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Free Space (free + space)
Selected AbstractsAn "Oasis of Freedom" in a "Closed Society": The Development of Tougaloo College as a Free Space in Mississippi's Civil Rights Movement, 1960 to 19641JOURNAL OF HISTORICAL SOCIOLOGY, Issue 4 2007MARIA R. LOWE The school served as an interracial "safe haven" for those involved in and sympathetic to the civil rights movement who in turn, helped to cultivate networks, ideas, and strategies that contributed to the movement in meaningful ways. The school's heritage, its sources of financial support, and its relative physical isolation allowed Tougaloo College to challenge Mississippi's closed society from within. [source] Hybrid Magnetic Materials Based on Nitroxide Free Radicals and Extended Oxalato-Bridged Bimetallic NetworksEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 2 2005Antonio Alberola Abstract A series of hybrid organic-inorganic magnets of formula p -rad[MIICr(ox)3] [M = Mn (1), Co (2), Ni (3), Zn (4)] and m -rad[MIICr(ox)3] [M = Mn (5), Co (6)], in which N -methylpyridinium cations bearing a nitronyl nitroxide moiety in positions 3 (m -rad) or 4 (p -rad) of the pyridine ring coexist with the 2D honeycomb-like oxalato-bridged bimetallic lattice, has been prepared and studied by AC and DC magnetic susceptibility measurements and EPR spectroscopy. In general, the physical properties of these magnets are not altered significantly by the insertion of the nitronyl nitroxide radicals although these paramagnetic molecules seem to interact weakly with the inorganic network as demonstrated by EPR spectroscopy. Some differences can also be observed between the p -rad and m -rad series, i.e. m -rad derivatives have smaller values for the critical temperatures and coercive fields. We also report on the X-ray crystal structures and magnetic properties of p -rad[Mn(H2O)Cr(ox)3]·2H2O (7) and m -rad[Mn(H2O)2Cr(ox)3]·2H2O (8), two extended oxalato-bridged compounds with new topologies. Compound 7 is antiferromagnetic and its structure is a 3D achiral lattice in which zigzag ferromagnetic MnCr chains (J/k = +0.8 K) are interconnected to form hellicoidal hexagonal channels with the cationic free radicals residing in the free space. Compound 8, however, exhibits a ladder-like structural pattern with competing magnetic interactions and paramagnetic behaviour down to low temperatures. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005) [source] Image reconstruction for a partially immersed imperfectly conducting cylinder by genetic algorithmINTERNATIONAL JOURNAL OF IMAGING SYSTEMS AND TECHNOLOGY, Issue 4 2009Wei Chien Abstract This article presents a computational approach to the imaging of a partially immersed imperfectly conducting cylinder. An imperfectly conducting cylinder of unknown shape and conductivity scatters the incident transverse magnetic (TM) wave in free space while the scattered field is recorded outside. Based on the boundary condition and the measured scattered field, a set of nonlinear integral equations, and the inverse scattering problem are reformulated into an optimization problem. We use genetic algorithm (GA) to reconstruct the shape and the conductivity of a partially immersed imperfectly conducting cylinder. The genetic algorithm is then used to find out the global extreme solution of the cost function. Numerical results demonstrated that, even when the initial guess is far away from the exact one, good reconstruction can be obtained. In such a case, the gradient-based methods often get trapped in a local extreme. In addition, the effect of random noise on the reconstruction is investigated. © 2009 Wiley Periodicals, Inc. Int J Imaging Syst Technol, 19, 299,305, 2009 [source] Comparison of image reconstruction by using near-field and far-field data for an imperfect conductorINTERNATIONAL JOURNAL OF RF AND MICROWAVE COMPUTER-AIDED ENGINEERING, Issue 2 2001Chien-Ching Chiu Abstract Image reconstruction by using near-field and far-field data for an imperfectly conducting cylinder is investigated. A conducting cylinder of unknown shape and conductivity scatters the incident wave in free space and the scattered near and far fields are measured. By using measured fields, the imaging problem is reformulated into an optimization problem and solved by the genetic algorithm. Numerical results show that the convergence speed and final reconstructed results by using near-field data are better than those obtained by