. There are partial solutions based on the deployment of a network of sensors (Local Positioning Systems or LPS). Other solutions only require the installation of an inertial sensor on the person’s body (Pedestrian Dead-Reckoning or PDR). PDR solutions integrate the signals coming from an Inertial Measurement Unit (IMU), which usually contains 3 accelerometers and 3 gyroscopes. The main problem of PDR is the accumulation of positioning errors due to the drift caused by the noise in the sensors. This paper presents a PDR solution that incorporates a drift correction method based on detecting the access ramps usually found in buildings. The ramp correction method is implemented over a PDR framework that uses an Inertial Navigation algorithm (INS) and an IMU attached to the person’s foot. Unlike other approaches that use external sensors to correct the drift error, we only use one IMU on the foot. To detect a ramp, the slope of the terrain on which the user is walking, and the change in height sensed when moving forward, are estimated from the IMU. After detection, the ramp is checked for association with one of the existing in a database. For each associated ramp, a position correction is fed into the Kalman Filter in order to refine the INS-PDR solution. Drift-free localization is achieved with positioning errors below 2 meters for 1,000-meter-long routes in a building with a few ramps.

Low-thickness high-quality aluminum nitride films for super high frequency solidly mounted resonators

We investigate the sputter growth of very thin aluminum nitride (AlN) films on iridium electrodes for electroacoustic devices operating in the super high frequency range. Superior crystal quality and low stress films with thicknesses as low as 160 nm are achieved after a radio frequency plasma treatment of the iridium electrode followed by a two-step alternating current reactive magnetron sputtering of an aluminum target, which promotes better conditions for the nucleation of well textured AlN films in the very first stages of growth. Solidly mounted resonators tuned around 8 GHz with effective electromechanical coupling factors of 5.8% and quality factors Q up to 900 are achieved.

Accurate pedestrian indoor navigation by tightly coupling foot-mounted IMU and RFID measurements

We present a new method to accurately locate persons indoors by fusing inertial navigation system (INS) techniques with active RFID technology. A foot-mounted inertial measuring units (IMUs)-based position estimation method, is aided by the received signal strengths (RSSs) obtained from several active RFID tags placed at known locations in a building. In contrast to other authors that integrate IMUs and RSS with a loose Kalman filter (KF)-based coupling (by using the residuals of inertial- and RSS-calculated positions), we present a tight KF-based INS/RFID integration, using the residuals between the INS-predicted reader-to-tag ranges and the ranges derived from a generic RSS path-loss model. Our approach also includes other drift reduction methods such as zero velocity updates (ZUPTs) at foot stance detections, zero angular-rate updates (ZARUs) when the user is motionless, and heading corrections using magnetometers. A complementary extended Kalman filter (EKF), throughout its 15-element error state vector, compensates the position, velocity and attitude errors of the INS solution, as well as IMU biases. This methodology is valid for any kind of motion (forward, lateral or backward walk, at different speeds), and does not require an offline calibration for the user gait. The integrated INS+RFID methodology eliminates the typical drift of IMU-alone solutions (approximately 1% of the total traveled distance), resulting in typical positioning errors along the walking path (no matter its length) of approximately 1.5 m.

Analysis of human cytochrome P450 3A4 cooperativity: Construction and characterization of a site-directed mutant that displays hyperbolic steroid hydroxylation kinetics

Cytochrome P450 3A4 is generally considered to be the most important human drug-metabolizing enzyme and is known to catalyze the oxidation of a number of substrates in a cooperative manner. An allosteric mechanism is usually invoked to explain the cooperativity. Based on a structure–activity study from another laboratory using various effector–substrate combinations and on our own studies using site-directed mutagenesis and computer modeling of P450 3A4, the most likely location of effector binding is in the active site along with the substrate. Our study was designed to test this hypothesis by replacing residues Leu-211 and Asp-214 with the larger Phe and Glu, respectively. These residues were predicted to constitute a portion of the effector binding site, and the substitutions were designed to mimic the action of the effector by reducing the size of the active site. The L211F/D214E double mutant displayed an increased rate of testosterone and progesterone 6β-hydroxylation at low substrate concentrations and a decreased level of heterotropic stimulation elicited by α-naphthoflavone. Kinetic analyses of the double mutant revealed the absence of homotropic cooperativity with either steroid substrate. At low substrate concentrations the steroid 6β-hydroxylase activity of the wild-type enzyme was stimulated by a second steroid, whereas L211F/D214E displayed simple substrate inhibition. To analyze L211F/D214E at a more mechanistic level, spectral binding studies were carried out. Testosterone binding by the wild-type enzyme displayed homotropic cooperativity, whereas substrate binding by L211F/D214E displayed hyperbolic behavior.

