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At least 1,387 records · Page 77Linked to original sources
PubMed2001

Microstructured glass chip for ion-channel electrophysiology.

We present a technique by which it is possible to produce a planar sensor for ion channel electrophysiology from glass substrates. Apertures with diameters in the low micrometer to submicrometer range are achieved by irradiation of a glass chip with a single heavy ion and subsequent wet track etching. The function of the device is demonstrated by recordings of single channel currents mediated by the model ion channel gramicidin A in lipid bilayers spanning the micromachined aperture.

Electrolytes↗
PubMed2006

Packet traffic analysis of scale-free networks for large-scale network-on-chip design.

Recent progress in integrated circuit technologies requires precise evaluation between dynamic characteristics and topological architecture design. In this paper, we have investigated the performance evaluation of network-on-chip (NoC) architectures constructed with diverse scale-free network topologies by dynamic packet traffic simulation and theoretical network analysis. Topological differences of scale-free networks are evaluated by the degree-degree correlations that indicate topological tendency between the degree of a node and that of the nearest neighbors. Our simulation results quantitatively show that the NoC architecture constructed with the topology where hubs mostly connect to lower-degree nodes is found to achieve short latency and low packet loss ratio since it can disperse traffic load and avoid the extreme concentration of load on hubs.

Journal Article↗
PubMed2000

Guiding neutral atoms on a chip

We demonstrate the guiding of neutral atoms by the magnetic fields due to microfabricated current-carrying wires on a chip. Atoms are guided along a magnetic field minimum parallel to and above the current-carrying wires. Two guide configurations are demonstrated: one using two wires with an external magnetic field, and a second using four wires without an external field. These guide geometries can be extended to integrated atom optics circuits, including beam splitters.

Journal Article↗
PubMed2000

Controlling cold atoms using nanofabricated surfaces: atom chips

Atoms can be trapped and guided using nanofabricated wires on surfaces, achieving the scales required by quantum information proposals. These atom chips form the basis for robust and widespread applications of cold atoms ranging from atom optics to fundamental questions in mesoscopic physics, and possibly quantum information systems.

Journal Article↗
PubMed2006

Experimental realization of an on-chip all-optical analogue to electromagnetically induced transparency.

We provide the first experimental observation of structure tuning of the electromagnetically induced transparency-like spectrum in integrated on-chip optical resonator systems. The system consists of coupled silicon ring resonators with 10 microm diameter on silicon, where the coherent interference between the two coupled resonators is tuned. We measured a transparency-resonance mode with a quality factor of 11,800.

Journal Article↗
PubMed2006

Resonator-aided single-atom detection on a microfabricated chip.

We use an optical cavity to detect single atoms magnetically trapped on an atom chip. We implement the detection using both fluorescence into the cavity and atom-induced reduction in cavity transmission. In fluorescence, we register 2.0(2) photon counts per atom, which allows us to detect single atoms with 75% efficiency in 250 micros. In absorption, we measure transmission attenuation of 3.3(3)% per atom, which allows us to count small numbers of atoms with a resolution of about 1 atom.

Journal Article↗
PubMed1994

A custom-chip-based functional electrical stimulation system.

The Functional Electrical Stimulation System consists of a host computer and up to 32 chips connected serially. Up to 256 different monophasic constant voltage (0 V-2.5 V), variable frequency (0 Hz-100 Hz in 2 Hz steps; 100 Hz-1700 Hz in 100 Hz steps), and adjustable duration (50 microseconds-200 ms in 50 microseconds steps) pulse trains can be continuously generated.

Computer Systems↗
PubMed2001

Implantation of silicon chip microphotodiode arrays into the cat subretinal space.

There are currently no therapies to restore vision to patients blinded by photoreceptor degeneration. This project concerns an experimental approach toward a semiconductor-based subretinal prosthetic designed to electrically stimulate the retina. The present study describes surgical techniques for implanting a silicon microphotodiode array in the cat subretinal space and subsequent studies of implant biocompatibility and durability. Using a single-port vitreoretinal approach, implants were placed into the subretinal space of the right eye of normal cats. Implanted retinas were evaluated post-operatively over a 10 to 27 month period using indirect ophthalmoscopy, fundus photography, electroretinography, and histology. Infrared stimulation was used to isolate the electrical response of the implant from that of the normal retina. Although implants continued to generate electrical current in response to light, the amplitude of the implant response decreased gradually due to dissolution of the implant's gold electrode. Electroretinograms recorded from implanted eyes had normal waveforms but were typically 10-15% smaller in amplitude than those in unimplanted left eyes. The nonpermeable silicon disks blocked choroidal nourishment to the retina, producing degeneration of the photoreceptors. The laminar structure of the inner retinal layers was preserved. Retinal areas located away from the implantation site appeared normal in all respects. These results demonstrate that silicon-chip microphotodiode-based implants can be successfully placed into the subretinal space. Gold electrode-based subretinal implants, however, appear to be unsuitable for long-term use due to electrode dissolution and subsequent decreased electrical activity.

