Serial Structures Research Articles

Experimental and theoretical evidence for the existence of photonic bandgaps and selective transmissions in serial loop structures

We have investigated the electromagnetic band structure, transmission, and phase time through a one-dimensional structure made of loops pasted together with segments of finite length. In this serial loop structure, the loops and segments are constituted of dielectric monomode materials. Analytic expressions are reported for the band structure for a large number N of loops and for transmission coefficients and phase times for any value of N. Experimental and numerical results show the existence of large gaps in these structures. These gaps originate both from the periodicity of the system and the loop resonant states that create zeroes of transmission. The gap widths depend on the lengths of the finite segment and the loop diameters. Defect modes may occur in these bandgaps by introducing defective segments in the structure. The localized states appear as very narrow peaks both in the transmission spectrum and in the transmission phase time of finite serial loop structures. The localized state behavior is analyzed as a function of the length and of the position of the defect segment. The transmission phase measurements enable us to derive the group velocity as well as the density of states in these structures. The experimental results are obtained using coaxial cables in the frequency range of few hundreds of MHz.

Electronic transmission in quasiperiodic serial stub structures

We present exact results on the electronic transmission through quantum stub waveguidesarranged in a Fibonacci quasiperiodic pattern. Discretizing the Schrödinger equation, wemap the problem into an equivalent tight binding form and study the transmissionspectrum using the transfer matrix method. We emphasize the effect of local positionalcorrelations in a Fibonacci quantum stub array that may lead to resonant eigenstates.Using the real space renormalization group ideas we unravel various local clusters of stubsresponsible for resonance. Extended eigenstates have been shown to exist and we find that,under some special circumstances, the electronic charge density exhibits a totally periodiccharacter in such a non-periodic sequence. Our method is completely generaland can be applied to any arbitrary sequence of stubs: periodic, quasiperiodicor random. This may lead to a possible experimental verification of the role ofpositional correlations in the transport behaviour of a class of mesoscopic devices.

Radix-2n serial–serial multipliers

All serial–serial multiplication structures previously reported in the literature have been confined to bit serial–serial multipliers. An architecture for digit serial–serial multipliers is presented. A set of designs are derived from the radix-2n design procedure, which was first reported by the authors for the design of bit level pipelined digit serial–parallel structures. One significant aspect of the new designs is that they can be pipelined to the bit level and give the designer the flexibility to obtain the best trade-off between throughput rate and hardware cost by varying the digit size and the number of pipelining levels. Also, an area-efficient digit serial–serial multiplier is proposed which provides a 50% reduction in hardware without degrading the speed performance. This is achieved by exploiting the fact that some cells are idle for most of the multiplication operation. In the new design, the computations of these cells are remapped to other cells, which make them redundant. The new designs have been implemented on the S40BG256 device from the SPARTAN family to prove functionality and assess performance.

Synthesis of Rice Processing Plants. II. MINLP Optimization

A systematic design approach was applied to develop the optimal process flowsheet for a rice processing plant. The optimization problem was formulated as a Mixed-Integer NonLinear Programme, MINLP, consisting of vectors of binary and continuous variables. A superstructure flowsheet comprising all serial structures of drying, cooling, and tempering units in the process was postulated. The set of optimum decision variables including the number of drying, cooling, and tempering units, temperature and relative humidity of drying air, drying time, cooling time, and tempering time were determine as the solution of the corresponding MINLP. Six objective functions were investigated as possible performance criteria: production time, number of the operating units, energy consumption, total operating cost, head rice yield, and the profit. The choice of objective function was found to have a significant effect on the optimal solution. Comparison with typical design and operating conditions, the MINLP results showed that a 22% reduction in energy consumption was possible along with a 2.4% increase in head rice yield. These savings, if applied to the world-wide rice industry, translate into more than $3 billion dollars/year increase in profit.

Stopping and filtering waves in phononic circuits

The acoustic band structures and transmissions through a one-dimensional (1D) monomodewaveguide made of asymmetric slender tube loops pasted together with slender tubes offinite length are investigated theoretically. These monomode circuits may exhibit large stopbands where the propagation of acoustic waves is forbidden. These stop bands (gaps)originate both from the periodicity of the system and the resonant modes of theloops. The width of these bandgaps depends on the geometrical parameters of thestructure and may be drastically increased in a tandem geometry made of severalsuccessive asymmetric serial loop structures (ASLSs) which differ in their geometricalcharacteristics. These ASLSs may have potential applications as ultra-wide-band filters.

