Takahiro K. Fujita

Antiferro-Quadrupolar Ordering at the Lowest Temperature and Anisotropic Magnetic Field–Temperature Phase Diagram in the Cage Compound PrIr2Zn20

The cage compound PrIr 2 Zn 20 with the non-Kramers doublet ground state shows a phase transition at T Q ∼0.11 K. To investigate the origin of the phase transition, we have carried out ultrasonic m...

MAT: an end-to-end mobile communication architecture with seamless IP handoff support for the next generation internet

The technological advancement in the area of handheld mobile devices has resulted in a movement towards total mobility. Real-time applications are demanding such a flexible mobility support that would not interact adversely with the existing protocols, especially with Quality of Service (QoS) and security mechanisms. We believe that this could be achieved by providing mobility services through the mobile nodes themselves rather than via proxies. This paper proposes an end-to-end mobile communication architecture, called Mobile IP with Address Translation (MAT). MAT does not require any modification in the core network. To realize mobility we use address translation within host-nodes at the IP layer. We describe MAT architecture and show its mobility capability by prototype implementation and evaluation. Preliminary results show that MAT is fully compatible and works fine in both IPv4 and IPv6 environment. We also compare its features with Mobile IPv4 (MIP), Mobile IPv6 (MIPv6) and Location Independent Network Architecture (LIN6) protocols. Furthermore we propose a handoff technique based on MAT which helps to reduce service disruption interval significantly.

Successive Phase Transitions and Anisotropic Magnetic Field–Temperature Phase Diagram in NdRu2Al10

To investigate the successive phase transitions in NdRu 2 Al 10 , we carried out ultrasonic measurements on single-crystalline samples. We found that the elastic moduli show an abrupt hardening at 2.4 K without hysteresis and a two-step softening at 1.3 and 1.0 K with clear hysteresis in the temperature sweep. The hardening at 2.4 K is very similar to that observed in CeRu 2 Al 10 and CeOs 2 Al 10 , suggesting that the second-order transition at 2.4 K originates from a similar mechanism of the transitions in CeRu 2 Al 10 and CeOs 2 Al 10 . Both transitions at 1.3 and 1.0 K would originate from an antiferromagnetic first-order spin ordering. We also clarified the anisotropic magnetic field H dependences of the transition temperatures in H along the a -, b -, and c -axes, and found a new phase above 2.5 T in H ∥ a .

Elastic Hardening at a Novel Phase Transition in Cage Compound CeRu2Al10

Elastic properties of the cage compound CeRu 2 Al 10 have been investigated by means of ultrasonic measurement. We found a sudden elastic hardening in all moduli below T 0 =27.3 K at which a novel phase transition occurs, and an abrupt elastic softening was observed in longitudinal moduli at T 0 . The magnitude of hardening in C 11 is the largest. We discuss these elastic behaviors from the viewpoint of a CDW transition and a spin-Peierls transition. We estimated the strain dependence of T 0 along the a -, b -, and c -axes from the Ehrenfest relation. No frequency dependence of elastic moduli was observed in the whole temperature range measured.

Ultrasonic Dispersion in All Elastic Moduli and Softening at Low Temperatures in Filled Skutterudite LaFe4Sb12

To clarify the origin of ultrasonic dispersion due to the so-called rattling motion in LaFe 4 Sb 12 , we measured the temperature dependences of elastic moduli and ultrasonic attenuation. We found the ultrasonic dispersion to be between 35 and 80 K in all elastic moduli, suggesting no-mode-selectivity of ultrasound. Experimental results and theoretically calculated density of states indicate that the d -electronic states of transition metal ions play an important role in ultrasonic dispersion. The theory based on the coupling between an acoustic phonon and some optical phonons interacting with electrons is compatible with no-mode-selective ultrasonic dispersion, and it suggests a stronger electron–phonon coupling in all elastic modes in LaFe 4 Sb 12 . Low-temperature elastic softening was observed in all elastic moduli, and it continues down to 0.4 K. There is a possibility that low-temperature softening originates from quantum tunneling motion or a novel quantum effect of rattling motion.

