A global approach for using kinematic redundancy to minimize base reactions of manipulators

An important consideration in the use of manipulators in microgravity environments is the minimization of the base reactions, i.e. the magnitude of the force and the moment exerted by the manipulator on its base as it performs its tasks. One approach which was proposed and implemented is to use the redundant degree of freedom in a kinematically redundant manipulator to plan manipulator trajectories to minimize base reactions. A global approach was developed for minimizing the magnitude of the base reactions for kinematically redundant manipulators which integrates the Partitioned Jacobian method of redundancy resolution, a 4-3-4 joint-trajectory representation and the minimization of a cost function which is the time-integral of the magnitude of the base reactions. The global approach was also compared with a local approach developed earlier for the case of point-to-point motion of a three degree-of-freedom planar manipulator with one redundant degree-of-freedom. The results show that the global approach is more effective in reducing and smoothing the base force while the local approach is superior in reducing the base moment

Integrated Wireless Multimedia Turbo-Transceiver Design Approaching the Rayleigh Channel's Capacity: Interpreting Shannon's Lessons in the Turbo-Era

Claude Shannon's pioneering work quantified the performance limits of communications systems operating over classic wireline Gaussian channels. However, his source and channel coding theorems were derived for a range of idealistic conditions, which may not hold in low-delay, interactive wireless multimedia communications. Firstly, Shannon's ideal lossless source encoder, namely the entropy encoder may have an excessive codeword length, hence exhibiting a high delay and a high error sensitivity. However, in practice most multimedia source signals are capable of tolerating lossy, rather than lossless delivery to the human eye, ear and other human sensors. The corresponding lossy and preferably low-delay multimedia source codecs however exhibit unequal error sensitivity, which is not the case for Shannon's ideal entropy codec. There are further numerous differences between the Shannonian lessons originally outlined for Gaussian channels and their ramifications for routinely encountered dispersive wireless channels, where typically bursty, rather than random errors are encountered. This paper elaborates on these intriguiging lessons in the context of a few turbo-transceiver design examples, using a jointly optimised turbo transceiver capable of providing unequal error protection in the context of MPEG-4 aided wireless video telephony. The transceiver investigated consists of Space-Time Trellis Coding (STTC) invoked for the sake of mitigating the effects of fading, Trellis Coded Modulation (TCM) or Bit-Interleaved Coded Modulation (BICM) as well as two different-rate Non-Systematic Convolutional codes (NSCs) or Recursive Systematic Convolutional codes (RSCs). A single-class protection based benchmarker scheme combining STTC and NSC is used for comparison with the unequal-protection scheme advocated. The video performance of the various schemes is evaluated when communicating over uncorrelated Rayleigh fading channels. It was found that the achievable performance of the proposed scheme is within 0.99~dB of the corresponding capacity of the Rayleigh fading channel

Burst-by-Burst Adaptive Decision Feedback Equalised TCM, TTCM and BICM for H.263-Assisted Wireless Video Telephony

Decision Feedback Equaliser (DFE) aided wideband Burst-by-Burst (BbB) Adaptive Trellis Coded Modulation (TCM), Turbo Trellis Coded Modulation (TTCM) and Bit-Interleaved Coded Modulation (BICM) assisted H.263-based video transceivers are proposed and characterised in performance terms when communicating over the COST 207 Typical Urban wideband fading channel. Specifically, four different modulation modes, namely 4QAM, 8PSK, 16QAM and 64QAM are invoked and protected by the above-mentioned coded modulation schemes. The TTCM assisted scheme was found to provide the best video performance, although at the cost of the highest complexity. A range of lower-complexity arrangements will also be characterised. Finally, in order to confirm these findings in an important practical environment, we have also investigated the adaptive TTCM scheme in the CDMA-based Universal Mobile Telecommunications System's (UMTS) Terrestrial Radio Access (UTRA) scenario and the good performance of adaptive TTCM scheme recorded when communicating over the COST 207 channels was retained in the UTRA environment

Non-equilibrium spatial distribution of Rashba spin torque in ferromagnetic metal layer

We study the spatial distribution of spin torque induced by a strong Rashba spin-orbit coupling (RSOC) in a ferromagnetic (FM) metal layer, using the Keldysh non-equilibrium Green's function method. In the presence of the s-d interaction between the non-equilibrium conduction electrons and the local magnetic moments, the RSOC effect induces a torque on the moments, which we term as the Rashba spin torque. A correlation between the Rashba spin torque and the spatial spin current is presented in this work, clearly mapping the spatial distribution of Rashba Spin torque in a nano-sized ferromagnetic device. When local magnetism is turned on, the out-of-plane (Sz) Spin Hall effect (SHE) is disrupted, but rather unexpectedly an in-plane (Sy) SHE is detected. We also study the effect of Rashba strength (\alpha_R) and splitting exchange (\Delta) on the non-equilibrium Rashba spin torque averaged over the device. Rashba spin torque allows an efficient transfer of spin momentum such that a typical switching field of 20 mT can be attained with a low current density of less than 10^6 A/cm^2

Induced Lorentz- and CPT-violating Chern-Simons term in QED: Fock-Schwinger proper time method

Using the Fock-Schwinger proper time method, we calculate the induced Chern-Simons term arising from the Lorentz- and CPT-violating sector of quantum electrodynamics with a $b_\mu \bar{\psi}\gamma^\mu \gamma_5 \psi$ term. Our result to all orders in $b$ coincides with a recent linear-in-$b$ calculation by Chaichian et al. [hep-th/0010129 v2]. The coincidence was pointed out by Chung [Phys. Lett. {\bf B461} (1999) 138] and P\'{e}rez-Victoria [Phys. Rev. Lett. {\bf 83} (1999) 2518] in the standard Feynman diagram calculation with the nonperturbative-in-$b$ propagator.Comment: 11 pages, no figur

Using an Internet-based GSS to Support Virtual Teams: An Empirical Investigation

The studied conducted by the cluster of NJIT (e.g., Dufner et al. 1995; Fjermestad et al. 1995; Kim, Hiltz and Turoff 1998; Ocker and Fjermestad 1998; Ocker et al. 1995 & 1996 & 1997) focused more on group outcomes, rather than group development. Impacts of different communication modes (FtF, FtF GSS, distributed GSS, asynchronous GSS, and combined communication) and structures/tools of GSS on group outcomes were the main issues examined in their research. They found out that using GSS tools improved group outcomes (Dufner et al. 1995), groups with leadership performed better than those without leadership (Kim, Hiltz and Turoff 1998), and asynchronous GSS groups performed better than FtF groups in creativity (Ocker and Fjermestad 1998; Ocker et al. 1995 & 1996). Their findings suggest that to improve group performance, suitable GSS tools/structures should be used and further, more tools/structures should constructed and embedded into GSS

Rotational covariance and light-front current matrix elements

Light-front current matrix elements for elastic scattering from hadrons with spin~1 or greater must satisfy a nontrivial constraint associated with the requirement of rotational covariance for the current operator. Using a model $\rho$ meson as a prototype for hadronic quark models, this constraint and its implications are studied at both low and high momentum transfers. In the kinematic region appropriate for asymptotic QCD, helicity rules, together with the rotational covariance condition, yield an additional relation between the light-front current matrix elements.Comment: 16 pages, [no number