A substance P (neurokinin-1) receptor mutant carboxyl-terminally truncated to resemble a naturally occurring receptor isoform displays enhanced responsiveness and resistance to desensitization

Two isoforms of the substance P (SP) receptor, differing in the length of the cytoplasmic carboxyl-terminus by ≈8 kDa, have been detected previously in rat salivary glands and other tissues. The binding and functional properties of these two isoforms have been investigated using full-length (407 amino acids) and carboxyl-terminally truncated (324 amino acids) rat SP receptors transfected stably into Chinese hamster ovary cells. Both the full-length and the truncated receptor bound radiolabeled SP with a similar Kd (≈0.1 nM). The average number of high affinity SP binding sites per cell was 1.0 × 105 and 0.3 × 105 for the full-length and the truncated SP receptor, respectively. In both cell lines, SP induced a rapid but transient increase in cytosolic calcium concentration ([Ca2+]i), which consisted of the release of Ca2+ from intracellular stores and the influx of extracellular Ca2+. Both components are dependent on phospholipase C activation. Although the full-length and the truncated receptor utilize the same calcium pathways, they differ in their EC50 values (0.28 nM for the full-length; 0.07 nM for the truncated). These differences in responsiveness may be related to the observed differences in receptor desensitization. The truncated receptor, in contrast to the full-length receptor, does not undergo rapid and long-lasting desensitization. Cells possessing the short isoform of the SP receptor would thus be expected to exhibit a prolonged responsiveness.

B cell receptor-associated protein α4 displays rapamycin-sensitive binding directly to the catalytic subunit of protein phosphatase 2A

Recently, TAP42 was isolated as a high copy suppressor of sit4−, a yeast phosphatase related to protein phosphatase 2A (PP2A). TAP42 is related to the murine α4 protein, which was discovered independently by its association with Ig-α in the B cell receptor complex. Herein we show that a glutathione S-transferase (GST)–α4 fusion protein bound the catalytic subunit (C) of human PP2A from monomeric or multimeric preparations of PP2A in a “pull-down” assay. In an overlay assay, the GST–α4 protein bound to the phosphorylated and unphosphorylated forms of C that were separated in two-dimensional gels and immobilized on filters. The results show direct and exclusive binding of α4 to C. This is unusual because all known regulatory B subunits, or tumor virus antigens, bind stably only to the AC dimer of PP2A. The α4–C form of PP2A had an increased activity ratio compared with the AC form of PP2A when myelin basic protein phosphorylated by mitogen-activated protein kinase and phosphorylase a were used as substrates. Recombinant α4 cleaved from GST was phosphorylated by p56lck tyrosine kinase and protein kinase C. A FLAG-tagged α4 expressed in COS7 cells was recovered as a protein containing phosphoserine and coimmunoprecipitated with the C but not the A subunit of PP2A. Treatment of cells with rapamycin prevented the association of PP2A with FLAG-α4. The results reveal a novel heterodimer α4–C form of PP2A that may be involved in rapamycin-sensitive signaling pathways in mammalian cells.

The chitinase PfCHT1 from the human malaria parasite Plasmodium falciparum lacks proenzyme and chitin-binding domains and displays unique substrate preferences

