Thermal Expansion of Alkaline‐Doped Lanthanum Ferrite Near the Néel Temperature

The thermal expansion and magnetic behaviors of divalent, alkaline‐doped lanthanum ferrites (La_0.9M_0.1FeO₃, M=Ca, Sr, Ba) were assessed using a combination of dilatometry, magnetometry, time‐of‐flight neutron diffraction, and high‐temperature X‐ray diffraction. Néel temperatures were determined through vibrating sample magnetometry and correlated well with changes in thermal expansion behavior observed during both dilatometry and X‐ray diffraction. The Néel temperatures observed for pure, Ca‐doped, Sr‐doped, and Ba‐doped lanthanum ferrites were 471°C, 351°C, 465°C, and 466°C, respectively. The effect of divalent substitutions on the magnetic behavior are attributed to charge compensation mechanisms and structural changes in the material.     

Fluorescent dye encapsulated ZnO particles with cell-specific toxicity for potential use in biomedical applications

Fluorescein isothiocyanate (FITC)-encapsulated SiO₂ core-shell particles with a nanoscale ZnO finishing layer have been synthesized for the first time as multifunctional “smart” nanostructures. Detailed characterization studies confirmed the formation of an outer ZnO layer on the SiO₂–FITC core. These ~200 nm sized particles showed promise toward cell imaging and cellular uptake studies using the bacterium Escherichia coli and Jurkat cancer cells, respectively. The FITC encapsulated ZnO particles demonstrated excellent selectivity in preferentially killing Jurkat cancer cells with minimal toxicity to normal primary immune cells (18% and 75% viability remaining, respectively, after exposure to 60 μg/ml) and inhibited the growth of both gram-positive and gram-negative bacteria at concentrations ≥250–500 μg/ml (for Staphylococcus aureus and Escherichia coli, respectively). These results indicate that the novel FITC encapsulated multifunctional particles with nanoscale ZnO surface layer can be used as smart nanostructures for particle tracking, cell imaging, antibacterial treatments and cancer therapy.     

Blind channel estimation for multiple input multiple output uplink guard-band assisted code division multiple access systems with layered space frequency equalisation

Single carrier (SC) code division multiple access (CDMA) with block transmission has been shown to be more effective while utilising a low-complexity equaliser to combat frequency-selective fading channels, when compared with conventional direct sequence CDMA technology. It also has lower peak-to-average power ratio and lower frequency sensitivity compared with multicarrier CDMA. The authors propose two blind channel estimation methods for uplink multiple input multiple output SC-CDMA systems with block transmisssion-one is the subspace-based method and the other is the so-called autocorrelation contribution method (ACM). Both the methods provide close performance to the case with perfect channel knowledge at high signal-to- noise ratio (SNR) without any training data required. It is shown that ACM yields a better performance than the subspace method at a lower SNR, and a similar performance at a high SNR, with the advantages of avoiding rank determination and noise power estimation as in the subspace method. In addition, the authors integrate layered space frequency equalisation with blind channel estimation, which provides improved performance over the conventional linear equalisation, by employing successive interference cancellation.     

Gelatin electrospun nanofibrous matrices for cardiac tissue engineering applications

The generation of in vitro tissue constructs using biomaterials and cardiac cells is a promising strategy for screening novel therapeutics and their effects on cardiac regeneration. Current cardiac mimetic tissue constructs are unable to stably maintain functional characteristics of cardiomyocytes for long-term cultures. The objective of our study was to fabricate and characterize nanofibrous matrices of gelatin for prolonged cultures of primary cardiomyocytes which previously has been used as copolymer or hydrogels. Gelatin nanofibrous matrices were successfully electrospun using a benign binary solvent, cross-linked without swelling and fusing and evaluated by scanning electron microscopy (SEM) and uniaxial tensile measurement. Scaffolds exhibited modulus 19.6 ± 3.6 kPa similar to native human myocardium tissue with fiber diameters of 200–600 nm and average porosity percentage of 49.9 ± 5.6. Myoblasts showed good cell adhesion and proliferation. Neonatal rat cardiomyocytes cultured on gelatin nanofibrous matrices showing synchronized contracting cardiomyocytes (beating) for 27 days were studied by video microscopy. Confocal microscopic analysis of immunofluorescence stained sections indicated the presence of cardiac specific Troponin T in long-term cultures. Semiquantitative RT-PCR analysis of 3D versus 2D cultures revealed enhanced expression of contractile protein desmin. Our studies show that the biophysical and mechanical properties of electrospun gelatin nanofibers are ideal for in vitro engineered cardiac constructs (ECC), to explore cardiac function in drug testing and tissue replacement. Together with stem cell techniques, they may be an ideal platform for prolongedin vitro studies in alternatives to animal usage for the pharmaceutical industry.     

