Polypyrrole-derived N-doped carbon nanoribbon for broadband microwaves absorption

In this work, we successfully synthesize N-doped carbon nanoribbon (NCNR) from polypyrrole precursor and investigate their dielectric and microwaves absorption (MA) properties. NCNR appears as two-dimensional ribbon-like microstructure with tunable N-doping ratio. The dielectric property of NCNR can be tuned by N-doping content controlling. The results demonstrate that NCNR exhibits excellent MA performance at a filler-loading ratio of only 5 wt%. When the sample thickness is 3.3 mm, the maximal absorption reaches ??73.76 dB at 10.48 GHz. The maximum efficient bandwidth gets to 7.4 GHz (10.6–18 GHz), under a sample thickness of 2.7 mm. A model that refers to conductive loss, polarization relaxation, and impedance match is adopted to explain the MA mechanism of NCNR. This research opens up the exploration of NCNR in the field of MA, and provides a new idea for the design of carbon-related broad band MA materials.

     

Throughput Enhancement for NOMA Systems Using Intelligent ReflectingSurfaces

In this article, we optimize the powers associated to Non Orthogonal Multiple Access (NOMA) users, sensing and harvesting duration for Cognitive Radio Networks (CRN). The secondary source harvests energy from node A signal. Then, it senses the channel to detect primary source. Then, the secondary source transmits a signal that is reflected by Intelligent Reflecting Surfaces (IRS) so that all reflections have a zero phase at any user. A set Ii of reflectors are associated to user Ui. The use of M = Mi = 512, 256, 128, 64, 32, 16, 8 reflectors per user offers 45, 42, 39, 36, 33, 30, 27 dB gain vs. the absence of IRS. We also suggest the use of IRS in energy harvesting. The use P = 8 reflectors for energy harvesting and M = Mi = 8 reflectors per user for data communications offers 7 and 38 dB gain vs. one IRS M = Mi = 8 and the absence of IRS. The use of P = 16 reflectors for energy harvesting and M = Mi = 8 reflectors per user for data communications offers 9 and 42 dB gain vs. one IRS M = Mi = 8 and the absence of IRS.     

A heuristic 0–1 integer programming method

Summary In this paper, we present a novel relaxation method for the integer programming problem:Ax=b,A {–1,0,+1}^m×N,x {0,1}^N, N>m. The report includes experimental results of problems with up tom=100 equations andN=400 variables.     

Correlation of acoustic emission with stress intensity factor and plastic zone size for notched tensile specimens of AISI type 304 stainless steel

Abstract

Correlation of acoustic emission (AE) total counts N with stress intensity factor K and plastic zone size r_p has been examined for data generated during tensile deformation of notched specimens of nuclear and commercial grade AISI type 304 stainless steel. The variation of total AE counts with stress intensity factor in log-log scale has indicated that N is related to K as N=AK^m where A and m are constants but the magnitudes of A and m are different at low and high K regimes. Both the steels indicate higher values of m up to macroyielding than those obtained from analysis of AE data between macroyielding and the stress corresponding to K _max values in the experiments. The magnitudes of m were found to be higher for the commercial grade steel than that for the nuclear grade one and dependent on thickness. Analysis of AE data has also indicated that the relationship between N and r _p can be expressed by the equation N=αr^β_p. The value of the constant β was experimentally found to be 1.3 via microhardness measurements. This value is higher than the theoretically assumed value of β~ 1in the literature. The value of m in the equation N=AKm can be obtained from the value of the exponent β of the relationship N=α r^β as m=2β and such values of m can be correlated to the directly estimated values of the exponent in the N-K relationship. The amounts of strain induced α' martensite formed at notch tips in the two steels were found to increase with increasing applied stress below the nominal yield strength of unnotched specimens.     

