Showing papers by "University of Mons published in 2008"
TL;DR: The Compact Muon Solenoid (CMS) detector at the Large Hadron Collider (LHC) at CERN as mentioned in this paper was designed to study proton-proton (and lead-lead) collisions at a centre-of-mass energy of 14 TeV (5.5 TeV nucleon-nucleon) and at luminosities up to 10(34)cm(-2)s(-1)
Abstract: The Compact Muon Solenoid (CMS) detector is described. The detector operates at the Large Hadron Collider (LHC) at CERN. It was conceived to study proton-proton (and lead-lead) collisions at a centre-of-mass energy of 14 TeV (5.5 TeV nucleon-nucleon) and at luminosities up to 10(34)cm(-2)s(-1) (10(27)cm(-2)s(-1)). At the core of the CMS detector sits a high-magnetic-field and large-bore superconducting solenoid surrounding an all-silicon pixel and strip tracker, a lead-tungstate scintillating-crystals electromagnetic calorimeter, and a brass-scintillator sampling hadron calorimeter. The iron yoke of the flux-return is instrumented with four stations of muon detectors covering most of the 4 pi solid angle. Forward sampling calorimeters extend the pseudo-rapidity coverage to high values (vertical bar eta vertical bar <= 5) assuring very good hermeticity. The overall dimensions of the CMS detector are a length of 21.6 m, a diameter of 14.6 m and a total weight of 12500 t.
5,193 citations
TL;DR: In this paper, a grafting from a poly(e-caprolactone) (PCL) polymers to cellulose nanocrystals by Sn(Oct)2-catalyzed ring-opening polymerization (ROP) was demonstrated.
Abstract: A ‘grafting from’ approach was used to graft poly(e-caprolactone) (PCL) polymers to cellulose nanocrystals by Sn(Oct)2-catalyzed ring-opening polymerization (ROP). The grafting efficiency was evidenced by the long-term stability of suspension of PCL-grafted cellulose nanocrystals in toluene. These observations were confirmed by Fourier Transform Infrared Spectroscopy (FT-IR) and Time-of-Flight Secondary Ion Mass Spectrometry (TOF-SIMS). Extracted nanohybrids were characterized by Differential Scanning Calorimetry (DSC), X-ray photoelectron spectroscopy (XPS), and contact angle measurements. The morphology and crystalline structure of the PCL-grafted cellulose nanocrystals was examined by transmission electron microscopy (TEM) and X-Ray diffraction, respectively. Results showed that cellulose nanocrystals kept their initial morphological integrity and their native crystallinity. Nanocomposites with high content of cellulose nanocrystals were prepared using either neat cellulose nanocrystals or PCL-grafted cellulose nanocrystals and high molecular weight PCL as matrix using a casting/evaporation technique. Thermo-mechanical properties of processed nanocomposites were studied by DSC, dynamical mechanical analyses (DMA) and tensile tests. A significant improvement in terms of Young's modulus and storage modulus was obtained.
607 citations
TL;DR: The meaning of the priority vector derived from the principal eigenvalue method used in AHP is addressed, and the role of AHP’s consistency ratio is analysed.
325 citations
TL;DR: A novel genetic tool, inducible cassette exchange, enabling rapid generation of isogenetically modified cells with conditional and variable transgene expression is described, and a hypothesis for FSHD is proposed in which DUX4 expression interferes with Pax7 in satellite cells, and inappropriately regulates Pax targets, including myogenic regulatory factors, during regeneration.
Abstract: Facioscapulohumeral muscular dystrophy (FSHD) is caused by an unusual deletion with neomorphic activity. This deletion derepresses genes in cis; however which candidate gene causes the FSHD phenotype, and through what mechanism, is unknown. We describe a novel genetic tool, inducible cassette exchange, enabling rapid generation of isogenetically modified cells with conditional and variable transgene expression. We compare the effects of expressing variable levels of each FSHD candidate gene on myoblasts. This screen identified only one gene with overt toxicity: DUX4 (double homeobox, chromosome 4), a protein with two homeodomains, each similar in sequence to Pax3 and Pax7. DUX4 expression recapitulates key features of the FSHD molecular phenotype, including repression of MyoD and its target genes, diminished myogenic differentiation, repression of glutathione redox pathway components, and sensitivity to oxidative stress. We further demonstrate competition between DUX4 and Pax3/Pax7: when either Pax3 or Pax7 is expressed at high levels, DUX4 is no longer toxic. We propose a hypothesis for FSHD in which DUX4 expression interferes with Pax7 in satellite cells, and inappropriately regulates Pax targets, including myogenic regulatory factors, during regeneration.
