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Regional mobility in terms of air transportation is of fundamental importance for regional economic and social development by connecting countries, people and cultures. In this respect, novel turboprop designs will contribute to environmentally friendly and sustainable means of transportation. Turboprop configurations are efficient providing fuel savings of up to 20 percent with respect to equivalent technology turbofan aircrafts, and novel propeller design enables cruise speeds up to Mach 0.8. Moreover, additional drag reduction is achieved by utilizing natural laminar wing technology requiring smooth and continuous flow over the particularly shaped wing upper surface. The integration of turboprop engines into the airframe, and the design of high-lift devices for landing and take-off, presenting some unique aerodynamic challenges in particular when utilizing natural laminar flow wings for additional drag reduction. The Clean Sky 2 project WTM-RECYCLE, completed during 2021, supported the development and assessment of new and conceptual versatile aerodynamic high lift technologies as well as turboprop integration effects. Wind tunnel measurements of a 5m span large-scale turboprop aircraft model together with complementary CFD analyses were used to study the effect of morphing devices for drooped wing leading edge, geometry morphed flaps and winglets. Two different wing profile geometries in cruise, landing and take-off configurations were studied. Propeller installation effects were included by powered thrusting propellers in the wind-tunnel installation as well as in the CFD model. The large 5m span wind tunnel model of a complete aircraft with wing, fuselage, tail and running propeller engines was designed by IBK with a central wing core with hydraulic routing for the engines. The different wings, winglets and high-lift devices were made as interchangeable modules for rapid configuration changes within the wind tunnel enabled by highest precision manufacturing at Eurotech. Moreover, setting of control surfaces such as elevator, rudder, ailerons as well as inner and outer flaps were implemented. The model was instrumented with a 6DOF balance, flap balances and surface pressure taps. More than 300 lift/drag polars were measured at RUAG LWTE wind tunnel. Oil flow patterns of the separation onset over the wing and flaps were recorded for comparison with CFD. The CFD model was made by neptech with the same principle of interchangeable mesh modules of the different components, which are combined for all different configurations. Each mesh module is carefully designed with structure-like surface and boundary-layer meshes for best accuracy with wall-resolved RANS computations. The meshing process is accelerated by the scripting capabilities of Pointwise enabling automatic and modularized meshing for rapid turn-around times. The CFD solver M-Edge with the Spalart-Allmaras and Wallin-Johansson EARSM turbulence models was used by KTH with the model installed in the wind tunnel for comparison with measurements and for extrapolation to free flight. Moreover, transition predictions by a data-base method were made at KTH. The paper and presentation will show major results from the wind-tunnel campaign for the different configurations and control surface settings including thrusting engines. Moreover, CFD comparisons for wind-tunnel conditions and extrapolated to free flight will be presented. This project WTM-RECYCLE has received funding from the Clean Sky 2 Joint Undertaking under the European Unions Horizon 2020 research and innovation programme under grant agreement No 755605.

This paper deals with the actuation system design of a full-scale morphing aileron for regional aircraft. The aileron is allowed to smoothly change its geometrical configuration and perform the in-flight transition from a baseline shape to a set of optimal morphed ones pre-defined on the basis of aerodynamic requirements. The design of such innovative aileron is aimed not only at substituting the conventional aileron installed on a real aircraft but also to provide additional functionality. The aileron is free to rotate around its main hinge axis and it is also allowed to smoothly modify camber with two independent actuation systems. In such manner it can be used also during cruise with a symmetric deflection between the two half wings in order to reduce drag in off design condition. To accomplish variable aileron shape, a rigid-body mechanism was designed. The proposed aileron architecture is characterised by segmented adaptive ribs rigidly linked each other with spanwise reinforcements such as spars and stringers in a multi-box arrangement. Each rib is split into two movable plates connected by means of rotational hinges in a finger-like mechanism. The mechanism is driven by a load-bearing actuator by means of a kinematic chain opportunely tied based on the structural requirements in terms of shape to be matched and load to be withstood. The proposed device is an innovative arrangement of the quick-return mechanism composed of a beam leverage, commercial linear guides and a crank. The actuator shaft is directly inserted in the crank, which transmits the rotation to the linear guide that slide along a rail moving upward or downward the beam thus resulting in a camber variation. The entire aileron is moved by three leverages internally contained and distributed along the first two bays while the most external ribs are considered passive and their movement slaved. Two actuation layouts are analytically and numerically studied, the analytical theory is presented and validated by means of a multi-body simulation. Moreover, a linear static analysis was carried out under the hypothesis of glued contact between linear guides components simulating a jamming condition. This assumption has been formulated because it represents the most severe condition that envelop all the operative loads to which the actuation system is subjected. The analyses conducted are preliminarily aimed to verify that no failure occur under the imposed loads. In this first design loop, the vertical static force acting on the linear carriage exceeded allowable value and then a new configuration with double-sided linear guides was then investigated.

