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N S Xu

Publications and source records attributed to N S Xu.

At least 19 recordsLinked to original sources
PubMed2001

Characterization of a high voltage flat panel display unit using nanotube-based emitters.

Details are given of an experimental investigation carried out to study the field electron emission characteristics of a field emission flat panel display unit using a carbon nanotube-epoxy composite as electron emission material. These include: (i) dependence of direct emission current-voltage characteristic on vacuum gap spacing, (ii) the variation of the proportion of emission current passing through an aperture hole of a gate electrode with changing structural parameters of the device, and (iii) the uniformity and display characteristics of a typical display unit. Our findings indicate that it is very likely for one to produce a near-market prototype high voltage field emission flat panel display, if more sophisticated fabrication and assembly technique is adapted.

Journal Article↗
PubMed2001

Microfabrication and characterization of gated amorphous diamond-based field emission electron sources.

Gated field emission electron sources of amorphous diamond (a-D) coated Si tips and a-D diodes on a rough Si substrate were studied, detailing the deposition and characterization of the thin film, the fabrication processes and the emission behavior of the electron sources. Mechanisms responsible for the emission process of the a-D coated devices are proposed. A comparison of the field emission performance of the two types of devices is presented. In addition, future improvements of the a-D diode on a rough Si cathode are discussed.

Journal Article↗
PubMed2001

Study of field electron emission spectral characteristics of amorphous carbon-nitride film.

The study of field electron energy spectra from amorphous carbon-nitride (a-CN) films is essential to understand the mechanism of field emission from this promising material. In this work, the electron energy spectrum is studied by measuring the distribution of electron field emitted from individual emitting sites. The spectra are recorded at different electrical fields. It is found that the peak shift as well as the half-width increase with increasing applied fields. Furthermore, multi-peak features are observed at the low-energy side of the spectra. It is assumed that these peaks might originate from the interband states of a-CN film. We propose that although the emission mainly originates from current injection into conduction band of a-CN film, the electrons may also be emitted from interband states.

Journal Article↗
PubMed2001

Study of the frequency response of the thin film cold cathode electron source of a lighting element.

Details of the recent experimental and theoretical studies of the frequency characteristic of the field emission electron source of a lighting element are given. The response times at different frequencies (0.02-200 kHz) and applied gap fields, acting on cathode surface, have been studied. A correlation has been found to exist between the response time and the frequency of applied voltage pulse. The response time remains almost constant within a range of frequencies between 1 and 30 kHz, and it remains nearly constant with increasing applied gap field higher than the threshold field. Finally, the cutoff frequency of the electron source is found, and with the current design of the electron source, it can be as high as 40 kHz. An equivalent circuit model is proposed, and theoretical results based on this model agree well with experimental findings.

Journal Article↗
PubMed1999

Endomorphin-1 and endomorphin-2, endogenous ligands for the mu-opioid receptor, inhibit electrical activity of rat rostral ventrolateral medulla neurons in vitro.

The classic opioid peptide, enkephalin, and the novel member of the opioid family, nociceptin/orphanin FQ, inhibit the spontaneous electrical activity of neurons recorded from the rostral ventrolateral medulla, presumably cardiovascular neurons. In this study, the putative effects of endomorphin-1 and endomorphin-2, the newly discovered endogenous ligands for the micro-opioid receptor, on the electrical activity of rostral ventrolateral medulla neurons were investigated in rat brain slices in vitro. Like enkephalin and nociceptin, perfusion of endomorphin-1 or endomorphin-2 profoundly inhibited spontaneous discharges of 43% and 38% of the medullary neurons, respectively. No excitatory response to perfusion of either endomorphin was found in all neurons surveyed. Both endomorphins produced concentration-dependent inhibition. However, endomorphin-1 was more potent than endomorphin-2 for production of the inhibition, as demonstrated by the greater and longer suppression induced by endomorphin-1 than that induced by endomorphin-2 at the same concentration. Among the four opioid agonists tested, EC50 values (in nM) were 3.17 (endomorphin-1), 3.02 (nociceptin), 10.1 (endomorphin-2) and 150.0 (enkephalin). The non-selective opioid receptor antagonist, naloxone, blocked the inhibitory responses of the neurons to endomorphin-1, endomorphin-2 and enkephalin, but not to nociceptin. The selective mu antagonist, beta-funaltrexamine, prevented the neuronal inhibition induced by endomorphins, but not by enkephalin and nociceptin. Neither naloxone nor beta-funaltrexamine alone had a significant effect on the firing rate of the neurons. These results demonstrate that endomorphin-1 and, to a lesser extent, endomorphin-2 exert an inhibitory modulation of the electrical activity of rostral ventrolateral medulla neurons, which is mediated through the stimulation of mu-opioid receptors.