Animals↗
PubMed2004

Optic nerve signals in a neuromorphic chip I: Outer and inner retina models.

We present a novel model for the mammalian retina and analyze its behavior. Our outer retina model performs bandpass spatiotemporal filtering. It is comprised of two reciprocally connected resistive grids that model the cone and horizontal cell syncytia. We show analytically that its sensitivity is proportional to the space-constant-ratio of the two grids while its half-max response is set by the local average intensity. Thus, this outer retina model realizes luminance adaptation. Our inner retina model performs high-pass temporal filtering. It features slow negative feedback whose strength is modulated by a locally computed measure of temporal contrast, modeling two kinds of amacrine cells, one narrow-field, the other wide-field. We show analytically that, when the input is spectrally pure, the corner-frequency tracks the input frequency. But when the input is broadband, the corner frequency is proportional to contrast. Thus, this inner retina model realizes temporal frequency adaptation as well as contrast gain control. We present CMOS circuit designs for our retina model in this paper as well. Experimental measurements from the fabricated chip, and validation of our analytical results, are presented in the companion paper [Zaghloul and Boahen (2004)].

Action Potentials↗
PubMed2003

Algorithm to model gene expression on Affymetrix chips without the use of MM cells.

DNA microarrays are powerful tools for quantifying gene expression patterns. However, obtaining reliable estimates of gene expression from raw measurements on microarrays presents several problems due to background contributions, nonspecific probe response, possible variation in probe sensitivities, and possible nonlinear responses of the probes to transcript concentration. In an effort to address the nonspecific response of probes, Affymetrix GeneChip arrays use two probes for each measurement. One of these probes, the mismatch (MM) probe, is intended to reflect the nonspecific response of the corresponding perfect match (PM) probe. However, the reliability of this approach has not been established by published experiments. Indeed, some research has shown that at high transcript concentrations, the nonspecific component of the PM signal is a negligible part of the MM signal. Five variations of a method to model and estimate levels of gene expression on Affymetrix chips, without the use of MM cells, are presented. To test the validity of the algorithms, six different concentrations of human liver cRNA were prepared. Each of these solutions was then hybridized on five Affymetrix hg95A arrays using five different scanners. The expression estimates obtained using each of the five algorithms bore a strong linear relationship to the cRNA concentrations, particularly at low cRNA concentrations. The five variations were applied to a Latin square data set and the results compared with those obtained using Affymetrix MAS 5.0 and using robust multichip analysis. R2 values obtained using the new techniques were comparable, while fold changes were superior.

Algorithms↗
PubMed2006

An analog VLSI chip emulating polarization vision of Octopus retina.

Biological systems provide a wealth of information which form the basis for human-made artificial systems. In this work, the visual system of Octopus is investigated and its polarization sensitivity mimicked. While in actual Octopus retina, polarization vision is mainly based on the orthogonal arrangement of its photoreceptors, our implementation uses a birefringent micropolarizer made of YVO4 and mounted on a CMOS chip with neuromorphic circuitry to process linearly polarized light. Arranged in an 8 x 5 array with two photodiodes per pixel, each consuming typically 10 microW, this circuitry mimics both the functionality of individual Octopus retina cells by computing the state of polarization and the interconnection of these cells through a bias-controllable resistive network.

Algorithms↗
PubMedDate not supplied

Human papillomavirus (HPV) genotyping by HPV DNA chip in cervical cancer and precancerous lesions.

OBJECTIVES: The human papillomavirus (HPV) is a well-known cause of cervical cancer. HPV tests are used as an adjunct test to decrease the false-negative rate of cytological screening. However, attempts are being made to replace the cytological screening with HPV tests. Therefore, this study was performed to examine the possibility of using HPV tests as screening test. MATERIALS AND METHODS: The results of the tests that were performed at the same time including the ThinPrep cytology, the high-risk group hybrid capture II (HC-II) test, the HPV DNA chip (HD-C) test, and a punch biopsy were compared in 400 women who were referred to us due to abnormal cytology or cervicogram. The accuracy of each test was then evaluated, and the type of virus was investigated using a HD-C test. RESULTS: The positive predictive values detected by the high-risk group HC-II test and HD-C test according to the histological diagnosis outcomes were 56.8 and 53.8%, respectively, for cervicitis; 91.5 and 91.5%, respectively, for cervical intraepithelial neoplasia I (CIN I); 88.1% and 81.0%, respectively, for CIN II; 88.6 and 84.2%, respectively, for CIN III, and 92.5 and 88.7%, respectively, for cancer (in 53 patients). The most prevalent types of HPV according to the HPV tests were types 16, 58, 18, and 52 in which type 16 was detected in the more advanced lesions. The sensitivity was 88.4% for the ThinPrep cytology, 89.9% for the HC-II for the high-risk group, and 86.2% for the HD-C test. CONCLUSION: These results suggest the possibility of using the HC-II and HD-C tests as screening tests, which have a similar sensitivity as the ThinPrep cytology. Nonetheless, randomized controlled trials will be needed before the actual application of the HPV tests as screening tests. Despite the fact that the importance of HPV type 16 in cancer development was confirmed, the prevalence of types 58 and 52 were relatively high compared with those found in other studies, showing a need for further studies on this subject. These HPV types need to be considered in vaccine development.

