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Showing papers by "Rensselaer Polytechnic Institute published in 2004"


Journal ArticleDOI
TL;DR: A critical history of the environmental Kuznets curve (EKC) can be found in this article, where a new generation of decomposition and efficient frontier models can help disentangle the true relations between development and the environment and may lead to the demise of the classic EKC.

2,904 citations


Journal ArticleDOI
13 May 2004-Nature
TL;DR: The results suggest that outbreaks can be contained by a strategy of targeted vaccination combined with early detection without resorting to mass vaccination of a population.
Abstract: Here we present a highly resolved agent-based simulation tool (EpiSims), which combines realistic estimates of population mobility,based on census and land-use data, with parameterized models for simulating the progress of a disease within a host and of transmission between hosts10. The simulation generates a largescale,dynamic contact graph that replaces the differential equations of the classic approach. EpiSims is based on the Transportation Analysis and Simulation System (TRANSIMS) developed at Los Alamos National Laboratory, which produces estimates of social networks based on the assumption that the transportation infrastructure constrains people’s choices about where and when to perform activities11. TRANSIMS creates a synthetic population endowed with demographics such as age and income, consistent with joint distributions in census data. It then estimates positions and activities of all travellers on a second-by-second basis. For more information on TRANSIMS and its availability, see Supplementary Information. The resulting social network is the best extant estimate of the physical contact patterns among large groups of people—alternative methodologies are limited to physical contacts among hundreds of people or non-physical contacts (such as e-mail or citations) among large groups.

2,095 citations


Journal ArticleDOI
TL;DR: A dynamic programming algorithm for prediction of RNA secondary structure has been revised to accommodate folding constraints determined by chemical modification and to include free energy increments for coaxial stacking of helices when they are either adjacent or separated by a single mismatch.
Abstract: A dynamic programming algorithm for prediction of RNA secondary structure has been revised to accommodate folding constraints determined by chemical modification and to include free energy increments for coaxial stacking of helices when they are either adjacent or separated by a single mismatch. Furthermore, free energy parameters are revised to account for recent experimental results for terminal mismatches and hairpin, bulge, internal, and multibranch loops. To demonstrate the applicability of this method, in vivo modification was performed on 5S rRNA in both Escherichia coli and Candida albicans with 1-cyclohexyl-3-(2-morpholinoethyl) carbodiimide metho-p-toluene sulfonate, dimethyl sulfate, and kethoxal. The percentage of known base pairs in the predicted structure increased from 26.3% to 86.8% for the E. coli sequence by using modification constraints. For C. albicans, the accuracy remained 87.5% both with and without modification data. On average, for these sequences and a set of 14 sequences with known secondary structure and chemical modification data taken from the literature, accuracy improves from 67% to 76%. This enhancement primarily reflects improvement for three sequences that are predicted with <40% accuracy on the basis of energetics alone. For these sequences, inclusion of chemical modification constraints improves the average accuracy from 28% to 78%. For the 11 sequences with <6% pseudoknotted base pairs, structures predicted with constraints from chemical modification contain on average 84% of known canonical base pairs.

1,481 citations


Journal ArticleDOI
TL;DR: The second data release of the Sloan Digital Sky Survey (SDSS) as mentioned in this paper is the most recent data set to be publicly available, which consists of 3.5 million unique objects, 367,360 spectra of galaxies, quasars, stars, and calibrating blank sky patches selected over 2627 deg2 of this area.
Abstract: The Sloan Digital Sky Survey (SDSS) has validated and made publicly available its Second Data Release. This data release consists of 3324 deg2 of five-band (ugriz) imaging data with photometry for over 88 million unique objects, 367,360 spectra of galaxies, quasars, stars, and calibrating blank sky patches selected over 2627 deg2 of this area, and tables of measured parameters from these data. The imaging data reach a depth of r ≈ 22.2 (95% completeness limit for point sources) and are photometrically and astrometrically calibrated to 2% rms and 100 mas rms per coordinate, respectively. The imaging data have all been processed through a new version of the SDSS imaging pipeline, in which the most important improvement since the last data release is fixing an error in the model fits to each object. The result is that model magnitudes are now a good proxy for point-spread function magnitudes for point sources, and Petrosian magnitudes for extended sources. The spectroscopy extends from 3800 to 9200 A at a resolution of 2000. The spectroscopic software now repairs a systematic error in the radial velocities of certain types of stars and has substantially improved spectrophotometry. All data included in the SDSS Early Data Release and First Data Release are reprocessed with the improved pipelines and included in the Second Data Release. Further characteristics of the data are described, as are the data products themselves and the tools for accessing them.

