Mechanically Corner-Coupled Square Microresonator Array for Reduced Series Motional Resistance

Substantial reductions in vibrating micromechanical resonator series motional resistance R_x have been attained by mechanically coupling and exciting a parallel array of corner-coupled polysilicon square plate resonators. Using this technique with seven resonators, an effective R_x of 480 Omega has been attained at 70 MHz, which is more than 5.9X smaller than the 2.82 kOmega exhibited by a stand-alone transverse-mode corner-supported square resonator, and all this achieved while still maintaining an effective Q>9000. This method for R_x-reduction is superior to methods based on brute force scaling of electrode-to-resonator gaps or dc-bias increases, because it allows a reduction in R_x without sacrificing linearity, and thereby breaks the R_x versus dynamic range tradeoff often seen when scaling. This paper also compares two types of anchoring schemes for transverse-mode square micromechanical resonators and models the effect of support beam parameters on resonance frequency     

Robustness of periodic trajectories

A robustness problem for periodic trajectories is considered. A nonautonomous system with a periodic solution is given. The problem is to decide whether a stable periodic solution remains in a neighborhood of the nominal periodic solution when the dynamics of the system is perturbed. The case with a structured dynamic perturbation is considered. This makes the problem a nontrivial generalization of a classical problem in the theory of dynamical systems. A solution to the robustness problem will be obtained by using a variational system obtained by linearizing the system dynamics along a trajectory, which is uncertain but within the prespecified neighborhood of the nominal trajectory. This gives rise to robustness conditions that can be solved using integral quadratic constraints for linear time periodic systems.     

Design of luminescent inorganic materials: new photophysical processes studied by optical spectroscopy

Recent spectroscopic results in the emerging area of transition-metal NIR-to-visible upconversion are related. The examples of Ti(2+)-, Re(4+)-, and Os(4+)-doped materials showing upconversion illustrate GSA/ESA, GSA/ETU, and photon avalanche multiphoton excitation mechanisms, respectively. Strategies for manipulation of such upconversion processes using the spectroscopic or magnetic properties of the host material are described. High-resolution low-temperature continuous-wave absorption and emission and time-resolved emission experiments combine to yield information about energy splittings, intensities, and excited-state dynamics, and assist in the design and development of luminescent materials showing novel multiphoton excitation properties.     

Distribution of GABA and glycine receptors on bipolar and ganglion cells in the mammalian retina

The amino acids GABA and glycine mediate synaptic transmission via specific neurotransmitter receptors. Molecular cloning studies have shown that there is a great diversity of GABA and glycine receptors. In the present article, the distribution of GABA and glycine receptors on identified bipolar and ganglion cell types in the mammalian retina is reviewed. Immunofluorescence obtained with antibodies against GABA and glycine receptors is punctate. Electron microscopy shows that the puncta represent a cluster of receptors at synaptic sites. Bipolar cell types were identified with immunohistochemical markers. Double immunofluorescence with subunit-specific antibodies was used to analyze the distribution of receptor clusters on bipolar axon terminals. The OFF cone bipolar cells seem to be dominated by glycinergic input, whereas the ON cone bipolar and rod bipolar cells are dominated by GABAergic input. Ganglion cells were intracellularly injected with Neurobiotin, visualized with Streptavidin coupled to FITC, and subsequently stained with subunit specific antibodies. The distribution and density of receptor clusters containing the alpha1 subunit of the GABA(A) receptor and the alpha1 subunit of the glycine receptor, respectively, were analyzed on midget and parasol cells in the marmoset (a New World monkey). Both GABA(A) and glycine receptors are distributed uniformly along the dendrites of ON and OFF types of parasol and midget ganglion cells, indicating that functional differences between these subtypes of ganglion cells are not determined by GABA or glycinergic input.     

Short-pulse properties of optical frequency comb generators

An optical frequency comb generator, based on a simple electro-optic modulator in an optical resonator, can produce high-repetition-rate picosecond pulses. Unlike conventional picosecond lasers, the properties of these pulses are greatly affected by detuning the optical cavity and by dispersion caused by the electro-optic crystal. Picosecond pulses were studied in a physical device by numerical simulation and intensity autocorrelation measurements. The pulse width and pulse-to-pulse spacing were greatly affected by detuning the input laser frequency and the resonance of the optical resonator, and the numerical simulations showed that dispersion causes temporal ripples that are antisymmetric between pulse pairs.     

Organic photorefractive glass with infrared sensitivity and fast response

Infrared imaging materials with high speed and dynamic range are required for a variety of imaging and diagnostic techniques. We present an organic photorefractive glass that shows high diffraction efficiencies of as great as 40% with 25-mum-thick samples and fast response times of 4.3 ms under irradiation at 790 nm. Furthermore, the intensity dependence and field dependence of the grating decay are investigated.     

