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Precise prediction of the antigens that bind to major histocompatibility complex (MHC) molecules is one of the most important steps for many immune response-related studies including identification of neoantigen capable of recognizing cancer cells for the implementation of personalized immunotherapy as well as vaccine/therapeutic protein development. To overcome the limitations of the limited prediction performance of the existing models, we developed a new convolutional neural network (CNN)-based epitope prediction model by incorporating new features including protein sequence vectors (Prot2Vec), chemical and structural characteristics of an epitope and MHC molecule. Our new model is optimized to achieve better prediction performance than the conventional methods when validated with a benchmark dataset from the Immune Epitope Database (IEDB). Along with the new prediction model, we also developed a web-based framework, called Kepre, to provide interfaces to our novel CNN-based epitope prediction functionalities. Kepre provides a user-friendly and automated interface for epitope prediction. Upon the researcher's submission of a sequence of interest, Kepre predicts the binding probability between the sequence and each type of the MHC molecules. Kepre runs the prediction analysis on high-throughput computing infrastructure and provides the prediction results in a user-interactable GUI and also in a pdf formatted report file.

This paper proposes a novel automatic classifier of rapid-eye-movement (REM), non-rapid-eye-movement (NREM, combined light and deep sleep stages (SS)), and wake stages based on wrist photoplethysmography and wrist 3-axis accelerometer data. The quality and robustness of the classifier are achieved by a multilevel learning framework, which consists of features extraction, preprocessing, signal treatment, machine learning, and post-processing modules. Subjectspecific Z-score normalization and exponential smoothing are applied to reduce intra-subject and inter-subject variability. The novel features are based on heart rate variability and motion statistics. Leave-one-subject-out cross-validation technique is applied to estimate the quality of the model. Our solution, based on linear discriminant analysis (LDA), shows the Cohen’s Kappa coefficient of 0.58 and accuracy of 77 % for the four class (wake, REM, light, deep) classification problem and Cohen’s Kappa coefficient of 0.67 and accuracy of 85 % for the three class (wake, REM, NREM) classification problem. Comparison of different ML algorithms, like LDA, support vector machines, and random forest is done. The obtained results of sleep stages classification exceed the analogous state of the art solutions.

Fabricating perovskite on textured silicon surface is important for maximizing current density and the power conversion efficiency (PCE) of perovskite/silicon tandem solar cells. However, producing conformal perovskite on textured silicon surface is difficult because most of high efficiency perovskite solar cells have been produced by solution based process. Herein, we investigated possibility of producing perovskite solar cells on textured silicon surface by dry two-step conversion process and analyzing them with periodically patterned texture and photoluminescence mapping. Thickness scale difference between perovskite and silicon substrate have induced focusing problems.

Accuracy of the Yb optical lattice clock being developed at KRISS has been improved due to better measurements of light shifts and collisional shift. Its accuracy uncertainty is now 5.6×10$^{\mathbf {-17}}$, three times better than our previous result. The second Yb optical lattice clock is now being built for lower blackbody radiation shift using a thermal shield made of copper. Its preliminary estimation of temperature uncertainty is below 50 mK, which corresponds to frequency uncertainty of low 10$^{\mathbf {-18}}$level.

A new clock laser system using an optical cavity with $4.8 \times 10^-17$ thermal noise limit has been developed for rapid evaluation of ytterbium lattice clocks. This was realized by using a 30-cm-long ULE cavity, fused-silica mirror substrates, and crystalline mirror coatings. The frequency stability of the beating signal between the new clock laser and the old clock laser was limited by the latter. The linewidth and the frequency stability of the new clock laser will be measured by comparing the frequency between two similar systems.

The systematic uncertainty of the Yb optical lattice clock has been improved to 8.3×10−17at KRISS, and the absolute frequency has been measured with uncertainty of 9.6×10−16referenced to the SI second (TT). We also describe future prospects to further reduce the systematic uncertainty and the absolute frequency measurement uncertainty. A new clock laser system has been developed to evaluate the uncertainties in reasonably short time.

