Ji-Hoon Lee

Dynamics of electro-optical switching processes in surface stabilized biaxial nematic phase found in bent-core liquid crystal

The dynamics of electro-optical switching processes in the biaxial nematic phase of an oxadizole-based bent-core liquid crystal (LC) was studied. This LC exhibits optical biaxiality in the lower temperature range of the nematic phase although it exhibits optical uniaxiality in the higher temperature range. In particular, the short axis and the long axis of the LC were independently switched when an electric field was applied in the biaxial nematic phase. The switching time of the short axis was much faster than that of the long axis in response to the applied field as well as in relaxation.

An adaptive resource allocation mechanism including fast and reliable handoff in IP-based 3G wireless networks

The aim of the all-IP architecture in third-generation wireless networks is to allow operators to deploy IP technology in delivering third-generation services, that is, an architecture based on packet technologies and IP telephony for simultaneous real-time and non-real-time services. We present a new handoff management scheme that utilizes simultaneous multiple bindings in IP-based 3G wireless networks. The proposed handoff scheme minimizes packet losses and incurs negligible delays during handoff. We also present an adaptive resource allocation scheme that allocates connection resources to incoming calls depending on the network conditions. The resources accumulated by bandwidth degradation for on-going calls are utilized to minimize dropping probability of handoff calls and blocking probability of new calls.

Smectic A phase in a new bent-shaped mesogen based on a 2,3-naphthalene central core with an acute-subtended angle

A new bent-shaped molecule which consists of an acute-angled central core and all-ester linking groups has been prepared: 2,3-naphthylene bis[4-(4-n-dodecyloxybenzoyloxy)benzoate]. Its mesomorphic properties have been investigated by DSC, polarizing microscopy, and X-ray diffraction measurements. Moreover, we have carried out detailed electro-optical investigations including birefringence, switching current response, IR dichroism, and second-harmonic generation (SHG) measurements. On the basis of the experimental data a plausible model for the mesophase alignments has been proposed.

QoS support in mobile/wireless IP networks using differentiated services and fast handoff method

In the mobile/wireless IP network where frequent mobility is encountered, it is required to accommodate Internet quality of service (QoS) mechanisms such as differentiated services (DiffServ) for mobile hosts. We consider the issue of integration of mobile IP and DiffServ including handoff condition and propose the schemes with a hierarchical agent architecture for supporting QoS in mobile/wireless IP networks. To support DiffServ for mobile hosts, we configure foreign agent to have pre-allocated resources in advance for static service level agreement (SLA) case. In case foreign network has no pre-configured SLA or enough resources for mobile host, we configure new SLA among bandwidth brokers to be set up using dynamic SLA. Also, we propose the signaling and data procedures with DiffServ with respect to fast handoff.

Memory effects in polymer stabilized ferroelectric liquid crystals, and their dependence on the morphology of the constituent molecules

The origin of distinct memory states (multistable, bistable, monostable) was verified in thiol-ene polymer stabilized ferroelectric liquid crystal system. The stabilization is obtained by the polymerized ene in the interlayer space. The multistability and the resolution of memory states has strong correlation with the dichroic ratio of thiol. As the thiol lengthens, thiols are more intersticed between ferroelectric liquid crystal molecules in the layer and the multistability and the resolution were also enhanced, consequently. In addition, it was found that the binding of thiol to the ene through polymerization was essential for the realization of multistable memory states. The cone mode viscosity was decreased as the thiol lengthens, and this also seems to promote multistability and resolution of memory.

Edge-oriented two-step interpolation based on training set

Preserving the sharpness of edge structures is highly challenging to image interpolation. In this paper, we propose an edge-oriented two-step interpolation method that utilizes an edge training set. For edge interpolation, the LR edge map is converted into the HR edge map by using the training set. Then, an image is classified into smooth and edge regions using the HR edge map, and both regions are interpolated separately. For edge regions, adaptive edge-oriented interpolation is performed by using the detailed edge structures learned from training. The proposed method is extensively evaluated, and its performance is compared with the conventional edge-based methods. Experimental results show that the proposed method can not only reconstruct the missed edge information by the training set, but also significantly reduce blurring and jagging artifacts around edges by separately interpolating smooth and edge regions.

Inducing an antiferroelectric phase by segregating the layers of an intrinsically ferroelectric phase-only liquid crystal with linear-shaped molecules

This paper demonstrates the possibility of inducing an antiferroelectric phase from an intrinsically ferroelectric phase-only liquid crystal by doping with linear-shaped molecules, thus separating the neighboring smectic layers of the ferroelectric liquid crystal from each other. Such an intrinsically impossible process is, in fact, shown to be quite possible due to its entropy-related origin. When the temperature of the doped cell is increased, the antiferroelectric phase reverts to the ferroelectric phase as the dopant molecules change position from interlayer space to intralayer space, a result that coincides with the sawtooth model suggested by Glaser and Clark [Phys. Rev. E 66, 021711 (2002)]. The macroscopic spontaneous polarization of the induced antiferroelectric phase (13.5nC∕cm2) is smaller than that of the ferroelectric phase (73.3nC∕cm2), which shows that the charge fluctuation is not the origin of the conversion.

Polarity-sensitive switching induced by the electric field in a self- assembled nematic system from two different achiral species of molecules

A polarity-sensitive switching behavior was observed in the nematic phase of a system of unit blocks self-assembled from an achiral rod-shaped liquid crystal (LC) and an achiral tripod-shaped dopant. This unit block has a shape of a tripod with extended legs and showed a spontaneous polarization under the applied electric field. Although the polarity-sensitive switching in the achiral LCs is intrinsically impossible, our system of the tripod-shaped unit blocks made with the linear-shaped achiral 8CB bound to the stretched branches of the tripod-shaped achiral dopant by the steric interaction or by the hydrogen bonding showed the polarity-sensitive switching. At zero applied field state, the unit blocks were aligned helically to compensate the macroscopic polarization value. As the field was applied, the helical structure was unwound and the optic axis of the sample rotated clockwise or counterclockwise depending on the sign of the applied field. The threshold field to show the polarity-sensitive switching...

Fast and lossless handoff method considering duplicate address detection in IPv6-based mobile/wireless networks

IPv6 has an inherent characteristic of supporting mobility. When a mobile host (MH) undergoes handoff from one link to another, it needs to obtain a new Care-of Address (CoA) at the New Access Router (N.AR) as soon as possible in order to be able to send and receive IP packets. The basic MIPv6 is the case that MH acquired CoA after moving to handoff expected candidate region. MH obtained CoA before handoff, MH have experienced in reduced handoff latencies. The latency involved in forming a new CoA in MIPv6 comes mainly from both Neighbor Discovery (ND) and Duplicate Address Detection (DAD) in stateless auto-configuration scheme. As MH obtained CoA before handoff and P.AR is using a buffer management, our proposed method is fast and lossless. It is expected that DAD check is indispensable to detect the bad guys who use MHs address by stealth.

Adaptive resource allocation mechanism during handoff for mobile Internet telephony

We present an overview of recent research efforts in developing adaptive delivery models for Internet multimedia applications, which dynamically adjust the transmission rate according to network conditions. The proposed mechanism utilizes service priority in multimedia applications. Simulation results show that the average rate of quality degradation increases as utilization increases. However, the degradation rate should be weighted against the increased handoff blocking probability, as priority is assigned to each channel within the permitted range that meets the traffic needs of each channel. The handoff dropping probability is reduced, in situations where resources were highly utilized, by the proposed mechanism.