Multiple serial and parallel concatenated single parity-check codes

Single parity-check (SPC) codes are applied in both parallel and serial concatenated structures to produce high-performance coding schemes. The number of concatenations or stages, M, is increased to improve system performance at moderate-to-low bit-error rates without changing the overall code parameters (namely, code rate and code block length). Analytical bounds are presented to estimate the performance at high signal-to-noise ratios. The SPC concatenated codes are considered with binary phase-shift keying and with 16-quadrature amplitude modulation bit-interleaved coded modulation on the additive white Gaussian noise channel and the independent Rayleigh fading channel. Simulations show that the four-stage serial or parallel concatenated SPC codes can, respectively, outperform or perform as well as 16-state turbo codes. Furthermore, decoding complexity is approximately 9-10 times less complex than that of 16-state turbo codes. The convergence behavior of both serial and parallel concatenated SPC codes is also discussed.

Observation of large photonic band gaps and defect modes in one-dimensionalnetworked waveguides

The photonic band structures and transmission spectra of serial loop structures(SLSs), made of loops pasted together with segments of finite length, areinvestigated experimentally and theoretically. These monomode structures,composed of one-dimensional dielectric materials, may exhibit large stop bandswhere the propagation of electromagnetic waves is forbidden. The width of theseband gaps depends on the geometrical and compositional parameters of thestructure and may be drastically increased in a tandem geometry made upof several successive SLSs which differ in their physical characteristics.These SLSs may have potential applications as ultrawide-band filters.

Magnonic spectral gaps and discretetransmission in serial loop structures

In the frame of the long-wavelength Heisenberg model, themagnonic bandgaps and the selective transmission in a serialloop structure, made of loops pasted together with segments offinite length, are investigated theoretically. The loops and thesegments are assumed to be one-dimensional ferromagneticmaterials. Using a Green function method, we obtainedclosed-form expressions for the band structure and thetransmission coefficients for an arbitrary value of the numberN of loops in the serial loop structure. It was found that thegaps originated from the periodicity of the system. The width ofthese forbidden bands depends on the structural andcompositional parameters. We also present analytical andnumerical results for the transmission coefficient through adefective geometry where the length of one finite branch hasbeen modified. It was demonstrated that the presence of thisdefect in the structure can give rise to localized states insidethe gaps. We show especially that these localized states arevery sensitive to the size of the loops and to the periodicity aswell as to the length and the location of the defect branch.

Magneto-transport in asymmetric serial loop structures

In the frame of the long-wavelength Heisenberg model, the magnonic band structures and transmission spectra of asymmetric serial loop structures (ASLS), made of asymmetric loops pasted together with segments of finite length, are examined theoretically. These monomode structures, composed of one-dimensional ferromagnetic materials, may exhibit large stop bands where the propagation of spin waves is forbidden. The width of these band gaps depends on the geometrical parameters of the structure and may be drastically increased in a tandem geometry made of several successive ASLS which differ by their geometrical characteristics. These ASLS's may have potential applications in spin-injection devices.

Spin-wave transport in serial loop structures

Spin-wave transport in serial loop structures

Anisogrid lattice structures – survey of development and application

An integrated design, manufacturing and testing process is described in application to high performance lattice structures made by continuous filament winding from carbon and aramid epoxy composites and used as structural elements of airplane frames and space launch vehicles. The history of the Soviet project, basic design conceptions and industrial fabrication methods are presented and illustrated with actual experimental and serial structures developed in the Central Research Institute of Special Machine Building (CRISMB), the leading Russian Composite Center.