A new wing-tip concept with morphing upper surface and interchangeable conventional and morphing ailerons was designed, manufactured, bench and wind-tunnel tested. The development of this wing-tip model was performed in the frame of an international CRIAQ project, and the purpose was to demonstrate the wing upper surface and aileron morphing capabilities in improving the wing-tip aerodynamic performances. During numerical optimisation with ‘in-house’ genetic algorithm software, and during wind-tunnel experimental tests, it was demonstrated that the air-flow laminarity over the wing skin was promoted, and the laminar flow was extended with up to 9% of the chord. Drag coefficient reduction of up to 9% was obtained when the morphing aileron was introduced.

Sensorised structures aimed at Structural Health Monitoring implementation in aircraft components are among the most promising approaches for a next future evolution of the current maintenance procedures (and consequently for operative costs reduction) but also for relevant modifications of design rules and manufacturing processes. Adhesive bonds represent an efficient manufacturing process for composite structural parts due to the possibility to co-bond or co-cure together thin plates and stiffeners leading to weight saving, although they have not been massively employed yet. One of the showstoppers for the full implementation of adhesive bonds in composites are the airworthiness certification requirements for composite aircraft structures as presented within the FAA Advisory Circular 20-107B. In that document the general methods for substantiating the limit load capacity of any bonded stiffener, the failure of which would result in catastrophic loss of the airplane, are prescribed. Among the suggested methods, the only one really permitting to achieve the optimal bonding efficiency without the addiction of disbond stoppers (i.e. rivets), is a “repeatable and reliable non-destructive inspection techniques ensuring the strength of each joint”. This paper presents experimental activities that the authors have carried out to characterize two stiffened plates that are “nominally” equal, but obtained by different manufacturing processes; the two plates have been statically characterized performing strength tests, inspected by traditional NDI (ultrasonic C-Scan) and implementing a guided waves based SHM system designed for stringer debonding detection and characterization. A critical analysis of the experimental results as well as a comparison with the expected nominal structural performances will be presented. Afterward a comparison of the three approaches adopted for structural health status characterization before and after stiffener disbonding will be presented looking at the possible implementation of a SHM system committed at satisfying the certification requirements of the AC 20-107B.

The in-flight control of the wing shape is widely considered as one of the most promising solutions to enhance the aerodynamic efficiency of the aircraft thus minimizing the fuel burnt per mission ([1]-[26]). In force of the fallout that the implementation of such a technology might have on the greening of the next generation air transport, ever increasing efforts are spent worldwide to investigate on robust solutions actually compliant with industrial standards and applicable airworthiness requirements. In the framework of the CleanSky2, a research program in aeronautics among the largest ever founded by the European Union, the authors focused on the design and validation of two devices enabling the camber-morphing of winglets and flaps specifically tailored for EASA CS-25 category aircraft ([29]). The shape transition was obtained through smart architectures based on segmented (finger-like) ribs with embedded electromechanical actuators. The combined actions of the two smart systems was conceived to modulate the load distribution along the wing while keeping it optimal at all flight conditions with unequalled benefits in terms of lift-over-drag ratio increase and root bending moment alleviation. Although characterized by a quasi-static actuation, and not used as primary control surfaces, the devices were deeply analysed with reference to their impact on aircraft aeroelastic stability. Rational approaches were adopted to duly capture their dynamics through a relevant number of elastic modes; aeroelastic coupling mechanisms were identified in nominal operative conditions as well as in case of systems’ malfunctioning or failure. Trade off flutter and divergence analyses were finally carried out to assess the robustness of the adopted solutions in terms of movable parts layout, massbalancing and actuators damping.