Animals↗
PubMed1998

Inhibitory effect of GABA on firing activity of rostral ventrolateral medullary neurons of rat in vitro.

Extracellular single-unit discharges were obtained from 106 spontaneously active neurons in the region of the rostral ventrolateral medulla (RVLM) by glass microelectrode from 73 brain alices of Sprague-Dawley rats. Exogenous gamma-aminobutyric acid (GABA, 0.1-3.0 mmol/L) inhibited the electrical activity of 84 out of 106 RVLM neurons dose-dependently. The inhibitory effect of GABA could be blocked by GABAA receptor antagonist bicuculline methiodide (BMI) and Cl- channel blocker picrotoxin (PTX). When perfused with BMI or PTX alone, the firing rates of most of the RVLM neurons were significantly increased. In 41 neurons responding to GABA, baclofen (0.1-3.0 mumol/L), a GABAB receptor selective agonist, inhibited the discharges of 33 of the neurons dose-dependently. GABAB receptor antagonist CGP35348 (n = 13) blocked the inhibition due to baclofen (n = 21). After perfused with CGP35348 alone, the firing rates of most of the RVLM neurons were significantly increased. Taken together, the inhibition of GABA on RVLM neurons is mediated through either GABAA or GABAB receptors and some intrinsic GABA neurons exert tonic inhibition activity.

Animals↗
PubMed1997

[Effects of ACh on the electric activity of rostral ventrolateral medullary neurons of rat in vitro].

Extracellular single-unit discharges were obtained from 165 spontaneously active neurons within the region of the rostral ventrolateral medulla (RVLM) by glass microelectrode from 89 brain slices of the Sprague-Dawley rats. The units could be divided into three types: regular (61.8%), irregular (24.2%) and silent (14%). Acetylcholine (ACh, 0.1, 0.3 mumol/L) showed four kinds of effects on spontaneous discharges of RVLM neurons: excitatory, inhibitory, biphasic and non-responsive, counting respectively 41.8%, 20%, 3% and 35.2% of the neurons tested. The excitatory effect of ACh was dose-dependent. The effects, either excitatory or inhibitory, of ACh (n = 49) were mostly blocked by atropine (0.3 mumol/L, n = 42). The excitatory effect of ACh (n = 14) could be blocked mainly by selective antagonist of M1 receptor, pirenzepine (PZ, 30 nmol/L, n = 9), but not by selective antagonist of M2 receptor, methoctramine (MT) and AFDX-116. The inhibitory effect of ACh (n = 10) could be blocked mostly by M2 receptor antagonist MT (30 nmol/L, n = 7); and this inhibitory effect (n = 9) could be blocked mostly by another M2 receptor antagonist AFDX-116 (30 nmol/L, n = 6), but not by M1 receptor antagonist PZ.

Acetylcholine↗
PubMed1993

N-terminal arginylation of proteins in explants of injured sciatic nerves and embryonic brains of rats.

