Uniform Geometry Research Articles

Efficient Method of Passive Localization for Mixed Far-Field and Near-Field Sources

An effective second-order statistics (SOS)-based algorithm is addressed for scenarios where both far-field and near-field narrowband sources may exist simultaneously. After estimating the direction-of-arrivals (DOAs) and powers of far-field signals, the related far-field components can be eliminated from the signal subspace. Then, based on the symmetric property of the uniform linear array geometry, a near-field estimator without two-dimensional search or parameter pairing is performed. Compared to the previous SOS based method, the resultant algorithm can provide an improved estimation accuracy, as well as realize a more reasonable classification of the signal types. Simulation results are carried out to demonstrate the performance of the proposed algorithm.

Research on Preparation and Biological Properties of Dense Hydroxyapatite Spheres

By using carboxy methyl chitosan(CMCS) and gelatin(Gel) as adhesive,the nano–HA slurry which was fabricated via a precipitation process as the raw material,dense HA spheres with a uniform size distribution and good geometry were prepared successfully by means of Sol-Gel method.Dense HA spheres with a porosity of 4.7%±0.6% have a higher compressive strength(8.9±0.4) MPa than that of porous HA spheres(7.9±0.2) MPa with a porosity of 16.4%±0.5%(particles with diameter of 0.5 mm).The results of biomimetic mineralization and cell culture show that dense HA spheres have an excellent biological property.

Aeroacoustics of Twin Supersonic Jets: A Review

Interaction of twin supersonic jets can dramatically alter the dynamic pressures in the near-field and cause fatigue of aircraft structures. This review paper focuses on the twin jet coupling situation that is rich in fluid flow physics, requires sophisticated analysis tools and is of relevance to aircraft with closely spaced engines and other industrial situations involving multiple jet flows. The review consists of four sections: (i) a historical survey of twin jet exhaust coupling, (ii) rectangular twin jets with both spanwise uniform and non-uniform geometry, (iii) a description of multi-modes and mode jumps using higher order spectral analysis, and (iv) the suppression of twin jet coupling. The parameters that affect twin jet coupling include nozzle geometry, internozzle spacing and nozzle operating conditions. Certain modes of resonant coupling increase the dynamic pressures drastically in the inter-nozzle region, whereas other coupling modes can suppress unsteady pressure levels. Since coupled resonances can cause fatigue failure of components, mitigation approaches need to be considered. Successful techniques include nozzle inserts, beveled nozzles, water injection, and miniature pins and cavities.

Badania efektywnosci dzialania wytlaczarki nowej generacji. Cz. III. WSPOLDZIALANIE TULEI OBROTOWEJ ZE STREFA ROWKOWANA CYLINDRA

The effect of application of the rotational sleeve of the barrel cooperating with grooved barrel zone in the single screw plasticizing system on the course of low density polyethylene (PE-LD) extrusion process was determined. Research was conducted on a special test stand with an extruder equipped with plasticizing system of modular structure, containing a segment with a rotating sleeve of the barrel and a grooved cylinder zone, interchangeably, with six and eight rectilinear grooves. Selected parameters characterizing the extrusion process were determined during the extrusion of PE-LD with a variable screw speed and barrel sleeve rotation speed. It was found that the use of a grooved cylinder zone cooperating with a rotating sleeve of the barrel in the plasticizing system has a significant impact on the effectiveness of sleeve and the course of the extrusion process. Increasing the polymer mass flow rate with rotation speed of the sleeve is in the whole range screw speed test, which was not observed in the case of a uniform zone geometry, cylindrical without grooves.

Effect of the mechanical activation of Ln2O3 Oxides (with Ln = Gd, Dy, Ho, and Lu) on the surface tension and density of borate melts

Effect of the mechanical activation of Gd2O3, Dy2O3, Ho2O3, and Lu2O3 oxides on surface tension σ and density ρ of borate melts is studied. Linear temperature dependences of σ and ρ are found, and the temperature coefficients are calculated. The dependence of σ on the lanthanide number in the periodic table is found and exhibits nonmonotonic behavior of the melts. The effect of mechanical activation on σ and ρ is explained by the formation of complex lanthanide ions, which have uniform geometry in the borate melts.

Imaging of central airway stenting with multidetector computed tomography

Imaging of central airway stenting with multidetector computed tomography

Geometry and composition comparisons between c-plane disc-like and m-plane core-shell InGaN/GaN quantum wells in a nitride nanorod

With the nano-imprint lithography and the pulsed growth mode of metalorganic chemical vapor deposition, a regularly-patterned, c-axis nitride nanorod (NR) array of quite uniform geometry with simultaneous depositions of top-face, c-plane disc-like and sidewall, m-plane core-shell InGaN/GaN quantum well (QW) structures is formed. The differences of geometry and composition between these two groups of QW are studied with scanning electron microscopy, cathodoluminescence, and transmission electron microscopy (TEM). In particular, the strain state analysis results in TEM observations provide us with the information about the QW width and composition. It is found that the QW widths are narrower and the indium contents are higher in the sidewall m-plane QWs, when compared with the top-face c-plane QWs. Also, in the sidewall m-plane QWs, the QW width (indium content) decreases (increases) with the height on the sidewall. The observed results can be interpreted with the migration behaviors of the constituent atoms along the NR sidewall from the bottom.