using far-field data. This work provides both comparative and quantitative information. © 2001 John Wiley & Sons, Inc. Int J RF and Microwave CAE 11: 69,73, 2001. [source] Switching contact task control in hydraulic actuators: Stability analysis and experimental evaluationINTERNATIONAL JOURNAL OF ROBUST AND NONLINEAR CONTROL, Issue 17 2009P. Sekhavat Abstract A switching contact task control for hydraulic actuators is proposed. The controller is built upon three individually designed control laws for three phases of motion: (1) position regulation in free space, (2) impact suppression and stable transition from free to constrained motion and (3) force regulation in sustained-contact motion. The position and force control schemes are capable of asymptotic set-point regulation in the presence of actuator friction and without the complexity of sliding mode or adaptive control techniques. The intermediate impact control scheme is included for the first time to dampen the undesirable impacts and dissipate the impact energy that could potentially drive the whole system unstable. The solution concept and the stability of the complete switching control system are analyzed rigorously using the Filippov's solution concept and the concept of Lyapunov exponents. Both computer simulations and experiments are carried out to demonstrate the efficacy of the designed switching control law. Copyright © 2009 John Wiley & Sons, Ltd. [source] The effect of within-genet and between-genet competition on sexual reproduction and vegetative spread in Potentilla anserina ssp. egediiJOURNAL OF ECOLOGY, Issue 3 2004PIRJO RAUTIAINEN Summary 1Patterns of biomass allocation to sexual and vegetative reproduction were examined in a perennial stoloniferous clonal plant, Potentilla anserina (L.) Rydb. ssp. egedii (Wormsk.) Hiitonen, in relation to intraspecific competition between monoclonal and multiclonal ramets. 2We predicted that a lack of competition would generate allocation to rapid, short-distance spread (vegetative propagation), while the presence of competition would increase allocation to long-distance dispersal (sexual reproduction), and that the allocation shift would be more pronounced where the competing ramets were related. 3P. anserina ramets were grown in a glasshouse in small pots, either alone (no competition) or with a size-matched ramet that originated from the same clone (within-genet competition) or a different one (between-genet competition). 4Competition suppressed both growth and reproduction, but there was no treatment response in relative investment at the level of a whole genet, although both mother ramets and their daughters showed clear effects when analysed separately. 5When experiencing competition, the mother ramet allocated relatively more to flowers, whereas allocation to vegetative growth was more intense when competition was absent. Allocation patterns were independent of the relatedness of competitors. 6The results imply that P. anserina can modify the allocation of resources to different life-history traits according to competitive stress. Such flexibility is likely to reflect a shift in the optimal allocation strategy during the life cycle of a plant with a guerilla growth form with rapid exploitation of free space in a new patch by vegetative spread favoured. When spread becomes limited by competition, long-distance dispersal in space (seeds) or time (persistence) becomes beneficial. [source] Investigation of the effects of partial coherence on exit wave reconstructionJOURNAL OF MICROSCOPY, Issue 1 2004L. J. ALLEN Summary In a recent work we presented an iterative wave function reconstruction (IWFR) method that reconstructs a wave function from measurements of its amplitude taken as it propagates in free space (a focal series of images). Although the ideal environment for application of the IWFR method is in a coherent imaging system, it has been developed so that it can be applied in a partially coherent imaging system, in particular for a high-resolution transmission electron microscope using a field-emission gun. In this paper we investigate the effects of partial coherence on the accuracy of results obtained using the IWFR method. We then show how results obtained under such conditions can be improved by estimating and subtracting components from the amplitude measurements of the wave function that derive from incoherence in the electron beam. [source] Experimental observation of a strange temporal oscillation