Robust joint precoder/receive filter designs for multiuser MIMO downlink

In this paper, we consider robust joint linear precoder/receive filter designs for multiuser multi-input multi-output (MIMO) downlink that minimize the sum mean square error (SMSE) in the presence of imperfect channel state information at the transmitter (CSIT). The base station (BS) is equipped with multiple transmit antennas, and each user terminal is equipped with one or more receive antennas. We consider a stochastic error (SE) model and a norm-bounded error (NBE) model for the CSIT error. In the case of CSIT error following SE model, we compute the desired downlink precoder/receive filter matrices by solving the simpler uplink problem by exploiting the uplink-downlink duality for the MSE region. In the case of the CSIT error following the NBE model, we consider the worst-case SMSE as the objective function, and propose an iterative algorithm for the robust transceiver design. The robustness of the proposed algorithms to imperfections in CSIT is illustrated through simulations.

Synthesis, structure and magnetic behavior of a new three-dimensional Manganese phosphite-oxalate: [C2N2H10][Mn-2(II)(OH2)(2)(HPO3)(2)(C2O4)]

A novel manganese phosphite-oxalate, [C2N2H10][Mn-2(II)(OH2)(2)(HPO3)(2)(C2O4)] has been hydothermally synthesized and its structure determined by single-crystal X-ray diffraction. The structure consists of neutral manganese phosphite layers, [Mn(HPO3)](infinity), formed by MnO6 octahedra and HPO3 units, cross-linked by the oxalate moieties. The organic cations occupy the middle of the 8-membered one dimensional channels. Magnetic studies indicate weak antiferromagnetic interactions between the Mn2+ ions. (C) 2009 Elsevier Inc. All rights reserved.

Bioabsorbable materials for osteosynthesis and small joint arthroplasty in the hand

Fractures and arthritic joint destruction are common in the hand. A reliable and stable fracture fixation can be achieved by metal implants, which however, become unnecessary or even harmful after consolidation. The silicone implant arthroplasty is the current method of choice for reconstruction of metacarpophalangeal joints in rheumatoid patients. However, the outcome tends to worsen with long-term follow-up and implant-related complications become frequent. To address these problems, bioabsorbable implants were designed for the hand area. Aims of the studies were: 1) to evaluate the biomechanical stabilities provided by self- reinforced (SR) bioabsorbable implants in a transverse and an oblique osteotomy of small tubular bones and to compare them with those provided by metal implants; 2) to evaluate the SR poly-L/DL-lactide 70/30 plate for osteosynthesis in a proof-of-principle type of experiment in three cases of hand injuries; and 3) to evaluate the poly-L/D-lactide (PLA) 96/4 joint scaffold, a composite joint implant with a supplementary intramedullary Polyactive® stem and Swanson silicone implant in an experimental small joint arthroplasty model. Methods used were: 1) 112 fresh frozen human cadaver and 160 pig metacarpal bones osteotomised transversally or obliquely, respectively, and tested ex vivo in three point bending and in torsion; 2) three patient cases of complex hand injuries; and 3) the fifth metacarpophalangeal joints reconstructed in 18 skeletally-mature minipigs and studied radiologically and histologically. The initial fixation stabilities provided by bioabsorbable implants in the tubular bones of the hand were comparable with currently-employed metal fixation techniques, and were sufficient for fracture stabilisation in three preliminary cases in the hand. However, in torsion the stabilities provided by bioabsorbable implants were lower than that provided by metal counterparts. The bioabsorbable plate enhanced the bending stability for the bioabsorbable fixation construct. PLA 96/4 joint scaffolds demonstrated good biocompatibility and enabled fibrous tissue in-growth in situ. After scaffold degradation, a functional, stable pseudarthrosis with dense fibrous connective tissue was formed. However, the supplementary Polyactive® stem caused a deleterious tissue reaction and therefore the stem can not be applied to the composite joint implant. The bioabsorbable implants have potential for use in clinical hand surgery, but have to await validation in clinical patient series and controlled trials.

