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Soft systems that respond to external stimuli, such as heat, magnetic field, and light, find applications in a range of fields including soft robotics, energy harvesting, and biomedicine. However, most of the existing systems exhibit nondirectional, nastic movement as they can neither grow nor sense the direction of stimuli. In this regard, artificial systems are outperformed by organisms capable of directional growth in response to the sense of stimuli or tropic growth. Inspired by tropic growth schemes of plant cells and fungal hyphae, here we report an artificial multistimuli-responsive tropic tip-growing system based on nonsolvent-induced phase separation of polymer solution, where polymer precipitates as its solvent dissolves into surrounding nonsolvent. We provide a theoretical framework to predict the size and velocity of growing precipitates and demonstrate its capability of sensing the directions of gravity, mechanical contact, and light and adjusting its growing direction in response. Exploiting the embedded physical intelligence of sensing and responding to external stimuli, our soft material system achieves multiple tasks including printing 3D structures in a confined space, bypassing mechanical obstacles, and shielded transport of liquids within water.

Living organisms use stingers that vary in length L over eight orders of magnitude, from a few tens of nanometres to several metres, across a wide array of biological taxa. Despite the extreme variation in size, their structures are strikingly similar. However, the mechanism responsible for this remarkable morphological convergence remains unknown. Using basic physical arguments and biomimetic experiments, we reveal an optimal design strategy that links their length, base diameter d0, Young’s modulus E and friction force per unit area μp0. This principle can be framed simply as $${d}_{0} \approx {(\mu {p}_{0}/E)}^{1/3}L$$ . Existing data from measurements on viruses, algae, marine invertebrates, terrestrial invertebrates, plants, terrestrial vertebrates, marine vertebrates—as well as man-made objects such as nails, needles and weapons—are consistent with our predictions. Our results highlight the evolutionary adaptation of mechanical traits to the constraints imposed by friction, elastic stability and cost. The structures of stingers of living organisms are surprisingly similar despite their vastly different lengths. Now, stingers are found to obey a unifying mechanistic principle that characterizes the stingers resistance to buckling.

Controlling fluid flow is a fundamental problem with applications from biomedicine to environmental engineering. Contemporary solutions combine electromechanical sensors, valves, and pumps; however, these are expensive and difficult to maintain. We report an autonomous flow control principle inspired by vascular transport in plants. Combining experiments on real and biomimetic tissues, we show that networks of cells linked by nonlinear valves permit the physical programming of a nearly arbitrary pressure drop versus flow rate relation. The nonlinearity is a consequence of fluid-structure interactions that allow a flexible element to selectively block the valve aperture. We report four applications: parallel connections that function as (i) a nonlinear flow controller, (ii) a constant flow controller, (iii) a reverse Ohm flow controller, and a serial connection that acts as (iv) a fluidic on-off switch.

We propose an optimal cold sink temperature for thermoelectric dehumidifiers based on theoretical and experimental investigations. We show that the optimal condition is such that the latent heat absorption rate per unit power supplied to the dehumidifier is maximized. In consideration of the cooling ability of Peltier pellet and the heat exchange characteristics of the cold sink, we estimate the condensation rate as a function of the cold sink temperature. The theoretical predictions are compared with the results of experiments by using a prototype dehumidifier. We emphasize that the cold sink temperature is a critical parameter that determines the performance of dehumidification. Our study may provide an important insight to the thermoelectric dehumidification system and to designing a cold sink for thermoelectric dehumidifiers with improved energy efficiency.

Shaping a plant root into an ideal structure for water capture is increasingly important for sustainable agriculture in the era of global climate change. Although the current genetic engineering of crops favours deep-reaching roots, here we show that nature has apparently adopted a different strategy of shaping roots. We construct a mathematical model for optimal root length distribution by considering that plants seek maximal water uptake at the metabolic expenses of root growth. Our theory finds a logarithmic decrease of root length density with depth to be most beneficial for efficient water uptake, which is supported by biological data as well as our experiments using root-mimicking network systems. Our study provides a tool to gauge the relative performance of root networks in transgenic plants engineered to endure a water deficit. Moreover, we lay a fundamental framework for mechanical understanding and design of water-absorptive growing networks, such as medical and industrial fluid transport systems and soft robots, which grow in porous media including soils and biotissues.