of X-ray Pendellösung fringesJOURNAL OF SYNCHROTRON RADIATION, Issue 5 2009Jun-ichi Yoshimura As a strange property not explained by existing theories, it has been known from experiment that X-ray moiré and Pendellösung interference fringes show a small spatial oscillation in the beam path in free space that the diffraction image carrying those fringes is propagated after emerging from the crystal. In connection with the investigation into this strange fringe oscillation, it has been found, by an experiment successively recording Pendellösung-fringe topographs using an X-ray CCD camera, that X-ray Pendellösung fringes also show a small temporal oscillation. Characteristics of this temporal Pendellösung-fringe oscillation, namely irregularities in the fringe profile, the manner of fringe oscillation and a reciprocal correlation between oscillation amplitude and fringe contrast, are shown to be very similar to those of the previously reported spatial oscillation of moiré and Pendellösung fringes. Therefore this temporal oscillation is supposed to have the same origin as the spatial oscillation, revealing another section of the same phenomenon. This discovery of the temporal oscillation advances a step nearer to the full understanding of this strange phenomenon, while disclosing a new property of Pendellösung fringes. As well as the above, a three-dimensional profile representation (surface plot) is given of the image of Pendellösung fringes, to make it clear that unidentified fine intensity modulations, called subfringes in this paper, are produced superposed on the main fringe system. Overall inspection of the intensity profiles of the fringe-imaged topographs suggests that temporal intensity oscillations also occur on a more global scale than the extension of individual fringes, as an unidentified action of the wavefield. [source] Role of host identity in effects of phytogenic mounds on plant assemblages and species richness on coastal arid dunesJOURNAL OF VEGETATION SCIENCE, Issue 5 2007Magdy I. El-Bana Abstract Question: Phytogenic mounds (nebkhas) - the natural accumulation of wind-blown sediments within or around the canopies of plants - have been proposed as important structures for locally maintaining high species richness in coastal and arid ecosystems. Nebkhas are assumed to increase habitat heterogeneity, but what is the importance of the nebkha host species relative to other nebkha characteristics in determining the associated plant assemblages? Are some host species more effective in creating diversity hotspots, or does a single species-area relationship apply to all nebkhas, regardless of host species? Can the influence of the host be ascribed to its indirect effects on abiotic attributes of the nebkha complex? Methods and location: We investigated plant species richness and composition on nebkhas around six psammophytic species on Mediterranean coastal dunes of the Sinai Peninsula. Results: Plant species richness was significantly related to nebkha size by the single power function according to the general prediction of island biogeography theory, but this relationship was modified - though to a limited degree - by nebkha host species identity. Canonical Correspondence Analysis revealed that nebkha host species identity and nebkha environmental and non-environmental factors significantly explained species composition on the nebkhas, but host species identity did so to a greater extent. The latter might reflect differences in seed trapping ability or free space for colonization between host species. Conclusion: Differences in community composition and richness among nebkhas formed by different host species represent a key factor in the maintenance of plant diversity on arid coastal dunes. [source] Revivals for a two-level atom in a free space under bichromatic excitationLASER PHYSICS LETTERS, Issue 3 2005S. Ya. Abstract A two level atom in a free space excited by a bichromatic symmetrical field is shown to display the property of revivals for relatively small frequency detunings and a large driving field amplitude. (© 2005 by Astro, Ltd. Published exclusively by WILEY-VCH Verlag GmbH & Co. KGaA) [source] Colonization by barnacles on fossil Clypeaster: an exceptional example of larval settlementLETHAIA, Issue 4 2008ANA G. SANTOS The presence of c. 1450 individuals of the balanid barnacle Balanus crenatus Bruguière encrusting the test of a clypeasteroid sea urchin from the Late Miocene of the Guadalquivir Basin (southwestern Spain) allows proposing a settlement pattern linked to the growth of the encrusting organism. The possible influence of dip angle was controlled by dividing the test into four concentric zones ranging from lowest margin to apex (0,15°, 15,30°, 30,50° and 0°). Contour diagrams were prepared to identify areas of highest barnacle density as well as size categories distribution in relationship to the pitch of the sea urchin test. The orientation of balanid tests was recorded and plotted on rose diagrams from 0° to 180°. Four size categories of barnacles were distinguished: (1) < 1 mm, (2) 1,2 mm, (3) 2,3 mm and (4) 3,4 mm; these correspond to a growth sequence ranging from post-larval forms to juveniles. Two areas of maximum settlement density are situated on the posterior margin of the test, on aboral as well as oral surfaces. The aboral surface shows the maximum number of barnacles. Two groups of individuals are defined on the basis of their location, that is, those encrusting the posterior medium part of the urchin, and those located on the anterior half. The results suggest that larval settlement was initially controlled by the availability of free space and afterwards by an intensification effect. Orientation and dip of the test may have played a secondary role in the settlement of the larvae. Substrate colonization seems to have been closely related to the biostratinomic history of the sea urchin test and although several scenarios are possible, our data are congruent with a synchronous settlement of both surfaces (aboral and oral) by one spat or several. [source] Low-profile radio frequency identification tag antenna using a trapezoid patch mountable on metallic surfacesMICROWAVE AND OPTICAL TECHNOLOGY LETTERS, Issue 8 2010Horng-Dean Chen Abstract A trapezoid patch antenna, designed for ultra high frequency band radio frequency identification tag mountable on metallic surfaces, is presented in this article. The proposed antenna has a simple and low-profile (0.8 mm thick) structure. The impedance matching can be easily achieved by adjusting the upper-side width and the height of the trapezoid patch. The reading range of the proposed antenna is verified by calculation and measurement, which shows good agreement. Varying antenna size can provide applicable reading range to suit different applications. The results obtained show that the proposed antenna can work efficiently in free space and on metallic objects. © 2010 Wiley Periodicals, Inc. Microwave Opt Technol Lett 52: 1697,1700, 2010; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.25310 [source] On-chip slot antennas in 0.18 ,m CMOS for wireless applicationMICROWAVE AND OPTICAL TECHNOLOGY LETTERS, Issue 5 2008Liang Jiang Abstract Two on-chip slot antennas resonating near 30 GHz with different widths (10 and 100 ,m) in standard 0.18 ,m CMOS are presented. S21 between two 10 ,m width slot antennas and between two 100 ,m width ones both with ,3 mm distance through free space is measured. The results indicate that designing on-chip slot antennas with standard CMOS process is feasible, which will support farther improvement of CMOS integration. The slot antennas can be used in compact and low cost transceivers for short range wireless communications. © 2008 Wiley Periodicals, Inc. Microwave Opt Technol Lett 50: 1187,1191, 2008; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.23325 [source] Hybrid mode matching and auxiliary sources technique for horn antenna analysisMICROWAVE AND OPTICAL TECHNOLOGY LETTERS, Issue 3 2007S. G. Diamantis Abstract A hybrid technique for the analysis of horn antennas is described based on a rigorous description of the horn aperture-free space discontinuity. The transition from the feeding waveguide to the radiating aperture is analyzed by using the mode matching technique (MMT) employing a stepped-waveguide approach. The discontinuity between the horn aperture and the free space is modeled by combining the method of auxiliary sources with the MMT for the stepped waveguide section. Results for the input standing wave ratio are given and compared with the available measurements, which demonstrate the very good performance of the method. © 2007 Wiley Periodicals, Inc. Microwave Opt Technol Lett 49: 734,739, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.22233 [source] Transmission peak at low frequencies by a fractal distribution of metamaterials layers in free spaceMICROWAVE AND OPTICAL TECHNOLOGY LETTERS, Issue 1 