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Faculty of Informatics - Papers (Archive)

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Articles 1621 - 1650 of 2013

Full-Text Articles in Physical Sciences and Mathematics

Optimization Of Orthogonal Polyphase Spreading Sequences For Wireless Data Applications, Beata J. Wysocki, Tadeusz A. Wysocki Oct 2001

Optimization Of Orthogonal Polyphase Spreading Sequences For Wireless Data Applications, Beata J. Wysocki, Tadeusz A. Wysocki

Faculty of Informatics - Papers (Archive)

We propose a simple but efficient method for optimizing correlation properties of polyphase spreading sequences for asynchronous DS CDMA applications. The proposed method can be used to minimize the mean square value of aperiodic crosscorrelation or the mean square value of aperiodic autocorrelation, the maximum value of aperiodic crosscorrelation functions, merit factor or other properties of the sequence set. The important feature of the method is that when applied to orthogonal sequences, it modifies correlation properties of the sequence set, while it preserves their orthogonality for perfect synchronization.

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Visualization As A Key Element In Learning, J. Fulcher Aug 2001

Visualization As A Key Element In Learning, J. Fulcher

Faculty of Informatics - Papers (Archive)

Experience with teaching undergraduate and postgraduate computer science (CS) subjects has shown that students benefit substantially from being able to visualize fundamental topics. Examples are presented from five different CS areas, namely: (i) communications, (ii) parallel computing, (iii) artificial neural networks, (iv) genetic algorithms and (v) data mining. The majority of these examples stemmed from student projects, rather than commercial software products. Accordingly, students benefit twofold from the visually-oriented subject presentations, firstly in facilitating the learning of basic concepts, and secondly in the development of educational software packages as part of their project work.

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The Advantage Of Industrial R&D In The Training Of University Students, J. Fulcher Aug 2001

The Advantage Of Industrial R&D In The Training Of University Students, J. Fulcher

Faculty of Informatics - Papers (Archive)

Experience gained through industrial R&D projects supports the proposition that several benefits flow through to both students and faculty staff beyond that of simply providing associated student project titles. To be more specific, enhancing lecture material with not only specific research findings but also general experience gained from working on such projects are secondary benefits of such university-industry links. Moreover, the reputation and standing of both individual researchers and university research groups are further enhanced by such relationships. This in turn often leads to subsequent industrial R&D projects (and so the cycle continues...).

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Scalable Audio Coding Employing Sorted Sinusoidal Parameters, M. Raad, I. Burnett, Alfred Mertins Aug 2001

Scalable Audio Coding Employing Sorted Sinusoidal Parameters, M. Raad, I. Burnett, Alfred Mertins

Faculty of Informatics - Papers (Archive)

This paper describes the use of sorted sinusoidal parameters to produce a fixed rate, scalable, wideband audio coder. The sorting technique relies on the perceptual significance of the sinusoidal parameters. Sinusoidal coding permits the representation of a given signal through the summation of sinusoids. The parameters of the sinusoids (the amplitudes, phases and frequencies) are transmitted to allow signal reconstruction. The sinusoidal parameters are sorted according to energy content and perceptual significance. The most significant parameters are transmitted first, allowing the use of only a small set of the parameters for signal reconstruction. The proposed scheme incurs a low delay …

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Boundary Filter Optimization For Segmentation-Based Subband Coding, Alfred Mertins Aug 2001

Boundary Filter Optimization For Segmentation-Based Subband Coding, Alfred Mertins

Faculty of Informatics - Papers (Archive)

This paper presents boundary optimization techniques for the nonexpansive decomposition of arbitrary-length signals with multirate filterbanks. Both biorthogonal and paraunitary filterbanks are considered. The paper shows how matching moments and orthonormality can be imposed as additional conditions during the boundary filter optimization process. It provides direct solutions to the problem of finding good boundary filters for the following cases: (a) biorthogonal boundary filters with exactly matching moments and (b) orthonormal boundary filters with almost matching moments. With the proposed methods, numerical optimization is only needed if orthonormality and exactly matching moments are demanded. The proposed direct solutions are applicable to …

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Using Webct To Support Team Teaching, A. Fuller, Gene Awyzio, Penelope Mcfarlane Aug 2001

Using Webct To Support Team Teaching, A. Fuller, Gene Awyzio, Penelope Mcfarlane

Faculty of Informatics - Papers (Archive)

Advanced learning technologies facilitate team teaching at the college/university level. Team teaching has been shown to benefit both students and faculty. This paper explores the benefits of using a course management package in an interdisciplinary team environment. Among those benefits are: better communication, student monitoring and support, flexibility in subject deliver, and fostering a collaborative environment. The success in the early developmental stage of integrating one such learning technology (Web Course Tools, or WebCT) into our course has seen the package move from a simple tool to an essential member of a teaching team.