Posttranslational modification of proteins by arginine and lysine has been demonstrated in crude extracts of vertebrate nerves and brain but not in intact cells. In the present experiments we have exploited the fact that Arg is added posttranslationally only at the N-terminus of target proteins, to demonstrate these reactions in intact cells of sciatic nerves and embryonic brains of rats. Sciatic nerves were crushed in anaesthesized rats and 2 hrs later segments of nerve, including the site of the crush, were removed and incubated in media containing [3H]Arg. Incorporation of [3H]Arg into total proteins was analyzed by acid precipitation and the presence of label at the N-terminus was determined by a modification of the Edman degradation procedure. Approximately 25% of protein bound [3H]Arg was released from the N-terminus by the Edman reaction indicating that it was added posttranslationally rather than through protein synthesis. N-terminal labeling was not detectable in nerves not crushed prior to explant and incubation. Slices of embryonic day 20 visual cortex, when incubated under similar conditions as injured sciatic nerves, also showed approximately 25% of the protein incorporated [3H]Arg at the N-terminus, while arginylation was not detectable in adult rat brain slices. Since Lys is not added posttranslationally to the N-terminus, we have attempted to observe lysylation of proteins in intact cells by using cycloheximide (Cx) to block protein synthesis without interfering with protein modification. The posttranslational incorporation of Arg/Lys into proteins was found to be insensitive to up to 2.0 mM Cx in tissue extracts (in vitro).(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1993

[Inhibitory effect of diazepam or flurazepam on pressor response induced by the stimulation of midbrain in the rabbit].

Experiments were performed on 32 rabbits anaesthetized with alpha-chloralose and urethane, paralyzed with flaxidil and artificially ventilated. The pressor response was elicited by stimulation of dorsal part of midbrain periaqueductal gray (dPAG). Intravenous injection of diazepam (2 mg/kg) or intracerebroventricular application of flurazepam (2 mg/50 microliters) resulted in attenuation of the pressor response induced by the stimulation of midbrain. Bilateral microinjection of flurazepam (100 micrograms in 0.25 microliter) into rostral ventrolateral medulla (rVLM) depressed the pressor response to midbrain stimulation. Microinjection of flurazepam of the same dosage into caudal ventrolateral medulla (cVLM), however, had no depressant effect. Pretreatment with bicuculline in rVLM prevented the inhibitory effect of flurazepam on the pressor response. These results mentioned above suggest that diazepam or flurazepam inhibits the pressor response evoked by midbrain stimulation, and the effect may be mediated by the activation of the GABAA receptor in rVLM.

Animals↗
PubMed1989

[Mechanism of depressing effect of diazepam on the blood pressure and on ventricular extrasystoles induced by hypothalamic stimulation in the rabbit].

Experiments were carried out on 62 rabbits anesthetized with urethane and chloralose and immobilized with gallamine triethiodide under artificial ventilation. Ventricular extrasystoles were induced by electrical stimulation of the hypothalamic defence area (HVE). Following intravenous administration of diazepam (0.5 mg/kg), the pressor response and HVE induced by electrical stimulation of the hypothalamus were attenuated, as blood pressure (BP) dropped. Bilateral microinjection of flurazepam (200 micrograms in 0.5 microliters) or GABA (3 micrograms in 0.5 microliters) into the rostral ventrolateral medulla (rVLM) resulted in a significant decrease in BP, and pressor response during hypothalamic stimulation as well as reduction in the amount of HVE. Bilateral microinjection of picrotoxin (7.5 micrograms in 0.5 microliters) into the rVLM facilitated HVE and increased BP. Microinjection of flurazepam, GABA of the same doses into the caudal ventrolateral medulla (cVLM), however, had no such effect. The depressant effect of intravenous injection of diazepam could be prevented by bilateral microinjection of GABA receptor antagonist bicuculline (3 micrograms in 0.5 microliters) or picrotoxin (7.5 micrograms in 0.5 microliters) into the rVLM. Whereas bilateral microinjection of atropine (0.25 micrograms in 0.5 microliters), scopolamine (0.15 micrograms in 0.5 microliters), naloxone (0.5 micrograms in 0.5 microliters), strychnine (1 microgram in 0.5 microliters) into the rVLM no depressant effect was observed. These results suggest that the depressant effect of diazepam on BP, the pressor response and HVE may be mediated by activation of the GABA receptors in the rVLM.