We present a hybrid fiber link to realize the local two-way optical frequency comparison with self-synchronization. It enables us to detect round-trip fiber noise and one-way fiber noise, and estimate the residuals. Moreover, we can check, to the best of our knowledge for the first time, the reciprocity of the accumulated noise forth and back over a bi-directional fiber, and also evaluate the noise correlation between two adjacent fibers with the hybrid setup.

We design and develop a new clock laser system for the second Yb optical lattice clock (OLC) at KRISS with the targeted uncertainty of 10−18 level. With a longer ULE cavity, the fused silica substrates, and the crystalline mirror coatings, the overall thermal limit is expected to be 4.3×10−17. The rapid evaluation of the systematic uncertainties of the second OLC will be possible with this new clock laser system.

We present a frequency comb-assisted experimental setup which enables us to both coherently transfer the stability and accuracy of a remote near-infrared (NIR) ultrastable laser to a mid-infrared (MIR) quantum cascade laser (QCL), and widely tune the QCL frequency for spectroscopic applications. The QCL is stabilized at the level of 2×10−15 from 1 to 100 s, with an accuracy of 10−14 after 100 s. The achievable frequency tuning paves the way for high-resolution saturated absorption spectroscopy of molecular transitions, in particular in spectral regions that were previously inaccessible with standard stabilized MIR lasers. Preliminary results show a sensitivity at the kHz level on transition center frequencies.

This paper introduces an atomic gravimeter under development at KRISS for precise measurement of gravitational acceleration. The gravimeter based on atom interferometer uses two counter-propagating Raman lasers of π/2-π-π/2 pulse sequence and laser cooled 87Rb atoms in free fall. Atomic interference fringes caused by Raman lasers were observed at various time intervals between the three Raman pulses. The frequency sweep rate α which compensates Doppler shift due to gravitational acceleration g was obtained from the interference fringes. In the presentation, the current status and recent results of the KRISS atomic gravimeter will be discussed.

This paper reports implementation and operation of a frequency synthesizer based on a cryocooled cryogenic Sapphire oscillator (cryoCSO) for the Cesium atomic fountain clock developing at KRISS, KRISS-Fl(Cs). With use of this highly stable local oscillator, the short-term stability of KRISS-F1(Cs) was greatly improved and reaches the quantum projection noise limit, resulting in the measured lowest Allan deviation of 2.6×10−14. In addition, the long-term drift (4.8×10−14/day) of the cryoCSO could be compensated and reach below 5×10−16/day as low as state-of-the-art active hydrogen masers.

Based on the its nonintrusive characteristics, ballistocardiography(BCG) has applied in the estimation of sleep structure without attaching any sensors to the subject's body. Loadcell or polyvinylidenefluoride (PVDF) film sensors are installed on the mattress for the monitoring of BCG. BCG peak was detected and heart rate variability parameters are derived. Parameters representing sleep structure and quality are estimated using these parameters. Sleep efficiency, four stages of sleep structure and sleep onset latency are estimated and results are compared with the results derived from polysomnographic recording.

The development of an Yb optical lattice clock at the Korea Research Institute of Standards and Science (KRISS) is reported with current systematic uncertainty of 2.9×10. A highly stable clock laser at 578 nm was developed with a shortterm linewidth of 3.5 Hz. The laser was locked to the clock transition and the fractional frequency stability was 2.0×10 at 1 s. Collisional frequency shift for Rabi spectroscopy was theoretically and experimentally investigated and the uncertainty was greatly reduced to 2.9×10. We identified conditions to further reduce the collisional shift uncertainty to 10 level. Index Terms — Optical clock, optical lattice, Ytterbium, collisional shift, sub-Hz laser.

A laser source at 578 nm with output power of more than 10 mW was obtained using a waveguide periodically-poled-lithium-niobate crystal as a nonlinear medium for second harmonic generation. To achieve this result, we made a high power 1156-nm external-cavity diode laser with maximum output power of more than 250 mW. This system is expected to be an excellent alternative to systems using sum-frequency generation with advantages of simplicity and cost-effectiveness, and will be used as a clock laser of an ytterbium optical lattice clock with robust and reliable operation.