Generalized Least Squares with Misspecified Serial Correlation Structures

Summary Summary. The regression literature contains hundreds of studies on serially correlated disturbances. Most of these studies assume that the structure of the error covariance matrix Ω is known or can be estimated consistently from data. Surprisingly, few studies investigate the properties of estimated generalized least squares (GLS) procedures when the structure of Ω is incorrectly identified and the parameters are inefficiently estimated. We compare the finite sample efficiencies of ordinary least squares (OLS), GLS and incorrect GLS (IGLS) estimators. We also prove new theorems establishing theoretical efficiency bounds for IGLS relative to GLS and OLS. Results from an exhaustive simulation study are used to evaluate the finite sample performance and to demonstrate the robustness of IGLS estimates vis-à-vis OLS and GLS estimates constructed for models with known and estimated (but correctly identified) Ω. Some of our conclusions for finite samples differ from established asymptotic results.

Giant magnonic band gaps and defect modes in serial stub structures: application to the tunneling between two wires

In the frame of the long-wavelength Heisenberg model, we investigate the existence of giant gaps in the band structure of a comblike geometry composed of a one-dimensional magnonic waveguide along which N ′ dangling side branches are grafted at N equidistant sites. These gaps originate not only from the periodicity of the system but also from the resonance states of the grafted branches (which play the role of resonators). The width of these gaps is sensitive to the length of the side branches as well as to the numbers N and N ′. The presence of defect branches in the comblike structure can give rise to localized states inside the gaps. These states may have useful applications in the band structure engineering of nanostructure materials. In the second part of this work, we consider the tunneling between two monomode quantum wires through a coupling device. We give the conditions for selective transfer of a single propagating magnon from one wire to the other, leaving all the neighbor states unaffected. The magnon channel drop tunneling in this system is due to one localized state situated within a gap of the coupling device.

A φ-model solution for the inverse position problem of calibrated robots using virtual elementary motions

It is central to the control of manipulators to calculate the set/sets of joint-displacements which correspond to a given spatial pose (position and orientation) of the end-effector. This problem, which is referred to as the inverse position problem, represents one of the most difficult mathematical challenges in the field of robotics, particularly when performed for calibrated robots (or robots with general structures). In such cases, closed form solutions are too impractical to implement and iterative solutions suffer from numerical singularities. In the present work a procedure is introduced to obtain multiple inverse position solutions for serial robotic structures. For calibrated robots, the procedure involves a simple iterative technique designed to ensure fast convergence and eliminate the occurrence of singularity. However, inverse position solutions for spherical-wrist manipulators will be obtained in a straight-forward non-iterative fashion. A published kinematic notation, referred to as the ϕ-model, was used to develop the system equations.

Digit identity and digit number: indirect support for the descent of birds from theropod dinosaurs

The evolutionary origin of birds is the subject of heated debate. As more data are collected, a consensus is emerging in favour of a descent from theropod dinosaurs. However, in 1997, important evidence refuting this hypothesis was put forward by Burke and Feduccia. They provided new data that confirmed old claims that the digit identity of the three fingers of the hand in theropods differs from that of birds (digits I, II and III versus II, III and IV), which implies that there is no homology between the first, second and third digits of the hand of these groups.In 1999, Wagner and Gauthier subsequently proposed a hypothesis that reconciled the differences in digit homology with an avian descent from theropods. They suggested that changes in digit identity are the cause of homeotic changes (i.e. changes of the identity of one structure into the identity of another structure). Homeotic changes of identity in serial structures are a common occurrence in the vertebral column (e.g. 5% of humans have a thoracic vertebra with a rib instead of the first ribless lumbar one). Also, shifts in identity for an entire group of serial structures, such as that proposed by Wagner and Gauthier, have been amply documented for vertebrae in transgenic mice. There are several different mutations that shift the identity of one vertebra along the entire vertebral column in either the anterior or the posterior direction (e.g. mutations of the polycomb-group and trithorax-group genes). However, no firm evidence for homeotic changes in digits had been found, although it is plausible that the presence of two opposable digits instead of one in koalas and many tree-dwelling birds represents such a homeotic change (here, a change is the identity of the second digit into that of the first).In a new paper, Drossopoulou et al. 1xA model for anteroposterior patterning of the vertebrate limb based on sequential long- and short-range Shh signalling and Bmp signalling. Drossopoulou, G. et al. Development. 2000; 127: 1337–1348PubMedSee all References now present evidence for the developmental independence of the determination of digit number and digit identity. In an elegant experiment, they demonstrate that the important gene Sonic hedgehog (Shh) is initially involved in the determination of the number of digits and later on in the specification of digit identity via the induction of Bmp genes. This complies with existing knowledge that ectopic expression of Shh induces supernumerary digits (polydactyly). By carefully manipulating the gene activity of Shh and Bmp2, they produced phenotypes with the same number of (supernumerary) digits but with differences in digit identity (digit 2, 3 or 4), thus showing that the identity of digits can be changed without a change in the number of digits. Evolutionarily, it is important to realize that Shh is not unique in this respect. At present, at least one other gene is known that has an effect comparable to Shh on the development of supernumerary digits – the related Indian hedgehog gene.Although the evidence is far from complete, these results indirectly support the hypothesis of Wagner and Gauthier. They prove the underlying assumption that homeotic changes in the identity of digits are possible and can occur without a change in digit number. Apart from the relevance to the interpretation of the evolution of birds, Drossopoulou et al. have also provided an important piece in the intriguing puzzle of limb and digit development.