273 citations
TL;DR: In this paper, the uniqueness of the minimal couplings between higher-spin fields and gravity has been studied in the context of higher spin field equations with ε > 0 and ε = 3.
Abstract: We address the uniqueness of the minimal couplings between higher-spin fields and gravity. These couplings are cubic vertices built from gauge non-invariant connections that induce non-abelian deformations of the gauge algebra. We show that Fradkin-Vasiliev's cubic 2?s?s vertex, which contains up to 2s?2 derivatives dressed by a cosmological constant ?, has a limit where: (i) ????0; (ii) the spin-2 Weyl tensor scales non-uniformly with s; and (iii) all lower-derivative couplings are scaled away. For s = 3 the limit yields the unique non-abelian spin 2?3?3 vertex found recently by two of the authors, thereby proving the uniqueness of the corresponding FV vertex. We extend the analysis to s = 4 and a class of spin 1?s?s vertices. The non-universality of the flat limit high-lightens not only the problematic aspects of higher-spin interactions with ? = 0 but also the strongly coupled nature of the derivative expansion of the fully nonlinear higher-spin field equations with ??0, wherein the standard minimal couplings mediated via the Lorentz connection are subleading at energy scales (|?|)1/2??E??Mp. Finally, combining our results with those obtained by Metsaev, we give the complete list of all the manifestly covariant cubic couplings of the form 1?s?s? and 2?s?s?, in Minkowski background.
202 citations
TL;DR: It is shown that in this limit the gravitational theory can be reformulated in terms of billiard motion in a region of hyperbolic space, revealing that the dynamics is completely determined by a (possibly infinite) sequence of reflections, which are elements of a Lorentzian Coxeter group.
Abstract: We review the intimate connection between (super-)gravity close to a spacelike singularity (the “BKL-limit”) and the theory of Lorentzian Kac-Moody algebras. We show that in this limit the gravitational theory can be reformulated in terms of billiard motion in a region of hyperbolic space, revealing that the dynamics is completely determined by a (possibly infinite) sequence of reflections, which are elements of a Lorentzian Coxeter group. Such Coxeter groups are the Weyl groups of infinite-dimensional Kac-Moody algebras, suggesting that these algebras yield symmetries of gravitational theories. Our presentation is aimed to be a self-contained and comprehensive treatment of the subject, with all the relevant mathematical background material introduced and explained in detail. We also review attempts at making the infinite-dimensional symmetries manifest, through the construction of a geodesic sigma model based on a Lorentzian Kac-Moody algebra. An explicit example is provided for the case of the hyperbolic algebra E10, which is conjectured to be an underlying symmetry of M-theory. Illustrations of this conjecture are also discussed in the context of cosmological solutions to eleven-dimensional supergravity.
165 citations
TL;DR: In this paper, a specific PLA grade (L/D isomer ratio of 96:4, high molecular weight) was melt-mixed with selected plasticizers: bis(2-ethylhexyl) adipate (DOA), glyceryl triacetate (GTA), and tributyl O-acetylcitrate (TBAC).
Abstract: Polylactide (PLA) is an attractive candidate for replacing petrochemical polymers because it is biodegradable and produced from annually renewable resources. Characterized by high tensile strength, unfortunately the brittleness and rigidity of PLA limit its applicability. For a great number of applications such as packaging,fibers,films, etc., it is of high interest to formulate new grades with improved flexibility and better impact properties. In this objective, a specific PLA grade (L/D isomer ratio of 96:4, high molecular weight) was melt-mixed with selected plasticizers: bis(2-ethylhexyl) adipate (DOA), glyceryl triacetate (GTA), and tributyl O-acetylcitrate (TBAC). Their effect on the molecular, thermal, and mechanical properties of PLA was investigated for content up to 20wt% plasticizer and the results were correlated with a particular attention to the relationship between property and application. Using the solubility and interaction parameters, a tentative evaluation of the product that could act as the most effective plasticizer for PLA has been performed and the obtained results have been corroborated with the materials physical properties. Excellent mechanical performances were obtained using the plasticizer having the lowest molecular mass (GTA) and the best interaction parameter. In relation to plasticizer amount/nature, the glass transition temperature of PLA (62-C) is decreased by plasticizing by more than 30-C, whereas better impact properties and lower stiffness are measured. The optimal formulations targeted to the final applications are clearly characterized by specific end-use properties: improved crystallization rates (PLA-DOA); high elongation at break and tensile strength (PLA-GTA, PLA-TBAC), medium to high impact properties (PLA-DOA, PLA-GTA) compositions. Copyright # 2008 John Wiley & Sons, Ltd.
