On the Behaviour of Hematite and Graphite Blend during Ball Milling and Heating Up Reduction of Milled Mixture

The effect of ball milling under argon and air atmospheres on the reaction behaviour of the mixture of sintered hematite and graphite was investigated. Thermo‐gravimetry / differential thermal analysis (TG‐DTA) was adopted to determine the effect of milling time on the reduction process during heating up under Ar atmosphere. The samples were heated at a constant heating rate of 10 °C/min from room temperature up to 1100 °C and maintained at this temperature for 30 minutes. TGL (thermo‐gravimetry loss) curves showed a decrease of onset temperature of reduction with increase of milling time. XRD patterns of milled samples at room temperature revealed that the peaks of graphite disappeared after 48 hours milling. This represents the transformation of crystalline structure of graphite to the amorphous structure. By increasing the milling time to 72 hours, magnetite peaks appeared in the XRD pattern as a result of reduction of hematite with graphite during milling. However, the amount of magnetite formed during milling process increased as milling proceeded. The powders milled under Ar atmosphere became more active than the powders milled under air and consequently the carbothermic reduction of hematite in powders milled under Ar atmosphere was observed at lower temperatures compared with air‐milled powders. It was observed that the reduction time of hematite in powder mixture was decreased with increase of sintering time of hematite prior to milling.     

Entanglement of three-level atomic system and spontaneous emission fields in a vacuum and near the 1D photonic crystal band gap

The time evolution of the quantum entropy in a GaAs/AlAs one-dimensional photonic crystal (1DPC) with an atomic system defect layer is investigated in this work. The entanglement between atomic system and their spontaneous emission fields near the edge of the photonic band gap (PBG) is coherently controlled by the coupling field. Comparison between the atom-photon entanglement of the atomic system in the vacuum surrounding and that near the PBG of the 1DPC shows that the degree of entanglement strongly depends on the PBG. We find that degree of entanglement is strongly dependent on the intensity and detuning of the coupling and probe fields. Furthermore, the effect of the phase difference between applied fields on the atom-photon entanglement is studied. The potentially possible technological applications can be provided by the proposed model in the quantum optics and quantum communications based on photonic crystal.     

Rabi oscillation generation in the microring resonator system with double-series ring resonators

In this paper, a microring resonator (MRR) system using double-series ring resonators is proposed to generate and investigate the Rabi oscillations. The system is made up of silicon-on-insulator and attached to bus waveguide which is used as propagation and oscillation medium. The scattering matrix method is employed to determine the output signal intensity which acts as the input source between two-level Rabi oscillation states, where the increase of Rabi oscillation frequency with time is obtained at the resonant state. The population probability of the excited state is higher and unstable at the optical resonant state due to the nonlinear spontaneous emission process. The enhanced spontaneous emission can be managed by the atom (photon) excitation, which can be useful for atomic related sensors and single-photon source applications.     

Multifractality in fidelity sequences of optimized Toffoli gates

We analyze the multifractality in the fidelity sequences of several engineered Toffoli gates. Using quantum control methods, we consider several optimization problems whose global solutions realize the gate in a chain of three qubits with XY Heisenberg interaction. Applying a minimum number of control pulses assuring a fidelity above 99 % in the ideal case, we design stable gates that are less sensitive to variations in the interqubits couplings. The most stable gate has the fidelity above 91 % with variations about 0.1 %, for up to 10 % variation in the nominal couplings. We perturb the system by introducing a single source of 1 / f noise that affects all the couplings. In order to quantify the performance of the proposed optimized gates, we calculate the fidelity of a large set of optimized gates under prescribed levels of coupling perturbation. Then, we run multifractal analysis on the sequence of attained fidelities. This way, gate performance can be assessed beyond mere average results, since the chosen multifractality measure (the width of the multifractal spectrum) encapsulates into a single performance indicator the spread of fidelity values around the mean and the presence of outliers. The higher the value of the performance indicator the more concentrated around the mean the fidelity values are and rarer is the occurrence of outliers. The results of the multifractal analysis on the fidelity sequences demonstrate the effectiveness of the proposed optimized gate implementations, in the sense they are rendered less sensitive to variations in the interqubits coupling strengths.     

Isolation enhancement of rectangular dielectric resonator antennas using wideband double slit complementary split ring resonators

A wideband epsilon‐negative structure is employed as one‐layer and two‐layer isolators to reduce mutual coupling in multiple‐input multiple‐output systems composed of two E‐coupled rectangular dielectric resonator antennas. The proposed unit cell with ?15 dB bandwidth for S₂₁ extending from 1970 to 3317 MHz, is a double slit complementary split ring resonator etched on the ground plane of a stripline. Each layer is composed of a 2 × 3 array of the suggested unit cell. Reduction in isolation of more than 11 dB for the one‐layer case and higher than 20 dB for the two‐layer case are measured within the frequency range of 2.604 to 2.64 GHz which includes WiMAX. The highest isolation level of 36 dB is realized at 2.868 GHz. The impedance matching, gain, radiation efficiency, and envelope correlation are improved compared to the original case. A prototype is designed, fabricated, and tested. Simulation data and measurement results are in good agreement.     