Within the framework of the JTI-Clean Sky (CS) project, and during the first phase of the Low Noise Configuration Domain of the Green Regional Aircraft – Integrated Technological Demonstration (GRA-ITD, the preliminary design and technological demonstration of a novel wing flap architecture were addressed. Research activities were carried out to substantiate the feasibility of morphing concepts enabling flap camber variation in compliance with the demanding safety requirements applicable to the next generation green regional aircraft, 130- seats with open rotor configuration. The driving motivation for the investigation on such a technology was found in the opportunity to replace a conventional double slotted flap with a single slotted camber-morphing flap assuring similar high lift performances -in terms of maximum attainable lift coefficient and stall angle- while lowering emitted noise and system complexity. Studies and tests were limited to a portion of the flap element obtained by slicing the actual flap geometry with two cutting planes distant 0.8 meters along the wing span. Further activities were then addressed in order to increase the TRL of the validated architecture within the second phase of the CS-GRA. Relying upon the already assessed concept, an innovative and more advanced flap device was designed in order to enable two different morphing modes on the basis of the A/C flight condition / flap setting: Mode1, Overall camber morphing to enhance high-lift performances during take-off and landing (flap deployed); Mode2, Tab-like morphing mode. Upwards and downwards deflection of the flap tip during cruise (flap stowed) for load control at high speed. A true-scale segment of the outer wing flap (4 meters span with a mean chord of 0.9 meters) was selected as investigation domain for the new architecture in order to duly face the challenges posed by real wing installation. Advanced and innovative solutions for the adaptive structure, actuation and control systems were duly analyzed and experimentally validated thus proving the overall device compliance with industrial standards and applicable airworthiness requirements.

A new wing-tip concept with morphing upper surface and interchangeable conventional and morphing ailerons was designed, manufactured, bench and wind tunnel tested. The development of this wing tip was done in the frame of an international CRIAQ project, and the purpose was to demonstrate the upper surface morphing and aileron morphing capabilities in improving the wing tip aerodynamic performances. During numerical optimization with ‘in-house’ genetic algorithm software, and during wind tunnel experimental tests, it was demonstrated that the air flow laminar state was extended and drag coefficient reduction were obtained., 55th AIAA Aerospace Sciences Meeting, 9-13 January 2017, Grapevine, Texas, USA

This paper presents a study aimed at evaluating how viscoelastic materials embedded in composite plates affect structural damping during the flight of a civil aircraft. The vibro-acoustic responses of composite fuselage structures realized with embedded viscoelastic damping treatments have been experimentally characterized at different temperature conditions. The real influence of viscoelastic materials on composite structures has been investigated, focusing the investigations on aspects still unknown, related mostly to temperature effects. In order to simulate the temperature level of commercial transport aircraft in cruise flight conditions, tests were performed using a climatic room where temperature and humidity were controlled. Vibrational tests were performed on two composite fuselage skin coupons: one treated with embedded viscoelastic damping treatments and the other one untreated. The tests were performed at temperatures of [Formula: see text] for the untreated composite fuselage structure, and [Formula: see text] and [Formula: see text] for the treated composite fuselage structure. The damping values were carried out by the impulse response decay method and the loss factor was obtained as an average of many repeated acquisitions. In order to maximize the damping effect, the best temperature interval for the treated composite fuselage skin coupon was evaluated, and the behavior for both composite fuselage structures (treated and untreated) was characterized. Thanks to the high number of tests, a statistical analysis was performed in order to validate the approach used.

