Unequal Distances Research Articles

Design of a simple three-element quasi-Yagi antenna with a broad impedance bandwidth up to 2.4 : 1

This paper introduces a method for designing a broadband three-element quasi-Yagi antenna (QYA) with a simple geometry and compact size. The proposed QYA consists of simple strip-type elements with unequal widths and distances between them to obtain the desired performance. The proposed QYA fed by a microstrip (MS) line is compact because it has an MS line-to-coplanar strip (CPS) line transition integrated on the CPS line, without requiring additional space for the transition. When a rectangular patch-type director is placed close to the driver dipole fed by a CPS line, the antenna becomes a triple resonance structure, and the impedance bandwidth is extensively increased up to 2.4 : 1 (82.3%) for a VSWR < 2. An example design for a QYA with a gain >4 dBi and a frequency band of 1.6–3.6 GHz is presented. The optimized antenna is fabricated on an FR4 substrate with dimensions of 90 mm × 90 mm and is tested experimentally. The results demonstrate an impedance bandwidth of 2.4 : 1 (1.56–3.74 GHz, 82.3%) for a VSWR < 2, a realized gain of >4 dBi, a cross-polarization level of <−21 dB, and a front-to-back ratio of >13.6 dB within the bandwidth.

Van der Waals density-functional study of 100% hydrogen coverage on bilayer graphene

We investigate all hydrogen configurations that exist in a 1×1 unit cell of bilayer graphene at 100% coverage to find the low energy competing configurations using density functional theory (DFT). Other unique configurations, obtained from a 2×1 supercell, are also investigated. The GGA-PBE functional and four variants of non-local van der Waals density functionals namely, vdW-DF, vdW-DF2, vdW-DF-C09x, and vdW-DF2-C09x are used to account for the exchange correlation effects. Ten unique hydrogen configurations are identified for 1×1 unit cell bilayer graphene, and nine of these structures are found to be energetically stable with three low energy competing configurations. One arrangement found to exist in both 1×1 and 2×1 cell sizes is the most energetically stable configuration of all considered. For some of the configurations identified from the 2×1 supercell, it is found that the effect of hydrogenation results in greatly distorted hexagonal layers resulting in unequal bond distances between the carbon atoms. Also, interaction between the hydrogen-decorated planes greatly affects the energetics of the structures. The vdW-DF-C09x functional is found to predict the shortest interlayer distances for all the configurations, whereas the GGA-PBE functional predicts the largest. For the most energetically favorable configuration, hydrogenation is found to reduce the elastic properties compared with pristine bilayer graphene.

Sum Rate Analysis of ZF Receivers in Distributed MIMO Systems

The performance of single-cell distributed multiple-input multiple-output (D-MIMO) systems is not only affected by small-scale Rayleigh fading but also from large-scale fading and path-loss. In this paper, we elaborate on the sum rate of D-MIMO systems employing linear zero-forcing receivers, accounting for both large and small-scale fading effects, as well as spatial correlation at the transmit side. In particular, we consider the classical lognormal model and propose closed-form upper and lower bounds on the achievable sum rate. Using these bounds as a starting point, we pursue a "large-system" analysis and provide asymptotic expressions when the number of antennas at the base station (BS) grow large, and when the number of antennas at both ends grow large with a fixed and finite ratio. A detailed characterization in the asymptotically high and low signal to noise ratio regimes is also provided. An interesting observation from our results is that in order to maximize the sum rate, the RPs should be placed at unequal distances to the BS when they experience the same level of shadowing. The resulting closed-form expressions are compared with the corresponding results on MIMO optimal receivers.

Padina ditristromatica sp. nov. and Padina pavonicoides sp. nov. (Dictyotales, Phaeophyceae), two new species from the Mediterranean Sea based on morphological and molecular markers