MHD flow past a sphere at low and moderate Reynolds numbers

The steady incompressible magnetohydrodynamic (MHD) flow past a sphere with an applied magnetic field parallel to the main flow is studied for the Reynolds number, Re, up to 100 and interaction parameter, N, up to 0.7. The magnetic Reynolds number is assumed to be small. It is observed that drag coefficient increases as N increases. The Finite difference method is used to solve the vorticity-stream function form of the non-linear Navier-Stokes equations. The multigrid method is used to solve the finite difference equations. The fifth decimal place convergent solutions are obtained upto the finest grid of 1024×512. Graphs of the streamlines, vorticity lines, surface vorticity and drag coefficient are presented.The authors are grateful to the Principal, Pondicherry Engineering College and Head, Department of Mathematics, Pondicherry Engineering College for providing the necessary facilities. The authors are thankful to Dr. Umamaheswara Rao, Department of Applied Mathematics, Andhra University, Visakhapatnam and Dr. R. Sivakumar, Department of Physics, Pondicherry Engineering College, for their encouragement.     

A facile synthesis strategy for structural property control of mesoporous alumina and its effect on catalysis for biodiesel production

A facile synthesis route for the production of mesoporous alumina (MA) with tuneable structural properties including BET surface area, pore volume and pore size was systematically investigated by tailoring the amount of template P123 used in the synthesis. The general synthesis strategy was based on a sol–gel process by hydrolysis of aluminium isopropoxide associated with nonionic block copolymer (P123) as the template in a water system. The results showed that the addition of P123 played a crucial role in the synthesis process, leading to very regular variations in the surface area (146.6–261.6 m²/g), pore volume (0.164–2.152 cm³/g) and pore size (3.5–29.9 nm). MA-supported K species (MA-K) were prepared using KNO₃ as the potassium precursor and adopted as the catalysts for biodiesel production. The introduction of K species to MA caused a reduction in the BET surface area and pore volume, but gave rise to a significant increase in pore size, especially when the K species was higher than 10%. K incorporation resulted in the formation of disordered, but significantly larger mesopores. In catalysis, by introducing 20% molar fraction of K species to MA, very high yield of biodiesel was achieved (92.2%) and further increased to 94.4% with 25% K. Based on the control of structural properties of MA, a series of MA-20K catalysts with the same K loading (20%) but different structural properties were prepared by varying P123 addition and were further tested in biodiesel synthesis. Higher biodiesel yields were obtained over the MAs with higher surface area, pore volume and bigger pore size, which were attributed to the reduced mass transfer limitation in catalysis.     

Focused ion beam assisted analysis of the oxidation of a NiAl coating on pure Ni

Abstract

Discs of (pure nickel 15mm diameter and 4mm thickness) have been polished to a 1 μm finish, aluminised using a standard pack CVD process to give a β-NiAl coating and then the surface of this coating polished to a 1 μm finish again. Samples have then been isothermally oxidised in a muffle furnace for 1, 2, 4, 8, 16, 32, 64, 128, 256, 512 and 1024 hours at 950°C, and subjected to surface and cross-sectional microscopy and analysis. Scales were also cross-sectioned and imaged using Focused Ion Beam Milling. The oxidation rate was determined to be 2:6×10^?13 g² cm^?4 s^?1 and for times less than 512 hours the predominant alumina phase was θ alumina. Al depletion effects were observed due to both oxidation and interdiffusion between the Ni substrate and the NiAl coating. Using these effects, it has been shown that tensile strains of up to 9% can arise and these strains readily explain the formation of intrefacial elliptical pores observed by FIB cross sectioning. FIB sectioning also indicated that different coating grains exhibit different oxide-coating interfaces which arise due to different grain orientations. The faceting of the coating-oxide interface and the development of cuboidal faceted coating structures beneath spalled oxide is thought to be due to substructure development (sub-grain development or recrystallisation) arising from the plastic strains generated by Al depletion effects.     