Both symmetric and non symmetric bis(aryl)acenaphthenequinonediimine ligands, featured by substituents in meta-positions of the aryl rings, have been applied for the first time as ancillary ligands for the palladium catalyzed CO/vinyl arene copolymerization. The nature and the number of substituents affect both the productivity and the molecular weight of the synthesized copolymers. Palladium complexes containing the nonsymmetric ligands are the most efficient catalysts reported so far for the synthesis of atactic polyketones.

Phospholipase C zeta (PLCz) is a sperm protein linked to oocyte activation and zygote development in diverse species. Human intracytoplasmic sperm injection (ICSI) success is poor when sperm PLCz is reduced or mutated. We hypothesised that the expression of PLCz in stallion sperm corresponds with cleavage rates after ICSI. For this study, we selected sperm from 4 of 21 stallions for which frozen-thawed sperm were evaluated using flow cytometry to assess mean fluorescence intensity (MFI) and percentage of sperm positively labelled with PLCz. Before flow cytometric assessment, Western blotting and immunofluorescence were performed to validate antibody binding and to identify PLCz as a 71-kDa protein in stallion sperm, located in the acrosomal and postacrosomal region, and the tail (Gonzalez-Castro et al. 2017 Reprod. Fertil. Dev. 30, 228). Frozen sperm from 4 stallions were selected based on MFI and percentage of PLCz-labelled sperm per total sperm population, respectively (High, 87% with 10,384 MFI and 84% with 10,784 MFI; Low, 56% with 4,789 MFI and 59% with 5,360 MFI). The samples were selected so that other fertility indicators, such as normal morphology (> 70%), DNA integrity (

Nature teaches that the flight of the birds succeeds perfectly since they are able to change the shape of their wings in a continuous manner. The careful observation of this phenomenon has re-introduced in the recent research topics the study of “metamorphic” wing structures; these innovative architectures allow for the controlled wing shape adaptation to different flight conditions with the ultimate goal of getting desirable improvements such as the increase of aerodynamic efficiency or load control effectiveness. In this framework, the European research project SARISTU aimed at combining morphing and smart ideas to the leading edge, the trailing edge and the winglet of a large commercial airplane (EASA CS25 category) while assessing integrated technologies validation through high-speed wind tunnel test on a true scale outer wing segment. The design process of the adaptive trailing edge (ATED) addressed by SARISTU is here outlined, from the conceptual definition of the camber-morphing architecture up to the assessment of the device executive layout. Rational design criteria were implemented in order to preliminarily define ATED structural layout and the general configuration of the embedded mechanisms enabling morphing under the action of aerodynamic loads. Advanced FE analyses were then carried out and the robustness of adopted structural arrangements was proven in compliance with applicable airworthiness requirements.

The human body is colonized by a large number of microbes that are collectively referred to as the microbiota. They interact with the hosting organism and some do contribute to the physiological maintenance of the general good health thru regulation of some metabolic processes while some others are essential for the synthesis of vitamins and short-chain fatty acids. The abnormal variation, in the quality and/or quantity of individual bacterial species residing in the gastro-intestinal tract, is called “dysmicrobism”. The immune system of the host will respond to these changes at the intestinal mucosa level which could lead to Inflammatory Bowel Diseases (IBD). This inflammatory immune response could subsequently extend to other organs and systems outside the digestive tract such as the thyroid, culminating in thyroiditis. The goal of the present study is to review and analyze data reported in the literature about thyroiditis associated with inflammatory bowel diseases such as Ulcerative Colitis (UC) and Crohn’s Disease (CD). It was reported that similarities of some molecular bacterial components with molecular components of the host are considered among the factors causing IBD through an autoimmune reaction which could involve other non-immune cell types. The axis dysmicrobism-IBD-autoimmune reaction will be investigated as a possible etiopathogenic mechanism to Autoimmune Thyroiditis. If such is the case, then the employment of specific probiotic strains may represent a useful approach to moderate the immune system.