156 citations
TL;DR: The authors' analysis shows that the wettability hysteresis controls the limit between deposition and rebound events, which corresponds to a constant Weber number.
Abstract: Water drop impacts are performed on porous-like superhydrophobic surfaces. We investigate the influence of the drop size and of the impact velocity on the event. The Cassie-Baxter/Wenzel transition is observed to be a function of the drop size, as well as the outcomes of the impact or deposition process, which can be deposition, rebound, sticking, or fragmentation. A quantitative analysis on the experimental conditions required to observe rebound is provided. Our analysis shows that the wettability hysteresis controls the limit between deposition and rebound events. This limit corresponds to a constant Weber number. A survey of literature results on impact over patterned superhydrophobic surfaces is provided as a comparison.
155 citations
TL;DR: When the efficacy profiles of the two drugs were compared, acamprosate was found to be more effective in preventing a lapse, whereas naltrexone was better in prevented a lapse from becoming a relapse.
Abstract: Two pharmacological agents have repeatedly been shown to be efficacious for relapse prevention in alcohol dependence: The putative glutamate-antagonist acamprosate and the opioid-antagonist naltrexone. Clinical evidence for both drugs is based on various outcome criteria. Whereas for acamprosate primarily abstinence maintenance has been demonstrated, studies with naltrexone have mostly emphasised the prevention of heavy drinking. The remaining effects of both drugs are not always reported; accordingly the corresponding database is fragmentary. Thus, the primary objective of the present meta-analysis was to complete the efficacy profiles for acamprosate and naltrexone and to compare them with each other. Unreported results, requested from the study investigators and the drug manufacturers, were integrated in the computation of effect sizes. For the meta-analysis, emphasis was placed on the conceptual distinction between having a first drink and returning to heavy drinking. Naltrexone was found to have a significant effect on the maintenance of abstinence as well as the prevention of heavy drinking. Acamprosate was shown only to support abstinence; it did not influence alcohol consumption after the first drink. When the efficacy profiles of the two drugs were compared, acamprosate was found to be more effective in preventing a lapse, whereas naltrexone was better in preventing a lapse from becoming a relapse. The superiority of either one drug or over the other one cannot be determined as a general rule, it rather depends on the therapeutic target. Benefits in the treatment of alcohol dependence might be optimized by matching the efficacy profiles of specific antidipsotropics with the motivational status of alcohol-dependent patients.
128 citations
TL;DR: Bombus terrestris is one of the most abundant bumblebee species in the West-Palaearctic, but its autumn and winter populations rely on a restricted choice of flowers so they may be threatened locally by scrub clearance and the destruction of their favourite autumnal flowers.
Abstract: Bombus terrestris is one of the most abundant bumblebee species in the West-Palaearctic. Its widespread domestication results in the movement of many colonies. The aim of this paper is to describe the 9 subspecies currently recognised and to list some of their most obvious characteristics. Bombus terrestris is not declining anywhere, on the contrary, its synanthropic spread through domestication may be expected. However, its autumn and winter populations rely on a restricted choice of flowers so they may be threatened locally by scrub clearance and the destruction of their favourite autumnal flowers.
127 citations
01 Jan 2008
TL;DR: This introductory chapter starts with a historic overview of the research domain of software evolution, and briefly introduces the important research themes in software Evolution, and identifies research challenges for the years to come.
Abstract: The ability to evolve software rapidly and reliably is a major challenge for software engineering. In this introductory chapter we start with a historic overview of the research domain of software evolution. Next, we briefly introduce the important research themes in software evolution, and identify research challenges for the years to come. Finally, we provide a roadmap of the topics treated in this book, and explain how the various chapters are related.
TL;DR: In this article, the authors proposed a new approach in formulating novel melt-processable polyester grades with improved characteristic features using PLA as biodegradable polymer matrix, which are clearly characterized by easier processing, notable thermo-mechanical performances and good filler dispersion.