<i>Ab Initio</i> Study of Electronic and Magneto-Optical Properties of InSb:Mn and InAs:Mn

Energy difference between the ferromagnetic and antiferromagnetic collinear orderings has been calculated for the uniform and dimer Mn-pair geometries in order to find the ground state distribution of the Mn atoms in InSb (As) hosts. We find the preference of the dimer ferromagnetic configuration of Mn dopants and an importance of optimizing the atomic site positions. The frequency-dependent optical and magneto-optical properties, namely the reflectivity, the electron energy loss spectra, on-and off-diagonal conductivity tensor and the polar Kerr effect, are calculated for comparison with available experimental data. Our calculated MO resonance in In1-xMnxSb (x=1.56%) are found to be in good agreement with corresponding experimental MO spectra. The origin of the large Kerr rotation is discussed.

Mesoporous titanium dioxide nanobelts: Synthesis, morphology evolution, and photocatalytic properties

Abstract

Mechanical properties of human tympanic membrane in the quasi-static regime from in situ point indentation measurements

The tympanic membrane is a key component of the human auditory apparatus. Good estimates of tympanic membrane mechanical properties are important to obtain realistic models of middle ear mechanics. Current literature values are almost all derived from direct mechanical tests on cut-out strips. For a biomedical specimen like the tympanic membrane, it is not always possible to harvest strips of uniform and manageable geometry and well-defined size suitable for such mechanical tests.In this work, elastic and viscoelastic properties of human tympanic membrane were determined through indentation testing on the tympanic membrane in situ. Indentation experiments were performed on three specimens with a custom-built apparatus that was also used in previously published works. Two types of indentation tests were performed on each specimen: (i) sinusoidal indentation at 0.2 Hz yielding the quasi-static Young's modulus and (ii) step indentation tests yielding viscoelastic properties in the quasi-static regime (0–20 Hz).In the cyclic indentation experiments (type i), the indentation depth and resulting needle force were recorded. The unloaded shape of the tympanic membrane and the membrane thickness were measured and used to create a specimen-specific finite element model of the experiment. The Young's modulus was then found through optimization of the error between model and experimental data; the values that were found for the three different samples are 2.1 MPa, 4.4 MPa and 2.3 MPa. A sensitivity analysis showed that these values are very sensitive to the thickness used in the models.In the step indentation tests (type ii), force relaxation was measured during 120 s and the relaxation curves were fitted with a 5 parameter Maxwell viscoelastic model. The relaxation curves in the time domain were transformed to complex moduli in the frequency domain, yielding viscoelastic properties in the quasi-static regime only.

In-Situ Phosphrous Doping in ZnTe Nanowires with Enhanced p-type Conductivity

Single-crystalline undoped and phosphrous-doped (P-doped) p-type ZnTe nanowires (NWs) were synthesized via a simple vapor transport and deposition method. Both undoped and P-doped ZnTe nanowires have zinc blende structure and uniform geometry. X-ray diffraction peaks of the P-doped ZnTe nanowires show an obvious shift toward higher diffraction angle as compared with the undoped ZnTe nanowires. X-ray photoelectron spectroscopy confirms the existence of P-dopant in the ZnTe nanowires. Field-effect transistors based on both undoped and P-doped ZnTe nanowires were fabricated and characterized. Electrical measurements demonstrated that P-doping led to an enhancement in ptype conductivity of ZnTe nanowires. A defect reaction mechanism was proposed to explain the p-type behaviors of both undoped and P-doped ZnTe nanowires.

Monitoring Personalized Trait Using Oscillometric Arterial Blood Pressure Measurements

The blood pressure patterns obtained from a linearly or stepwise deflating cuff exhibit personalized traits, such as fairly uniform peak patterns and regular beat geometry; it can support the diagnosis and monitoring of hypertensive patients with reduced sensitivity to fluctuations in Blood Pressure (BP) over time. Monitoring of personalized trait in Oscillometric Arterial Blood Pressure Measurements (OABPM) uses the Linear Discriminant Analysis (LDA) algorithm. The representation of personalized traits with features from the oscillometric waveforms using LDA algorithm includes four phases. Data collection consists of blood pressure data using auscultatory measurements and pressure oscillations data obtained from the oscillometric method. Preprocessing involves the normalization of various sized oscillometric waveforms to a uniform size. Feature extraction involves the use of features from oscillometric amplitudes, and trait identification involves the use of the LDA algorithm. In this paper, it presents a novel OABPM‐based blood pressure monitoring system that can monitor personalized blood pressure pattern. Our approach can reduce sensitivity to fluctuations in blood pressure with the features extracted from the whole area in oscillometric arterial blood pressure measurement. Therefore this technique offers reliable blood pressure patterns. This study provides a cornerstone for the diagnosis and management of hypertension in the foreseeable future.