2007A. S. Saleh Abstract A periodic distribution of metamaterials layers in free space generates wide forbidden bands. This work investigates the Cantor bar distribution of metamaterials slabs in free space. This distribution provides narrow transmission peaks in the forbidden bands. A design of narrow bandpass filter with a signification gain of dimension is proposed. © 2006 Wiley Periodicals, Inc. Microwave Opt Technol Lett 49: 105,109, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.22048 [source] The interaction between bird predation and plant cover in determining habitat occupancy of darkling beetlesOIKOS, Issue 1 2001Elli Groner Tenebrionid beetles in the Negev Desert exhibit size-related habitat segregation, with larger species found in denser cover. Size-dependent predation by birds has been suggested as the mechanism behind this habitat segregation. Two predictions of this hypothesis were tested: (1) plant cover reduces the predation efficiency of birds upon large tenebrionids, and (2) birds prefer larger species. Both predictions were supported: plant cover reduced predation rate by the most common spring and summer predatory birds: white storks (Ciconia ciconia) and stone curlews (Burhinus oedicnemus), in cage experiments. Results from preference experiments suggest that tenebrionid species can be divided according to their profitability as prey. Large species are the most profitable, medium-sized species are less profitable but still acceptable and small species are unprofitable and therefore ignored. Field observations demonstrated that the well-vegetated wadi habitats are dominated by large and small species whereas acceptable, medium-sized species are under-represented in this habitat. The results of the cage experiments indicate possible apparent competition between the large profitable and the medium acceptable tenebrionid species in the wadis. Aggregative response of predators in the profitable habitat is suggested as the mechanism leading to truncated distribution of prey species. Large profitable species are refuge-dependent, medium-sized acceptable species use enemy free space and small species are predator independent. [source] Influence of target type and RAF rule on the measurement of near point of convergenceOPHTHALMIC AND PHYSIOLOGICAL OPTICS, Issue 1 2007Paul M. Adler Abstract Purpose:, This study was designed to investigate if the use of different target types or the RAF rule affected the measurement of near point of convergence (NPC). Methods:, The subjects comprised three groups: (1) 20 children aged 6,9 years (2) 17 children aged 11,13 years (3) 14 adults aged 20,30 years. Five targets were used to measure the NPC: (1) pencil tip, (2) fingertip, (3) penlight, (4) N5 letter and (5) vertical line target on the RAF rule. Results:, There was no significant difference in NPC measurements between the pencil tip, fingertip and N5 target in free space. The penlight resulted in significantly more remote NPC break and recovery points compared with the fingertip and pencil tip (p < 0.05). The RAF rule influences the NPC obtained (p < 0.001). The greatest difference in NPC measurements was observed when comparing the RAF line target and the finger in free space; the former resulted in NPC values of 1.9 times (95% CI 1.6,2.2 times) as much as those obtained with the finger. Conclusions:, Use of the penlight and RAF rule resulted in a more distant NPC break point compared with other targets. The effect of the RAF rule was more apparent for more receded NPC points. [source] Sorption of sulfuryl fluoride by food commoditiesPEST MANAGEMENT SCIENCE (FORMERLY: PESTICIDE SCIENCE), Issue 8 2008Venkata-rao Sriranjini Abstract BACKGROUND: The use of sulfuryl fluoride, a structural fumigant for termite and woodborer control, has recently been expanded to treating stored food commodities and food facilities. There is, however, a lack of data on the sorption of sulfuryl fluoride by food commodities. Knowledge about sorption is important in the context of effective treatment and residues. RESULTS: When sulfuryl fluoride was applied at a dose of 50 g m,3 to various food commodities (total 68) with 300 g per replicate in 0.75 L gas wash bottles (fumigation chambers) at 25 ± 1 °C, in most cases (81%) the gas concentrations in the free space of the commodities exceeded 50 g m,3 (range 51,80 g m,3) at the end of 24 h exposure. In chambers without the substrate, an average concentration of 49.7 g m,3 was recorded. About 