1,098 citations


Journal ArticleDOI
TL;DR: In this paper, the authors suggest that a cognitive perspective may provide important insights into key aspects of the entrepreneurial process and suggest that this perspective can help the field of entrepreneurship to answer three basic questions it has long addressed: (1) Why do some persons but not others choose to become entrepreneurs? (2) Why did some persons not others recognize opportunities for new products or services that can be profitably exploited? (3) Why are some entrepreneurs so much more successful than others).

1,061 citations


Journal ArticleDOI
TL;DR: The time synchronization problem and the need for synchronization in sensor networks is reviewed, then the basic synchronization methods explicitly designed and proposed for sensor networks are presented.
Abstract: Time synchronization is an important issue in multihop ad hoc wireless networks such as sensor networks. Many applications of sensor networks need local clocks of sensor nodes to be synchronized, requiring various degrees of precision. Some intrinsic properties of sensor networks, such as limited resources of energy, storage, computation, and bandwidth, combined with potentially high density of nodes make traditional synchronization methods unsuitable for these networks. Hence, there has been an increasing research focus on designing synchronization algorithms specifically for sensor networks. This article reviews the time synchronization problem and the need for synchronization in sensor networks, then presents in detail the basic synchronization methods explicitly designed and proposed for sensor networks.

906 citations


Journal ArticleDOI
TL;DR: In this paper, a qualitative analysis of the role of organizational practices in the successful knowledge transfer at research universities has been conducted based on 55 structured interviews of 98 UITT stakeholders associated with five US research universities.

828 citations


Journal ArticleDOI
27 May 2004-Langmuir
TL;DR: The results indicate that the size of the nanoparticle, perhaps because of the contributions of surface curvature, influences adsorbed protein structure and function.
Abstract: Adsorption of chicken egg lysozyme on silica nanoparticles of various diameters has been studied. Special attention has been paid to the effect of nanoparticle size on the structure and function of the adsorbed protein molecules. Both adsorption patterns and protein structure and function are strongly dependent on the size of the nanoparticles. Formation of molecular complexes is observed for adsorption onto 4-nm silica. True adsorptive behavior is evident on 20- and 100-nm particles, with the former resulting in monolayer adsorption and the latter yielding multilayer adsorption. A decrease in the solution pH results in a decrease in lysozyme adsorption. A change of protein structure upon adsorption is observed, as characterized by a loss in alpha-helix content, and this is strongly dependent on the size of the nanoparticle and the solution pH. Generally, greater loss of alpha helicity was observed for the lysozyme adsorbed onto larger nanoparticles under otherwise similar conditions. The activity of lysozyme adsorbed onto silica nanoparticles is lower than that of the free protein, and the fraction of activity lost correlates well with the decrease in alpha-helix content. These results indicate that the size of the nanoparticle, perhaps because of the contributions of surface curvature, influences adsorbed protein structure and function.