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Irrational Rotations Motivate Measurable Sets, R. Nillsen Aug 2001

Irrational Rotations Motivate Measurable Sets, R. Nillsen

Faculty of Informatics - Papers (Archive)

In 1914 Constantin Carathéodory gave his definition of a measurable set, a definition that is crucial in the general theory of integration. This is because a “primitive” notion of area or measure, on a smaller family of sets, can be extended to the larger family of measurable sets, and it is this larger family that has the necessary properties for a natural and complete theory of integration. This more general theory of integration is of enormous practical importance, for it leads to quite broad conditions under which basic operations on integrals are valid. However, Carathéodory’s definition itself remains mysterious, and …

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Low Rate Wi Sew Representation Using A Rew-Implicit Pulse Model, J. Lukasiak, I. Burnett Aug 2001

Low Rate Wi Sew Representation Using A Rew-Implicit Pulse Model, J. Lukasiak, I. Burnett

Faculty of Informatics - Papers (Archive)

Reducing the bit rate of waveform interpolation speech coders while maintaining the perceptual quality has been the focus of a great deal of research. This letter proposes a new method of slowly evolving waveform (SEW) quantization specifically targeted at low rate coding. The proposed method uses a pulse model whose parameters are implicitly contained in the quantized rapidly evolving waveform (REW) parameters, thus requiring no bits for transmission. Results indicate no degradation in perceptual speech quality when compared to that of the existing SEW quantization method. This retention of perceptual quality is in spite of a 12% reduction in the …

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On Circulant Best Matrices And Their Applications, S. Georgiou, C. Koukouvinos, Jennifer Seberry Jul 2001

On Circulant Best Matrices And Their Applications, S. Georgiou, C. Koukouvinos, Jennifer Seberry

Faculty of Informatics - Papers (Archive)

Call four type 1(1,-1) matrices, x1,x2,x3,x4; of the same group of order m (odd) with the properties (i) (Xi-I)T = -(Xi-I), i=1,2,3, (ii)XT4 = X4 and the diagonal elements are positive, (iii) XiXj = XjXi and (iv) X1XT1 + X2XT2+X3XT3 +X4XT4 = 4mIm, best matrices. We use a computer to give, for the first time, all inequivalent best matrices …

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Hidden Terminal Jamming Problems In Ieee 802.11 Mobile Ad Hoc Networks, C. Ware, Tadeusz A. Wysocki, Joe F. Chicharo Jun 2001

Hidden Terminal Jamming Problems In Ieee 802.11 Mobile Ad Hoc Networks, C. Ware, Tadeusz A. Wysocki, Joe F. Chicharo

Faculty of Informatics - Papers (Archive)

This paper addresses experimental measurements from an IEEE 802.11 ad hoc network testbed, which indicate a strong signal strength dependence in the ability of a hidden terminal to gain access to the radio channel. We present analytical results investigating the `hidden terminal jamming' ability of the IEEE 802.11 DSSS physical layer. Results indicate that in a hidden terminal topology, the presence of an interfering transmission with a signal strength marginally greater than the transmission currently being received will result in an intolerable increase in BER, effectively jamming the ongoing transmission. These results confirm previous experimental measurements which show that after …

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A Security Analysis For Label Switching Routers, M. Al-Ibrahim, M. Savsar, W. Adi Jun 2001

A Security Analysis For Label Switching Routers, M. Al-Ibrahim, M. Savsar, W. Adi

Faculty of Informatics - Papers (Archive)

Label Switching Routers (LSR), such as IP switching of Ipsilon, use separate Virtual Circuits (VC)from different sources even having the same destination. Merging switches, on the other hand, allow multiple VCs of upstream traffic to use a single output VC if having same destination criteria. In this paper, we study IP switching of Ipsilon and identify certain security threats. We found that oscillation between routing and switching as a result of a malicious frequent suspension and releasing of flows is a main security threat that decreases performance of such systems. To stabilize the performance in face of such an attack, …

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Perfect Reconstruction Integer-Modulated Filter Banks, Alfred Mertins, T. Karp May 2001

Perfect Reconstruction Integer-Modulated Filter Banks, Alfred Mertins, T. Karp

Faculty of Informatics - Papers (Archive)

In this paper, we present design methods for perfect reconstruction (PR) integer-modulated filter banks, including biorthogonal (low-delay) filter banks. Both the prototype filter and the modulation sequences are composed of integers, thus allowing,efficient hardware implementations. To derive such filter banks, we first extend the PR conditions known for cosine modulation to other, more general, modulation schemes. We present solutions where the PR conditions on the prototype and the modulation are entirely decoupled and where some simple coupling is introduced. The conditions are derived for both even and odd numbers of channels. Design examples are presented for both cases.