54% of the commodities showed low-level ( , 25%) sorption of sulfuryl fluoride, 34% showed medium-level (26,50%) sorption and only 12% were highly sorptive (>50%). The latter include white oats (terminal gas concentration 17.8 g m,3), some of the decorticated split pulses (24.0,29.3 g m,3), chickpea flour (26.3 g m,3), dried ginger (29.0 g m,3), refined wheat flour (30.3 g m,3) and coriander powder (40.5 g m,3). In unfumigated control commodities, owing to interfering volatiles, Fumiscope® readings in the range 0,13 were noted. CONCLUSION: Sulfuryl fluoride has the advantage of a low or moderate level of sorption with the majority of the food commodities. Copyright © 2008 Society of Chemical Industry [source] Asymptotics in Knuth's parking problem for caravans,RANDOM STRUCTURES AND ALGORITHMS, Issue 1 2006Jean Bertoin Abstract We consider a generalized version of Knuth's parking problem, in which caravans consisting of a random number of cars arrive at random on the unit circle. Then each car turns clockwise until it finds a free space to park. Extending a recent work by Chassaing and Louchard Random Struct Algor 21(1) (2002), 76,119, we relate the asymptotics for the sizes of blocks formed by occupied spots with the dynamics of the additive coalescent. According to the behavior of the caravans' size tail distribution, several qualitatively different versions of the eternal additive coalescent are involved. © 2005 Wiley Periodicals, Inc. Random Struct. Alg., 2006 [source] Thermosensitive Copolymer Networks Modify Gold Nanoparticles for Nanocomposite EntrapmentCHEMISTRY - A EUROPEAN JOURNAL, Issue 8 2007Dongxiang Li Dr. Abstract The core-shell gold nanoparticles and copolymer of N -isopropylacrylamide (NIPAM) and N,N,-methylenebisacrylamide (MBAA) hybrids (Au@copolymer) were fabricated through surface-initiated atom-transfer radical polymerization (ATRP) on the surface of gold nanoparticles in 2-propanol/water mixed solvents. The surface of citrate-stabilized gold nanoparticles was first modified by a disulfide initiator for ATRP. The slight cross-linking polymerization between NIPAM and MBAA occurred on the gold surface and resulted in the formation of core-shell Au@copolymer nanostructures that were characterized by TEM, and FTIR and UV-visible spectroscopy. Such synthesized Au@copolymer hybrids possess clearly thermosensitive properties and exhibit "inspire" and "expire" water behavior in response to temperature changes in aqueous solution. Because of this property, we enable to trap and encapsulate smaller nanoparticles by using the free space of the copolymer-network scaffold anchored at the gold surface. [source] Enhancement of Förster Energy Transfer within a Microspherical CavityCHEMPHYSCHEM, Issue 11 2005Hideki Fujiwara Dr. Abstract Energy transfer from pyrene to perylene molecules co-doped within a poly(methyl methacrylate) latex microsphere was drastically accelerated relative to free space. Fluorescence spectra of the microspheres showed that the relative emission intensities of pyrene and perylene changed with the sphere diameter. Analyses of emission decay profiles clarified that Förster-type energy-transfer processes were induced and that the transfer rates increased within the microspherical cavity. This enhancement can be ascribed not only to the quantum electrodynamic effects on the pyrene emission rate, but also the cavity effect of increasing the overlapping factor between donor emission and acceptor absorption spectra. [source] Efficient location of free spaces in TCAM to improve router performanceINTERNATIONAL JOURNAL OF COMMUNICATION SYSTEMS, Issue 4 2005Weidong Wu Abstract A ternary content-addressable memory (TCAM) is a popular hardware device for performing fast IP-address lookup. Because keeping all entries sorted in TCAM, we need move the entries for inserting a new entry. In this paper, we have presented a scheme for minimizing route update overheads in TCAM-based forwarding engines. Our optimizations are based on the hierarchy of prefixes in the routing table. The number of memory movement per update depends on the sequence of the new-inserted prefixes, instead of the initial prefixes in routing table. For the real route update traces, the average number of movements is less than 0.01. Further, when compared to an existing optimization algorithm, in the average case, our algorithm shows a 90% reduction in movement overheads. Copyright © 2005 John Wiley & Sons, Ltd. [source] | ||||||||||||||||||||||