A study of the genus Padina in the Mediterranean Sea, based on detailed morphological and molecular analyses using chloroplast rbcL and mitochondrial cox3 gene sequences, as well as RuBisCO spacer and partial rbcS sequences, revealed the presence of two new species, P. ditristromatica Ni-Ni-Win & H. Kawai and P. pavonicoides Ni-Ni-Win & H. Kawai. They are two to three-layered and three-layered species, respectively. Padina ditristromatica is characterized by a thallus composed of two cell layers from the marginal portion to the inrolled margin and a mixture of two and three layers in the other portions; heavy calcification on both surfaces of the thallus except for the hair lines; alternating hair lines that are spaced at unequal distances between the upper and lower surfaces; and broad indusiate oogonial and tetrasporangial sori forming broken lines or patches arranged in a concentric row, which are distally close to the hair lines and half immersed in the epidermis layer only on the lower surface. Padina pavonicoides is characterized by a thallus composed of three cell layers from the base to the marginal portion and two layers at the inrolled margin; alternating hair lines that are spaced at equal distances between the upper and lower surfaces; and indusiate oogonial and tetrasporangial sori forming patches located distal to the hair lines only on the lower surface. All molecular phylogenetic analyses indicated that the new species are closely related to P. pavonica, a common species in the Mediterranean Sea. However, the cox3 region could not be amplified for P. ditristromatica. Therefore, the RuBisCO spacer and partial rbcS were analysed for the Mediterranean specimens in order to confirm their identity as well as their closest relationships. The combined rbcL, RuBisCO spacer and partial rbcS data also support their genetic separation and show that P. pavonica is more closely related to P. pavonicoides than P. ditristromatica, as in other molecular analyses.

Electron-vibron coupling in halogenated acenaphthenequinone upon O K-edge soft x-ray absorption

We present high resolution oxygen K near-edge x-ray absorption spectra of the acenaphthenequinone (ANQ) derivative 3,8-dibromo-5,6-dichloro-ANQ (Br(2)Cl(2)-ANQ). The spectral features exhibit an almost identical vibronic fine structure compared to that shown by ANQ. The unequal distances of the vibronic levels as derived from the least-squares fit analysis of the vibronic progressions allows us to determine the anharmonicity of the excited state potentials involved. We conclude that a single vibrational progression couples to the resonant excitation of O 1s core electrons preferentially. Comparison of the two ANQ derivatives gives a clear indication that the vibronic mode corresponds to a C=O stretching mode, rather than coupling to a C-H mode as suggested previously. These conclusions are supported by density functional theory calculations.

Multi-cabinet implementation for Load-Balanced Optical Switch

Load-Balanced Optical Switch (LBOS) [20] ensures close-to-100% throughout and all-optical transmission between linecards. In this paper, we extend LBOS for multi-cabinet implementation. The challenges lie in the fact that the practical implementation requirements in single-cabinet LBOS become un-scalable for multi-cabinet scenario. First of all, we remove the restriction on LBOS that propagation delay ( t p) between adjacent linecards must equal to the transmission time ( t pkt) for sending one packet. The delay t p is relaxed to be any value, which can accommodate the long and unequal distances fibers among cabinets. Secondly, we outstrip the upper bound of switch size N = 160 in LBOS. The basic idea is that the adjacent linecards share an identical channel/wavelength. Then LBOS can be scaled to support the large switch size of multi-cabinet. Last but not least, a more feasible fair scheduler is devised to replace the original one in LBOS. The simulation results show that multi-cabinet LBOS yields a much better delay/throughput performance than other multi-cabinet optical switches (e.g. Fasnet [8]).

The reaction of a potentially N2S-donor bis[benzo(thiazole/imidazole)] with the fac-[Re(CO)3]+ and cis-[ReO2]+ cores

The reactions of bis(benzothiazol-2-ylethyl)sulfide (bts) and its benzimidazole analogue (btn), both with a N 2 S-donor atom set, with [Re(CO) 5 Br] and cis -[ReO 2 I(PPh 3 ) 2 ] were studied. The X-ray crystal structure of fac -[Re(CO) 3 (bts)Br] shows that bts acts as a bidentate NS-donor ligand, with a free uncoordinated benzothiazole group. With rhenium(V) the dimer ( μ -O) 2 [Re 2 O 2 (btn) 2 ]I 2 was isolated, in which btn acts as a tridentate N 2 S chelate to each metal centre. Each oxo-bridge is unsymmetrical, with unequal Re-O distances.

