Improvement in Light Extraction Efficiency of InGaN/GaN Blue Light Emitting Diodes Using Sidewall Texturing.

Herein, we reported the effects of the geometric morphology of the sidewall on the extraction efficiency of GaN-based light-emitting diodes (LEDs). We performed numerical analysis based on the ray-tracing method. We found that the extraction efficiency of the LEDs increased with the texturing of the sidewall. The light output intensity of the LEDs (at an injection current of 100 mA) increased by 13.8% after sidewall texturing. These results confirmed that the geometric morphology of the sidewall plays an important role in improving the extraction efficiency of LEDs.

Development of a simple pressure and heat stimulator for intra- and interdigit functional magnetic resonance imaging.

For this study, we developed a simple pressure and heat stimulator that can quantitatively control pressure and provide heat stimulation to intra- and interdigit areas. The developed stimulator consists of a control unit, drive units, and tactors. The control unit controls the stimulation parameters, such as stimulation types, intensity, time, and channel, and transmits a created signal of stimulation to the drive units. The drive units operate pressure and heat tactors in response to commands from the control unit. The pressure and heat tactors can display various stimulation intensities quantitatively, apply stimulation continuously, and adjust the stimulation areas. Additionally, they can easily be attached to and detached from the digits. The developed pressure and heat stimulator is small in total size, easy to install, and inexpensive to manufacture. The new stimulator operated stably in a magnetic resonance imaging (MRI) environment without affecting the obtained images. A preliminary functional magnetic resonance imaging (fMRI) experiment confirmed that differences in activation of somatosensory areas were induced from the pressure and heat stimulation. The developed pressure and heat stimulator is expected to be utilized for future intra- and interdigit fMRI studies on pressure and heat stimulation.

Development of a simple MR-compatible vibrotactile stimulator using a planar-coil-type actuator.

For this study, we developed a magnetic resonance (MR)-compatible vibrotactile stimulator using a planar-coil-type actuator. The newly developed vibrotactile stimulator consists of three units: control unit, drive unit, and planar-coil-type actuator. The control unit controls frequency, intensity, time, and channel, and transfers the stimulation signals to the drive unit. The drive unit operates the planar-coil-type actuator in response to commands from the control unit. The planar-coil-type actuator, which uses a planar coil instead of conventional electric wire, generates vibrating stimulation through interaction of the current of the planar coil with the static magnetic field of the MR scanner. Even though the developed tactile stimulating system is small, simple, and inexpensive, it has a wide range of stimulation frequencies (20 ~ 400 Hz, at 40 levels) and stimulation intensities (0 ~ 7 V, at 256 levels). The stimulation intensity does not change due to frequency changes. Since the transient response time is a few microseconds, the stimulation time can be controlled on a scale of microseconds. In addition, this actuator has the advantages of providing highly repeatable stimulation, being durable, being able to assume various shapes, and having an adjustable contact area with the skin. The new stimulator operated stably in an MR environment without affecting the MR images. Using functional magnetic resonance imaging, we observed the brain activation changes resulting from stimulation frequency and intensity changes.

High-numerical-aperture image simulation using Babinet's principle.

Simulation techniques are developed for high-numerical-aperture (NA) polarized microscopy with Babinet's principle, including partial coherence and vector diffraction for non-periodic geometries. The model includes vector illumination and diffraction in high-NA (up to NA=3.5) object space that is imaged into low-NA image space and recorded on an image sensor. A mathematical model for the Babinet approach is developed and interpreted that includes partial coherence using expanded mutual intensity, where object reflective characteristics modify the coherence functions. Simulation results of the Babinet's principle approach are compared with those of rigorous coupled wave theory (RCWT) for periodic structures to investigate the accuracy of this approach and its limitations.

Microscope system for Blu-ray disc samples.

We introduce a microscope system using a solid immersion lens (SIL) to image Blu-ray disc samples without removing the protective cover layer. The aberration caused by the cover layer is minimized with a truncated SIL. A subsurface imaging simulation is achieved by using the rigorous coupled wave theory, partial coherence, vector diffraction, and the Babinet principle. Simulated results are compared with experimental images and atomic force microscopy measurements.