On the mechanical behavior of compacted pack ice : A theoretical and numerical investigation

Pack ice is an aggregate of ice floes drifting on the sea surface. The forces controlling the motion and deformation of pack ice are air and water drag forces, sea surface tilt, Coriolis force and the internal force due to the interaction between ice floes. In this thesis, the mechanical behavior of compacted pack ice is investigated using theoretical and numerical methods, focusing on the three basic material properties: compressive strength, yield curve and flow rule. A high-resolution three-category sea ice model is applied to investigate the sea ice dynamics in two small basins, the whole Gulf Riga and the inside Pärnu Bay, focusing on the calibration of the compressive strength for thin ice. These two basins are on the scales of 100 km and 20 km, respectively, with typical ice thickness of 10-30 cm. The model is found capable of capturing the main characteristics of the ice dynamics. The compressive strength is calibrated to be about 30 kPa, consistent with the values from most large-scale sea ice dynamic studies. In addition, the numerical study in Pärnu Bay suggests that the shear strength drops significantly when the ice-floe size markedly decreases. A characteristic inversion method is developed to probe the yield curve of compacted pack ice. The basis of this method is the relationship between the intersection angle of linear kinematic features (LKFs) in sea ice and the slope of the yield curve. A summary of the observed LKFs shows that they can be basically divided into three groups: intersecting leads, uniaxial opening leads and uniaxial pressure ridges. Based on the available observed angles, the yield curve is determined to be a curved diamond. Comparisons of this yield curve with those from other methods show that it possesses almost all the advantages identified by the other methods. A new constitutive law is proposed, where the yield curve is a diamond and the flow rule is a combination of the normal and co-axial flow rule. The non-normal co-axial flow rule is necessary for the Coulombic yield constraint. This constitutive law not only captures the main features of forming LKFs but also takes the advantage of avoiding overestimating divergence during shear deformation. Moreover, this study provides a method for observing the flow rule for pack ice during deformation.

Electrical switching behavior of bulk Si15Te85-xSbx chalcogenide glasses - A study of compositional dependence

Studies on the electrical switching behavior of melt quenched bulk Si15Te85-xSbx glasses have been undertaken in the composition range (1 <= x <= 10), in order to understand the effect of Sb addition on the electrical switching behavior of Si15Te85-x base glass. It has been observed that all the Si15Te85-xSbx glasses studied exhibit a smooth memory type switching. Further, the switching voltages are found to decrease almost linearly with Sb content, which indicates that the metallicity of the dopant plays a dominant role in this system compared to network connectivity/rigidity. The thickness dependence of switching voltage (V-th) indicates a clear thermal origin for the switching mechanism. The temperature variation of switching voltages reveals that the Si15Te85-xSbx glasses studied have a moderate thermal stability. (C) 2009 Elsevier B.V. All rights reserved.

Surface spin glass behavior in sol–gel derived La0.7Ca0.3MnO3 nanotubes

We report the fabrication of La0.7Ca0.3MnO3 nanotubes (LCMONTs) with a diameter of about 200 nm, by a modified sol-gel method utilizing nanochannel alumina templates. High resolution transmission electron microscopy confirmed that the obtained LCMONTs are made up of nanoparticles (8-12 nm), which are randomly aligned in the wall of the nanotubes. The strong irreversibility between zero field cooling (ZFC) and field cooling (FC) magnetization curves as well as a cusplike peak in the ZFC curve gives strong support for surface spin glass behavior.

Scanning Tunneling Spectroscopy on Pr0.68Pb0.32MnO3 single crystals

Scanning tunneling microscopy/spectroscopy studies were carried out on single crystals of colossal magnetoresistive manganite Pr0.68Pb0.32MnO3 at different temperatures in order to probe their spatial homogeneity across the metal-insulator transition temperature TM-I(similar to 255 K). A metallic behavior of the local conductance was observed for temperatures T < TM-I. Zero bias conductance (dI/dV)v=(0), which is directly proportional to the local surface density of states at the Fermi level, shows a single distribution at temperatures T < 200 K suggesting a homogeneous electronic phase at low temperatures. In a narrow temperature window of 200 K < T < TM-I, however, an inhomogeneous distribution of (dI/dV)v=(0) has been observed. This result gives evidence for phase separation in the transition region in this compound.

Scanning Tunneling Spectroscopy on Pr0.68Pb0.32MnO3 single crystals

Scanning tunneling microscopy/spectroscopy studies were carried out on single crystals of colossal magnetoresistive manganite Pr0.68Pb0.32MnO3 at different temperatures in order to probe their spatial homogeneity across the metal-insulator transition temperature TM-I(similar to 255 K). A metallic behavior of the local conductance was observed for temperatures T < TM-I. Zero bias conductance (dI/dV)v=(0), which is directly proportional to the local surface density of states at the Fermi level, shows a single distribution at temperatures T < 200 K suggesting a homogeneous electronic phase at low temperatures. In a narrow temperature window of 200 K < T < TM-I, however, an inhomogeneous distribution of (dI/dV)v=(0) has been observed. This result gives evidence for phase separation in the transition region in this compound.