In plants, plasmodesmata (PD) are nanopores that serve as channels for molecular cell-to-cell transport. Precise control of PD permeability is essential to regulate processes such as growth and tissue patterning, photoassimilate distribution and defense against pathogens. Callose deposition modulates PD transport but little is known of the rapid events that lead to PD closure in response to tissue damage or osmotic shock. We propose a mechanism of PD closure as a result of mechanosensing. Pressure forces acting on the dumbbell-shaped ER-desmotubule complex cause it to be displaced from its equilibrium position, thus closing the PD aperture. The filamentous protein tethers that link the plasma membrane to the ER-desmotubule complex play a key role in determining the selectivity of the PD pore. This model of PD control compares favorably with experimental data on the pressure-generated closure of PD., Plasmodesmata channels connect neighbouring plant cells and respond to external stimuli via changes in permeability. Here Park et al. propose that mechanical forces can displace the dumbbell-shaped ER-desmotubule complex that spans the central plasmodesmatal cylinder leading to closure of the pore.

Microrobots that are light and agile yet require no artificial power input can be widely used in medical, military, and industrial applications. As an actuation system to drive such robots, here we report a biologically inspired bilayer structure that harnesses the environmental humidity energy, with ratchets to rectify the motion. We named this actuator-ratchet system the hygrobot. The actuator uses a hygroscopically responsive film consisting of aligned nanofibers produced by directional electrospinning, which quickly swells and shrinks in lengthwise direction in response to the change of humidity. The ratchets based on asymmetric friction coefficients rectify oscillatory bending motion in a directional locomotion. We mathematically analyzed the mechanical response of the hygrobot, which allowed not only prediction of its performance but also the optimal design to maximize the locomotion speed given geometric and environmental constraints. The hygrobot sterilized a trail across an agar plate without any artificial energy supply.

The multi-level holographic storage system can store more than one bit per pixel. In this paper, we introduce a 6-pixel 4-level modulation code and compare with 4-level 6/9 modulation code and 2/3 modulation code. The proposed 6-pixel modulation code has the minimum Euclidean distance 3. The 6-pixel modulation code is approximately 1dB better than the other modulation codes. ※ 이 논문은 2013년도 정부(교육부)의 재원으로 한국연구재단의 지원을 받아 수행된 기초연구사업임(NRF-2013R1A1A2059077). First Author : School of Electronic Engineering, Soongsil University, pkhroma@gmail.com, 학생회원 ° Corresponding Author : School of Electronic Engineering, Soongsil University, zlee@ssu.ac.kr, 종신회원 논문번호:KICS2015-08-271, Received August 28, 2015; Revised September 11, 2015; Accepted September 11, 2015 I. 서 론 오늘날 데이터 사용량이 급격히 증가하면서 데이터 의 효율적인 보관, 관리 및 이용을 위한 대용량 저장 장치에 대한 기술이 요구되고 있다 [1] 홀로그래픽 데이 터 저장장치는 체적으로 데이터를 저장하기에 대용량 저장에 용이하다. 기본적인 원리를 살펴보면 신호빔과 기준빔이 매질 내에서 간섭을 일으켜 매질 내에 패턴 이 형성되어 저장된다. 입력 데이터는 SLM (Spatial Light Modulator)을 통해 변조 형태의 입력 패턴이 만 들어진다. 만들어진 패턴에 레이저 빔을 조사하여 신 호빔을 만든다. 이 신호빔이 여러 각도, 파장, 혹은 위 상코드로 기준 빔(Reference Beam)과 간섭시켜 홀로 그램 매질에 기록한다. [2] 이처럼 홀로그래픽 데이터 저장장치는 신호빔으로 데이터를 보낼 때, 데이터를 페이지 형식으로 보내기 때문에 저장 용량을 높일 수 있고, 2차원으로 데이터를 저장하므로 데이터 전송률 또한 높일 수 있다. [3] 하지만 홀로그래픽 저장장치는 기존 저장장치들과 달리 중요한 2가지 오류요인이 있 다. 먼저 2차원 인접 심볼 간 간섭(Inter-symbol 논문 / 홀로그래픽 데이터 저장장치를 위한 4-레벨 변조 부호의 성능 비교