The employment of viscoelastic materials for the passive control of noise and vibration transmitted through panels made of composite material is widely considered as an effective solution in the aerospace field. In the following paper a modelling technique based on the finite elements method able to describe the dynamic properties of a typical fuselage panel is implemented and numerically validated: natural frequencies and damping properties of a panel treated by viscoelastic layer are evaluated. This technique is essentially based on: proper choice of structural elements for the model of panel, proper link of the different elements and a correct description of the boundary conditions. Different models have been developed for a long panel with high width over thickness ratio such to be considered infinite: a 2D model; a 3D model consisting in all brick elements and a 3D model consisting in shell elements for the structural top and bottom plates and in brick elements for the damping layer. In this last case much care has been paid for the description of the boundary conditions. Once validated the technique for infinite panels, a finite element model of a panel supported on the four sides with a damping layer integrated in the mid plane has been developed and the results have been compared with an analytical solution available in literature. The comparison showed a good agreement between the dynamic properties predicted by the technique herein presented and the ones provided by the analytical model and confirmed the care that should be paid for a proper choice of the constraints well representing the structural behaviour of the panel.

we study a higher dimensional Lehmer problem, or alternatively the Lehmer problem for a power of the multiplicative group. More precisely, if α1, . . . , αn are multiplicatively independent algebraic numbers, we provide a lower bound for the product of the heights of the αi’s in terms of the degree D of the number field generated by the αi’s. This enables us to study the successive minima for the height function in a given number field. Our bound is a generalisation of an earlier result of Dobrowolski and is best possible up to a power of log(D). This, in particular, shows that the Lehmer problem is true for number fields having a small Galois group.

In this paper the airframe noise of civil transport aircraft is numerically evaluated and compared with measurements taken in some european airports with the target of separating the airframe contribution from other noise contributions effective on a typical aircraft. The attention has been focused on airframe noise since it sets a lower limit below whichever reduction of noise generated by engine have no significant effect on the overall noise level perceived by an observer and due to the aircraft flyover. The intensity of airframe noise depends on the aircraft configuration: during the cruise the aircraft exhibit an aerodynamically ‘clean’ configuration that produces less noise than the configuration assumed by the aircraft during landing and take-off, that usually is referred as ‘dirty’ one. The configuration with slats extended, flaps down and undercarriage lowered is more noisy than the clean configuration. In this paper the results of numerical simulations performed on common operating aircraft are presented: these simulations allow the contribution breakdown and, therefore, the classification of the most noisy airframe components for the different approach and take-off configurations.

The use of polar nonlinear processing to reject a constant carrier envelope (and possibly wideband) jammer of a DS/SS spread spectrum link is explored, with the additional objective of ensuring constant false alarm rate (CFAR) in the reception of the associated DS/SS synchronization preamble. It is shown that the constant carrier envelope jammer can be rejected very effectively, with CFAR, whether it is transmitted continuously or pulsed at some maximally damaging duty cycle.

The issues discussed are summarised by a minimal checklist which should be applied to any DS/SS link architecture for use in a dense scatterer environment. For effective mitigation of fading the chip interval T, should be at most equal to the RMS delay spread /spl Delta/, indeed preferably much smaller. For minimal intersymbol interference the symbol duration T/sub s/ should be much longer than /spl Delta/. On a fast-moving antenna platform the distance traversed by the antenna during one symbol interval should be much less than 0.38 /spl lambda/. Otherwise, coherent symbol correlation becomes difficult, and a high irreducible error rate may result. The so-called mean bit error rates are just that. They are probabilistic means over the full range of antenna travel. If the antenna tends to remain stationary or travel very slowly, then perhaps it is more meaningful to speak of the maximum (or worst-case) error rate over a specified large fraction of all antenna locations. The chip stream should be as random as possible; that is, the chip values should be statistically uncorrelated. A chip-matched filter, adaptive to the continual metamorphoses of the arriving chip pulse shape and the mean chip arrival time, is essential to symbol detection at those frequently occurring antenna locations where the received power is a minimum, dispersion is a maximum, and the chip pulses arrive with essentially zero mean value. Such situations crop up roughly once per wavelength of antenna travel. In DPSK signaling the matched filter could be as simple as a single time delay of duration T/sub s/.