TL;DR: In this paper, the authors investigated whether successive recruitment failures in the anchovy fishery in the Bay of Biscay were due to changes in the zooplankton biomass or composition.
Abstract: The objective of this study was to investigate whether successive recruitment failures in the anchovy fishery in the Bay of Biscay were due to changes in the zooplankton biomass or composition. Image analysis and automatic recognition were used to analyse zooplankton samples collected during diel egg production method spring surveys from 1998 to 2006. We were not able to detect any trend in zooplankton biomass during this period. The zooplankton spatial distribution showed permanent features with large organisms being more abundant over the shelf break and outer areas. Finally, we found a negative correlation between anchovy recruitment and zooplankton biomass which suggests that the 2002‐2006 failures in anchovy recruitment in the Bay of Biscay are not due to a decrease in mesozooplankton biomass.
TL;DR: The statistical analysis on these molecular junctions, for which the processing parameters were varied and the influence on the junction resistance was measured, allows for the tentative interpretation that the perpendicular electrical transport through these monolayer junctions is factorized.
Abstract: The ultimate target of molecular electronics is to combine different types of functional molecules into integrated circuits, preferably through an autonomous self-assembly process. Charge transport through self-assembled monolayers has been investigated previously, but problems remain with reliability, stability and yield, preventing further progress in the integration of discrete molecular junctions. Here we present a technology to simultaneously fabricate over 20,000 molecular junctions—each consisting of a gold bottom electrode, a self-assembled alkanethiol monolayer, a conducting polymer layer and a gold top electrode—on a single 150-mm wafer. Their integration is demonstrated in strings where up to 200 junctions are connected in series with a yield of unity. The statistical analysis on these molecular junctions, for which the processing parameters were varied and the influence on the junction resistance was measured, allows for the tentative interpretation that the perpendicular electrical transport through these monolayer junctions is factorized.
TL;DR: It is suggested that upregulation of DUX4c can have a deleterious effect on muscle homeostasis and regeneration, and point to a possible role for Dux4c in the pathology of FSHD.
TL;DR: In this article, a preprogrammed self-assembly of p-conjugated rod-and disc-like oligomers into ordered and anisotropic architectures is proposed for nanoelectronic devices.
Abstract: The controlled and preprogrammed self-assembly of p-conjugated rodand disc-like oligomers into ordered and anisotropic architectures is an important goal in view of the tailoring of their physico-chemical properties and, ultimately, for their application in molecularand nanoelectronics. Among weak interactions, p-stacking has been the first to be employed to drive the self-assembly of conjugated (macro)molecular systems into well-defined nanoscale assemblies that feature a high degree of order at the supramolecular level. Later, other types of weak yet directional non-covalent interactions, in particular H-bonds, have been used to form both monoand multicomponent p-conjugated architectures, and their application in the fabrication of optoelectronic device prototypes such as photovoltaic diodes and ambipolar transistors has been attempted. Lipophilic guanosines are very versatile building blocks: depending on the experimental conditions they can undergo different self-assembly pathways, leading to the formation of either H-bonded ribbons or quartet-based columnar structures (Fig. 1). Given the possibility to functionalize the guanosines in the side-chains they appear as ideal building blocks for the fabrication of complex architectures with a controlled high rigidity, thus paving the way towards their future use for
TL;DR: In this article, the action and global charges of the asymptotically anti-de Sitter solutions in EGS were computed by adding boundary counterterms to the gravitational action, and the general expression of the counterterms and the boundary stress tensor was presented for spacetimes of dimension d ≤ 9.
Abstract: We propose to compute the action and global charges of the asymptotically anti-de Sitter solutions in Einstein-Gauss-Bonnet theory by adding boundary counterterms to the gravitational action. The general expression of the counterterms and the boundary stress tensor is presented for spacetimes of dimension d ≤ 9. We apply this tehnique for several different types of black objects. Apart from static and rotating black holes, we consider also Einstein-Gauss-Bonnet black string solutions with negative cosmological constant.
TL;DR: In this article, the existence of five-dimensional rotating black holes with equal magnitude angular momenta in Einstein-Gauss-Bonnet theory with negative cosmological constant was shown.
TL;DR: A new mechanism to generate wrinkled patterns, based on the coupling between molecular diffusion and the buckling instability of rigid membranes "glued" on a polymer layer is proposed.