811 citations


Journal ArticleDOI
TL;DR: In this article, the authors presented 2.5-30 mum spectra from the Short-Wavelength Spectrometer of the Infrared Space Observatory for a total of 23 sources, including embedded young stellar objects spanning a wide range of mass and luminosity.
Abstract: We present 2.5-30 mum spectra from the Short-Wavelength Spectrometer of the Infrared Space Observatory for a total of 23 sources. The sources include embedded young stellar objects spanning a wide range of mass and luminosity, together with field stars sampling quiescent dark clouds and the diffuse interstellar medium. Expanding on results of previous studies, we use these spectra to investigate ice composition as a function of environment. The spectra reveal an extremely rich set of absorption features attributed to simple molecules in the ices. We discuss the observed properties of these absorption features and review their assignments. Among the species securely identified are H2O, CO, CO2, CH3OH, and CH4. Likely identified species include OCS, H2CO, and HCOOH. There is also evidence for NH3 and OCN- ice features, but these identifications are more controversial. Features that continue to defy identification include the 3.3-3.7 mum "ice band wing'' and the bulk of the 6.8 mum feature. In addition, we find evidence for excess absorption at 6.0 mum that cannot be attributed to H2O ice. We examine the degree of intercorrelation of the 6.8 mum, 4.62 mum ("XCN'') and 6.0 mum (excess) features. Our results are consistent with the interpretation of the 6.8 and 4.62 mum features as due to NH4+ and OCN- ions, respectively, though alternative explanations cannot currently be ruled out. We find that the optical depth correlations are dependent on the profile of the 6.8 mum feature but not on the mass of the YSO nor the ice temperature along the line of sight. We discuss the implications for our current understanding of ice processing. We briefly discuss the composition, origin, and evolution of interstellar ices.

785 citations


Journal ArticleDOI
TL;DR: A probabilistic model is developed to model human fatigue and to predict fatigue based on the visual cues obtained, and it was found to be reasonably robust, reliable, and accurate in fatigue characterization.
Abstract: This paper describes a real-time online prototype driver-fatigue monitor. It uses remotely located charge-coupled-device cameras equipped with active infrared illuminators to acquire video images of the driver. Various visual cues that typically characterize the level of alertness of a person are extracted in real time and systematically combined to infer the fatigue level of the driver. The visual cues employed characterize eyelid movement, gaze movement, head movement, and facial expression. A probabilistic model is developed to model human fatigue and to predict fatigue based on the visual cues obtained. The simultaneous use of multiple visual cues and their systematic combination yields a much more robust and accurate fatigue characterization than using a single visual cue. This system was validated under real-life fatigue conditions with human subjects of different ethnic backgrounds, genders, and ages; with/without glasses; and under different illumination conditions. It was found to be reasonably robust, reliable, and accurate in fatigue characterization.

749 citations


Journal ArticleDOI
TL;DR: In this paper, the degradation rate of white LEDs was investigated and it was shown that the degradation process depends on both the junction temperature and the amplitude of short-wavelength radiation.

Journal ArticleDOI
TL;DR: In this article, the authors estimate the distribution of interseismic coupling on the subduction zone interface beneath the North Island and the kinematics of the tectonic block rotations.
Abstract: [1] The GPS velocity field in the North Island of New Zealand is dominated by the long-term tectonic rotation of the eastern North Island and elastic strain from stress buildup on the subduction zone thrust fault. We simultaneously invert GPS velocities, earthquake slip vectors, and geological fault slip rates in the North Island for the angular velocities of elastic crustal blocks and the spatially variable degree of coupling on faults separating the blocks. This approach allows us to estimate the distribution of interseismic coupling on the subduction zone interface beneath the North Island and the kinematics of the tectonic block rotations. In agreement with previous studies we find that the subduction zone interface beneath the southern North Island has a high slip rate deficit during the interseismic period, and the slip rate deficit decreases northward along the margin. Much of the North Island is rotating as several, distinct tectonic blocks (clockwise at 0.5-3.8 deg Myr -1 ) about nearby axes relative to the Australian Plate. This rotation accommodates much of the margin-parallel component of motion between the Pacific and Australian plates. On the basis of our estimation of the block kinematics we suggest that rotation of the eastern North Island occurs because of the southward increasing thickness of the subducting Hikurangi Plateau. These results have implications for our understanding of convergent margin plate boundary zones around the world, particularly with regard to our knowledge of mechanisms for rapid tectonic block rotations at convergent margins and the role of block rotations in the slip partitioning process.