A geometric propagation model is developed for simulating the reception of direct sequence pseudonoise (DSPN) satellite signals by a directional or omni directional antenna in the dense scatterer mobile environment. The model is used to predict fading statistics. As expected, the mitigation of fading is closely related to the ratio of DSPN chip duration to delay spread of the scatterer medium for both the omni and directional antennas. The results suggest a general, frequency domain interpretation for the value of DSPN in mitigating multipath fading. >

A means is proposed for attaining the twin goals of a rectangular power spectral density (PSD) and a constant-carrier envelope for direct-sequence code division multiple-access (DS-CDMA) waveforms. Mitigation bandwidth is shown to be an especially appropriate metric for CDMA waveforms. Shaping of the PSD structure is explored using the M-ary orthogonal CPFSK modulation format. An important consequence for this type of signal is that the Shannon channel capacity is maximized when the PSD is made rectangular. The results of this exploration highlight the steady decrease in out-of-band power as the number of bits per symbol is increased.

A geometric propagation model is developed for simulation of the dense scatterer mobile radio communications environment. The model is validated by direct comparison of diffuse Doppler spectra with theoretical spectra for directional antennas and narrowband signals. The model is then used to predict fading statistics for direct-sequence pseudonoise (DSPN) signaling combined with directional antennas. As expected, the mitigation of fading is closely related to the ratio of DSPN chip duration to delay spread of the scatterer medium. >

Improvement of the anti-jam performance of spread spectrum systems can be effected at many different levels of the signal and receiver structure. Spread spectrum processing gain, interleaved forward error correction coding, spectral excision of jammers, and nonlinear rejection of non-Gaussian jammers are some of the common methods. The present paper explores the use of nonlinear processing to reject a constant carrier envelope (and possibly wideband) jammer of a DS-SS spread spectrum link, with the additional objective of ensuring constant false alarm rate (CFAR) in the reception of the associated DS-SS synchronization preamble. That is, the false alarm performance of the preamble processor must remain fixed whether the jammer is present or not, and independently of any level of received thermal noise. This latter objective may also be named perfect automatic gain control (AGC). It is shown that the constant carrier envelope jammer can be rejected very effectively whether it is transmitted continuously or pulsed at some maximally damaging duty cycle. The effect of incidental additive Gaussian noise is also evaluated.

The regrowth of OQPSK power spectral sidelobes from AM/AM and AM/PM amplifier nonlinearity is analyzed. The time-domain expression for amplifier output shows how spectral regrowth will depend on the cubic coefficient of the Taylor's series of the amplifier nonlinearity as well as input amplitude ripple. Closed form spectrum calculations show that the spectral sidelobes produced by AM/PM take the same form as those produced by AM/AM. The rate of growth of AM/PM sidelobes is, however, not as great as for AM/AM.

This paper addresses the dual objective of (a) rejecting a single near/far CDMA interferer and (b) ensuring a constant false alarm rate (CFAR) in preamble reception in the presence of the same interferer. It is shown that an adaptive A/D converter will reject the constant carrier envelope near/far signal very effectively. The collective effect of all other unwanted received signals in the CDMA signal set, treated as incidental additive Gaussian noise, is also evaluated.

Let d ≥ 5 and k ≥ 1 be two integers, and let n = 10k + 1. A well-known example of E. Mayr and A. Meyer (see [MM]) shows that there are n polynomials f 1,…,f n Є C[x 1,…, x n ] of degree ≤ d such that x 1 belongs to the ideal generated by f 1,…, f n that and each solution a 1,…, a n of the equation

Previous work has defined the mitigation bandwidth of DSPN as employed to combat fading over the dense scatterer mobile digital link. The Letter gives a simple, elegant method for computing mitigation bandwidth. No sacrifice of precision is conceded, and closed-form expressions are given for BPSK and MSK chip modulation.

A new class of basic pulses is introduced into the MSK signaling format to gain improvements in the out-of-band power spectral density characteristic. Some loss in communications efficiency is incurred, but the loss may in certain cases be outweighed by the spectral improvements that are made available.