Abstract: In this Letter, we propose a new mechanism to generate wrinkled patterns, based on the coupling between molecular diffusion and the buckling instability of rigid membranes "glued" on a polymer layer. The geometry of the diffusion front and the minimization of wrinkling energy conspire to generate various patterns of folds (e.g., parallel or radial folds, herringbone) and various dynamics (continuous or discrete). The diffusion process gives us the opportunity to study the stability of the various wrinkled patterns and to follow the creation or annihilation of topological defects.
TL;DR: In this paper, the effect of processing conditions (temperature, shear, residence time) on the morphology of performed polymer nanocomposites (PNC) was investigated.
Abstract: An experimental study was carried out to design polylactide (PLA)-clay nanocomposites for developing fibers. PLA and 1–10 wt % of a selected organomodified bentonite (Bentone® 104-B104) were melt mixed to examine the effect of processing conditions (temperature, shear, residence time) on the morphology of performed polymer nanocomposites (PNC). Because of a good compatibility with PLA matrix, the dispersion of B104 occurred under different conditions without difficulty, and a similar morphology was obtained. The results obtained showed that at low temperature of mixing, the shear stress exerted on polymer has a key role on the extent of intercalation and delamination. Upscale experiments were further performed using optimized conditions and 4 wt % B104 was added to PLA matrix by melt blending to produce PNC for spinning. Then, the recovered PNC were melt spun to produce multifilaments yarns, and it was demonstrated that surprisingly, it is not necessary to use a plasticizer to spin a blend with 4 wt % B104. The properties of the yarns have been studied in terms of clay dispersion as well as thermal, mechanical, and shrinkage properties. B104 could be added up to 4 wt % into PLA without detrimentally sacrificing the tensile strength of melt-spun filaments, especially at high draw ratio. Interestingly, the PNC-based multifilaments were knitted and the flammability studied using cone calorimeter at 35 kW/m2. A strong decrease, up to 46%, of the heat release rate was measured. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008
TL;DR: Recent evidence suggests a relationship between fast oscillation and cerebellar long term depression (LTD), which may have major implications for future therapeutic targeting.
TL;DR: It is suggested thathost-plant associations are maintained over time in many lineages, but that host switches to unrelated plant families are also common, suggesting that floral morphology plays a key role in host-plant evolution in bees.
Abstract: Bees and the angiosperms they pollinate have developed intimate and often complex interactions over the past 100 million years. As in other insect-plant interactions, host-plant specificity is variable among taxa. While many solitary bee species display an obvious preference for a narrow spectrum of host-plants (oligolecty), others regularly visit a diversified array of pollen hosts (polylecty). Few studies have examined the patterns of host-plant associations in bees using well-resolved phylogenies at the species level combined with accurate and quantitative data on host-plant preferences. In this study, we examined the evolution of bee-plant relationships in several genera of specialist (oligolectic) bees. We used the Melittidae s.l. as a model taxon by mapping the preferred pollen hosts onto species-level phylogenies to investigate the frequency and pattern of host-plant switching. Our results suggest that host-plant associations are maintained over time in many lineages, but that host switches to unrelated plant families are also common. We find some evidence that host-switches occur more frequently to morphologically similar, rather than closely-related, host-plants suggesting that floral morphology plays a key role in host-plant evolution in bees.
TL;DR: The most numerous larval abnormalities were found in a site near Algiers identified as highly polluted by lead, and the levels of the other metals across the study area fell within the background concentrations reported in the literature for the Mediterranean Sea, with the exception of zinc, which showed high values in female gonads.
Abstract: Soualili, D., Dubois, P., Gosselin, P., Pernet, P., and Guillou, M. 2008 Assessment of seawater pollution by heavy metals in the neighbourhood of Algiers: use of the sea urchin, Paracentrotus lividus, as a bioindicator. - ICES Journal of Marine Science, 65: 132-139.The objective of the study was to assess the levels of contamination by heavy metals near the Algiers metropolis, using a combination of chemical and toxicological data gained from analyses of sediments and biological parameters characteristic of the sea urchin, Paracentrotus lividus. Zinc, lead, cadmium, copper, and iron concentrations were determined in sediments and in sea urchin gonads. Sediment toxicity was assessed by bioassay based on the larval development of sea urchins. The most numerous larval abnormalities were found in a site near Algiers identified as highly polluted by lead. The levels of the other metals across the study area fell within the background concentrations reported in the literature for the Mediterranean Sea, with the exception of zinc, which showed high values in female gonads.