Journal ArticleDOI
TL;DR: The fabrication of freestanding monolithic uniform macroscopic hollow cylinders having radially aligned carbon nanotube walls, with diameters and lengths up to several centimetres are reported, which may allow them to compete with ceramic- and polymer-based separation membranes used commercially.
Abstract: Over the past decade of nanotube research, a variety of organized nanotube architectures have been fabricated using chemical vapour deposition. The idea of using nanotube structures in separation technology has been proposed, but building macroscopic structures that have controlled geometric shapes, density and dimensions for specific applications still remains a challenge. Here we report the fabrication of freestanding monolithic uniform macroscopic hollow cylinders having radially aligned carbon nanotube walls, with diameters and lengths up to several centimetres. These cylindrical membranes are used as filters to demonstrate their utility in two important settings: the elimination of multiple components of heavy hydrocarbons from petroleum-a crucial step in post-distillation of crude oil-with a single-step filtering process, and the filtration of bacterial contaminants such as Escherichia coli or the nanometre-sized poliovirus ( approximately 25 nm) from water. These macro filters can be cleaned for repeated filtration through ultrasonication and autoclaving. The exceptional thermal and mechanical stability of nanotubes, and the high surface area, ease and cost-effective fabrication of the nanotube membranes may allow them to compete with ceramic- and polymer-based separation membranes used commercially.

Journal ArticleDOI
TL;DR: In this paper, Pb diffusion in both synthetic (CePO4) and natural monazites run under dry, 1-atm conditions is reported. And the Arrhenius relation for in-diffusion experiments on synthetic monazite is given by: D=0.94 exp (−592±39 kJ mol −1 /RT) m 2 s −1

Journal ArticleDOI
TL;DR: This paper considers the problem of partitioning a set of m points in the n-dimensional Euclidean space into k clusters, and considers a continuous relaxation of this discrete problem: find the k-dimensional subspace V that minimizes the sum of squared distances to V of the m points, and argues that the relaxation provides a generalized clustering which is useful in its own right.
Abstract: We consider the problem of partitioning a set of m points in the n-dimensional Euclidean space into k clusters (usually m and n are variable, while k is fixed), so as to minimize the sum of squared distances between each point and its cluster center. This formulation is usually the objective of the k-means clustering algorithm (Kanungo et al. (2000)). We prove that this problem in NP-hard even for k e 2, and we consider a continuous relaxation of this discrete problem: find the k-dimensional subspace V that minimizes the sum of squared distances to V of the m points. This relaxation can be solved by computing the Singular Value Decomposition (SVD) of the m × n matrix A that represents the m pointss this solution can be used to get a 2-approximation algorithm for the original problem. We then argue that in fact the relaxation provides a generalized clustering which is useful in its own right. Finally, we show that the SVD of a random submatrix—chosen according to a suitable probability distribution—of a given matrix provides an approximation to the SVD of the whole matrix, thus yielding a very fast randomized algorithm. We expect this algorithm to be the main contribution of this paper, since it can be applied to problems of very large size which typically arise in modern applications.

Journal ArticleDOI
TL;DR: In this paper, the authors use classical molecular dynamics simulations to study the interfacial resistance for heat flow between a carbon nanotube and octane liquid and find that the thermal conductivity of carbon-nanotube polymer composites and organic suspensions will be limited by the interface thermal resistance.
Abstract: We use classical molecular dynamics simulations to study the interfacial resistance for heat flow between a carbon nanotube and octane liquid. We find a large value of the interfacial resistance associated with weak coupling between the rigid tube structure and the soft organic liquid. Our simulation demonstrates the key role played by the soft vibration modes in the mechanism of the heat flow. These results imply that the thermal conductivity of carbon-nanotube polymer composites and organic suspensions will be limited by the interface thermal resistance and are consistent with recent experiments.