Freezing in Resonance Structures for Better Packing: XeF2 Becomes (XeF+)(F−) at Large Compression

Recent high-pressure experiments conducted on xenon difluoride (XeF(2)) suggested that this compound undergoes several phase transitions up to 100 GPa, becoming metallic above 70 GPa. In this theoretical study, in contrast to experiment, we find that the ambient pressure molecular structure of xenon difluoride, of I4/mmm symmetry, remains the most stable one up to 105 GPa. In our computations, the structures suggested from experiment have either much higher enthalpies than the I4/mmm structure or converge to that structure upon geometry optimization. We discuss these discrepancies between experiment and calculation and point to an alternative interpretation of the measured cell vectors of XeF(2) at high pressure. At pressures exceeding those studied experimentally, above 105 GPa, the I4/mmm structure transforms to one of Pnma symmetry. The Pnma phase contains bent FXeF molecules, with unequal Xe-F distances, and begins to bring other fluorines into the coordination sphere of the Xe. Further compression of this structure up to 200 GPa essentially results in self-dissociation of XeF(2) into an ionic solid (i.e., [XeF](+)F(-)), similar to what is observed for nitrous oxide (N(2)O) at high pressure.

Metal derivatives of thiosemicarbazones: crystal and molecular structures of mono- and di-nuclear copper(I) complexes with N1-substituted thiosemicarbazones

The reactions of copper(II) chloride with a series of N1-substituted thiosemicarbazones, {R1(H)C2=N3–N2(H)–C1(=S)–N1HMe, R1 = furan, Hftsc-N-Me; thiophene, Httsc-N-Me; phenyl, Hbtsc-N-Me} in 1 : 2 molar ratio yield copper(I) complexes : sulfur-bridged dinuclear complexes, [Cu2Cl2(μ-S-Hftsc-N-Me)2(η1-S-Hftsc-N-Me)2] (1), [Cu2Cl2(μ-S-Httsc-N-Me)2(η1-S-Httsc-N-Me)2] (2), and a mononuclear complex [CuCl(η1-S–Hbtsc-N-Me)2] (3). Complexes 1–3 have been characterized by elemental analysis (C, H, N), spectroscopy (IR, 1H NMR) and X-ray crystallography. The Cu(μ-S)2Cu cores in 1 and 2 form parallelograms with unequal bond distances {Cu–S, 2.2831(3), 2.5955(4) Å (1); 2.2641(9), 2.8006(10) Å (2)}. Bond angles at sulfur and copper are, Cu–S–Cu, S–Cu–S, 69.86(11), 110.12(17)° (1); 75.84(3), 104.16(3)° (2), respectively. The Cu ··· Cu separations are 2.806 Å (1) and 3.141 Å (2) with each copper center a distorted tetrahedron (96.67–119.28°). Bond parameters of 3, Cu–S, 2.227(3), 2.224(3) Å, and 118.97–121.11° are different.

Superdisks and the structural asymmetry of radio galaxies

We present a sample of 16 radio galaxies, each of which is characterized by a wide, elongated emission gap with fairly sharp and straight edges between the two radio lobes. This particular subset of the “superdisk” radio galaxies is chosen because of a highly asymmetric location of the host elliptical galaxy relative to the gap’s central axis. In addition to posing a considerable challenge to the existing models, such a morphology also means that the two jets traverse highly unequal distances through the superdisk material. One thus has a possibility to directly investigate if the marked asymmetry between the two jets’ interaction with the (much denser) ambient medium, during their propagation, has a significant import for the brightness of the hot spot forming near each jet’s extremity. We also propose a new explanation for the formation of superdisks through the merger of a smaller elliptical galaxy with the massive host, in which the gas attached to the infalling galaxy deposits its angular momentum into the host’s circumgalactic gas, thereby causing it to flatten into a fat pancake, or superdisk. The asymmetric location of the host galaxy can be assisted by the kick imparted to it during the merger. We also suggest a physical link between these radio galaxies and those with X-shaped and Z-symmetric radio lobes, commonly believed to arise from mergers of two galactic nuclei, each harboring a supermassive black hole.