Robust brain MRI denoising and segmentation using enhanced non‐local means algorithm

Image denoising is an integral component of many practical medical systems. Non‐local means (NLM) is an effective method for image denoising which exploits the inherent structural redundancy present in images. Improved adaptive non‐local means (IANLM) is an improved variant of classical NLM based on a robust threshold criterion. In this paper, we have proposed an enhanced non‐local means (ENLM) algorithm, for application to brain MRI, by introducing several extensions to the IANLM algorithm. First, a Rician bias correction method is applied for adapting the IANLM algorithm to Rician noise in MR images. Second, a selective median filtering procedure based on fuzzy c‐means algorithm is proposed as a postprocessing step, in order to further improve the quality of IANLM‐filtered image. Third, different parameters of the proposed ENLM algorithm are optimized for application to brain MR images. Different variants of the proposed algorithm have been presented in order to investigate the influence of the proposed modifications. The proposed variants have been validated on both T1‐weighted (T1‐w) and T2‐weighted (T2‐w) simulated and real brain MRI. Compared with other denoising methods, superior quantitative and qualitative denoising results have been obtained for the proposed algorithm. Additionally, the proposed algorithm has been applied to T2‐weighted brain MRI with multiple sclerosis lesion to show its superior capability of preserving pathologically significant information. Finally, impact of the proposed algorithm has been tested on segmentation of brain MRI. Quantitative and qualitative segmentation results verify that the proposed algorithm based segmentation is better compared with segmentation produced by other contemporary techniques.     

Hydrogels of Thermoreversible Comb‐Polymers Exhibit Increased Resistance for Dissolution

The N‐isopropylacrylamide (NiPAM) polymers exhibit thermoreversible properties in aqueous solutions. The resiliency of NiPAM hydrogels is believed to influence the outcome when the polymers are utilized in biomedical applications. To determine the influence of polymer architecture on hydrogel resiliency, polymers of NiPAM, methyl methacrylate (MMA) and acrylic acid were synthesized as random polymers and as comb polymers, where MMA was incorporated as side‐chains. Random polymers exhibited a Lower Critical Solution Temperature (LCST) that decreased in proportion to MMA content in polymers. The LCST of comb polymers was not dependent on MMA content or the length of MMA side‐chain (between 3.0 and 10.1 kD). Whereas low molecular weight (～100 kD) random polymers did not form intact gels, comb‐polymers of equivalent molecular weight were capable of forming intact gels. Gel resiliency, as determined by propensity of hydrogels to dissolve upon cooling, was improved when the molecular weight of comb‐polymers was increased but the length of the MMA side‐branch did not influence the gel resiliency. We conclude that hydrogel dissolution was dependent on polymer architecture as well as the polymer molecular weight.     

Vibration characteristics of laminated composite beams with magnetorheological layer using layerwise theory

Vibration characteristics of laminated composite beams with magnetorheological (MR) layer are investigated using layerwise theory. In most studies, shear strain across the thickness of MR layer has been considered as a constant value, which does not precisely describe the shear strain. In this study, layerwise theory is employed to develop a finite element formulation to investigate MR-laminated beams. Experimental tests under different magnetic fields are carried out to verify the numerical results. Layerwise numerical results are compared with the experimental results and other theories. An empirical expression for complex shear modulus is presented. The effects of MR layer thickness on vibration of MR-laminated beams are examined.     

A robust zero-watermarking algorithm for copyright protection of text documents

The widespread use of Internet and other communication technologies has brought about ease in reproducing, disclosing and distributing digital content. In addition to getting the benefits of information exchange, the digital community is confronted with authentication, forgery and copyright protection issues. Text is the most frequently used medium travelling over the Internet, along with images, audio and video. Majority of the content of books, newspapers, web pages, advertisements, research papers, legal documents and many other documents is basically, plain text. Therefore, copyright protection of plain text is a most important issue. In this article, we propose a robust zero-watermarking algorithm based on prepositions and double letters for copyright protection of plain text. The embedding algorithm uses occurrences of prepositions and double letters in the text to generate a key based on watermark. The extraction algorithm extracts the watermark from the noisy text to identify the original owner. Experimental results illustrate the effectiveness of the proposed algorithm on text encountering combined insertion, deletion and re-ordering attacks, both in the dispersed and localized forms. The results are also compared to a recent work on text watermarking.