Protein Structural Characterization by Scanning Tunneling Microscopy with Electrochemistry

The structure characterization of proteins or enzymes by STM on electrochemically prepared HOPG surface studied in this laboratory is reviewed. The serial structures of Hb were observed. The differences between the denaturation and inactivation of HRP were investigated by in situ and ex situ STM. The structural variation of Hb in an organic solvent was imaged while protein denaturation was easily observed in a polar solvent.

Linear interference cancellation in CDMA based on iterative techniques for linear equation systems

It has previously been shown that well known iterations for solving a set of linear equations correspond to linear interference cancellation structures. Here, we suggest applying a block-wise iteration that consists of an outer and an inner iteration. The outer iteration used is the Gauss-Seidel (GS) method, while for the inner iteration, we study direct matrix inversion, the Jacobi over-relaxation iteration, and the conjugate gradient iteration. When a true inner iteration is used, this approach allows for a timely derivation of the acceleration parameters required by advanced iterations. The block iteration is based on a symbol-level implementation which leads to the same detection delay profile for both parallel and serial structures at the expense of differences in the amount of serial processing required. This is discussed in some detail and quantified for comparison. The performance of the detectors is studied via computer simulations where it is found that the block approach can provide significantly faster convergence, leading to improved detection delay over the simpler GS iteration. The improvements are obtained at the expense of an increase in the required serial processing speed.

Substructural control design for serial flexible structures using the linear quadratic Gaussian method

A substructural control technique is developed for serial flexible structures using the linear quadratic Gaussian control method. A flexible structure is suitably decomposed into substructures, and subcontrollers and subobservers are designed for the substructures. The subcontroller forces generated within the substructures are taken into account when designing the subcontrollers and subobservers, which are assembled to obtain the global controller and observer for the entire structure. The technique is illustrated with the aid of a numerical example, which demonstrates the accuracy of the proposed substructural control technique compared with the complete structural control technique. The substructural control technique is expected to yield great computational savings in the control design of large serial flexible structures with accuracy.

Homooxacalix[ n]thiophenes: Their one-pot serial synthesis and X-ray structures

A series of homooxacalix[ n]thiophenes ( 1 n , n = 3∼7) was prepared from 2,5-thiophenedimethanol in a one-pot way via acid-catalyzed dehydration under mild conditions. X-Ray crystallographic analysis revealed that homooxacalix[3]thiophene ( 1 3 ) has helical chirality in the solid state.

Quantum waveguide theory of serial stub structures

The electronic behaviors in quantum wires with serial stubs are studied. A general theory of quantum waveguide based on transfer matrix method is developed and is used to treat periodic stub structures, serial stub structures with a defect stub, and Fibonacci stub structures. A number of interesting physical properties in connection with electronic transmission, energy spectra, and charge density distributions in these structures, are found theoretically. In particular, we find that whether there are periodicity and symmetry in the transmission and energy spectra depends on the commensurability of the length parameters. If one length ratio is incommensurate, then the transmission and energy spectra do not exhibit periodicity and symmetry even for periodic stub structures. In particular, the quasiperiodic behaviors are shown in Fibonacci stub structures proposed by us whenever the length parameters are commensurate. The experimental relevance is also addressed briefly.