Optimally Interleaved Signals for SFN

This paper focuses on how designing transmit signals improves performance of single frequency networks (SFNs), employing multiple distributed transmit antennas. Considering the effect of multipath fading, pairwise error probability conditioned on shadowing is derived to show that the achievable diversity order of SFNs increases as the number of resolvable channel taps between transmit and receive antennas increases. One transmit signal based on interleaved-partition subcarrier grouping is proposed to obtain the achievable diversity order. Further, we show that different interleaving methods result in different performance due to asynchronous delays caused by unequal distances between distributed transmit antennas and mobile receivers. To optimize the proposed transmit signal, one interleaving scheme, establishing a tradeoff between mobile receivers' location and performance, is introduced in terms of the asynchronous delays. Simulation results are presented in a representative scenario to demonstrate the performance gains offered by the proposed optimum transmit signal. The proposed scheme does not introduce any changes at the mobile receivers.

Performance analysis of rectangular quadrature amplitude modulation with combined arbitrary transmit antenna selection and receive maximal ratio combining in Nakagami-m fading

The average symbol error probability (SEP) performance of arbitrary rectangular quadrature amplitude modulation in the context of arbitrarily ordered transmit antenna selection and receive maximal ratio combining diversity system is analysed. The channel gains are assumed to follow Nakagami-m fading distribution with in general arbitrary fading parameters. Exact expressions for the average SEP performance are derived for the general case of unequal in-phase and quadrature decision distances as well as distinct in-phase and quadrature modulation orders. The results generalise many previous case studies, and can be used to investigate the impact of various diversity-combining schemes and different modulation and channel parameters on the system average SEP performance.

Clinical Experience of a Microvascular Venous Coupler Device in Free Tissue Transfers

Most free flap failures result from technical problems in performing vascular anastomoses, such as endothelial intima lacerations, distortion of the vessels, and unequal intersuture distances. These incorrect practices can lead to thrombosis formation and, ultimately, flap failure. Solving this problem is a challenging issue for all micro-reconstructive surgeons. In the last decade, a vascular anastomotic coupler instrument was developed and reported on. We review our recent experiences of free tissue transfer using this vascular coupler device, and discuss how venous problems can be overcome with its aid. We believe the excellent patency rate of the coupler may minimize the well-described problems of venous thrombosis in the challenging field of free tissue reconstructions.

Master blood pressure variation in office, by self, and in sleep recordings

Variation inherent to each session in any recording situation has to be mastered to obtain informative mean values and differences. Variation due to time trend and unsteady consecutive readings versus inter‐arm variations in blood pressure (BP) in the operator‐initiated, self‐initiated, and sleep recordings were studied by oscillometry. They were small in operator‐initiated recordings, increased in self‐recordings, and were paramount in sleep. A passive supine patient and simultaneous recordings with cuffs placed in equal horizontal positions are essential conditions for the estimation of a real mean inter‐arm difference. The relative variation of pulse pressure (PP), compared with other components, was largest within each situation. Most of the systolic BP (SBP)/diastolic BP (DBP) variation in sleep was due to unequal vertical cuff distances to the heart level. Only sleep PP was independent of the vertical position of cuffs. A plot of inter‐arm differences can visualize systematic errors in sequences of sleep SBP/DBP. As is well known, every doubling of variation (SD) requires quadrupling the number of independent recordings in order to retain the same size of confidence interval (CI) for a mean value.

Marker-Based Prediction of the Parental Genome Contribution to Inbred Lines Derived From Biparental Crosses

Molecular markers can be employed to predict the parental genome contribution to inbred lines. The proportion alpha of alleles originating from parent P1 at markers polymorphic between the parental lines P1 and P2 is commonly used as a predictor for the genome contribution of parent P1 to an offspring line. Our objectives were to develop a new marker-based predictor xi for the parental genome contribution, which takes into account not only the alleles at marker loci but also their map distance, and to compare the prediction precision of xi with that of alternative methods. We derived formulas for xi for inbreds derived from biparental crosses (F1 and backcrosses) with the single-seed descent or double-haploid method and presented an extension xi* possessing statistical optimum properties. In a simulation study, alpha showed a systematic overestimation of large parental genome contribution that was not observed for xi. The mean squared prediction error of xi was at least 50% smaller than that of alpha for linkage maps with unequal distances between adjacent markers. A data set from a study on plant variety protection in maize was used to illustrate the application of xi. We conclude that xi provides substantially greater prediction precision than the commonly used predictor alpha in a broad range of applications in genetics and breeding.

