Complex Adaptive LMS Algorithm Employing the Conjugate Gradient Principle for Channel Estimation and Equalization

The Complex Block Least Mean Square (LMS) technique is widely used in adaptive filtering applications because of its simplicity and efficiency from a theoretical and implementation standpoint. However, the limitations of the Complex Block LMS technique are slow convergence and dependence on the proper choice of the stepsize or convergence factor. Moreover, its performance degrades significantly in time-varying environments. In this paper, a novel adaptive LMS technique named the Complex Block Conjugate LMS algorithm, CBC-LMS, is presented. Based on the Conjugate Gradient Principle, the proposed technique searches orthogonal directions to update the filter coefficients instead of the negative gradient directions used in the Complex Block LMS algorithm. In addition, the CBC-LMS algorithm derives optimal stepsizes to adjust the adaptive system coefficients at each iteration. As a result, the developed method overcomes the inherent limitations of the existing Complex Block LMS algorithm. The performance of the CBC-LMS technique is tested in wireless channel estimation and equalization applications, using both computer simulations and laboratory experiments. Furthermore, the developed technique is compared to the Complex Block LMS method and a recently proposed method, which is called Complex Optimal Block Adaptive LMS (OBA-LMS). The experimental and simulation results confirm that the proposed CBC-LMS technique achieves faster convergence with comparable accuracy and reduced computational complexity, relative to the existing techniques.     

Observation of kinks and antikinks in colloidal monolayers driven across ordered surfaces

Friction between solids is responsible for many phenomena such as earthquakes, wear or crack propagation. Unlike macroscopic objects, which only touch locally owing to their surface roughness, spatially extended contacts form between atomically flat surfaces. They are described by the Frenkel-Kontorova model, which considers a monolayer of interacting particles on a periodic substrate potential. In addition to the well-known stick-slip motion, such models also predict the formation of kinks and antikinks, which greatly reduce the friction between the monolayer and the substrate. Here, we report the direct observation of kinks and antikinks in a two-dimensional colloidal crystal that is driven across different types of ordered substrate. We show that the frictional properties only depend on the number and density of such excitations, which propagate through the monolayer along the direction of the applied force. In addition, we also observe kinks on quasicrystalline surfaces, which demonstrates that they are not limited to periodic substrates but occur under more general conditions.     

Optimal utilization of computerized cranial tomography and radionuclide brain imaging

The results of computerized cranial tomography and radionuclide brain imaging in 490 patients were compared in relationship to the patients' clinical presentation. In 195 patients with focal neurologic abnormalities, both tests detected most lesions, but computerized cranial tomography was slightly more accurate overall. Results of both studies were normal in 69 percent of 295 patients with nonfocal neurologic presentations, and radionuclide imaging failed to detect lesions in only five patients with nonfocal presentations. These results suggest that radionuclide imaging can be used to accurately screen most patients with nonfocal neurologic presentations. An exception is the patient presenting with dementia, in whom computerized cranial tomography provides details of the anatomy of the ventricular cavities and cerebral cortex. This study demonstrates a continuing role of importance for radionuclide imaging in the evaluation of patients with neurologic disease and provides data to allow a rational approach to the optimum use of both techniques.     

An Efficient Image Representation Technique Using Vector Quantization in Multiple Transform Domains

A novel technique for the efficient representation of still images is presented which employs vector quantization in multiple transform domains of the image signal. The system projects the subimages, obtained by partitioning the images used for training, into multiple transform domains. Energy-based split vector quantization is used to form code books in each of these domains. An adaptive algorithm to further optimize the accuracy of the code books in each transform domain is also developed. Simulations using sample imges show that this scheme provides improved reconstruction quality over existing methods for the same compression ratios, or equivalently, employing the proposed technique, fewer bits per pixel are used for the same reconstruction quality. This is achieved at the expense of increased computation at the encoder. The benefits from the improved representation efficiency of ten outweigh the increased computational complexity.     

Transsphenoidal microsurgery of pituitary macroadenomas with long-term follow-up results

The authors have reported on 108 patients with pituitary macroadenomas (measuring 2 cm in at least one diameter) who underwent 117 transsphenoidal operations and five craniotomies, and were followed for periods ranging from 6 months to 14 years. Vision improved in 90% of the patients. Gross total tumor removal with no evidence of residual tumor tissue demonstrable on the postoperative computerized tomography scan was accomplished in 41% of cases. However, gross total tumor removal is not synonymous with complete tumor removal. Endocrine cure was possible in 25% of prolactin-secreting and 20% of growth hormone-secreting adenomas. The incidence of recurrence was 12%, with the majority occurring from 4 to 8 years postoperatively. Both the tumors with suprasellar extension of more than 2 cm and the hard fibrotic tumors had a higher recurrence rate. Postoperative administration of radiation therapy has been associated with a significantly lower recurrence rate than when this therapy was withheld. Transsphenoidal surgery of pituitary macroadenomas confined to the extra-arachnoid space is associated with a relatively small number of complications. The operative technique used in this series is described.     