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Structure Of The Internet?, Ah Chung Tsoi May 2001

Structure Of The Internet?, Ah Chung Tsoi

Faculty of Informatics - Papers (Archive)

We consider a major component in the design of an Internet search engine, viz., how the relevance of a Web page can be determined. A number of methods are described. A number of design issues related to search engines are also discussed.

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Sew Representation For Low Rate Wi Coding, J. Lukasiak, I. S. Burnett May 2001

Sew Representation For Low Rate Wi Coding, J. Lukasiak, I. S. Burnett

Faculty of Informatics - Papers (Archive)

This paper considers low-rate waveform interpolation (WI) coding. It compares the existing, common slowly evolving waveform (SEW) quantisation scheme with two new schemes for representing and quantising the SEW. The first scheme uses a minimum phase estimate to reconstruct the SEW whilst the second scheme uses a pulse model whose parameters are implicitly transmitted in the quantised rapidly evolving waveform (REW). These new schemes maintain or reduce the bit rate required for transmission of the SEW. Results indicate that, for low rate WI coding, necessarily coarse SEW magnitude spectrum quantisation limits the contribution of the SEW to perceptual quality. Perceptual …

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Audio Coding Using Sorted Sinusoidal Parameters, Mohammed Raad, I. Burnett May 2001

Audio Coding Using Sorted Sinusoidal Parameters, Mohammed Raad, I. Burnett

Faculty of Informatics - Papers (Archive)

This paper describes a new audio coding scheme based on sinusoidal coding of signals. Sinusoidal coding permits the representation of a given signal through the summation of sinusoids. The parameters of the sinusoids (the amplitudes, phases and frequencies) are transmitted to allow the signal reconstruction. In the proposed scheme, the sinusoidal parameters are sorted according to energy content and perceptual significance. The most significant parameters are transmitted first allowing the use of only a small set of the parameters for signal reconstruction. The proposed scheme incurs a low delay and uses a 20 ms frame length. Results show that the …

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Boundary Filters With Maximum Coding Gain And Ideal Dc Behavior For Size-Limited Paraunitary Filter Banks, Alfred Mertins May 2001

Boundary Filters With Maximum Coding Gain And Ideal Dc Behavior For Size-Limited Paraunitary Filter Banks, Alfred Mertins

Faculty of Informatics - Papers (Archive)

This paper presents boundary optimization techniques for the processing of arbitrary-length signals with paraunitary multirate filter banks. The boundary filters are designed to maximize the coding gain while providing an ideal DC behavior. Thus, all filters except the lowpass filter are designed to have zero mean. The proposed methods give direct solutions to the problem of finding optimal boundary filters and do not require numerical optimization.

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Temporal Decomposition For Low Rate Wideband Speech Compression, C. H. Ritz, I. Burnett Apr 2001

Temporal Decomposition For Low Rate Wideband Speech Compression, C. H. Ritz, I. Burnett

Faculty of Informatics - Papers (Archive)

An investigation into low bit rate wideband speech coding for applications such as unicast streaming is presented. Wideband spectral parameters are quantised below 1 kbit/s using temporal decomposition (TD) applied to the line spectral frequencies. Quantisation using TD performs significantly better than split vector quantisation at an equivalent bit rate.

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Simulating Ultrasonic Sensing With The Lattice Gas Model, Phillip J. Mckerrow, S. M. Zhu, S. New Apr 2001

Simulating Ultrasonic Sensing With The Lattice Gas Model, Phillip J. Mckerrow, S. M. Zhu, S. New

Faculty of Informatics - Papers (Archive)

People have difficulty understanding ultrasonic sensing because they cannot see sound. The purpose of simulation is to overcome this problem by visualizing the scattering of ultrasonic waves off objects. The lattice gas model calculates wave behavior with finite difference equations to produce data suitable for grayscale visualization. This visualization is useful when designing ultrasonic sensing systems for navigating mobile robots. Situations that result in the sensor failing to detect an object can be studied with the simulator.

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New D-Optimal Designs Of Order 110, R. J. Fletcher, Jennifer Seberry Mar 2001

New D-Optimal Designs Of Order 110, R. J. Fletcher, Jennifer Seberry

Faculty of Informatics - Papers (Archive)

We give two new D-optimal designs of order 110.