An Yb optical lattice clock is under development at KRISS. Yb atoms were trapped in an optical lattice and further optimization is underway. Linewidth of the probe laser at 578 nm developed by sum frequency generation (SFG) method was reduced to less than 100 Hz. We also developed an optical frequency synthesizer (OFS) with the carrier-envelope-offset frequency locked to 0 Hz using the “direct locking method.”

We present a current status of a Rb/Cs double fountain clock developing at KRISS. Fountain clock has cooling laser beam with (111)-geometry so as to enlarge cooling beam diameter. Currently few 107 Cs atoms are trapped and cooled in MOT. And we observed Ramsey fringes. The linewith of central Ramsey fringe was measured to be 1 Hz with the S/N of 600.

We present a current status of an atomic gravimeter, which is based on Mach-Zehnder-type atom interferometer using stimulated Raman transition, developing at KRISS. Cooling beams with (111) geometric configuration was used for magnetic optical trap (MOT). Rubidium87 (Rb87) atoms are trapped and cooled in MOT. Temperature of the trapped atoms was measured to be about 1.7µK by time of flight measurement after a deep cooling.

Heart sounds are generated by the fluctuations of blood velocity and the vibrations of cardiac structure. The auscultation of heart sounds is one of the basic tools for patient diagnosis and provides a lot of information associated with cardiovascular systems. For converting mechanical sound waves into electronic signals, PVDF (polyvinylidene fluoride) film sensor was used as heart sounds measurement device. After suited filtering process, the first (S1) and the second (S2) heart sounds components were plainly distinguished and their peak timings were closely corresponded to reference heart sounds signals measured by microphone. Lastly, there was high correlation between S1 intervals (from PVDF signals) and RR intervals (from ECG signals). So it is expected that S1 intervals can replace RR intervals. In future application, these methods have possibilities for non-intrusive heart rate estimation.

The weighted mean is widely used in combining data sets of experimental measurements with a weight proportional to the value of the data number divided by the sample variance in a conventional method. However, this standard procedure is not appropriate for obtaining the weighted mean frequency of a phase-stabilized signal with white phase noise, since the data are autocorrelated. The autocorrelation is obtained in the case of white phase noise and a new weighting method is proposed. Using this, the uncertainty associated with the weighted mean frequency of a phase-stabilized signal with white phase noise is given. The effect of counter dead-time is also discussed. The result is significantly different from the conventional method, so that the weight is proportional to the square of data number divided by the sample variance, and as a result the uncertainty of the estimated mean is proportional to the sample standard deviation divided by the data number. In an optical frequency comb comparison, frequency combs are phase-locked to a common frequency reference and the frequency difference between optical frequency combs shows white phase noise properties. Thus, it is expected that this new weighting method can be utilized in frequency comparisons of optical frequency combs, settling existing controversy, and providing a way of achieving lower uncertainty.

This paper describes the current status of an ytterbium lattice clock under development at KRISS. After the success of 399 nm magneto-optical-trap (MOT) at a temperature 1 mK, we constructed the 2nd stage cooling laser system at a wavelength of 556 nm to cool atoms further down to several muK. We are also developing an ultra-narrow linewidth laser at a wavelength of 578 nm to probe the clock transition by doubling the frequency output of a commercial 1156 nm ECDL. Efforts to reduce the linewidth are under way.

We have developed a simple laser system for generation of coherent 556 nm light by using frequency doubling of a diode laser. 1112 nm light from an external cavity diode laser is amplified via Yb-doped fiber amplifier and 200 mW of the amplified light is injected to wave-guided MgO-doped PPLN, which produces a 30 mW green light. The frequency diode laser is stabilized to a resonance peak of a high-finesse cavity with finesse ~10000.