Effectiveness factor for thin catalytic coatings: Improved analytical approximation using perturbation techniques

The classical theory of diffusion and reaction inside catalytic pellets, based on the effectiveness factor concept, is applied to thin coatings supported on microchannels or nonporous pellets. We take advantage of this distinct geometrical characteristic to simplify the general problem. In particular, we show that the contribution from the geometry curvature can be written in terms of the effectiveness factor for a slab catalyst. An approximate method for the evaluation of η is proposed, which is accurate for linear and nonlinear kinetics, in uniform and nonuniform geometries. This presents a more convenient procedure for calculating η in structured reactors for process intensification.

Rectilinear Leaky-Wave Antennas With Broad Beam Patterns Using Hybrid Printed-Circuit Waveguides

A theoretical study on the design of broadbeam leaky-wave antennas (LWAs) of uniform type and rectilinear geometry is presented. A new broadbeam LWA structure based on the hybrid printed-circuit waveguide is proposed, which allows for the necessary flexible and independent control of the leaky-wave phase and leakage constants. The study shows that both the real and virtual focus LWAs can be synthesized in a simple manner by tapering the printed-slot along the LWA properly, but the real focus LWA is preferred in practice. Practical issues concerning the tapering of these LWA are investigated, including the tuning of the radiation pattern asymmetry level and beamwidth, the control of the ripple level inside the broad radiated main beam, and the frequency response of the broadbeam LWA. The paper provides new insight and guidance for the design of this type of LWAs.

Improving the quality factor of an RF spiral inductor with non-uniform metal width and non-uniform coil spacing

An improved inductor layout with non-uniform metal width and non-uniform spacing is proposed to increase the quality factor (Q factor). For this inductor layout, from outer coil to inner coil, the metal width is reduced by an arithmetic-progression step, while the metal spacing is increased by a geometric-progression step. An improved layout with variable width and changed spacing is of benefit to the Q factor of RF spiral inductor improvement (approximately 42.86%), mainly due to the suppression of eddy-current loss by weakening the current crowding effect in the center of the spiral inductor. In order to increase the Q factor further, for the novel inductor, a patterned ground shield is used with optimized layout together. The results indicate that, in the range of 0.5 to 16 GHz, the Q factor of the novel inductor is at an optimum, which improves by 67% more than conventional inductors with uniform geometry dimensions (equal width and equal spacing), is enhanced by nearly 23% more than a PGS inductor with uniform geometry dimensions, and improves by almost 20% more than an inductor with an improved layout.

COSMOLOGICAL IMPLICATIONS OF CONFORMAL FIELD THEORY

Requiring all massless elementary fields to have conformal scaling symmetry removes the conflict between gravitational theory and the quantum theory of elementary particles and fields. Extending this postulate to the scalar field of the Higgs model, dynamical breaking of both gauge and conformal symmetries determines parameters for the interacting fields. In uniform isotropic geometry a modified Friedmann cosmic evolution equation is derived with nonvanishing cosmological constant. Parameters determined by numerical solution are consistent with empirical data for redshifts z ≤ z* = 1090, including luminosity distances for observed type Ia supernovae and peak structure ratios in the cosmic microwave background (CMB). The theory does not require dark matter.

Simple and elegant design of a virion egress structure in Archaea

Some viruses of Archaea use an unusual egress mechanism that involves the formation of virus-associated pyramids (VAPs) on the host cell surface. At the end of the infection cycle, these structures open outward and create apertures through which mature virions escape from the cell. Here we describe in detail the structure and composition of VAPs formed by the Sulfolobus islandicus rod-shaped virus 2 (SIRV2) in cells of its hyperthermophilic archaeal host. We show that the VAPs are stable and autonomous assemblies that can be isolated from membranes of infected cells and purified without affecting their structure. The purified VAPs are heterogeneous in size, reflecting the dynamics of VAP development in a population of infected cells; however, they have a uniform geometry, consisting of seven isosceles triangular faces forming a baseless pyramid. Biochemical and immunoelectron microscopy analyses revealed that the 10-kDa P98 protein encoded by the SIRV2 virus is the sole component of the VAPs. The VAPs were produced in Sulfolobus acidocaldarius and Escherichia coli by heterologous expression of the SIRV2-P98 gene. The results confirm that P98 is the only constituent of the VAPs and demonstrate that no other viral protein is involved in the assembly of pyramids. P98 was able to produce stable structures under conditions ranging from moderate to extremely high temperatures (80 °C) and from neutral to extremely acidic pH (pH 2), demonstrating another remarkable property of this exceptional viral protein.