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Application Of The Discrete Fourier Transform To The Search For Generalised Legendre Pairs And Hadamard Matrices, R. J. Fletcher, M. Gysin, Jennifer Seberry Mar 2001

Application Of The Discrete Fourier Transform To The Search For Generalised Legendre Pairs And Hadamard Matrices, R. J. Fletcher, M. Gysin, Jennifer Seberry

Faculty of Informatics - Papers (Archive)

We introduce Legendre sequences and generalised Legendre pairs (GL-pairs). We show how to construct a Hadamard matrix of order 2ℓ + 2 from a GL—pair of length ℓ. We review the known constructions for GL-pairs and use the discrete Fourier transform (DFT) and power spectral density (PSD) to enable an exhaustive search for GL-pairs for lengths ℓ ≤ 45 and partial results for other ℓ.

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On Infinite Families Of Sequences With One And Two Valued Autocorrelation And Two Valued Crosscorrelation Function, M. Gysin, Jennifer Seberry Mar 2001

On Infinite Families Of Sequences With One And Two Valued Autocorrelation And Two Valued Crosscorrelation Function, M. Gysin, Jennifer Seberry

Faculty of Informatics - Papers (Archive)

We show how to construct infinite families of sequences that have one and two valued autocorrelation and two valued crosscorrelation function. These sequences are obtained via the discrete Fourier transform of integer sequences. The sequences obtained can be complex valued or having entries ε {0, 1, ... , p}, p prime, depending on the construction used.

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On Plateaued Functions, Y. Zheng, X. M. Zhang Mar 2001

On Plateaued Functions, Y. Zheng, X. M. Zhang

Faculty of Informatics - Papers (Archive)

The focus of this correspondence is on nonlinear characteristics of cryptographic Boolean functions. First, we introduce the notion of plateaued functions that have many cryptographically desirable properties. Second, we establish a sequence of strengthened inequalities on some of the most important nonlinearity criteria, including nonlinearity, avalanche, and correlation immunity, and prove that critical cases of the inequalities coincide with characterizations of plateaued functions.We then proceed to prove that plateaued functions include as a proper subset all partially bent functions that were introduced earlier by Claude Carlet. This solves an interesting problem that arises naturally from previously known results on partially …

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On Ternary Complementary Pairs, M. Gysin, Jennifer Seberry Mar 2001

On Ternary Complementary Pairs, M. Gysin, Jennifer Seberry

Faculty of Informatics - Papers (Archive)

Let A = {a0, ... aℓ-1 }, B = {b0, . . . , bℓ-1 } be two finite sequences of length ℓ. Their nonperiodic autocorrelation function NA,B (s) is defined as: NA,B(s) = ∑aiai+1 + ∑b1bi+1, s = 0,…,ℓ-1 where x* is the complex conjugate of x. If NA,B (s) = 0 for s = 1, ... , ℓ - 1 then A, B is called a complementary pair. If, furthermore, ai, bi ε {-1,1}, i = 0,...,ℓ-1 , or, ai, bi ε {-1,0,1}, i = 0, ... , ℓ-1, then A, B is called a binary complementary pair …

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Boundary Filters For Size-Limited Paraunitary Filter Banks With Maximum Coding Gain And Ideal Dc Behavior, Alfred Mertins Feb 2001

Boundary Filters For Size-Limited Paraunitary Filter Banks With Maximum Coding Gain And Ideal Dc Behavior, Alfred Mertins

Faculty of Informatics - Papers (Archive)

This paper presents boundary optimization techniques for the processing of arbitrary-length signals with paraunitary multirate filter banks. The boundary filters are designed to maximize the coding gain while providing an ideal DC behavior where all filters except the low-pass filters have zero mean. Moreover, solutions are presented that have similar frequency responses as the original subband filters. The proposed methods give direct solutions to the problem of finding the optimal boundary filters with maximum coding gain and do not require numerical optimization. Thus, they are even applicable to systems with a large number of subbands and/or very long filter impulse …

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Equitability In Retroactive Data Confiscation Versus Proactive Key Escrow, Y. Desmedt, M. Burmester, Jennifer Seberry Feb 2001

Equitability In Retroactive Data Confiscation Versus Proactive Key Escrow, Y. Desmedt, M. Burmester, Jennifer Seberry

Faculty of Informatics - Papers (Archive)