Application of Non-Destructive Rapid Determination of Piperine in Piper nigrum L. (Black Pepper) Using NIR and Multivariate Statistical Analysis: A Promising Quality Control Tool.

Piperine is a bioactive alkaloid compound which provides a unique spicy flavor derived from plants of the Piper nigrum L. Black pepper (n = 160) collected from Vietnam was studied using non-destructive near infrared spectroscopy (NIRS). The spectral acquisition ranged from 1100 to 2500 nm, and a chemometrics analysis program was performed to quantify the piperine contents. High performance liquid chromatography (HPLC) analysis was carried out to develop a chemometric model based on reference values. The black pepper samples were divided into two groups used for calibration (n = 120) and prediction (n = 40) sets. The optimum calibration model was developed by pretreatment of the spectra. The analyses results based on the prediction samples included a coefficient of determination (R2) of 0.914, a root mean square error of prediction (RMSEP) and a standard error of prediction (SEP) of about 0.220 g/100 g, and a ratio performance to deviation (RPD) value of 3.378 regarding the partial least square (PLS) regression model, and an R2 of 0.921, an RMSEP and SEP of 0.210 g/100 g, and an RPD of 3.571, with respect to the principal components (PC) regression model. These results indicate that NIRS can be applicable as a control, or as an alternative rapid and effective method to quantify piperine in P. nigrum L.

Feasibility of rapid piperine quantification in whole and black pepper using near infrared spectroscopy and chemometrics.

Piperine is a bioactive alkaloid that possesses various health benefits and is responsible for the pungent aroma of pepper. Piperine content in whole and ground black pepper (n = 132) was analyzed by near-infrared spectroscopy (NIRS) in the 950 to 1650 nm wavelength window. Chemometric modeling using partial least square regression was performed, and outliers were checked and removed during the preparation of the calibration curve by considering sample residual variance and sample leverage. Model accuracy was evaluated with a low root-mean-square error of cross-validation (RMSECV) and a high ratio performance to deviation (RPD). The optimal model had a coefficient of determination (R2 ) of 0.726, RMSECV of 0.289 g/100 g, and RPD of 1.744 for the whole black pepper. The results of R2 , RMSECV, and RPD for the ground black pepper were 0.850, 0.231 g/100 g, and 2.424, respectively. Therefore, based on the perspective of onsite process, the proposed NIRS method can be employed for selecting abnormal samples during the inspection of black pepper raw material and for quantifying piperine contents of final black pepper product. PRACTICAL APPLICATION: Generally, the quality indicators of black pepper are graded solely based on their external appearance, quality, and size. This study discloses the development of a near-infrared spectroscopy-based fast and accurate nondestructive analytical method for the detection of piperine, a bioactive constituent of pepper, as a tool for the quality control of whole and ground black pepper.

Direct reconstruction of an object from dual exposure Fourier intensity measurements.

The reconstruction of an object with a method using a dual exposure single inverse Fourier transform is investigated. The method calculates phase information in the Fourier plane to perform the inverse Fourier transform. The phase information in the Fourier plane is calculated from the intensity distributions formed by an object with and without a reference electric field. The method successfully reconstructs an object in a simple and fast manner. For the practical use of the method, the effects of the intensity digitization and the noise in the intensity distributions are examined in reconstructing an object.

Development of a magnetic resonance-compatible galvanic skin response measurement system using optic signal.

The purpose of the current study is to develop a magnetic resonance (MR)-compatible galvanic skin response (GSR) measurement system that can measure the GSR signal during MR image acquisition. If GSR signals are measured simultaneously with the acquisition of MR images, there can be a mutual interference effect. The present system was designed to block noises caused by the main magnetic field, the gradient magnetic field, and the radio frequency (RF) pulse when MR images are acquired. To minimize the distortion of MR images, the GSR measurement system was shielded. Especially, this system used analog, not digital, elements in order to remove any possible effects on MR images. An RF-interference-free optical data link using the pulse-width modulation technique was adopted in order to transmit GSR signals measured inside the MR room. The experiment verified that a reliable GSR signal can be obtained without deteriorating the MR image. It is expected that this system can be used for diverse medical and neuroscience studies.