On the Astm electromigration test structure applied to Al–1%Si/TiN/Ti bamboo metal lines

The applicability of NIST-ASTM electromigration test patterns when used to test ‘bamboo’ metal lines is discussed. Wafer level tests on passivated and non-passivated samples employing the Al–1%Si/TiN/Ti metallization scheme were performed. Straight metal lines 1000 μm long and 0·9 μm or 1·4 μm wide were tested at two different current densities. j = 3 MA cm² and j = 4·5 MA/cm², at constant stress temperature (T = 230·C). The failures mainly occurred in the end-segment areas and hindered the evaluation of the electromigration resistance of the ‘bamboo’ test lines. In order to avoid this problems, completely different test patterns based on different approaches must be designed.     

Comparison of retardation behaviour of 2024-T3 and 7075-T6 Al alloys

Retardation in fatigue crack growth rate following the application of single and periodic tensile overloads was studied for 2024‐T3 and 7075‐T6 aluminium alloys. Tests were performed at constant stress and at constant stress intensity factor ranges, at a load ratio of R= 0.1, at a baseline ΔK in the 10–20 MPa√m range which corresponds to the Paris regime. Overload ratios of 1.3–1.65 were studied with overload spacing, n, varying from 20 to 10 000 cycles. 2024‐T3 displayed an order of magnitude higher retardation, N_d, due to single tensile overloads compared to 7075‐T6. Periodic overloads induced maximum retardation when n/N_d≈ 0.5 for both alloys, the magnitude being only 15% higher for 2024‐T3.     

Dielectric losses and ac conductivity of Si–LiNbO3 heterostructures grown by the RF magnetron sputtering method

Single-axis <0001> textured polycrystalline LiNbO₃ films were grown on (001) Si substrates by the RF magnetron sputtering method. Dielectric losses that occur in the Si–LiNbO3 heterostructures are caused by the conductivity of the LiNbO3 films. Analysis of temperature and frequency dependence of ac conductivity in the frequency range f = 25/10⁵ Hz has demonstrated that it is expressed by the power law σ(ω) = Aω^s and is described in the framework of the correlated barrier-hopping model. Thermal annealing (TA) of the Si–LiNbO3 heterostructures causes an increase in the density of the localized states in the band gap of LiNbO3 from D = 7 × 10²⁴ m^?3 to D = 2 × 10²⁵ m^?3. The conduction mechanism is changed radically after TA and phonon-assisted tunneling influences ac conductivity at the frequency of up to 800 Hz. At high frequency (f > 800 Hz), dielectric relaxation predominates affecting frequency dependence σ(ω) on relaxation time τ = 6.6 × 10^?5 s.     

Propagation and far-field beam quality of M × N Hermite–Gaussian beams propagating through atmospheric turbulence

The analytical propagation equation of M×N Hermite–Gaussian (H–G) beams, which are combined incoherently and propagate through atmospheric turbulence, is derived, which enables us to study their propagation properties and far-field beam quality. The propagation of M×N Gaussian beams through atmospheric turbulence and M×N H–G beams in free space are treated as special cases of our general result. The power in the bucket (PIB), β-parameter and Strehl ratio are chosen as the parameters characterizing the beam quality in the far field. The dependence of PIB, β-parameter and Strehl ratio of M×N H–G beams through atmospheric turbulence on the refraction index structure constant C _n ², beam numbers M, N, mode indices m, n and separate distances x_d , y_d is illustrated numerically and interpreted physically. It is found that M×N H–G beams are less sensitive to the effects of turbulence than M×N Gaussian beams.     

Maximum entropy and discretization of probability distributions

Using gaussian quadrature we can find m concentrations of probability that replace the density function of a random variable X and match 2m - 1 of its moments. This reduces a probabilistic analysis to m deterministic ones. Even small values of m provide excellent accuracy in many practical circumstances. When fewer than 2m - 1 moments are known there is arbitrariness in the choice of the concentrations, which is overcome by resorting to the maximum entropy formalism. Its use is here systematized for the case in which αXb and we know N moments of the density of X, so that calculation of N - 1 integrals suffices for finding the density function and any number of its moments. The approach is illustrated for m = 2 and 3, N = 2, 3, α = 0, B = ∞ and graphs are provided for finding the equivalent concentrations.     