Experiments on the contact angle of n-propanol on differently prepared silver substrates at various temperatures and implications for the properties of silver nanoparticles

In this paper we present the results of contact angle measurements between n-propanol and silver substrates in the temperature range from −10 °C to 30 °C. The interest in a potential temperature dependence of contact angles originates from recent experiments by S. Schobesberger et al. (Schobesberger S., Strange temperature dependence observed for heterogeneous nucleation of n-propanol vapor on NaCl particles. Master's thesis, University of Vienna, 2008; Schobesberger S. et al., Experiments on the temperature dependence of heterogeneous nucleation on NaCl and Ag particles. In preparation.) investigating the temperature dependence for heterogeneous nucleation of n-propanol vapour on NaCl and on silver particles. We determined dynamic advancing θ a and receding θ r angles on variously prepared silver probes. The Dynamic Wilhelmy method (Wilhelmy L., Über die Abhängigkeit der Capillaritäts-Constanten des Alkohols von Substanz und Gestalt des benetzten festen Körpers. Ann. Phys. Chem., 199:177–217, 1863) was applied using a Krüss K12 Tensiometer, with a refrigerated double-walled glass top. With respect to its potential influence on heterogeneous nucleation mainly the advancing angle is of interest. The uniform probe geometry required was achieved by accurate cutting and by multiple polishing stages up to the accomplishment of a 0.04 μm grain size. The original probes consist of 925 sterling silver including a 7.5% copper content. Additional coating with silver pro Analysi (p.A.) was applied making use of pure silver powder evaporation process via Physical Vapour Deposition (PVD). Results show that a surface contamination by copper cannot be neglected for the specification of contact angles. It turned out that additional PVD coatings not only change the values of θ a but also their temperature dependence. With increasing the number of coatings of a plate the contact angle decreases and its temperature dependence inverts. Since the contact angle hysteresis θ hyst. obtained for the variously often coated probes remained practically constant possible changes in surface roughness with increasing number of PVD layers could be excluded.

Enhanced p-Type Conductivity of ZnTe Nanoribbons by Nitrogen Doping

Single-crystalline intrinsic and N-doped p-type ZnTe nanoribbons (NRs) were synthesized via the thermal evaporation method in argon-mixed hydrogen and nitrogen-mixed ammonia, respectively. Both intrinsic and doped ZnTe nanoribbons had zinc blende structure and uniform geometry. X-ray diffraction peaks of N-doped ZnTe nanoribbons had an obvious shift toward higher angle direction as compared with intrinsic ZnTe. X-ray photoelectron spectroscopy detection confirmed that the dopant content of nitrogen in ZnTe nanoribbons was close to 1%. Field-effect transistors based on both intrinsic and N-doped ZnTe nanoribbons were constructed. Electrical measurements demonstrated that N-doping led to a substantial enhancement in p-type conductivity of ZnTe nanoribbons with a high hole mobility of 1.2 cm−2 V−1 S−1 and a low resistivity of 0.14 Ω cm in contrast to the 6.2 × 10−3 cm−2 V−1 S−1 and 45.1 Ω cm for intrinsic nanoribbons. Moreover, the defect reaction mechanism was proposed to explain the p-type behaviors of bot...

Elastic characterization of membranes with a complex shape using point indentation measurements and inverse modelling

The elasticity parameters of membranes can be obtained from tensile experiments on strips if adequate quantities of the material are available. For biomedical specimens, however, it is not always possible to harvest strips of uniform and manageable geometry suitable for tensile tests. A typical example is the human tympanic membrane. This small structure has a complex conical shape. In such case, elasticity parameters need to be measured in situ. A possible way to determine elasticity parameters of complex surfaces is the use of point indentation measurements. In this paper, this characterization procedure was applied on a scaled phantom model of the tympanic membrane. The model was built of natural latex rubber. In the characterization procedure, a point indentation is carried out on the membrane surface while forces and three-dimensional shapes are measured. Afterwards, a finite element simulation of the experiment is performed and parameters are found using an optimization routine. For validation purposes, the rubber was also subjected to a uniaxial tensile test. Several hyperelastic constitutive models are available to describe rubber-like behaviour. Among these, Mooney–Rivlin and Ogden models are the most popular. We used a low order Mooney–Rivlin and a higher order Ogden model to describe our experiments. Results show that there is a reasonable agreement between the tensile experiments output and the output of the inverse modelling of the indentation experiments.