Evaluating spatial autocorrelation and depletion in pitfall-trap studies of environmental gradients

Studies of environmental gradients like edge effects commonly employ designs where samples are collected at unequal distances within transects. This approach risks confounding species patterns caused by the environmental gradient with patterns resulting from the spatial arrangement of the sampling scheme. Spatial autocorrelation and depletion (reduced catch) have the potential to influence pitfall-trap collections of invertebrates. Readily available control data from a study of edge and riparian effects on forest litter beetles was used to assess autocorrelation and depletion effects. Data from control transects distant from the treatment transects located at habitat edges and streams were screened to determine whether the study design (pitfall traps at varying distances within transects) was imposing patterns on the data attributable to differential autocorrelation or depletion. Autocorrelation in species composition and assemblage structure was not detected within the 99 m transects. The abundance and species richness of beetles were not lower where traps were in closer proximity, indicating that the transect design was not causing measurable depletion or resulting in differential trap catch. These findings indicate that spatial autocorrelation and depletion are unlikely to impair further analyses of edge and riparian effects on litter beetles.

Speed of Sound in Pure Water at Temperatures between 274 and 394 K and at Pressures up to 90 MPa

A newly designed experimental apparatus has been used to measure the speed of sound u in high-purity water on nine isotherms between 274 and 394 K and at pressures up to 90 MPa. The measurement technique is based on a traditional double-reflector pulse-echo method with a single piezoceramic transducer placed at unequal distances from two stainless steel reflectors. The transit times of an acoustic pulse are measured at a high sampling rate by a digital oscilloscope. The distances between the transducer and the reflectors were obtained at ambient temperature and pressure by direct measurements with a coordinate measuring machine. The speeds of sound are subject to an overall estimated uncertainty of 0.05 %. The acoustic data were combined with available values of density ρ and isobaric heat capacity c p along one isobar at atmospheric pressure to calculate the same quantities over the whole temperature and pressure range by means of a numerical integration technique. These results were compared with those calculated from the IAPWS-95 formulation with corresponding relative deviations which are within 0.1%.

A possible interdependency between the wavy path of enamel rods, distances of Retzius lines, and mitotic activity at the cervical loop in human teeth: a hypothesis

In human enamel, the enamel rods do not run straight in most regions. Instead, they obtain an undulated path. The diameter of the enamel rods remains constant all the way, and a wavy pattern is necessary to produce the volume of the enamel mantle. It is not understood, how this undulated migration of ameloblasts is created. Considerations are presented to explain causal interdependencies between the wavy path of the enamel rods, unequal growth of the cervical loop cells and unequal distances of the striae of Retzius. To test these considerations, further research must record mitotic activity at the cervical loop during the stages of dental development. The distances of Retzius lines must be measured at different spots all over the whole enamel mantle, preferably in 3D. As a result, knowledge of the interdependency between the inner structure and the outer form of each tooth crown will lead to an understanding of tooth form and occlusion.

Influence of temperature on the reduction kinetics of Zn 2+ at a mercury electrode

The reduction of Zn 2+ at a mercury electrode has been studied by the a.c. impedance technique in the 263–318 K temperature range. Kinetic data have been analyzed in terms of a mechanism consisting of two consecutive charge transfer steps. The apparent activation enthalpies and charge transfer coefficients of both steps are found to be temperature independent. Differential capacity curves and potentials of zero charge of the NaClO 4 supporting electrolyte solutions were measured at each temperature of interest. Double layer effects on the Zn 2+ reduction rate constants were analyzed within the framework of the unequal distances of closest approach theory, and the corrected rate constants were found to be independent of supporting electrolyte concentration when allowance for changes in the Zn 2+ activity coefficient was made. The implications of the activation parameter values on the nature of the rate determining steps are also discussed.

Operating characteristics of X-bar charts with asymmetric control limits

When the assumptions behind the Shewhart chart are not met, policies other than the traditional 3-sigma limits may enable speedier and more economical detection of process change. If a process has unequal probabilities of downward and upward shifts, downward shifts of differing magnitude from upward shifts, and/or standard deviations after downward shifts different from those after upward shifts, then increases in the in-control average run length and decreases in the out-of-control average run length are simultaneously achievable with control limits placed at unequal distances from the process mean. The magnitude of these improvements is investigated for several types of process. The results are then extended to median charts for processes with output that is not normally distributed.