Patent
16 Apr 2004
TL;DR: Methods and systems for controlling the operation of a tool are provided in this paper, which can be applied to a broad range of tools and machining processes, such as a surgical drilling process, for the drilling of bone.
Abstract: Methods and systems for controlling the operation of a tool are provided These methods and systems may be used to control the operation of any tool, for example, a drill or a saw The methods and systems employ at least one sensor to detect at least one operational parameter of the tool, for example, drill speed or acceleration Instrumentation is used to process the data representing the parameter to determine characteristic values of the parameter, for example, amplitudes and frequencies These characteristic values are used to control the operation of the tool, to determine one or more properties of the material being acted on by the tool, or to monitor the condition of the tool Though aspects of the invention may be applied to a broad range of tools and machining processes, in one aspect, the methods and systems are used to monitor and control the operation of a surgical drilling process, for example, for the drilling of bone

Journal ArticleDOI
16 Nov 2004-Langmuir
TL;DR: Analysis of the secondary structure of the proteins via FT-IR spectroscopy revealed that both enzymes undergo structural changes upon adsorption, with substantial secondary structural perturbation observed for CT.
Abstract: We have examined the structure and function of two enzymes, alpha-chymotrypsin (CT) and soybean peroxidase (SBP), adsorbed onto single-walled carbon nanotubes (SWNTs). SBP retained up to 30% of its native activity upon adsorption, while the adsorbed CT retained only 1% of its native activity. Analysis of the secondary structure of the proteins via FT-IR spectroscopy revealed that both enzymes undergo structural changes upon adsorption, with substantial secondary structural perturbation observed for CT. Consistent with these results, AFM images of the adsorbed enzymes indicated that SBP retains its native three-dimensional shape while CT appears to unfold on the SWNT surface. This study represents the first in depth investigation of protein structure and function on carbon nanotubes, which is critical in designing optimal carbon nanotube-protein conjugates.

Journal ArticleDOI
TL;DR: In this article, the incorporation of 23 nm titanium dioxide nanoparticles into an epoxy matrix to form a nanocomposite structure is described, and it is shown that the use of nanometric particles results in a substantial change in the behavior of the composite, which can be traced to the mitigation of internal charge when a comparison is made with conventional TiO2 fillers.
Abstract: The incorporation of 23 nm titanium dioxide nanoparticles into an epoxy matrix to form a nanocomposite structure is described. It is shown that the use of nanometric particles results in a substantial change in the behaviour of the composite, which can be traced to the mitigation of internal charge when a comparison is made with conventional TiO2 fillers. A variety of diagnostic techniques (including dielectric spectroscopy, electroluminescence, thermally stimulated current, photoluminescence) have been used to augment pulsed electro-acoustic space charge measurement to provide a basis for understanding the underlying physics of the phenomenon. It would appear that, when the size of the inclusions becomes small enough, they act co-operatively with the host structure and cease to exhibit interfacial properties leading to Maxwell-Wagner polarization. It is postulated that the particles are surrounded by high charge concentrations in the Gouy-Chapman-Stern layer. Since nanoparticles have very high specific areas, these regions allow limited charge percolation through nano-filled dielectrics. The practical consequences of this have also been explored in terms of the electric strength exhibited. It would appear that there was a window in which real advantages accrue from the nano-formulated material. An optimum loading of about 10% (by weight) is indicated.

Posted Content
TL;DR: In this article, the authors measured team size by the number of authors on a scientific paper and found that team size increases by 50 percent over a 19-year period, indicating a sudden decline in the cost of collaboration, perhaps due to improvements in telecommunications.
Abstract: This paper explores recent trends in the size of scientific teams and in institutional collaborations. The data derive from 2.4 million scientific papers written in 110 leading U.S. research universities over the period 1981-1999. We measure team size by the number of authors on a scientific paper. Using this measure we find that team size increases by 50 percent over the 19-year period. We supplement team size with measures of domestic and foreign institutional collaborations, which capture the geographic dispersion of team workers. The time series evidence suggests that the trend towards larger and more dispersed teams accelerates at the start of the 1990s. This acceleration suggests a sudden decline in the cost of collaboration, perhaps due to improvements in telecommunications. Using a panel of top university departments we find that private universities and departments whose scientists have earned prestigious awards participate in larger teams, as do departments that have larger amounts of federal funding. Placement of former graduate students is a key determinant of institutional collaborations, especially collaborations with firms and foreign scientific institutions. Finally, the evidence indicates that scientific influence increases with team size and institutional collaborations. Since increasing team size implies an increase in the division of labor, these results suggest that scientific productivity increases with the scientific division of labor.