Cytodiagnosis↗
PubMed1994

Digital signal processing chip implementation for detection and analysis of intracardiac electrograms.

The adoption of digital signal processing (DSP) microchips for detection and analysis of electrocardiographic signals offers a means for increased computational speed and the opportunity for design of customized architecture to address real-time requirements. A system using the Motorola 56001 DSP chip has been designed to realize cycle-by-cycle detection (triggering) and waveform analysis using a time-domain template matching technique, correlation waveform analysis (CWA). The system digitally samples an electrocardiographic signal at 1000 Hz, incorporates an adaptive trigger for detection of cardiac events, and classifies each waveform as normal or abnormal. Ten paired sets of single-chamber bipolar intracardiac electrograms (1-500 Hz) were processed with each pair containing a sinus rhythm (SR) passage and a corresponding arrhythmia segment from the same patient. Four of ten paired sets contained intraatrial electrograms that exhibited retrograde atrial conduction during ventricular pacing; the remaining six paired sets of intraventricular electrograms consisted of either ventricular tachycardia (4) or paced ventricular rhythm (2). Of 2,978 depolarizations in the test set, the adaptive trigger failed to detect 6 (99.8% detection sensitivity) and had 11 false triggers (99.6% specificity). Using patient dependent thresholds for CWA to classify waveforms, the program correctly identified 1,175 of 1,197 (98.2% specificity) sinus rhythm depolarizations and 1,771 of 1,781 (99.4% sensitivity) abnormal depolarizations. From the results, the algorithm appears to hold potential for applications such as real-time monitoring of electrophysiology studies or detection and classification of tachycardias in implantable antitachycardia devices.

Algorithms↗
PubMed2005

Surface plasmon resonance imaging-based protein array chip system for monitoring a hexahistidine-tagged protein during expression and purification.

A surface plasmon resonance imaging-based Ni(2+)-iminodiacetic acid-coated gold chip system was developed to enable specific detection of a hexahistidine-tagged recombinant protein in crude extracts or in column chromatography fractions. This system is especially advantageous for high-throughput analysis of multiple proteins.

Escherichia coli↗
PubMed2001

Antimicrobial resistance and bacterial identification utilizing a microelectronic chip array.

Species-specific bacterial identification of clinical specimens is often limited to a few species due to the difficulty of performing multiplex reactions. In addition, discrimination of amplicons is time-consuming and laborious, consisting of gel electrophoresis, probe hybridization, or sequencing technology. In order to simplify the process of bacterial identification, we combined anchored in situ amplification on a microelectronic chip array with discrimination and detection on the same platform. Here, we describe the simultaneous amplification and discrimination of six gene sequences which are representative of different bacterial identification assays: Escherichia coli gyrA, Salmonella gyrA, Campylobacter gyrA, E. coli parC, Staphylococcus mecA, and Chlamydia cryptic plasmid. The assay can detect both plasmid and transposon genes and can also discriminate strains carrying antibiotic resistance single-nucleotide polymorphism mutations. Finally, the assay is similarly capable of discriminating between bacterial species through reporter-specific discrimination and allele-specific amplification. Anchored strand displacement amplification allows multiplex amplification and complex genotype discrimination on the same platform. This assay simplifies the bacterial identification process greatly, allowing molecular biology techniques to be performed with minimal processing of samples and practical experience.

Anti-Bacterial Agents↗
PubMed2004

Multiplex detection of mutations in clinical isolates of rifampin-resistant Mycobacterium tuberculosis by short oligonucleotide ligation assay on DNA chips.

A new approach, short-oligonucleotide-ligation assay on DNA chip (SOLAC), is developed to detect mutations in rifampin-resistant Mycobacterium tuberculosis. The method needs only four common probes to detect 15 mutational variants of the rpoB gene within 12 h. Fifty-five rifampin-resistant M. tuberculosis isolates were analyzed, resulting in 87.3% accuracy and 83.6% concordance relative to DNA sequencing.

Antibiotics, Antitubercular↗
PubMed2000

Frozen chips: an unusual cause of severe frostbite injury.

A case of severe frostbite injury to the right foot is presented. This was caused by the inappropriate application of a bag of frozen chips to the foot in an attempt to ease non-specific pain. No specific acute traumatic injury was identified. As the patient was a teacher of physical education, the pain had initially been assumed to originate from a minor musculoskeletal injury. Full recovery ensued after surgical excision of necrotic tissue and split skin grafting. The danger of inappropriate overenthusiastic use of ice packs or other frozen material to treat soft tissue injuries is emphasised. The need for education to prevent similar future injuries is discussed.

Adult↗