uhe Li

Salivary gland neoplasms in oral and maxillofacial regions: a 23-year retrospective study of 6982 cases in an eastern Chinese population

There is little information in the English-language literature about the epidemiology of salivary gland neoplasms in the eastern Chinese population. A large retrospective study (6982 primary salivary tumors during 23 years) was carried out to investigate the clinicopathological features (tumor location, patient sex and age) of these tumors in this population. 3593 tumors were in males and 3389 in females. Pleomorphic adenoma (69%) was the most common tumor and 20% were located in minor glands. 92% of Warthins tumors occurred in males. Malignant tumors were predominantly adenoid cystic carcinoma (30%) and mucoepidermoid carcinoma (30%). Incidences of lymphoepithelial carcinomas (5%) and polymorphous low-grade adenocarcinoma (1%) of malignant tumors were identified. 28% of tumors originated from minor glands. Most findings were similar to those in the literature, with some variations. The salivary tumors slightly predominated in males. Relatively higher incidences of minor gland tumors and specifically of pleomorphic adenoma in minor glands were noted. Adenoid cystic carcinoma and mucoepidermoid carcinoma constituted the most common malignancies. There was a high incidence of lymphoepithelial carcinomas but a low incidence of polymorphous low-grade adenocarcinoma. The historical significant male predominance of Warthins tumor was confirmed.

Contributions of the vestibular nucleus and vestibulospinal tract to the startle reflex

The startle reflex is elicited by strong and sudden acoustic, vestibular or trigeminal stimuli. The caudal pontine reticular nucleus, which mediates acoustic startle via the reticulospinal tract, receives further anatomical connections from vestibular and trigeminal nuclei, and can be activated by vestibular and tactile stimuli, suggesting that this pontine reticular structure could mediate vestibular and trigeminal startle. The vestibular nucleus, however, also projects to the spinal cord directly via the vestibulospinal tracts, and therefore may mediate vestibular startle via additional faster routes without a synaptic relay in the hindbrain. In the present study, the timing properties of the vestibular efferent pathways mediating startle-like responses were examined in rats using electrical stimulation techniques. Transient single- or twin-pulse electrical stimulation of the vestibular nucleus evoked bilateral, startle-like responses with short refractory periods. In chloral hydrate-anesthetized rats, hindlimb electromyogram latencies recorded from the anterior biceps femoris muscle were shorter than those for stimulation of the trigeminal nucleus, and similar to those for stimulation of the caudal pontine reticular nucleus or ventromedial medulla. In awake rats, combining vestibular nucleus stimulation with either acoustic stimulation or trigeminal nucleus stimulation enhanced the whole-body startle-like responses and led to strong cross-modal summation without collision effects. In both chloral hydrate-anesthetized and awake rats, combining vestibular nucleus stimulation with ventromedial medulla stimulation produced a symmetrical collision effect, i.e. a loss of summation at the same positive and negative stimulus intervals, indicating a continuous connection between the vestibular nucleus and ventromedial medulla in mediating vestibular startle. By contrast, combining trigeminal nucleus stimulation with ventromedial medulla stimulation resulted in an asymmetric collision effect when the trigeminal nucleus stimulation preceded ventromedial medulla stimulation by 0.5 ms, suggesting that a monosynaptic connection between the trigeminal nucleus and ventromedial medulla mediates trigeminal startle. We propose that the vestibulospinal tracts participate strongly in mediating startle produced by activation of the vestibular nucleus. The convergence of the vestibulospinal tracts with the reticulospinal tract within the spinal cord therefore provides the neural basis of cross-modal summation of startling stimuli.

Hybrid evaporation: Glow discharge source for plasma immersion ion implantation

In order to achieve stable operation for elements with a low melting point or high vapor pressure, a quasiequilibrium evaporation–glow discharge evaporation source has been designed and investigated for plasma immersion ion implantation. The important relationship between the pressure in the evaporation chamber and the implantation chamber is studied for optimal performance. Our experimental results show that the hybrid evaporation–glow discharge source is an effective method to produce ions from materials with low melting point and high vapor pressure.

Experimental investigation of hybrid-evaporation-glow discharge plasma immersion ion implantation

High-voltage pulsed glow discharge is applied to plasma immersion ion implantation (PIII). In the glow discharge, the target constitutes the cathode and the gas tube forms the anode under a relatively high working gas pressure of 0.15–0.2Pa. The characteristics of the glow discharge and ion density are measured experimentally. Our results show resemblance to hollow-anode glow discharge and the anode fall is faster than that of general glow discharge. Because of electron focusing in the anode tube orifice, ions are ionized efficiently and most of them impact the negatively biased samples. The resulting ion current density is higher than that in other PIII modes and possible mechanisms of the glow discharge PIII are proposed and discussed.High-voltage pulsed glow discharge is applied to plasma immersion ion implantation (PIII). In the glow discharge, the target constitutes the cathode and the gas tube forms the anode under a relatively high working gas pressure of 0.15–0.2Pa. The characteristics of the glow discharge and ion density are measured experimentally. Our results show resemblance to hollow-anode glow discharge and the anode fall is faster than that of general glow discharge. Because of electron focusing in the anode tube orifice, ions are ionized efficiently and most of them impact the negatively biased samples. The resulting ion current density is higher than that in other PIII modes and possible mechanisms of the glow discharge PIII are proposed and discussed.