Numerical simulation for light extraction in nano-patterned light-emitting diodes.

We present numerical simulation results using the three-dimensional finite-difference time-domain method for light extraction in light-emitting diodes (LEDs) constructed on nano-patterned n-GaN substrates. We studied reasonable conditions for numerical calculation, including excitation source conditions, simulation size conditions, and boundary conditions and examined the effects of the size and distribution of nano-patterns on light extraction. Our findings revealed optimized structures for high extraction efficiency. Our simulation results were consistent with our experimental results and show the potential for the design of LED structures optimized for high light extraction.

A study on the cerebral sizes of Koreans in their 20S and 40S.

The purpose of this study was to measure the cerebral sizes of Korean adults in their third (20s) and fifth decades (40s) of life using Talairach-Nowinski reference points to determine the effect of sex and age on cerebral size and asymmetry. Magnetic resonance images of the brain of 94 adults between 20 and 29 years of age (43 males and 51 females) and 99 adults between 40 and 49 years of age (38 males and 61 females) were measured. The distance between reference points and cerebral size of males was greater than those of females. Cerebral width and the size of the left cerebrum of those in their 40s decreased more than those in their 20s. The effect of age on left cerebral atrophy of males was greater than that of females. Left cerebral size was greater than right cerebral size. There was no difference in cerebral asymmetry between the genders. Cerebral asymmetry of those in their 40s was smaller than of those in their 20s and the decrease of cerebral asymmetry of males due to age was greater than that of females. A positive relationship existed between cerebral height, and body height and weight for males in their 20s.

Hyperfine structure measurement of rubidium atom and tunable diode laser stabilization by using Sagnac interferometer.

The Rubidium saturated absorption spectra for D2 transition lines are used to measure the Fabry-Perot interferometer free spectral range (FSR). The scale linearity of the laser frequency tuning is determined. The Sagnac interferometer has been used for the laser stabilization. The result shows that the laser frequency is stabilized upto sub-mega Herz level. Also the hyperfine structure [5(2)S(1/2) F = 3 --> F' = 2, 3, 4 5(2)P(3/2) 85Rb] of the rubidium atom has been measured by using the tilt locking method, which shows the same result as the conventional saturation spectroscopy.

Responses of human sensory characteristics to 532 nm pulse laser stimuli.

BACKGROUND: Lasers are advantageous in some applications to stimulate a small target area and is used in various fields such as optogenetic, photoimmunological and neurophysiological studies. OBJECTIVE: This study aims to implement a non-contact sense of touch without damaging biological tissues using laser. METHODS: Various laser parameters were utilized in safety range to induce a sense of touch and investigate the human responses. With heat distribution simulation, the amount of changes in the temperature and the tendency in laser parameters of sensory stimulation were analyzed. RESULTS: The results showed the identified tactile responses in safety range with various laser parameters and temperature distribution for the laser stimulus was obtained through the simulation. CONCLUSIONS: This study can be applied to the areas of sensory receptor stimulation, neurophysiology and clinical medicine.

Mid-Air Tactile Stimulation Using Indirect Laser Radiation.

In this paper, we demonstrate that a laser irradiated on a thin light-absorbing elastic medium attached on the skin can elicit a tactile sensation of mechanical tap. First, we present simulation results that show laser irradiation to the elastic medium creates inner elastic waves on the basis of thermoelastic effects and these elastic waves trigger the bending deformation of the medium, which then stimulates the skin. Second, we analyze the physical properties of the associated stimulus by measuring its force profile. Third, we identify the perceptual characteristics of the stimulus in comparison to those of mechanical and electrical stimuli by means of a perceptual experiment employing dissimilarity rating. All the evidence indicates that indirect laser radiation provides a sensation of short mechanical tap. Furthermore, little individual difference was observed in the results of the perceptual experiment. To the best of our knowledge, this study is the first in reporting the feasibility of indirect laser radiation for mid-air tactile rendering.