Fluid-structure interactions are ubiquitous in nature and technology. However, the systems are often so complex that numerical simulations or ad hoc assumptions must be used to gain insight into the details of the complex interactions between the fluid and solid mechanics. In this paper, we present experiments and theory on viscous flow in a simple bioinspired soft valve which illustrate essential features of interactions between hydrodynamic and elastic forces at low Reynolds numbers. The setup comprises a sphere connected to a spring located inside a tapering cylindrical channel. The spring is aligned with the central axis of the channel and a pressure drop is applied across the sphere, thus forcing the liquid through the narrow gap between the sphere and the channel walls. The sphere's equilibrium position is determined by a balance between spring and hydrodynamic forces. Since the gap thickness changes with the sphere's position, the system has a pressure-dependent hydraulic resistance. This leads to a non-linear relation between applied pressure and flow rate: flow initially increases with pressure, but decreases when the pressure exceeds a certain critical value as the gap closes. To rationalize these observations, we propose a mathematical model that reduced the complexity of the flow to a two-dimensional lubrication approximation. A closed-form expression for the pressure-drop/flow rate is obtained which reveals that the flow rate $Q$ depends on the pressure drop $\Delta p$, sphere radius $a$, gap thickness $h_0$, and viscosity $\eta$ as $Q\sim \eta^{-1} a^{1/2}h_0^{5/2}\left(\Delta p_c-\Delta p\right)^{5/2}\Delta p$, where the critical pressure $\Delta p_c$ scales with the spring constant $k$ and sphere radius $a$ as $\Delta p_c\sim k a^{-2}$. These predictions compared favorably to the results of our experiments with no free parameters., Comment: 10 pages, 5 figures