Within hours after the ingestion of a blood meal, the mosquito midgut epithelium synthesizes a chitinous sac, the peritrophic matrix. Plasmodium ookinetes traverse the peritrophic matrix while escaping the mosquito midgut. Chitinases (EC 3.2.1.14) are critical for parasite invasion of the midgut: the presence of the chitinase inhibitor, allosamidin, in an infectious blood meal prevents oocyst development. A chitinase gene, PgCHT1, recently has been identified in the avian malaria parasite P. gallinaceum. We used the sequence of PgCHT1 to identify a P. falciparum chitinase gene, PfCHT1, in the P. falciparum genome database. PfCHT1 differs from PgCHT1 in that the P. falciparum gene lacks proenzyme and chitin-binding domains. PfCHT1 was expressed as an active recombinant enzyme in Escherichia coli. PfCHT1 shares with PgCHT1 a substrate preference unique to Plasmodium chitinases: the enzymes cleave tri- and tetramers of GlcNAc from penta- and hexameric oligomers and are unable to cleave smaller native chitin oligosaccharides. The pH activity profile of PfCHT1 and its IC50 (40 nM) to allosamidin are distinct from endochitinase activities secreted by P. gallinaceum ookinetes. Homology modeling predicts that PgCHT1 has a novel pocket in the catalytic active site that PfCHT1 lacks, which may explain the differential sensitivity of PfCHT1 and PgCHT1 to allosamidin. PfCHT1 may be the ortholog of a second, as yet unidentified, chitinase gene of P. gallinaceum. These results may allow us to develop novel strategies of blocking human malaria transmission based on interfering with P. falciparum chitinase.

Perceptual motion standstill in rapidly moving chromatic displays

In motion standstill, a quickly moving object appears to stand still, and its details are clearly visible. It is proposed that motion standstill can occur when the spatiotemporal resolution of the shape and color systems exceeds that of the motion systems. For moving red-green gratings, the first- and second-order motion systems fail when the grating is isoluminant. The third-order motion system fails when the green/red saturation ratio produces isosalience (equal distinctiveness of red and green). When a variety of high-contrast red-green gratings, with different spatial frequencies and speeds, were made isoluminant and isosalient, the perception of motion standstill was so complete that motion direction judgments were at chance levels. Speed ratings also indicated that, within a narrow range of luminance contrasts and green/red saturation ratios, moving stimuli were perceived as absolutely motionless. The results provide further evidence that isoluminant color motion is perceived only by the third-order motion system, and they have profound implications for the nature of shape and color perception.

A Specific Point Mutant at Position 1 of the Influenza Hemagglutinin Fusion Peptide Displays a Hemifusion Phenotype

We showed previously that substitution of the first residue of the influenza hemagglutinin (HA) fusion peptide Gly1 with Glu abolishes fusion activity. In the present study we asked whether this striking phenotype was due to the charge or side-chain volume of the substituted Glu. To do this we generated and characterized six mutants with substitutions at position 1: Gly1 to Ala, Ser, Val, Glu, Gln, or Lys. We found the following. All mutants were expressed at the cell surface, could be cleaved from the precursor (HA0) to the fusion permissive form (HA1-S-S-HA2), bound antibodies against the major antigenic site, bound red blood cells, and changed conformation at low pH. Only Gly, Ala, and Ser supported lipid mixing during fusion with red blood cells. Only Gly and Ala supported content mixing. Ser HA, therefore, displayed a hemifusion phenotype. The hemifusion phenotype of Ser HA was confirmed by electrophysiological studies. Our findings indicate that the first residue of the HA fusion peptide must be small (e.g., Gly, Ala, or Ser) to promote lipid mixing and must be small and apolar (e.g., Gly or Ala) to support both lipid and content mixing. The finding that Val HA displays no fusion activity underscores the idea that hydrophobicity is not the sole factor dictating fusion peptide function. The surprising finding that Ser HA displays hemifusion suggests that the HA ectodomain functions not only in the first stage of fusion, lipid mixing, but also, either directly or indirectly, in the second stage of fusion, content mixing.

Structure of human DNMT2, an enigmatic DNA methyltransferase homolog that displays denaturant-resistant binding to DNA