On the room-temperature ferromagnetism of Zn1−xCrxO thin films deposited by reactive co-sputtering

We report on the preparation and detailed characterization of ferromagnetic (FM) Zn_1−xCr_xO thin films deposited on Si substrates using reactive co-sputtering of Cr and Zn in controlled oxygen atmosphere. X-ray diffraction (XRD) data showed wurtzite ZnO peaks in the FM films prepared with lower Cr sputter powers, whose position and intensities are influenced by Cr doping. However, samples prepared with higher Cr powers did not show ferromagnetism but displayed evidence of Cr₂O₃ and ZnCr₂O₄ phases with no zinc oxide (ZnO) phase. The magnetization is higher (saturation magnetization M_s=18 emu/cm³) for lower Cr concentrations and decreases for higher Cr doping. The samples were investigated extensively to understand the film composition, dopant distribution, homogeneity and potential origin of the observed ferromagnetism. Particle-induced X-ray emission (PIXE) studies were employed to determine the chemical composition as well as the Cr/Zn ratio in the films. Film uniformity and homogeneity, investigated using Rutherford backscattering spectrometry, showed a relatively uniform ZnO layer in the as-prepared samples but, in a sample annealed at 800 °C, showed some diffusion of Si from the substrate. X-ray photoelectron spectroscopy (XPS) studies indicated that Cr ions are in the oxidized state, but showed changes in the binding energy and Cr concentration when measured after removing 10 nm from the surface using Ar ion sputtering. Possible origins of the observed FM behavior are discussed based on the comprehensive characterization results.     

Selective toxicity of zinc oxide nanoparticles to prokaryotic and eukaryotic systems

We report on the toxicity of ZnO nanoparticles (NPs) to gram-negative and gram-positive bacterial systems, Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus), and primary human immune cells. ZnO NP (~13 nm) showed complete inhibition of E. coli growth at concentrations 3.4 mM, whereas growth of S. aureus was completely inhibited for 1 mM. Parallel experiments using flow cytometry based assays clearly demonstrated that growth inhibitory properties of ZnO NP were accompanied by a corresponding loss of cell viability. Identical ZnO NP had minimal effects on primary human T cell viability at concentrations toxic to both gram-negative and gram-positive bacteria. Collectively, these experiments demonstrate selectivity in the toxic nature of ZnO NP to different bacterial systems and human T lymphocytes. Developing selective toxicity to biological systems and controlling it by NP design could lead to biomedical and antibacterial applications.     

Formation of an unusual copper(II) complex from the degradation of a novel tricopper(II) carbohydrazone complex

An unusual copper(II) complex [Cu(L^1a)₂Cl₂] CH₃OH·H₂O·H₃O⁺Cl⁻ (1a) was isolated from a solution of a novel tricopper(II) complex [Cu₃(HL¹)Cl₂]Cl₃·2H₂O (1) in methanol, where L^1a is 3-(2-pyridyl)triazolo[1,5-a]-pyridine, and characterized with single crystal X-ray diffraction study. The tricopper(II) complex of potential ligand 1,5-bis(di-2-pyridyl ketone) carbohydrazone (H₂L¹) was synthesized and physico-chemically characterized, while the formation of the complex 1a was followed by time-dependant monitoring of the UV–visible spectra, which reveals degradation of ligand backbone as intensity loss of bands corresponding to O → Cu(II) charge transfer.     

The Influences of Cell Type and ZnO Nanoparticle Size on Immune Cell Cytotoxicity and Cytokine Induction

Nanotechnology represents a new and enabling platform that promises to provide a range of innovative technologies for biological applications. ZnO nanoparticles of controlled size were synthesized, and their cytotoxicity toward different human immune cells evaluated. A differential cytotoxic response between human immune cell subsets was observed, with lymphocytes being the most resistant and monocytes being the most susceptible to ZnO nanoparticle-induced toxicity. Significant differences were also observed between previously activated memory lymphocytes and naive lymphocytes, indicating a relationship between cell-cycle potential and nanoparticle susceptibility. Mechanisms of toxicity involve the generation of reactive oxygen species, with monocytes displaying the highest levels, and the degree of cytotoxicity dependent on the extent of nanoparticle interactions with cellular membranes. An inverse relationship between nanoparticle size and cytotoxicity, as well as nanoparticle size and reactive oxygen species production was observed. In addition, ZnO nanoparticles induce the production of the proinflammatory cytokines, IFN-γ, TNF-α, and IL-12, at concentrations below those causing appreciable cell death. Collectively, these results underscore the need for careful evaluation of ZnO nanoparticle effects across a spectrum of relevant cell types when considering their use for potential new nanotechnology-based biological applications.     

Simplified receiver design for STBC binary continuous phase modulation

Existing space-time codes have focused on multiple- antenna systems with linear modulation schemes such as phase- shift keying and quadrature amplitude modulation. Continuous phase modulation (CPM) is an attractive scheme for digital transmission because of its constant envelope which is needed for power efficient transmitters. Recent research has shown that space-time coded CPM can achieve transmit diversity to improve performance while maintaining the compact spectrum of CPM signals. However, these efforts mainly combine space- time coding (STC) with CPM to achieve spatial diversity at the cost of a high decoding complexity. In this paper, we design space-time block codes (STBC) for binary CPM with modulation index h = 1/2 and derive low-complexity receivers for these systems. The proposed scheme has a much lower decoding complexity than STC CPM with the Viterbi decoder and still achieves near-optimum error performances.