The British Regulations of Investigatory Powers (RIP) Act 2000 is one of the first modern bills for mandatory disclosure of protected data in a democratic country. In this paper we compare this bill from a technical point of view with the US key escrow proposal (EES) and its variants and then, more generally we compare the merits of key confiscation vs key escrow. A major problem with key escrow is that once a private key is recovered it can be used to decipher ciphertexts which were sent well before a war-rant was issued (or after its expiration). Several alternative key …

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A Parameterised Algorithm For Mining Association Rules, N. Denwattana, J. R. Getta Jan 2001

A Parameterised Algorithm For Mining Association Rules, N. Denwattana, J. R. Getta

Faculty of Informatics - Papers (Archive)

A central part of many algorithms for mining association rules in large data sets is a procedure that finds so called frequent itemsets. This paper proposes a new approach to finding frequent itemsets. The approach reduces a number of passes through an input data set and generalises a number of strategies proposed so far. The idea is to analyse a variable number n of itemset lattice levels in p scans through an input data set. It is shown that for certain values of parameters (n,p) this method provides more flexible utilisation of fast access transient memory and faster elimination of …

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A Spatial-Temporal Statistical Approach To Command And Control Problems In Battle-Space Digitization, David A. Wendt, Noel A. Cressie, Gardar Johannesson Jan 2001

A Spatial-Temporal Statistical Approach To Command And Control Problems In Battle-Space Digitization, David A. Wendt, Noel A. Cressie, Gardar Johannesson

Faculty of Informatics - Papers (Archive)

There are considerable difficulties in the integration, visualization, and overall management of battle-space information for the purpose of Command and Control (C2). One problem that we see as being important is the timely combination of digital information from multiple (possibly disparate) sources in a dynamically evolving environment. That is, there is a need to assimilate incoming data rapidly, so as to provide the battle commander with up-to-date knowledge about the battle-space and thereby to facilitate the command-decision process. In this paper, we present a spatial-temporal approach to obtaining accurate estimates of the constantly changing battlefield, based on noisy data from …

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Application Of A Fuzzy Controller To Seismically Excited Nonlinear Buildings, Mohammed Al-Dawod, Bijan Samali, Kenny Kwok, Fazel Naghdy Jan 2001

Application Of A Fuzzy Controller To Seismically Excited Nonlinear Buildings, Mohammed Al-Dawod, Bijan Samali, Kenny Kwok, Fazel Naghdy

Faculty of Informatics - Papers (Archive)

Focuses on the benchmark control problems for seismically excited nonlinear buildings defined by Ohtori et al. (2000). This benchmark study focuses on three typical steel structures, 3-, 9- and 20-storey buildings designed for the SAC project for Los Angeles in the California region. The first stage of applying the fuzzy controller to this benchmark study for the 3-storey building is reported. The main advantage of the fuzzy controller is its inherent robustness and ability to handle the non-linear behaviour of the structure. This benchmark study is based on a number of evaluation criteria and control constraints and these limitations are …

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Development And Performance Analysis Of A Single Axis Linear Motor, Jeffrey W. Moscrop, Christopher David Cook, Fazel Naghdy Jan 2001

Development And Performance Analysis Of A Single Axis Linear Motor, Jeffrey W. Moscrop, Christopher David Cook, Fazel Naghdy

Faculty of Informatics - Papers (Archive)

The ever-increasing demands placed on industrial machine tool manufacturers, for greater speeds and accuracies, are beginning to exceed the capabilities of current machine tool technologies. However, the ongoing revolution in computer, sensor and actuator technologies has introduced the potential of economically meeting these higher demands through new approaches in machine tool design. One actuator technology currently influencing high precision industrial automation is the linear motor. This paper details the development of a single axis linear motor test-bed, replicating one axis of a laser cutting machine tool. Through analysis of system stiffness and torque disturbances, the performance of the linear motor …

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Values Of Minors Of (1,-1) Incidence Matrices Of Sbibds And Their Application To The Growth Problem, C. Koukouvinos, M. Mitrouli, Jennifer Seberry Jan 2001

Values Of Minors Of (1,-1) Incidence Matrices Of Sbibds And Their Application To The Growth Problem, C. Koukouvinos, M. Mitrouli, Jennifer Seberry

Faculty of Informatics - Papers (Archive)

We obtain explicit formulae for the values of the v - j minors, j = 0,1,2 of (1, -1) incidence matrices of SBIBD(v,k,λ). This allows us to obtain explicit information on the growth problem for families of matrices with moderate growth. An open problem remians to establish whether the (1, -1) CP incidence matrices of SBIBD(v,k,λ), can have growth greater than V for families other than Hadamard families.

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