We have measured the absolute frequency and the uncertainty of the excited state transition, 5P3/2-4D5/2, in 87Rb atom with a fs frequency comb, utilizing the double resonance optical pumping (DROP) method. The absolute energy level of 4D5/2 state is determined by measuring the absolute frequency of the 5S1/2-5P3/2 transition simultaneously. The hyperfine structure constants of the 4D5/2 state are obtained with the magnetic dipole constant uncertainty reduced ten-fold compared to the previous result and with the electric quadrupole constant determined for the first time.

We present an optical frequency synthesizer based on two DFB lasers that can be selectively injection-locked to a desired single mode among the femtosecond fiber laser comb components.

For the first time we compare two kinds of optical frequency combs, one of which is based on a Ti:sapphire femtosecond laser and the other is based on a mode-locked erbium-doped fiber laser. The comparison is performed by measuring an optical frequency standard with these two combs simultaneously. The two frequency measurements agree within 1.8 Hz ( $3.8{\times}10^{-15}$ ) with the uncertainty of 17.2 Hz ( $3.6{\times}10^{-14}$ ), from which it can be concluded that the Ti:sapphire-based frequency comb and the fiber-based frequency comb have no systematic discrepancy at this level of uncertainty.

The selected and amplified optical frequency comb by using diode laser is used in an optical clock configuration to measure the absolute frequency of stabilized ECDL. The ECDL is stabilized to F = 4 → F = 5 transition line of cesium D2 line with modulation transfer spectroscopy. The measured frequency is fECDL = 351 721 960 529 kHz with a statistical uncertainty of 3.5 kHz.

Micro forming is a well suited technology to manufacture very small metallic parts, in particular for mass production, as they are required in many industrial products resulting from micro technology. A15083 superplastic alloy have a great advantage in achieving deformation under low stress compared to conventional plastic deformation. This paper describes the basic characteristics of micro forming of A15083 superplastic alloy. Self-designed micro forging system with (100) silicon dies used to micro forming characteristic test of A15083 superplastic alloy.

A jig used in a welding equipment for car sashes and parts requires high precision for accurate alignment of parts and tools. Jig precision is determined by comparison between checkpoint of a jig obtained from CAD data and direct measured data from the jig itself. The creation of a check sheet that contains these checkpoints is generally done, in small-to-medium sized companies, by translating 3-D modeling data of a part into 2-D drawing and by selecting checkpoints from it, because that companies cannot usually afford to possess and utilize a high cost 3-D CAD package. And, because it is difficult and inaccurate to show free surfaces of a part in the 2-D drawing, the check sheet created in this way cannot avoid containing errors to some extent. Furthermore, the creation activity of the check sheet by use of a translated 2-D drawing requires time consuming manual operation and eventually reduces company's productivity. In order to solve all these problems, an automatic check sheet creation program for precision check of the jig in a car welding was developed.

Discretely tunable single-mode erbium-doped fiber ring laser is fabricated with tuning range over 70 nm in C- and L-band utilizing a Fabry-Perot etalon and a saturable absorber. This matches to ITU-T 25-GHz frequency grid at 361 channels with excellent flatness

We observed that the spatial distortions of a probe pulse from Kerr nonlinearity were eliminated almost perfectly when a strong coupling pulse copropagates with the probe on two-photon-resonance in /spl Lambda/-type 3 levels of atomic Sm.

In our experiment conical emission (CE) has no wavelength shift and the same polarization as the original beam. Varying laser power, detuning, and atomic density, the images of CE were captured and analyzed. Typical far-field images are presented. Under the blue detuning condition, manifest CE patterns were observed, and under red detuning, original beam blurs due to not only to self-defocusing but also the conical pattern were observed. By comparing laser power and atomic density dependence of cone angle and theoretical curve, we could estimate spectroscopic data such as nonlinear refractive index. From the density dependence data, we get the fact that cone angle is proportional to atomic density which supports the self-phase-modulation (SPM) model. In conclusion, we observed and analyzed CE from near-resonant Sm vapor. With this simple setup, we could measure spectroscopic data.