Halogenated boroxine dipotassium trioxohydroxytetrafluorotriborate K2[B3O3F4OH] inhibits emerging multidrug-resistant and β-lactamase-producing opportunistic pathogens

Abstract

Halogenated boroxine dipotassium trioxohydroxytetrafluorotriborate, K₂[B₃O₃F₄OH] (boroxine) was previously shown to be very effective in inhibition of several carcinoma cell lines, including the skin cancer. Here, we investigated its antimicrobial potential by targeting the multidrug-resistant opportunistic pathogens associated with skin and wound infections. The antimicrobial testing against eleven bacterial and four fungal species revealed good activity of boroxine against pathogenic filamentous fungi Penicillium funiculosum and Aspergillus niger (MIC₅₀ 64 and 128?µg/ml), and a moderate bioactivity against the yeast Candida albicans (MIC₅₀ 512?µg/ml). Among the tested multidrug-resistant bacteria, the best antibacterial effect, stable over a 24-h period, was observed against the methicillin-resistant Staphylococcus aureus strain (MRSA) at MIC of 1024?µg/ml. The atomic force microscopy (AFM) used to investigate the morphology of S. aureus cells revealed indentations on its cell envelope after the boroxine exposure. These results show that in addition to the antitumor effect, boroxine exerts wide spectrum antimicrobial activity, thus may help preventing the development of skin and wound-related opportunistic infections.     

Satellite peaks in the scattering of p-polarized light from a randomly rough film on a perfectly conducting substrate

Abstract

The diffuse scattering of p-polarized light from a one-dimensional, randomly rough dielectric film deposited on a planar, perfectly conducting surface is studied by means of small-amplitude perturbation theory. The dielectric constant ε_d and the thickness d of the dielectric film are chosen in such a way that in the absence of roughness the scattering system supports N (≥ 2) guided modes whose wavenumbers are q ₁ (ω), …,q _N(ω) at the frequency ω of the light incident at an angle θ_o. We investigate the occurrence of satellite peaks, in addition to the enhanced back-scattering peak, in the angular distribution of the intensity of the diffusely scattered light, at angles θ_s(n, m) given by sin θ_s(n, m)= ? sin θ₀± (c/ω) [Q_n(ω) ? q_m(ω)] for n, m=1, …, N(n ≠ m). These satellite peaks are multiple-scattering effects due to degenerate timereversal symmetry.     

Robust estimation in time series

The main purpose of this work is to study empirically by means of simulations, the robustness of a set of proposals to estimate the parameters in the MA(1) time series model. The non-normal populations are mixtures of normal distributions, defined byg(x)=pN(0,k)+(1-p)N(0,1), where the proportion of contamination most frequently used isp=0.10 andk is the variance of the distribution used in the contamination; α is taken to be 0.90, which is close to the region of non-invertibility. Key results are that the estimation procedures used in the study provide good results in terms of biases in the estimation of the parameters, and that the biases are not changed when contaminated errors (mixtures) are considered. The estimation of the variance of the contaminated errors is also studied through simulations.     

On the thin-section size dependent creep strength of a single crystal nickel-base superalloy

The combined effects of thin-section size, D, and microcracks on the creep behaviour of the single crystal MAR-M002 were investigated at the creep conditions of 300 MPa and 900 °C. It was observed that the creep rupture life, t _R is controlled by the mean microcrack size to thin-section size, (d _c/D), (or the total number, (N _m), of the mean-sized microcrack particles across the diameter, assuming D/d _c=N_m); reducing N _m continuously improves t _R. The creep rupture strain (or ductility), _R, can be improved sharply by increasing the total number, N _T, of microcrack particles across the cross-section, N _T D ² N _A, where N _A is the number of microcrack particles (cavity density) per cross-section. The behaviour of the creep rupture ductility was interpreted in terms of the weakest link, or largest-flaw concept; the observation of the higher proportion of the less likely dangerous (smaller in size) microcracks with increasing N _T was the underlining reason for the improvement in ductility.     