The minimum (frequency) shift keying (MSK) format is generalized to enable further improvements in the spectrum while retaining the well-known constant envelope property and the excellent communications efficiency of MSK. A specific alternative to MSK is presented, and the spectrum is compared with that of MSK. The theoretical limitations on possible further spectrum improvements are discussed.

The engineering of data communications systems invites involvement with a number of rather refined parametric concepts, such as bit error rate (BER), antenna gain, radiated power, communication efficiency, and bandwidth. Of these, none has been the subject of more lively discussion and revision than bandwidth. The implications of bandwidth can vary considerably from context to context, as the profusion of definitions of bandwidth will attest. The purpose of the present article is to explore the subject of data transmission bandwidth through an examination of its various definitions. The spectrum is finite, yet as technology manipulates it, a dazzling increase in bandwidth capability emerges.

Previous analyses are extended to give the performance of the adaptive 2 bit A/D converter in combined CW and Gaussian interference. The converter is seen to give substantial conversion gain even when the direct sequence pseudonoise (DSPN) spread signal is much weaker than the Gaussian component of interference. The upper bound on conversion gain depends primarily on the relative strengths of the Gaussian and CW components of interference. The relevant relationships are given in graphical form.

Considerable recent attention has been given to the use of pulse modification to reduce spectral sidelobes in constant envelope data transmission within the "offset" modulation format that includes offset QPSK and MSK. Analytic techniques have been developed which predict probabilistically (without dependence on simulation) the power spectral density that results from pulse modification combined with hard limiting where necessary to achieve constant envelope. Here the computational results are compared with experimental results. Agreement between theory and experiment is seen to be good. The implications for bandwidth efficiency and communication efficiency are discussed.

Knowing that the tails of the ideal \sin \pi t/ \pi t pulse represent a divergent series, the problem is stated of finding distortionless bandlimited waves which give rise to a minimum of the worst peaks of voltage that can appear on the channel in unit-height binary transmission. The optimization problem is then solved for all sampling rates up to 1/2 the Nyquist rate by the unique wave which never gives rise to more than one volt on the channel, just the magnitude of the data bits themselves. An upper bound is established on the worst channel voltage at higher rates by means of a class of pulses whose spectrum reduces to the optimum when the sampling rate parameter is chosen to be 1/2 the Nyquist rate. A time-domain optimization principle is stated which deals with zero manipulation, and the implications for the concept of dimensionality are discussed. The principal results of this paper are related to other system concepts, including timing-jitter immunity and duobinary transmission.

Alternatives to single sideband modulation are sought for the most efficient use of the voice-band channel in data transmission. Under a certain criterion on optimum data pulses, the direct use of the passband is as efficient as the conventional use of single sideband, which converts the available passband into an apparent lowpass channel. With the simultaneous practical constraints of distortionless transmission, strict passband limitation, and a spectrum free of discontinuities, the principles of pulse-shaping used at lowpass are also applicable for a passband. A class of bandpass pulses is derived which achieves, in addition, a firstorder immunity to timing jitter in the receiver clock, an important property for multilevel PAM systems. Extension to passband is discussed for duobinary transmission.

This paper describes a method of transmitter waveform generation which leads to an optimally "narrow" pulse at the receiver of a given linear time invariant digital communications channel. The resulting transmitter waveform is realizable in that it must be identically zero before t=0 . The instant at which the received pulse must have its peak may be specified. Two examples are given: the first is a purely analytic application to a first-order low-pass filter channel; the second demonstrates that the optimum transmitter waveform can be produced experimentally even when the phase characteristics of the channel are unknown and the channel amplitude response is known only empirically. It is seen that the transmitter waveform has the effect of equalizing both the channel amplitude response and the channel phase response. The basic method for phase equalization is recognized as time reversal, a presently practised method. Comparable theoretical works from the literature are discussed.

The minimum Gabor bandwidth of M orthogonal real signals which together occupy a given time interval is derived. For special values of M , one form of the optimum set of M signals is specified. Interrelations of the Gabor definition of bandwidth to other definitions are also discussed.