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排序方式: 共有425条查询结果,搜索用时 15 毫秒
31.
E.?Keshavarzi M.?Vahedpour S.?AlaviEmail author B.?Najafi 《International Journal of Thermophysics》2004,25(6):1747-1762
The high-frequency shear modulus, G, and shear relaxation time, shear, are obtained using the Zwanzig–Mountain equation for soft-sphere and Lennard-Jones potentials. The Hansen and Weis soft-sphere radial distribution function and the Matteoli–Mansoori Lennard-Jones radial distribution function are used in the equation. The shear relaxation times of different isotherms for both of these fluids pass through a minimum at a reduced density of about 0.7, which indicates a change from fluid-like behavior to viscoelastic behavior. The origins of this common density point are discussed. It is also shown that for the Lennard-Jones fluid, if the ratio of the reduced relaxation time to a power of the reduced temperature is plotted as a function of the reduced density, all isotherms become superimposed on a single curve. 相似文献
32.
This paper presents a low-power low-noise fully integrated bandpass operational amplifier for a variety of biomedical neural recording applications. A standard two-stage CMOS amplifier in a closed-loop resistive feedback configuration provides a stable ac gain of 39.3 dB at 1 kHz. A subthreshold PMOS input transistor is utilized to clamp the large and random dc open circuit potentials that normally exist at the electrode-electrolyte interface. The low cutoff frequency of the amplifier is programmable up to 50 Hz, while its high cutoff frequency is measured to be 9.1 kHz. The tolerable dc input range is measured to be at least +/- 0.25 V with a dc rejection factor of at least 29 dB. The amplifier occupies 0.107 mm2 in die area, and dissipates 115 microW from a 3 V power supply. The total measured input-referred noise voltage in the frequency range of 0.1-10 kHz is 7.8 microVrms. It is fabricated using AMI 1.5 microm double-poly double-metal n-well CMOS process. This paper presents full characterization of the dc, ac, and noise performance of this amplifier through in vitro measurements in saline using two different neural recording electrodes. 相似文献
33.
M. Taghizadeh F. Najafi A. Ghaffari 《Electrical Engineering (Archiv fur Elektrotechnik)》2009,91(2):79-87
In this article, to increase the tracking ability of pulse width modulation (PWM)-driven pneumatic servo systems, the pneumatic
circuit is modified such that an identical PWM signal is demanded by both fast switching valves. As a result, the problem
of allocating different duty cycles to the valves is vanished, due to the synchronized pulsing inputs. A simple PWM algorithm
is applied to compensate the dead zones in the relation between the duty cycle input and the valve flow output. An experimental
investigation is carried out to indicate the capabilities of the proposed circuit. Closed-loop tests are implemented and high
tracking performance for frequencies up to 5Hz are obtained, whereas experiments with frequencies up to 1Hz were reported
in previous studies. In similar conditions of load and cylinder size, experiments of the proposed circuit indicate acceptable
results with simple PD controller, compared with the more complicated controllers and circuits of previous studies. 相似文献
34.
Solid-State Electrodes for Multichannel Multiplexed Intracortical Neuronal Recording 总被引:1,自引:0,他引:1
BeMent Spencer L. Wise Kensall D. Anderson David J. Najafi Khalil Drake Kenneth L. 《IEEE transactions on bio-medical engineering》1986,(2):230-241
Thin-film arrays of extracellular recording electrodes have been developed for use in studies of information processing in neural structures and eventual use in closed-loop control of neural prostheses. These probes consist of a silicon substrate which supports an array of thin-film conductors. The conductors are insulated above and below with deposited dielectrics. The electrode sites are defined by openings in the upper dielectric layer and are inlaid with gold to form low-impedance recording surfaces. The probes are typically 15 pim in thickness with shank widths as narrow as 20 ?m. The probe fabrication process is compatible with the inclusion of signal processing circuitry directly on the probe substrate. A 12 channel on-chip signal processor design with per-channel gain of 100, bandwidth of 100 Hz-6 kHz, multiplexed output, and recording-site impedance check capability is described. The probes have adequate strength to penetrate the gerbil pia-arachnoid layer and have recorded single neuron activity of over 500 ?V peak-to-peak from tip, side, and mid-carrier sites. Signal-to-noise ratios as high as 10:1 have been achieved. An equivalent circuit model for the conducting leads, the recording site, and the electrode-electrolyte interface is described. Development of biocompatible insulation and encapsulation materials for long-term implantation of active probes is underway. 相似文献
35.