Evaluation of the possibility and response characteristics of laser-induced tactile sensation.

In this study, we examined the possibility and perceptual response characteristics of tactile sense induced by laser stimulation to the finger with different laser energy densities through human response experiments. 15 healthy adult males and 4 healthy adult females with an age of 22.6±2.2 years were tested. A frequency-doubled Q-switched laser was used with a wavelength of 532 nm and a 5 ns pulse width. The experimental trial spanned a total of 30 s and included a rest phase (19 s), a stimulation phase (7 s), and a response phase (4 s). During the rest phase, subjects kept their fingers comfortable. During the stimulation phase, one of three types of laser energy density (13.5, 16.6, 19.8 mJ/cm(2)) or a sham stimulation was used to irradiate the distal phalanx on the right index finger. During the response phase, the cognitive response to the laser stimulation was recorded by a PC by pressing the response button. The confusion matrix was configured to evaluate the possibility that the tactile sense was caused by the laser. In addition, changes in the response characteristics were observed according to three types of laser energy densities. From the analysis of the confusion matrix, the accuracy and sensitivity were not high. In contrast, precision and specificity were found to be high. Furthermore, there was a strong positive correlation between the laser irradiation and tactile perception, indicating that tactile sense can be induced using a laser in a mid-air manner. In addition, it was found that as the laser energy density increased, the tactile perception possibility also increased.

Photomechanical effect on Type I collagen using pulsed diode laser.

BACKGROUND: As the most abundant protein in human tissues, the use of collagen is essential in the fields of biological science and medicine. OBJECTIVE: The aim of this study is to investigate the mechanical effect of pulsed laser irradiation on collagen tissue. METHODS: With various laser parameters such as peak power, pulse width, and repetition rate, the induced stresses on samples were measured and analyzed. Monte Carlo simulation was performed to investigate the effect of laser parameters on the collagen sample. RESULTS: The results indicated that the magnitude of mechanical stress could be controlled by various laser parameters. CONCLUSIONS: This study can be used in biostimulation for therapy and mechanoreceptor stimulation for tactile application.

Laser-induced thermoelastic effects can evoke tactile sensations.

Humans process a plethora of sensory information that is provided by various entities in the surrounding environment. Among the five major senses, technology for touch, haptics, is relatively young and has relatively limited applications largely due to its need for physical contact. In this article, we suggest a new way for non-contact haptic stimulation that uses laser, which has potential advantages such as mid-air stimulation, high spatial precision, and long working distance. We demonstrate such tactile stimulation can be enabled by laser-induced thermoelastic effects by means of physical and perceptual studies, as well as simulations. In the physical study, the mechanical effect of laser on a human skin sample is detected using low-power radiation in accordance with safety guidelines. Limited increases (< ~2.5 °C) in temperature at the surface of the skin, examined by both thermal camera and the Monte Carlo simulation, indicate that laser does not evoke heat-induced nociceptive sensation. In the human EEG study, brain responses to both mechanical and laser stimulation are consistent, along with subjective reports of the non-nociceptive sensation of laser stimuli.

Development of an optical fiber sensor for angular displacement measurements.

For diagnostic and therapeutic purposes, the joint angle measurement of a patient after an accident or a surgical operation is significant for monitoring and evaluating the recovering process. This paper proposed an optical fiber sensor for the measurement of angular displacement. The effect of beveled fiber angle on the detected light signal was investigated to find an appropriate mathematical model. Beveled fiber tips redirected the light over a range of angles away from the fiber axis. Inverse polynomial models were applied to directly obtain and display the joint angle change in real time with the Lab-VIEW program. The actual joint angle correlated well with the calculated LabVIEW output angle over the test range. The proposed optical sensor is simple, cost effective, small in size, and can evaluate the joint angle in real time. This method is expected to be useful in the field of rehabilitation and sport science.