Book
05 Jan 2004
TL;DR: EntrePRENEURSHIP: A PROCESS PERSPECTIVE equips potential entrepreneurs with the tools and insight for success as discussed by the authors, which covers the entire process of building a business, from recognizing opportunity and building a team, and then assembling finances, the business plan, legal issues, marketing, growth, and exit strategies.
Abstract: Current, comprehensive, and cutting edge, ENTREPRENEURSHIP: A PROCESS PERSPECTIVE equips potential entrepreneurs with the tools and insight for success. With solid theory and relevant examples, this thorough resource covers the entire process of building a business. Seasoned instructors and entrepreneurial authorities, Professors Baron and Shane deliver a practical, applied process approach with a multidisciplinary perspective, drawing on knowledge from the studies of economics, psychology, and other areas. The book begins with recognizing opportunity and building a team, and then moves through assembling finances, the business plan, legal issues, marketing, growth, and exit strategies. Rather than getting bogged down in excessive discussions of theory, Baron and Shane use real-world examples to illustrate how students can apply chapter concepts to their own business ventures. Thoroughly updated and revised based on student and professor feedback, the second edition adds a chapter on legal issues specific to entrepreneurs--including intellectual property considerations--and an appendix on key accounting principles entrepreneurs should know. A new chapter on growth strategies for new ventures is coupled with a chapter on managing new ventures for growth. In addition, new boxed features shed light on common myths and misperceptions about entrepreneurship. The book is also packed with hands-on applications--including a case written specifically for each chapter--giving students experience putting text concepts into real-world action.

Journal ArticleDOI
TL;DR: A technique for visualizing detailed miRNA expression patterns in mouse embryos is reported, elucidate the tissue-specific expression of several miRNAs during embryogenesis, and negatively regulates Hoxb8 and miR-196a, indicating that its restricted expression pattern probably reflects a role in the patterning function of the Hox complex.
Abstract: MicroRNAs (miRNAs) are a class of short (∼22-nt) noncoding RNA molecules that downregulate expression of their mRNA targets. Since their discovery as regulators of developmental timing in Caenorhabditis elegans, hundreds of miRNAs have been identified in both animals and plants1. Here, we report a technique for visualizing detailed miRNA expression patterns in mouse embryos. We elucidate the tissue-specific expression of several miRNAs during embryogenesis, including two encoded by genes embedded in homeobox (Hox) clusters, miR-10a and miR-196a. These two miRNAs are expressed in patterns that are markedly reminiscent of those of Hox genes. Furthermore, miR-196a negatively regulates Hoxb8, indicating that its restricted expression pattern probably reflects a role in the patterning function of the Hox complex.

Journal ArticleDOI
TL;DR: In this paper, the authors focus on the impact of the services offered, namely infrastructure, coaching and networks, on the graduation rates of the respective incubators' tenants, and propose a more comprehensive model to explain how incubators affect the entrepreneurial process.
Abstract: We outline a model that improves our understanding of the role of incubators in the entrepreneurial process. Specifically, we focus on the impact of the services offered, namely infrastructure, coaching and networks, on the graduation rates of the respective incubators' tenants. The model is tested among three different types of incubators, for-profit, non-profit, university-based incubators. Based on our qualitative findings, we conclude that our initial model is ineffective, in the sense that it cannot fully explain the role of the incubators in facilitating entrepreneurship. Interviews with directors of incubator centers were also carried out simultaneously. Further analysis of the results along with interview responses from incubator directors, led us to propose a more comprehensive model to explain how incubators affect the entrepreneurial process.

Journal ArticleDOI
TL;DR: A volume sampling method to generate three-dimensional patterns is proposed and a systematic SEM-based analysis of the microstructure gives new insights toward a better understanding of the femtosecond laser interaction with fused silica glass.
Abstract: We present novel results obtained in the fabrication of high-aspect ratio micro-fluidic microstructures chemically etched from fused silica substrates locally exposed to femtosecond laser radiation. A volume sampling method to generate three-dimensional patterns is proposed and a systematic SEM-based analysis of the microstructure is presented. The results obtained gives new insights toward a better understanding of the femtosecond laser interaction with fused silica glass (a-SiO2).