Overview No.144 - Mechanical behavior of amorphous alloys

The mechanical properties of amorphous alloys have proven both scientifically unique and of potential practical interest, although the underlying deformation physics of these materials remain less firmly established as compared with crystalline alloys. In this article, we review recent advances in understanding the mechanical behavior of metallic glasses, with particular emphasis on the deformation and fracture mechanisms. Atomistic as well as continuum modeling and experimental work on elasticity, plastic flow and localization, fracture and fatigue are all discussed, and theoretical developments are connected, where possible, with macroscopic experimental responses. The role of glass structure on mechanical properties, and conversely, the effect of deformation upon glass structure, are also described. The mechanical properties of metallic glass-derivative materials – including in situ and ex situ composites, foams and nanocrystal-reinforced glasses – are reviewed as well. Finally, we identify a number of important unresolved issues for the field.

Dielectric, Ferroelectric and Relaxor Behavior of BaLaxBi4-xTi4O15 Ceramics

Monophasic BaLaxBi4-xTi4O15 (x = 0, 0.2, 0.4, 0.6 and 0.8) ceramics, fabricated from the powders synthesized via the solid-state reaction route exhibited relaxor behavior. Dielectric properties of the well sintered ceramics were measured in a wide frequency range (1 kHz-1 MHz) at different temperatures (300-750 K). The temperature of dielectri maximum (T-m) was found to decrease significantly from 696 K for an undoped sample (x = 0) to 395 K for the sample corresponding to the composition x = 0.8 accompanied by a decrease in the magnitude ofdielectric maximum (epsilon(m)). The temperature variation of the dielectric constant on the high temperature slope of the peak (T > T-m) was analyzed by using the Lorentz-ype quadratic law and the diffuseness of the peak was found to increase with increasing x. Vogel-Fulcher modelling of dielectric relaxation showed a decrease in freezing temperature (T-VF) (from 678 to 340 K) and an increase in the activation energy (5 to 24 meV) for the frequency dispersion with increase in x (La-3 divided by content). Strength of frequency dispersion of the phase transition increased with lanthanum content. Polarization (P)-electric field (E) hysteresis loops recorded at 373 showed a transition from a nearly squarish to slim loop hysteresis behavior with increasing lanthanum content.

Scanning Tunneling Spectroscopy on Pr0.68Pb0.32MnO3 single crystals

Scanning tunneling microscopy/spectroscopy studies were carried out on single crystals of colossal magnetoresistive manganite Pr0. 68Pb0.32MnO3 at different temperatures in order to probe their spatial homogeneity across the metal-insulator transition temperature TM-I(similar to 255 K). A metallic behavior of the local conductance was observed for temperatures T < TM-I. Zero bias conductance (dI/dV)v=(0), which is directly proportional to the local surface density of states at the Fermi level, shows a single distribution at temperatures T < 200 K suggesting a homogeneous electronic phase at low temperatures. In a narrow temperature window of 200 K < T < TM-I, however, an inhomogeneous distribution of (dI/dV)v=(0) has been observed. This result gives evidence for phase separation in the transition region in this compound.

Busy auditors, ethical behavior, and discretionary accruals quality in Malaysia

The required professional and ethical pronouncements of accountants mean that auditors need to be competent and exercise due care and skill in the performance of their audits. In this study, we examine what happens when auditors take on more clients than they should, thus raising doubts about their ability to maintain competence and audit quality. Using 2803 observations of Malaysian companies from 2010 to 2013, we find that auditors with multiple clients are associated with lower earnings quality, proxied by total accruals and discretionary accruals. Our results demonstrate that associating client firms’ reported discretionary accruals with individual auditors, rather than their firms or offices, is important in determining audit quality. Moreover, we demonstrate that the disclosure of auditors’ signatures on their reports is useful for assessing auditor quality at the individual level, thus contributing to the debate on the usefulness of having auditor identities on reports.

Ship collision avoidance and COLREGS compliance using simulation-based control behavior selection with predictive hazard assessment

This paper describes a concept for a collision avoidance system for ships, which is based on model predictive control. A finite set of alternative control behaviors are generated by varying two parameters: offsets to the guidance course angle commanded to the autopilot and changes to the propulsion command ranging from nominal speed to full reverse. Using simulated predictions of the trajectories of the obstacles and ship, compliance with the Convention on the International Regulations for Preventing Collisions at Sea and collision hazards associated with each of the alternative control behaviors are evaluated on a finite prediction horizon, and the optimal control behavior is selected. Robustness to sensing error, predicted obstacle behavior, and environmental conditions can be ensured by evaluating multiple scenarios for each control behavior. The method is conceptually and computationally simple and yet quite versatile as it can account for the dynamics of the ship, the dynamics of the steering and propulsion system, forces due to wind and ocean current, and any number of obstacles. Simulations show that the method is effective and can manage complex scenarios with multiple dynamic obstacles and uncertainty associated with sensors and predictions.