Shaping potentialities of aluminum nitride polymeric precursors: Preparation of thin coatings and 1D nanostructures in liquid phase

The present paper is focused on the synthesis of a series of poly[N-(alkylimino)alanes] of the type [HAlNR]_n as preceramic polymers for the preparation of aluminum nitride (AlN). Polymers were characterized by means of Fourier transform infrared spectra (FT-IR), liquid-state ¹H and ¹³C NMR spectrometry and elemental analyses. The polymers were prepared in different physical states going from viscous liquid to solid (soluble and/or fusible) compounds with the decrease of the carbon content in the polymer chain. Such properties offer potentialities in the preparation of complex forms of ceramics including thin coatings and 1D nanostructures. AlN thin coatings and 1D nanostructures were obtained from a solution of poly[N-(isopropylimino)alane] in toluene followed by heat-treatment in flowing ammonia up to 1000 °C resulting in a ceramic yield of 50.6%. Subsequent heat-treatment to 1800 °C in flowing nitrogen allowed the production of crystalline AlN coatings and nanorods identified by Raman spectrometry and X-ray diffraction.     

Preparation of ZnO nanoparticles localized on SiC@SiO2 nanocables by a physical templating method

Impregnation of interlaced SiC@SiO₂ nanocables (SiC NWs sheathed by SiO₂ coatings) into a ZnO sol at 0 °C yielded, after thermal treatment up to 600 °C under argon, SiC@SiO₂@ZnO nanostructures. These novel nanostructures consist in SiC@SiO₂ nanocables covered by numerous agglomerated ZnO nanoparticles. The latter are less than 5 nm in diameter. This result is to our knowledge the first example of a physical templating technique involving SiC-based nanowires. Moreover, we have obtained localized ZnO nanoparticles. This localization can be of interests for a further study of their physical properties. When a similar experiment was conducted with pure SiC nanowires, there was no interaction between the nanowires (NWs) and the solution, resulting in the formation of agglomerated ZnO NPs embedded into the 3D NWs network.     

Copolymerization of acrylonitrile with N-substituted maleimides

Acrylonitrile was copolymerized with three N-arylmaleimides as well as with N-octadecylmaleimide in dimethylformamide (DMF) using azobisisobutyronitrile (AIBN) as initiator. The monomer reactivity ratios were calculated by the Fineman-Ross and the Kelen-Tüd?s methods from which the Q- and e-parameters of these monomers were evaluated. The prepared copolymers were characterized by viscosity measurements and thermal analysis. The intrinsic viscosity decreases by increasing the maleimide content in the copolymer. Thermogravimetry TG and differential thermal analysis (DTA) data showed a remarkable improvement in the thermal behaviour of the investigated copolymers. A mechanism for the participation of the maleimide units in the nitrile oligomerization was also proposed. The investigation of the dyeing properties of the copolymers with the exception of those containing octadecylmaleimide, showed good affinity towards basic dyes as well as an appreciable improvement in their colour fastness towards UV light.     

Self-oscillations in field emission nanowire mechanical resonators: a nanometric dc-ac conversion

We report the observation of self-oscillations in a bottom-up nanoelectromechanical system (NEMS) during field emission driven by a constant applied voltage. An electromechanical model is explored that explains the phenomenon and that can be directly used to develop integrated devices. In this first study, we have already achieved approximately 50% dc/ac (direct to alternating current) conversion. Electrical self-oscillations in NEMS open up a new path for the development of high-speed, autonomous nanoresonators and signal generators and show that field emission (FE) is a powerful tool for building new nanocomponents.     

Understanding the Photothermal and Photocatalytic Mechanism of Polydopamine Coated Gold Nanorods

Localized surface plasmon resonance (LSPRs) shown by gold nanorods (AuNRs) has several applications in photocatalysis, sensing, and biomedicine. The combination of AuNRs with Polydopamine (PDA) shells results in a strong photo-thermal effect, making them appealing nanomaterials for biomedical applications. However, the precise roles and relative contributions of plasmonic effects in gold, and light-to-heat conversion in PDA are still debated. Herein, a hybrid nanoplatform made by an AuNR core surrounded by a polydopamine (PDA) shell is synthesized, and its photocatalytic behavior is studied. Synthesis is based on a seed-mediated growth followed by the further self-polymerization of dopamine hydrochloride (DA) on the surface of the AuNRs, and the effect of the thickness of the PDA shell on the plasmon response of the composite is the main examined parameter. Photocatalytic performance is tested toward Rhodamine 6G (Rh6G), with the nanocomposites achieving better performance than bare AuNRs and bare PDA nanoparticles. The degradation of 54% of Rh6G initial concentration is achieved within 60 min of irradiation with a catalyst concentration of 7.4 µg mL⁻¹. Photodegradation kinetics, time-resolved spectroscopy, and finite-element-method simulations of plasmons show that AuNRs plasmons, coupled with the low thermal conductivity of PDA, provide slow thermalization, while enhancing the charge carrier transfer.