TL;DR: The interaction between evaporated Pt and pristine or oxygen-plasma-treated multiwall carbon nanotubes (CNTs) is investigated in this article, where Pt is found to nucleate at defect sites, whether initially present or introduced by oxygen plasma treatment.
TL;DR: Vandermotten et al. as mentioned in this paper examined the reasons for the European Union tenacity to promote polycentrism and found no clear correlation between more polycentricity and more economic efficiency or even more spatial equity.
Abstract: Vandermotten C., Halbert L., Roelandts M. and Cornut P. European planning and the polycentric consensus: wishful thinking?, Regional Studies. European Union planning documents enhance the values of polycentrism as a tool to promote a more efficient, equitable and sustainable development. This paper highlights how and suggests why a descriptive approach of the European urban system became progressively a normative concept. It examines how biases in the measurement of polycentricity in the European Spatial Observatory Network (ESPON) 1.1.1. report (2005) are related to this normative approach. The empirical findings do not suggest any clear correlation between more polycentricity and more economic efficiency or even more spatial equity. The paper examines the reasons for the European Union tenacity to promote polycentrism. This concept seems to be the result of a political compromise and a strange hybrid between two competing approaches for the future of the European space. Vandermotten C., Halbert L., Roel...
TL;DR: In this article, the HFR and AUTOSTRUCTURE atomic structure codes are used to compute complete data sets of level energies, wavelengths, A-values, and radiative and Auger widths for K-vacancy states of the Ne, Mg, Si, S, Ar, and Ca isonuclear sequences.
Abstract: The HFR and AUTOSTRUCTURE atomic structure codes are used to compute complete data sets of level energies, wavelengths, A-values, and radiative and Auger widths for K-vacancy states of the Ne, Mg, Si, S, Ar, and Ca isonuclear sequences. Ions with electron number N > 9 are treated for the first time. Detailed comparisons with previous measurements and theoretical data for ions with N ≤ 9 are carried out in order to estimate reliable accuracy ratings.
TL;DR: In this paper, the electronic transport properties of stacks of perylene-bis(dicarboximide) (PDI) chromophores, covalently fixed to the side arms of rigid, helical polyisocyanopeptides, are studied using thin-film transistors.
Abstract: The electronic transport properties of stacks of perylene-bis(dicarboximide) (PDI) chromophores, covalently fixed to the side arms of rigid, helical polyisocyanopeptides, are studied using thin-film transistors. In device architectures where the transistor channel lengths are somewhat greater than the average polymer chain length, carrier mobilities of order 10−3 cm2 V−1 s−1 at 350 K are found, which are limited by inter-chain transport processes. The influence of π–π interactions on the material properties is studied by using PDIs with and without bulky substituents in the bay area. In order to attain a deeper understanding of both the electronic and the electronic-transport properties of these systems, studies of self-assembly on surfaces are combined with electronic characterization using Kelvin probe force microscopy, and also a theoretical study of electronic coupling. The use of a rigid polymer backbone as a scaffold to achieve a full control over the position and orientation of functional groups is of general applicability and interest in the design of building blocks for technologically important functional materials, as well as in more fundamental studies of chromophoric interactions.
TL;DR: Improvements of an adaptative Hough transform algorithm applied to the search of a common center of circular or partially circular components present in an image, designed for X-ray diffraction analysis.
TL;DR: The dimension of filler particles and their percentage in the continuous polymeric phase seem to be the most important parameters that determine the barrier properties of the PLA-AII composites to water vapor.
TL;DR: An uncertainty relation is derived for two unitary operators which obey a commutation relation of the form UV=e(i phi) VU which provides an uncertainty relation which smoothly interpolates between the well-known cases of the Pauli operators in two dimensions and the continuous variables position and momentum.
Abstract: We derive an uncertainty relation for two unitary operators which obey a commutation relation of the form UV=e(i phi) VU Its most important application is to constrain how much a quantum state can be localized simultaneously in two mutually unbiased bases related by a discrete fourier transform It provides an uncertainty relation which smoothly interpolates between the well-known cases of the Pauli operators in two dimensions and the continuous variables position and momentum This work also provides an uncertainty relation for modular variables, and could find applications in signal processing In the finite dimensional case the minimum uncertainty states, discrete analogues of coherent and squeezed states, are minimum energy solutions of Harper's equation, a discrete version of the harmonic oscillator equation