A holographic data storage (HDS) has some advantages of high storage capacity, fast transmission, and short access time. However, there are two major concerns with the system which are two-dimensional (2D) inter-symbol interference (ISI) and inter-page interference (IPI). Thus, this paper proposes a 4-level 6/9 modulation code which mitigate inter-symbol interference (ISI). ※ 이 논문은 2013년도 정부(교육부)의 재원으로 한국연구재단의 지원을 받아 수행된 기초연구사업임 (NRF-2013R1A1A2059077). First Author : Soongsil University, School of Electronic Engineering, kimbs@ssu.ac.kr, 학생회원 ° Corresponding Author : Soongsil University, School of Electronic Engineering, zlee@ssu.ac.kr, 종신회원 * Soongsil University, School of Electronic Engineering, pkhroma@gmail.com 논문번호:KICS2014-09-359, Received September 25, 2014; Revised October 1, 2014; Accepted October 1, 2014. I. 서 론 홀로그래픽 데이터 저장시스템 (holographic data storage system, HDS)은 표면에 정보를 저장하는 광 기록 저장장치(CD, DVD, BD)나 자기기록 저장 장치 (hard disk drive, HDD)와는 다르게 매질의 체적에 데 이터를 저장하기 때문에 저장용량을 현저히 증가시킬 수 있다. 이 때문에 근접장 기록(near field recording, NFR)이나 SUPER_RENS (Super REsolusion Near-Field Structure)와 함께 차세대 광기록 저장장치 로 연구되고 있다. HDS는 기록과 재생이 페이지 단위 로 이루어지므로 한 페이지가 가지는 총 비트 수와 다 중화된 홀로그램 수의 곱으로 저장 매질의 총 저장용 량이 결정된다. 입력 데이터가 홀로그램의 체적 내에 서 2차원 페이지의 단위로 기록하고 읽기 때문에 저 장용량을 크게 증가시킬 수 있다. (즉, 데이터 저장용 량은 한 공간에 많은 페이지를 저장하면 할수록, 그리 고 한 페이지에 많은 데이터를 저장하면 할수록 증가 한다.) 또한 2차원 페이지 단위로 신호처리가 가능하 기 때문에 데이터 전송속도 또한 매우 증가시킬 수 있 다. 기존의 데이터 저장장치와 같이 표면에 정보를 저 장하는 데이터 저장장치에서 주로 오류를 범하게 하는 요인이 인접심볼간 간섭 (inter-symbol interference, ISI)이라면 HDS는 페이지 단위로 매질의 체적에 겹 쳐 쓰면서 저장하기 때문에 인접 페이지간 간섭 (inter-page interference, IPI)이 존재한다 . 그리고 논문 / 홀로그래픽 데이터 저장장치를 위한 4레벨 6/9 변조부호 575 Fig. 1. Examples of severe ISI in four-level HDS Fig. 2. Structure of a codeword in the proposed modulation code Fig. 3. Example of codewords Fig. 4. Structure of encoding scheme. Table 1. Symbol mapping rule 페이지 단위로 데이터를 쓰고 읽기 때문에 ISI가 2차 원으로 영향을 준다. 이진 픽셀의 경우 가장 큰 ISI를 일으키는 상황은 0 (혹은 1) 픽셀이 1 (혹은 0) 픽셀들 로 둘러싸인 경우와 같은 고립된 픽셀 패턴(isolated pixel patterns)이다 . HDS가 멀티레벨인 경우는 최하위 레벨과 최상위 레벨이 인접한 경우 최상위 레 벨의 심볼이 최하위 레벨의 심볼에게 심한 간섭을 일 으키게 된다. 따라서 멜티레벨의 경우에 ISI를 줄이기 위해서는 최상위 레벨 심볼과 최하위 레벨 심볼이 인 접하지 않게 하여야 한다. 그림 1은 4-레벨 심볼인 경 우, 0 픽셀과 3 픽셀이 인접하여 이웃한 픽셀에 큰 ISI 를 발생하는 예이다. 본 논문에서는 그림 1과 같이 레벨 0 심볼과 레벨 3 심볼이 인접하는 상황이 발생하지 않도록 하기 위 한 변조부호를 제안하였다. II장에서는 본 논문에서 제안된 4-레벨 6/9 변조부호에 대하여 설명한다. III장 에서는 시뮬레이션 환경 및 결과를 보여주고, 마지막 IV장에서는 앞 장의 결과를 바탕으로 결론을 내린다. II. 제안된 4-레벨 6/9 변조부호 한 픽셀이 가질 수 있는 심볼의 종류가 4-레벨이므 로 입력되는 두 비트 (예: 00, 01, 10, 11)를 하나의 심 볼로 만든다. 그림 2는 3⨯3 배열의 코드워드 구조와 제안된 변조부호의 구성 방법을 보여준다. 6개의 심볼 데이터가 입력되어 9개의 심볼 데이터로 3⨯3 배열의 형태로 출력되게 되며, 한 코드워드는 두 부분으로 나 뉘어져 있다. (a, e, i) 위치의 픽셀들은 {0, 1, 2, 3} 레벨의 심볼이 올 수 있다. 나머지 픽셀들은 {1, 2} 레 벨의 심볼만 가능하다. 이렇게 하면 인접한 픽셀이 그 림 1과 같이 0 심볼과 3 심볼이 이웃하는 경우가 생기 지 않게 된다. 그림 3은 두 코드워드를 연결하였을 때, 제안된 변 조부호로 이루어진 코드워드가 인접한 어느 심볼도 레벨 0과 레벨 3이 인접하지 않는 것을 확인할 수 있 다. 이로 인해 제안된 변조부호는 2D-ISI를 완화할 수 있다. 제안된 변조부호의 코드율은 0.667(=6/9)이며 픽셀당 4/3비트를 기록한다. 6 심볼 (12 비트)의 입력 데이터는 그림 4와 같이 9 픽셀의 출력 코드워드로 변조된다. 먼저, a0, a1, a2 는 B0, B4, B8에 각각 순서대로 1-1 대응되고, 표 1에 있는 매핑 규칙에 따라 a3은 B1과 B3 픽셀에 해당하는 심볼들을 할당하고, a4는 B2와 B6에, a5는 B5와 B7에 각각 표 1과 같이 각 픽셀의 심볼값이 정해진다. 복조 과정은 데이터 변조 과정이 1:1 맵핑 방식이므로 변조 과정의 역순으로 진행된다.