Realizing high mobility through an end-to-end network architecture with IP diversity support for real time Internet applications

This paper presents a mobile-controlled handoff with an end-to-end communication architecture that helps to provide high mobility without requiring any special service from the visiting networks. The handoff utilizes the IP diversity created by dual network interfaces at the mobile node and exploits the overlapping area between subnets. The end-to-end network architecture is particularly suitable for low bit rate delay sensitive real time applications, where payload tends to be short and packet header overhead is particularly significant. We describe the network architecture and show the mobility support by prototype implementation and its performance evaluation. We also develop an analytical model of handoff and compare the performance of handoff in proposed network architecture and mobile IPv6. Performance evaluation shows that the handoff quality not only depends on the location but also on the implementation design of the location database servers. We see significant latency improvement due to our implementation as compare to mobile IPv6.

Elastic Softening in HoFe2Al10 due to the Quadrupole Interaction under an Orthorhombic Crystal Electric Field

To investigate 4f electronic states in HoFe2Al10 under an orthorhombic crystal electric field (CEF), we measured the specific heat, magnetic susceptibility, magnetization, and elastic modulus of single-crystalline samples. We found elastic softening of the transverse elastic moduli C55 and C66 below 20 and 130 K, respectively. With further decreasing temperature, C66 shows further elastic softening below 5 K. We observed two Schottky peaks in the specific heat at 2.2 and 20 K and small anisotropy of the magnetic susceptibility and magnetization in the paramagnetic region. By analyzing these experimental data, we obtained the CEF parameters of HoFe2Al10. From the analysis, we clarified that the softening of C55 and C66 originates from indirect quadrupole interactions of Ozx and Oxy, and propose that the overall CEF splitting is about 85 K.

Anomalous Elastic Softening due to the Crystal Electric Field Effect and Successive Phase Transitions in the Yb-Based Heavy-Fermion Antiferromagnet YbIrGe

To investigate the crystal electric field effect and antiferromagnetic transitions at 2.4 and 1.4 K, we carried out ultrasonic measurements on the Yb-based heavy-fermion antiferromagnet YbIrGe. We found characteristic softening of the elastic moduli originating from a quadrupole interaction. By theoretical analyses of the transverse elastic moduli, the magnetic susceptibility, and the Schottky specific heat between 10 and 300 K, we determined the crystal electric field: the ground doublet and an excited doublet separated by 138 K. The moduli exhibit elastic hardening below both 2.4 and 1.4 K, suggesting a strong coupling between a strain and magnetic order parameters. We estimated the strain dependence of the transition temperature at 2.4 K along the a- and c-axes from the Ehrenfest relation for the first time.

Large Softening of Longitudinal Elastic Modulus in TbB4

Rare earth tetraborides have a tetragonal crystalline structure with the space group P4/mbm. The rare earth ions form the Shastry-Sutherland lattice in the c plane in these compounds, which evokes us an interesting electronic property due to the geometric frustration of spins and orbitals. TbB4 undergoes two phase transitions at TN1 = 42.1 K and TN2 = 21.7 K, respectively. Because of the clear cusp-type anomaly in the temperature dependence of magnetic susceptibility, the transition at TN1 should be an antiferromagnetic one. The origin of the transition at TN2 is unclear at present. To investigate the possibility of multipolar ordering, we measured temperature dependencies of elastic moduli using the ultrasonic phase comparison method. The longitudinal elastic modulus C11 shows large softening with more than 17% reduction of the stiffness at TN2 in contrast to no anomaly at TN1. This result suggests ferro-type ordering of the quadrupole O?3 at TN2. The macroscopic spontaneous strain in the c plane emerging due to the ferroquadrupolar ordering may lift the geometric frustration.

Elastic anomalies at successive phase transitions in NdRu2Al10

We carried out ultrasonic measurements on NdRu2Al10 single crystals in order to clarify what kind of phase transition occurs in this compound. The elastic moduli were measured as a function of temperature from 0.5 K to 150 K using the phase comparison-type pulse echo method. As the temperature is decreased from 150 K, longitudinal elastic modulus C11 and transverse elastic modulus C44 show a monotonic enhancement. With further decreasing temperature, both elastic moduli show abrupt hardening at 2.4 K and then show two-step softening at 1.3 K and 1.0 K. We found obvious hysteresis around both transitions at 1.3 K and 1.0 K in the temperature sweep, whereas no hysteresis was observed around the transition at 2.4 K within our experimental accuracy. The abrupt hardening at 2.4 K is very similar to that found in CeRu2Al10 and CeOs2Al10, suggesting that the transition at 2.4 K originates from the same mechanism of the transitions in CeRu2Al10 and CeOs2Al10. This is the first report that NdRu2Al10 undergoes the successive phase transitions.