周期极化掺镁铌酸锂光学参量振荡器时域特性的实验研究

分别采用MOTORULA公司的硅基光电二极管探测器和JUDSON公司的InGaAs光电二极管探测器对泵浦光和信号光的脉宽进行了测量.研究了极化周期、工作温度以及抽运功率与周期极化掺镁铌酸锂光学参量振荡器输出的信号光脉冲宽度的作用关系.实验采用LD端面抽运的声光调Q Nd∶YVO4激光器作为抽运源,在晶体温度为30 ℃、极化周期为29.5 μm条件下,当抽运功率为1 008 mW时,获得了平均功率为238 mW的信号光输出,其光-光转换效率为23.6%,最窄脉冲宽度约为9.3 ns,相对抽运光脉宽被明显压窄.     

Fast hologram generation method for interactive holographic VR-CAD system

In a Virtual Reality based Computer-Aided Design (VR-CAD) system, the designer creates three-dimensional shapes using human-computer interaction (HCI) technique such as voice commands, hand motions, and finger motions. In this system, 3-D displays can provide the visual feedback to the designer a realistic graphical perception about the part she/he is designing. Especially, holographic method is particularly regarded as one of the most attractive approaches for creating the most authentic illusion of observing volumetric objects. Therefore, holographic 3-D display is the most suitable method for the VR-CAD system. Therefore, in this paper, we propose the fast generation method of 3-D hologram pattern using spatio-temporal redundant data of 3-D scene in VR-CAD system. Some experiments are carried out and its results are comparatively discussed with those of the conventional methods in terms of computational speed and required memory space.     

N-Acetylaspartate and epilepsy

Proton magnetic resonance spectra include signals from N-acetylaspartate, creatine + phosphocreatine, and choline-containing compounds. Abnormalities in these signals can be used in the assessment of patients with intractable epilepsy. In particular, they provide a means of identifying metabolic abnormalities within the temporal lobes, detecting bilateral and diffuse pathology, and aiding lateralization of the seizure focus. The pathology demonstrated on MRS can also be related to cognitive dysfunction.     

Physiological Studies of Retrusive Movements of the Human Tongue

SUMMARY: This study identified that physiologically the superior pharyngeal constrictor muscle at the level of the base of the tongue contributes to retrusive movement of the tongue with constriction of the mid-pharyngeal cavity and possesses unique properties in terms of motor speech control along with the genioglossus muscle. From a kinematic study involving trans-nasal fiberscopy and lateral X-ray fluorography, retrusive movement of the tongue was highly correlated with constrictive movement of the mid-pharyngeal cavity. An electromyographic study revealed that the superior pharyngeal constrictor muscle at the level of the base of the tongue contributes to retrusive movement of the tongue and that the genioglossus muscle contributes to protrusive movement. We also noted that this relationship between the activities of these two muscles were in response to postural changes during vowel productions without changes in the acoustic features. These findings suggest that these two muscles act not only antagonistically to produce retrusive and protrusive movement of the tongue, but also they complement each other to conserve the shape of the vocal tract for speech production. The functional relationship between these two muscles could contribute the consecutive movement of human speech production under various conditions and might be useful when applying rehabilitation approaches for the patients with neurological speech and swallowing disorders.     

Iterative two-step temporal phase-unwrapping applied to high sensitivity three-dimensional profilometry

Although temporal phase unwrapping method can be applied to solve some problems to measure an object with steep shapes, isolated parts or fringe undersampling in three-dimensional (3D) shape measurement, it needs to acquire and process a sequence of fringe pattern images which would take much time. Servin et al. proposed a 2-step temporal phase unwrapping algorithm, which only needs the 2 extreme phase-maps to achieve exactly the same results as standard temporal unwrapping method. But this method is only validated by computer simulation, shortage of experimental demonstration, its sensitivity coefficient G is limited, and it cannot be used when the G value is larger. We proposed an iterative two-step temporal phase-unwrapping algorithm which is an extension of Servin׳s method. First, add a fringe pattern with an intermediate sensitivity, project the fringe patterns of different sensitivity onto the tested object’s surface, and collect deformed fringe patterns with a CCD camera. Then we obtain the unwrapped phase with larger sensitivity coefficient G by cascading the sensitivity coefficients. And we derive the initial phase conditions of the 2-step temporal phase unwrapping algorithm. Finally, the experimental evaluation is conducted to prove the validity of the proposed method. The results are analyzed and compared with Servin׳s method. The experimental results show that the proposed method can achieve higher sensitivity and more accurate measurement, and it can overcome the main disadvantages encountered by Servin׳s method.     