Fish respire through gills, which have evolved to extract aqueous oxygen. Fish gills consist of filaments with well-ordered lamellar structures, which play a role in maximizing oxygen diffusion. It is interesting that when we anatomically observe the gills of various fish species, gill interlamellar distances (d) vary little among them, despite large variations in body mass (Mb). Noting that the small channels formed by densely packed lamellae cause significant viscous resistance to water flow, we construct and test a model of oxygen transfer rate as a function of the lamellar dimensions and pumping pressure, which allows us to predict the optimal interlamellar distance that maximizes the oxygen transfer rate in the gill. Comparing our theory with biological data supports the hypothesis that fish gills have evolved to form the optimal interlamellar distances for maximizing oxygen transfer. This explains the weak scaling dependence of d on Mb: d ∼ Mb(1/6).

In the airway network of a human lung, the airway diameter gradually decreases through multiple branching. The diameter reduction ratio of the conducting airways that transport gases without gas exchange is 0.79, but this reduction ratio changes to 0.94 in acinar airways beyond transitional bronchioles. While the reduction in the conducting airways was previously rationalized on the basis of Murray’s law, our understanding of the design principle behind the acinar airways has been far from clear. Here we elucidate that the change in gas transfer mode is responsible for the transition in the diameter reduction ratio. The oxygen transfer rate per unit surface area is maximized at the observed geometry of acinar airways, which suggests the minimum cost for the construction and maintenance of the acinar airways. The results revitalize and extend the framework of Murray’s law over an entire human lung.

The bubble oscillations play an important role in ultrasonic cleaning processes. In the ultrasonic cleaning of semiconductor wafers, the cleaning process often damages micro/nano scale patterns while removing contaminant particles. However, the understanding of how patterns in semiconductor wafers are damaged during ultrasonic cleaning is far from complete yet. Here, we report the observations of the motion of bubbles that induce solid wall damage under 26 kHz continuous ultrasonic waves. We classified the motions into the four types, i.e. volume motion, shape motion, splitting or jetting motion and chaotic motion. Our experimental results show that bubble oscillations get unstable and nonlinear as the ultrasonic amplitude increases, which may exert a large stress on a solid surface raising the possibility of damaging microstructures.

Although ultrasonic technology has been successfully adopted for semiconductor cleaning, a recent trend of extreme miniaturization of patterns calls for a novel process that can remove contaminant particles without damaging nanoscale patterns. Unstable bubble oscillations have been hypothesized to cause such surface damages, and here we show direct visualization results that a high acoustic pressure induces bubble instability leading to pattern damages. As a remedy for the conventional ultrasonic cleaning scheme, we introduce a novel cleaning system using dual transducers, in which one transducer generates bubbles with a high acoustic pressure in an acoustically isolated sub-chamber and the other drives the oscillation of bubbles around the cleaning area at a low acoustic pressure. The system is shown to achieve a high cleaning efficiency for submicron-sized particles while significantly suppressing the disruptive bubble instability thereby reducing the detachment of firmly attached nanoparticles. Comparison of the adhesion force of the firmly attached nanoparticles and the yield strength of nanopatterns allows us to anticipate that this scheme is capable of reducing damages of nanopatterns on semiconductor wafers and photomasks.

A holographic data storage (HDS) system can provide high storage capacity, faster transmission, and shorter access time. However, there are two major concerns with such systems: two-dimensional (2D) inter-symbol interference (ISI) and inter-page interference (IPI). The use of existing partial response maximum likelihood (PRML) detection can somewhat mitigate the problem of ISI. However, if the channel is subject to misalignment, the performance of PRML detection can be degraded. This problem can be remedied by a modulation code. Thus, this paper proposes a 6/9 modulation code, which mitigates ISI, and a modulation/demodulation scheme.