DNMT2 is a human protein that displays strong sequence similarities to DNA (cytosine-5)-methyltransferases (m5C MTases) of both prokaryotes and eukaryotes. DNMT2 contains all 10 sequence motifs that are conserved among m5C MTases, including the consensus S-adenosyl-l-methionine-binding motifs and the active site ProCys dipeptide. DNMT2 has close homologs in plants, insects and Schizosaccharomyces pombe, but no related sequence can be found in the genomes of Saccharomyces cerevisiae or Caenorhabditis elegans. The crystal structure of a deletion mutant of DNMT2 complexed with S-adenosyl-l-homocysteine (AdoHcy) has been determined at 1.8 Å resolution. The structure of the large domain that contains the sequence motifs involved in catalysis is remarkably similar to that of M.HhaI, a confirmed bacterial m5C MTase, and the smaller target recognition domains of DNMT2 and M.HhaI are also closely related in overall structure. The small domain of DNMT2 contains three short helices that are not present in M.HhaI. DNMT2 binds AdoHcy in the same conformation as confirmed m5C MTases and, while DNMT2 shares all sequence and structural features with m5C MTases, it has failed to demonstrate detectable transmethylase activity. We show here that homologs of DNMT2, which are present in some organisms that are not known to methylate their genomes, contain a specific target-recognizing sequence motif including an invariant CysPheThr tripeptide. DNMT2 binds DNA to form a denaturant-resistant complex in vitro. While the biological function of DNMT2 is not yet known, the strong binding to DNA suggests that DNMT2 may mark specific sequences in the genome by binding to DNA through the specific target-recognizing motif.

Paper-like electronic displays: Large-area rubber-stamped plastic sheets of electronics and microencapsulated electrophoretic inks

Electronic systems that use rugged lightweight plastics potentially offer attractive characteristics (low-cost processing, mechanical flexibility, large area coverage, etc.) that are not easily achieved with established silicon technologies. This paper summarizes work that demonstrates many of these characteristics in a realistic system: organic active matrix backplane circuits (256 transistors) for large (≈5 × 5-inch) mechanically flexible sheets of electronic paper, an emerging type of display. The success of this effort relies on new or improved processing techniques and materials for plastic electronics, including methods for (i) rubber stamping (microcontact printing) high-resolution (≈1 μm) circuits with low levels of defects and good registration over large areas, (ii) achieving low leakage with thin dielectrics deposited onto surfaces with relief, (iii) constructing high-performance organic transistors with bottom contact geometries, (iv) encapsulating these transistors, (v) depositing, in a repeatable way, organic semiconductors with uniform electrical characteristics over large areas, and (vi) low-temperature (≈100°C) annealing to increase the on/off ratios of the transistors and to improve the uniformity of their characteristics. The sophistication and flexibility of the patterning procedures, high level of integration on plastic substrates, large area coverage, and good performance of the transistors are all important features of this work. We successfully integrate these circuits with microencapsulated electrophoretic “inks” to form sheets of electronic paper.

Molecular dynamics of a grid-mounted molecular dipolar rotor in a rotating electric field

Classical molecular dynamics is applied to the rotation of a dipolar molecular rotor mounted on a square grid and driven by rotating electric field E(ν) at T ≃ 150 K. The rotor is a complex of Re with two substituted o-phenanthrolines, one positively and one negatively charged, attached to an axial position of Rh\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \setlength{\oddsidemargin}{-69pt} \begin{document} \begin{equation*}{\mathrm{_{2}^{4+}}}\end{equation*}\end{document} in a [2]staffanedicarboxylate grid through 2-(3-cyanobicyclo[1.1.1]pent-1-yl)malonic dialdehyde. Four regimes are characterized by a, the average lag per turn: (i) synchronous (a < 1/e) at E(ν) = |E(ν)| > Ec(ν) [Ec(ν) is the critical field strength], (ii) asynchronous (1/e < a < 1) at Ec(ν) > E(ν) > Ebo(ν) > kT/μ, [Ebo(ν) is the break-off field strength], (iii) random driven (a ≃ 1) at Ebo(ν) > E(ν) > kT/μ, and (iv) random thermal (a ≃ 1) at kT/μ > E(ν). A fifth regime, (v) strongly hindered, W > kT, Eμ, (W is the rotational barrier), has not been examined. We find Ebo(ν)/kVcm−1 ≃ (kT/μ)/kVcm−1 + 0.13(ν/GHz)1.9 and Ec(ν)/kVcm−1 ≃ (2.3kT/μ)/kVcm−1 + 0.87(ν/GHz)1.6. For ν > 40 GHz, the rotor behaves as a macroscopic body with a friction constant proportional to frequency, η/eVps ≃ 1.14 ν/THz, and for ν < 20 GHz, it exhibits a uniquely molecular behavior.