Influence of weld mis-matching on fatigue crack growth behaviors of electron beam welded joints

The influences of weld mis-match effects on fatigue crack growth (FCG) rate and crack path deviation (CPD) were studied by virtue of fatigue crack growth experiment of Ni-base superalloy electron beam welded (EBW) joints. The results show that the fatigue crack growth of electron beam welded joints is instable due to the influence of mechanical heterogeneities. The fatigue crack located in the weld metal of overmatched joints deviated from its original growth direction, and then spanned the welded seam and base metal in a mixed mode while propagating. Owing to the crack deviation at the weld metal and heat-affected-zone (HAZ), the effective growth driving force at the tip of fatigue crack was reduced with the reduction of the effective stress intensity factor (SIF) which finally causes fatigue crack rate decrease. As a result, the overmatched joints have the capacity of protecting fatigue crack joints from fast growth. Fatigue crack was strongly affected by size and the symmetrical characteristics of the plastic zone at the crack tip, thus the integrity of the welded structure containing the fatigue crack mainly depended on the toughness of the low strength zone.

Growth and nucleation of diamond-like carbon (DLC) film on aluminum

Diamond-like carbon (DLC) films were deposited on aluminum substrate using vacuum arc deposition (VAD) and plasma immersion ion implantation – deposition (PIII-D). Even though Raman and XPS results show that the carbon films deposited by VAD and PIII-D both possess DLC structures, atomic force microscopy (AFM) reveals that the two sets of films have very different surface morphologies. The growth mechanisms in these two techniques thus differ and the different nucleation and growth mechanisms of the DLC films deposited by VAD and PIII-D can be explained using the statistical formation theory. Growth models for VAD and PIII-D DLC films are proposed. 2003 Elsevier Science B.V. All rights reserved.

Perceived target-masker separation unmasks responses of lateral amygdala to the emotionally conditioned target sounds in awake rats

In a (simulated) reverberant environment, both human listeners and laboratory rats are able to perceptually integrate the direct wave of a sound source with the reflections of the source, leading to a fused image as coming from the location around the source (the precedence effect). This perceptual grouping effect produces perceived spatial separation between sound sources and facilitates selective attention to the target source. However, the neural correlates of the unmasking effects of perceived spatial separation have not been reported in the literature. The lateral nucleus of the amygdala (LA) is critical for processing ecologically salient sensory signals (e.g., threatening sounds) and mediating auditory fear conditioning. LA neuronal responses to a sound increase if the sound is fear conditioned. This study investigated whether in awake rats the perceptual fusion-induced separation between a fear-conditioned target sound and a noise masker enhances LA responses to the target. The results show that frequency-following responses (FFRs, i.e., sustained potentials based on phase-locked firing of neuron populations to periodical sound waveforms) recorded in the LA to a tone-complex, which was masked by a wideband noise, were enhanced after the tone-complex became fear conditioned. More importantly, the fear-conditioned tone-complex, but not the pseudo-conditioned tone-complex, elicited further larger LA FFRs when it was perceived as separated from the masker than when it was perceived as co-located with the masker. The results suggest that in the LA there exists a neural correlate of selective attention to ecologically significant sounds with a high degree of stimulus specificity.

Metabotropic glutamate receptors subtype 5 are necessary for the enhancement of auditory evoked potentials in the lateral nucleus of the amygdala by tetanic stimulation of the auditory thalamus

The lateral nucleus of the amygdala (LA) receives axonal projections from the auditory thalamus, the medial geniculate nucleus (MGN), and mediates auditory fear conditioning. Tetanic electrical stimulation of the MGN can induce long-term potentiation of acoustically-evoked responses (AEPs) recorded in the LA of anesthetized rats. The present study investigated the temporal development of tetanus-induced AEP potentiation recorded in the LA of anesthetized rats during the recording time up to 120 min after tetanization. In addition, the present study investigated whether the artificially-induced AEP potentiation is mediated by the metabotropic glutamate receptors subtype 5 (mGluR5). The results show that AEPs recorded in the LA to a broadband-noise burst were significantly enhanced immediately after tetanic but not low-frequency stimulation of the MGN. The AEP potentiation was well retained up to 120 min after tetanization. High-dose (1.5 microg/4 microl) microinjection of the selective antagonist of mGluR5, 2-methyl-6-(phenylethynyl)-pyridine (MPEP), into the ipsilateral lateral ventricle 30 min before tetanization completely blocked the AEP potentiation without affecting the baseline AEP. Low-dose (0.5 microg/4 microl) microinjection partially suppressed the AEP potentiation. When the high-dose MPEP was injected 40 min after tetanization, the AEP potentiation was not affected. These results indicate that in anesthetized rats mGluR5 receptors are necessary for the induction or early maintenance (40 min) of AEP potentiation in the LA by tetanic stimulation of the MGN.

Investigation of plasma distribution in electron-focused electric field enhanced glow discharge plasma immersion ion implantation

In enhanced glow discharge plasma immersion ion implantation (EGDPIII) that involves a small pointed anode and large area tabular cathode, the high negative substrate bias not only acts as the plasma producer but also supplies the implantation voltage. Consequently, an electric field is created to focus the electrons and the electron-focusing field enhances the glow discharge process. In this work, the plasma distribution is measured using a Langmuir probe to obtain the plasma density. Numerical interpolation is performed to obtain the plasma density distribution throughout the entire discharge region. The effects of different distances between the anode and cathode on the glow discharge characteristics and the influence of the plasma electron density are also evaluated. Our results experimentally verify the electron-focusing phenomenon and suggest optimal processing windows for enhanced ionization rates and efficiency in EGDPIII.

Impact energy and retained dose uniformity in enhanced glow discharge plasma immersion ion implantation

The implantation energy and retained dose uniformity in enhanced glow discharge plasma immersion ion implantation (EGD-PIII) is investigated numerically and experimentally. Depth profiles obtained from different samples processed by EGD-PIII and traditional PIII are compared. The retained doses under different pulse widths are calculated by integrating the area under the depth profiles. Our results indicate that the improvement in the impact energy and retained dose uniformity by this technique is remarkable.