Revival Hamiltonians,Phase Operators and Non-Gaussian Squeezed States

Abstract

The phase operators P ^± of the electromagnetic field, whose classical analogues are exp (? iθ), θ being the classical phase, and the number operator N associated with a harmonic oscillator mode are used to construct a class of operators T _m = N(P ^?)^m and T ⁺ _m = (P ⁺)^m N, m = 1, 2,…. It is shown that T _m, T ⁺ _m and N satisfy a simple algebra. T _m and T ⁺ _m are used to construct model Hamiltonians H _m describing the coupling of a two-level atom to a field that leads to decay and exact revivals in the atomic dynamics. In the second part of the paper, a family of unitary operators U _m is constructed in terms of T _m and T ⁺ _m. For m = 1 and m = 2 the states generated by U _m from the vacuum are non-Gaussian squeezed states. The variance properties of the squeezed states so constructed are analysed and compared with those of the Gaussian squeezed states. It is shown that the non-Gaussian squeezed states constructed in this paper have small values for the variance product that rise only logarithmically with for large values of , the mean number of quanta.     

Effect of salt concentration and exposure temperature on adhesion and cytotoxicity of positively charged nanoparticles toward yeast cells

We have comprehensively scrutinized the effect of NaCl salt concentration (C_NaCl = 5–600 mM) and exposure temperature (T_exp = 4 and 25 °C) on the adhesion and cytotoxicity of positively charged nanoparticles (NPs) of 100-nm diameter toward two yeast strains (Saccharomyces cerevisiae and Schizosaccharomyces pombe) during exposure of t_exp = 0.5–24 h. On the short-time exposure toward S. cerevisiae at T_exp = 25 °C, the number of the NPs adhered to a yeast cell (N_adh) monotonically decreased with C_NaCl to become negligibly small at C_NaCl ≥ 150 mM. The greater value of N_adh resulted in the higher cell mortality. Similar results were obtained for S. pombe at C_NaCl = 5–100 mM. Interestingly, N_adh for S. pombe increased with C_NaCl (=100 to 600 mM), where the cells considerably covered with the NPs showed relatively low mortalities during the short-time exposure. The favorable NaCl concentration was found as C*_NaCl = 150 and 100 mM for S. cerevisiae and S. pombe, respectively, to survive in the aqueous suspensions of positively charged NPs during 24 h. The lower-temperature exposure (T_exp = 4 °C) for each exposure duration caused the significantly decreasing mortality of every yeast strain at the NaCl concentrations around C*_NaCl.     

X-ray Diffraction Study of Mixed-Layer Compounds in the Pseudobinary System SnTe–Bi2Te3

X-ray diffraction studies of cleaved single-crystal specimens and powders demonstrate that the SnTe–Bi₂Te₃ system contains a homologous series of nSnTe · mBi₂Te₃ layered compounds (n = 1, 2; m = 1–3). In addition to the known compound SnBi₂Te₄, the compounds SnBi₄Te₇ (n = 1, m = 2) and SnBi₆Te₁₀ (n = 1, m= 3), structural analogues of GeBi₄Te₇ and GeBi₆Te₁₀, are identified. SnBi₄Te₇ has a 12-layer structure with lattice parameters a = 0.4392(1) nm andc = 2.399(1) nm (sp. gr. P m1). SnBi₆Te₁₀ has a 51-layer structure with a= 0.4391(1) nm and c= 10.264(5) nm (sp. gr. R m). The new structural data for nSnTe · mBi₂Te₃ compounds and earlier results are used to reassess the SnTe–Bi₂Te₃ phase diagram.     

Isomorphism Classes of Picard Curves over Finite Fields

In this paper we count the number of isomorphism classes of pointed Picard curves, i.e., nonsingular plane curves y³=f(x) of genus 3 with the fixed point at infinity, over finite fields of characteristic different from 3. In the process of doing this we also provide reduced forms of Picard curves that represent the isomorphism classes together with the number of such forms up to isomorphism. In addition to its own theoretical meaning, it has applications to cryptography.