Animals↗
PubMed1989

[Effects of microiontophoretically applied flurazepam on the respiratory units in the region of the nucleus parabrachialis of the rabbit].

Experiments were carried out on 36 urethane-chloralose aneasthesized, paralyzed, vagotomized and artificially ventilated rabbits. Five-barrel glass micropipettes were used to record unit discharges and to apply flurazepam iontophoretically in the region of the nucleus parabrachialis. Inspiratory units (IUs), expiratory units (EUs), phase-spanning units (I-EUs and E-IUs) and non-respiratory units (NRUs) were observed. 26 (55.3%) out of 47 IUs, 17 (94.4%) out of 18 EUs, 11 (91.7%) out of 12 I-EUs, 2 (18.1%) out of 11 E-IUs and 43 (60.6%) out of 71 NRUs were depressed by flurazepam. The depressant ratio of EUs and I-EUs was statistically different from that of IUs and E-IUs respectively. In flurazepam sensitive 5 IUs and 2 EUs, the depressant effect could not be antagonized by GABA-A receptor antagonist bicuculline. In 10 flurazepam sensitive NRUs, there were 6 (60%) units whose depressant effect of flurazepam could be antagonized by bicuculline. In addition, the effects of acetylcholine (ACh) on the respiratory units and NRUs were examined, 15 (75%) out of 20 IUs were excited and the remaining units were not influenced. The effects of ACh on the EUs, I-EUs and E-IUs were variable, but the effects of ACh on the NRUs were mainly excitatory. In 5 IUs and 1 phase-spanning respiratory units, the depressant effect of flurazepam could not be antagonized by ACh. The results showed that flurazepam mainly depressed the EUs and I-EUs in the region of nucleus parabrachialis, thus interfering with the normal phase transition between the inspiratory and expiratory phase and reducing the respiratory rate.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMedDate not supplied

Resonant field emission through amorphous diamond thin films (a model study).

A model for field emission through an amorphous diamond thin film with defects is constructed. Theoretical study shows that the emission is enhanced by attractive defects which would make the resonant emission observable for films with thickness of about 10nm. The emitted current density in typical parameters is calculated as functions of thickness, field strength and defect density. The energy distribution of emitted electrons is attained.

Journal Article↗
PubMedDate not supplied

A cold cathode lighting element prototype.

In this study, we present a prototype of lighting element in which a carbon-containing field emission material is used as the cathode. The operating characteristics, i.e. current-voltage characteristics, current stability, luminance and lifetime of the lighting element are tested. By applying high-voltage phosphor, a maximum brightness of 10000cd/m(2) has been recorded and a lighting element under lifetime test has been operating in DC driving mode for over 2500h without decay in emission current and brightness. These results imply that the prototype lighting element is suitable for commercial application.

Journal Article↗
PubMedDate not supplied

Effect of carbon nanotube structural parameters on field emission properties.

Experimental studies were devoted to the effect of structural parameters, i.e., tube diameter and density, on the field electron emission characteristics of carbon nanotubes. Thermal chemical vapor deposition system was employed to synthesize carbon nanotubes. Nanotubes with different diameters and densities were obtained by adjusting the thickness of the iron (Fe) catalyst film. The morphologies of the Fe and carbon nanotube film were characterized by scanning electron microscopy respectively. Further field emission measurement confirmed that the tube diameter and density could significantly affect the electron emission properties of the carbon nanotube. Possible physical reasons for the effect are discussed.

Journal Article↗