This paper describes the design and implementation of fully integrated rectifiers in BiCMOS and standard CMOS technologies for rectifying an externally generated RF carrier signal in inductively powered wireless devices, such as biomedical implants, radio-frequency identification (RFID) tags, and smartcards to generate an on-chip dc supply. Various full-wave rectifier topologies and low-power circuit design techniques are employed to decrease substrate leakage current and parasitic components, reduce the possibility of latch-up, and improve power transmission efficiency and high-frequency performance of the rectifier block. These circuits are used in wireless neural stimulating microsystems, fabricated in two processes: the University of Michigan's 3-/spl mu/m 1M/2P N-epi BiCMOS, and the AMI 1.5-/spl mu/m 2M/2P N-well standard CMOS. The rectifier areas are 0.12-0.48 mm/sup 2/ in the above processes and they are capable of delivering >25mW from a receiver coil to the implant circuitry. The performance of these integrated rectifiers has been tested and compared, using carrier signals in 0.1-10-MHz range. 相似文献
36.
37.
Kinetic study of styrene atom transfer radical polymerization from hydroxyl groups of graphene nanoplatelets: Heterogeneities in chains and graft densities
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Hossein Roghani‐Mamaqani Vahid Haddadi‐Asl Khezrollah Khezri Mehdi Salami‐Kalajahi Mohammad Najafi 《Polymer Engineering and Science》2015,55(8):1720-1732
Confinement effect of graphene nanoplatelets on the kinetics of styrene atom transfer radical polymerization was studied by a “grafting from” reaction. Graphene oxide was modified by different amounts of (3‐aminopropyl) triethoxysilane and then alpha‐bromoisobutyryl bromide from the hydroxyl groups. Polymerization of styrene in the presence of modified graphene and free initiator, ethyl alpha‐bromoisobutyrate, was accomplished at 110°C. Then, effect of various graft densities and different graphene loadings on the heterogeneous graft and free polystyrene chains characteristics and also kinetics of polymerization was studied by gas and gel permeation chromatographies. Efficiency of grafting reactions along with the graft contents was studied by X‐ray photoelectron spectroscopy, elemental analysis, and thermogravimetric analysis. Confinement effects of graphene on the relaxation behavior of polystyrene chains and also morphology of the graphenes were studied by differential scanning calorimetry and transmission electron microscopy, respectively. POLYM. ENG. SCI., 55:1720–1732, 2015. © 2014 Society of Plastics Engineers 相似文献
38.
The effects of saccharin concentration and pulsating peak current density on corrosion behaviour, surface brightness and surface
roughness of nanocrystalline nickel coatings were investigated and the results were compared with those of the conventional
decorative chromium coatings. The average grain size of nanocrystalline nickel coatings was determined using X-ray diffraction
patterns. Corrosion behaviour was evaluated using electrochemical impedance spectroscopy (EIS) in a 0.6 M sodium chloride
solution. A gloss meter and a Suftest device were used to evaluate surface brightness and roughness. Corrosion resistance
and brightness of the nanocrystalline nickel coatings increased with increasing the saccharin concentration in the bath. Moreover,
brighter nanocrystalline nickel coatings were obtained with increasing the peak current density. In addition, all nanocrystalline
nickel coatings were more corrosion resistant than chromium coatings. Those nanocrystalline nickel coatings with average grain
sizes of less than 38 nm were brighter and had smoother surfaces than conventional decorative chromium coatings. 相似文献
39.
Ji J. Cho S.T. Zhang Y. Najafi K. Wise K.D. 《Electron Devices, IEEE Transactions on》1992,39(10):2260-2267
A multiplexed ultraminiature pressure sensor designed for use in a cardiovascular catheter is described. The sensor operates from only two loads, which are shared by two sensors per catheter. The sensing chip is 350 μm wide by 1.4 mm long by 100 μm thick. CMOS readout circuitry at the sensing site converts applied pressure to a frequency variation in the supply current, which is detected at the end of the catheter by a microprocessor-controlled interface. The nominal pressure sensitivity is 2 kHz/fF about a zero-pressure output frequency of 2.7 MHz. This on-site circuitry contains two reference capacitors which allow external compensation for nonlinearity and temperature sensitivity and has an idle-state power dissipation of less than 50 μW. With the transducer sealed at ambient pressure, the device can resolve pressure variations of about 3 mmHg, while vacuum-sealed devices do considerably better and should permit <2 mmHg resolution in practical systems 相似文献
40.
Scaling limitations of silicon multichannel recording probes 总被引:1,自引:0,他引:1
This paper describes the scaling limitations of multichannel recording probes fabricated for use in neurophysiology using silicon integrated circuit technologies. Scaled silicon probe substrates 8 microns thick and 16 microns wide can be fabricated using boron etch-stop techniques. Theoretical expressions for calculating the thickness and width of silicon substrates have been derived and agree closely with experimental results. The effects of scaling probe dimensions on its strength and stiffness are described. The probe shank dimensions can be designed to vary the strength and stiffness for different applications. The scaled silicon substrates have a fracture stress of about 2 x 10(10) dyn/cm2, which is about six times that of bulk silicon, and are strong and very flexible. Scaling the feature sizes of recording electrode arrays down to 1 micron is possible with less than 1 percent electrical crosstalk between channels. 相似文献