Photothermal Conversion by Carbon Black Facilitates Aryl Migration by Photon-Promoted Temperature Gradients

The Newman Kwart Rearrangement (NKR) offers an efficient and high-yielding method for producing substituted thiophenols from phenols. While an industrially important protocol, it suffers from high activation energy barriers (35–43 kcal/mol), requiring the use of extreme temperatures (>200 °C) and specialty equipment. This report details a highly efficient and straightforward method for facilitating the NKR using photothermal conversion. This underused, unique reactivity pathway arises from the irradiation of nanomaterials that relax via a non-radiative decay pathway to generate intense thermal gradients. We show carbon black (CB) can be an inexpensive and abundant photothermal agent under visible light irradiation to achieve a facile NKR under mild conditions. The scope includes a wide array of stereo- and electronically diverse substrates with increasing difficulty of rearrangement, including BHT and BINOL as effective substrates. Furthermore, we demonstrate the unique application for temporal control in a thermal reaction and tunability of thermal gradients by modulating light intensity. Ultimately, photothermal conversion enables high-temperature reactions with simple, visible light irradiation.     

An improved temporal clustering analysis method applied to whole-brain data in fMRI study

Temporal clustering analysis (TCA) has been proposed as a method to detect the brain responses of an fMRI time series when the time and location of the activation are completely unknown. But TCA is still incompetent in dealing with the time series of the whole brain due to the existence of many inactive pixels. If only active pixels are considered, the sensitivity of TCA will be improved greatly and it could be applied to the whole brain. In this study, some modifications were made to TCA to remove inactive pixels, and the applicability of the modified TCA to the whole brain was validated with a set of visual fMRI data. Based on the time series of the modified TCA, activations of the whole brain corresponding to the visual stimulation were detected. Compared with the previous TCA, the modified TCA method shows a significant improvement in the sensitivity to detect activation peaks of the whole brain.     

亚乙基硫脲分子激发拉曼虚态的研究

本文从拉曼峰强入手,求得了亚乙基硫脲(ETU)分子的"时间分辨键极化率",并讨论了该分子的激发拉曼虚态性质,发现了该分子"激发虚态电子向分子外围键流动"、"电子弛豫后的键极化率分布与基态电子的密度分布相似"、"不同激发波长下的键极化率衰减时间满足不确定关系"等特点。本文还研究了该分子的表面增强拉曼光谱,指出"电荷转移机制"的极化率弛豫时间长于"电磁增强机制"等与表面增强拉曼效应相关的结论。     

Determining the etiology of mild vocal fold hypomobility

The prevalence of mild vocal fold hypomobility is unknown. In a study by Heman-Ackah et al, vocal fold hypomobility in a population of singing teachers was found to be associated more frequently with vocal complaints than was the presence of vocal fold masses.¹ The etiology of mild vocal fold hypomobility has not been previously explored. In the present study, a retrospective chart review was performed of 134 patients who presented to a tertiary laryngology referral center over a 6-month period for evaluation of vocal complaints. Of the 134 patients, 61 (46%) were found to have mild vocal fold hypomobility previously undiagnosed by the referring otolaryngologist. Imaging studies and laboratory tests to evaluate for structural, metabolic, and infectious causes of the decreased mobility had been ordered. Forty-nine patients completed the work-up. Of these, 41 out of 49 (84%) were found to have imaging or laboratory findings that could explain the hypomobility. Thyroid abnormalities were found to be associated with vocal fold hypomobility in 21 out of 49 (43%) of those with a complete evaluation. Other causes of vocal fold hypomobility included idiopathic (8 of 49, 16%), viral neuritis (5 of 49, 10%), central nervous system abnormality (4 of 49, 8%), neural tumor (3 of 49, 6%), joint dysfunction (3 of 49, 6%), iatrogenic nerve injury (2 of 49, 4%), myopathy (2 of 49, 4%), and noniatrogenic traumatic nerve injury (1 of 49, 2%), This study shows that unilateral vocal fold hypomobility often is associated with a physiologic process, and a complete investigation to determine the etiology is warranted in all cases.     

Nonmonotone BFGS-trained recurrent neural networks for temporal sequence processing

In this paper we propose a nonmonotone approach to recurrent neural networks training for temporal sequence processing applications. This approach allows learning performance to deteriorate in some iterations, nevertheless the network’s performance is improved over time. A self-scaling BFGS is equipped with an adaptive nonmonotone technique that employs approximations of the Lipschitz constant and is tested on a set of sequence processing problems. Simulation results show that the proposed algorithm outperforms the BFGS as well as other methods previously applied to these sequences, providing an effective modification that is capable of training recurrent networks of various architectures.