Cloning and functional characterization of a Caenorhabditis elegans muscarinic acetylcholine receptor

A cDNA clone encoding a muscarinic acetylcholine receptor (mAChR) has been isolated from the nematode Caenorhabditis elegans. The nematode mAChR, consisted of 585 amino acids, displays a high degree of amino acid sequence homology to other invertebrate and vertebrate mAChRs. Excluding a highly variable middle portion of the third intracellular loop, the C. elegans mAChR shares about 51% amino acid sequence identity with a Drosophila mAChR and 42-44% identity with human m1-m5 mAChR subtypes. Comparison of the cDNA sequence with the corresponding genomic sequence reveals that the C. elegans mAChR gene contains ten introns, eight of them in the coding region. Pharmacological profiles of the C. elegans mAChR expressed in Chinese hamster ovary (CHO) cells were shown to be similar to those of mammalian counterparts, indicating that ligand binding domains of the receptor have been conserved during evolution. When this cloned receptor was expressed in Xenopus oocytes, acetylcholine evoked a transient Cl- current. Furthermore, activation of the receptor with oxotremorine, acetylcholine or carbachol resulted in the stimulation of phosphatidylinositol metabolism in CHO cells, suggesting that the receptor is coupled to phospholipase C activation.     

Instruments for minimally invasive surgery: principles of ergonomic handles

Although the advantages of minimally invasive surgery (MIS) have been clearly established for the patient, the surgeon must cope with disadvantages caused by unergonomic instrument handles. Pressure areas and persisting nerve lesions have been described in the literature. The shape of the instrument handles has been identified as the reason for these disorders. To prevent these, it is necessary to use ergonomically designed handles for MIS instruments. Anatomic, physiologic, and ergonomic facts as well as the results of the authors' own experiences and tests are presented. On this basis, an ideal ergonomic working posture for the laparoscopic surgeon and an optimal grasp for manipulating the instruments' functional elements are recommended. To enable the surgeon to evaluate ergonomic handles for MIS instruments according to his own needs, 14 criteria for genuine "ergonomic handles" are established. On the basis of these criteria, deficiencies of handles currently available (ring and shank handles at an angle or with axial extension to the instrument shaft, and pistol handles) are discussed. Furthermore, new handles, developed by the authors according to the criteria for genuine ergonomic handles, are presented.     

Methodological considerations in analysing anaesthetists' habits of action in clinical situations

Human activity can be seen as an intentional, context-dependent enterprise explained through meanings the actors attach to their activity and their directly observable interactions with the environment. The authors have demonstrated previously a new conceptual framework to describe the anaesthetist's activity. One of the central concepts besides orientation is habit of action referring to the way in which the actor has organized his actions when interacting with his environment, in this case a patient with unique physiological potentials, information monitors and anaesthetic drugs. The activity dependent on contingent, particular circumstances, needs to be studied as it appears in a natural situation. Using an idiographic study design the authors have examined the activity of eight expert anaesthetists in clinical settings to determine the characteristics of their habits of action. To capture the fleeting circumstances during the anaesthetic process, a wide observational basis was necessary. It consisted of videotapes, detailed expert observations, and interviews. The conceptual analysis of the subject, habit of action, is described step-by-step. Two distinct habits of action could be identified, confirming earlier results. The interpretative habit of action was characterized by extensive use of situational information in order to construct a cumulative conception of the patient's physiological potentials to control the process accurately. Moreover, rich dialogue between formal professional knowledge and patient-specific, particular knowledge was evident. The reactive habit of action was characterized by a tendency to regulate the process by means of predetermined conventional ranges of measured patient parameters shown by monitors. The authors discuss their methodological solutions and results, and explicate their differences to the earlier approaches.     

Ultraviolet radiometry with synchrotron radiation and cryogenic radiometry

The combination of a cryogenic radiometer and synchrotron radiation enables detector scale realization in spectral regions that are otherwise difficult to access. Cryogenic radiometry is the most accurate primary detector-based standard available to date, and synchrotron radiation gives a unique broadband and continuous spectrum that extends from x ray to far IR. We describe a new cryogenic radiometer-based UV radiometry facility at the Synchrotron Ultraviolet Radiation Facility II at the National Institute of Standards and Technology. The facility is designed to perform a variety of detector and optical materials characterizations. The facility combines a high-throughput, normal incidence monochromator with an absolute cryogenic radiometer optimized for UV measurements to provide absolute radiometric measurements in the spectral range from 125 nm to approximately 320 nm. We discuss results on photodetector characterizations, including absolute spectroradiometric calibration, spatial responsivity mapping, spectroreflectance, and internal quantum efficiency. In addition, such characterizations are used to study UV radiation damage in photodetectors that can shed light on the mechanism of the damage process. Examples are also given for UV optical materials characterization.