Journal ArticleDOI
TL;DR: In this paper, the authors proposed a non-detection zone (NDZ) as a performance index to evaluate different anti-islanding schemes and derived the NDZ for three basic passive anti-ISL schemes: under/over voltage, underover frequency, and phase jump.
Abstract: This paper proposes a nondetection zone (NDZ) as a performance index to evaluate different anti-islanding schemes. The NDZ for three basic passive anti-islanding schemes: under/over voltage, under/over frequency, and phase jump are derived analytically and validated by simulation. Based on the NDZ, not only can the dominant factors that influence anti-islanding protection be identified, it may also support definition of optimal combined schemes that lead to a reduced NDZ. The methodology presented in the paper can be extended to the evaluation of other anti-islanding schemes.

Journal ArticleDOI
TL;DR: In this article, the authors study how the ordering of the liquid at the liquid-solid interface affects the interfacial thermal resistance of a simple monoatomic liquid and find no effect on the thermal transport either normal to surface or parallel to the surface.

Journal ArticleDOI
TL;DR: A new framework for associations based on the concept of closed frequent itemsets is presented, with the number of non-redundant rules produced by the new approach is exponentially smaller than the rule set from the traditional approach.
Abstract: The traditional association rule mining framework produces many redundant rules. The extent of redundancy is a lot larger than previously suspected. We present a new framework for associations based on the concept of closed frequent itemsets. The number of non-redundant rules produced by the new approach is exponentially (in the length of the longest frequent itemset) smaller than the rule set from the traditional approach. Experiments using several “hard” as well as “easy” real and synthetic databases confirm the utility of our framework in terms of reduction in the number of rules presented to the user, and in terms of time.

Journal ArticleDOI
TL;DR: Large differences in the optical properties (UV-visible absorption and Raman spectra) of purified extracellular nanospheres produced in this manner by the three different bacterial species differed substantially from those of amorphous Se(0) formed by chemical oxidation of H2Se and of black, vitreous Se(*) formed chemically by reduction of selenite with ascorbate.
Abstract: Certain anaerobic bacteria respire toxic selenium oxyanions and in doing so produce extracellular accumulations of elemental selenium [Se(0)]. We examined three physiologically and phylogenetically diverse species of selenate- and selenite-respiring bacteria, Sulfurospirillum barnesii, Bacillus selenitireducens, and Selenihalanaerobacter shriftii, for the occurrence of this phenomenon. When grown with selenium oxyanions as the electron acceptor, all of these organisms formed extracellular granules consisting of stable, uniform nanospheres (diameter, approximately 300 nm) of Se(0) having monoclinic crystalline structures. Intracellular packets of Se(0) were also noted. The number of intracellular Se(0) packets could be reduced by first growing cells with nitrate as the electron acceptor and then adding selenite ions to washed suspensions of the nitrate-grown cells. This resulted in the formation of primarily extracellular Se nanospheres. After harvesting and cleansing of cellular debris, we observed large differences in the optical properties (UV-visible absorption and Raman spectra) of purified extracellular nanospheres produced in this manner by the three different bacterial species. The spectral properties in turn differed substantially from those of amorphous Se(0) formed by chemical oxidation of H(2)Se and of black, vitreous Se(0) formed chemically by reduction of selenite with ascorbate. The microbial synthesis of Se(0) nanospheres results in unique, complex, compacted nanostructural arrangements of Se atoms. These arrangements probably reflect a diversity of enzymes involved in the dissimilatory reduction that are subtly different in different microbes. Remarkably, these conditions cannot be achieved by current methods of chemical synthesis.

Journal ArticleDOI
TL;DR: In this approach, cells growing on small electrodes and monitored by using electric cell-substrate impedance sensing are subjected to currents, resulting in severe electroporation and subsequent cell death.
Abstract: Confluent cell monolayers in tissue culture are fragile and can easily be mechanically disrupted, often leaving an area devoid of cells. This opening in the cell sheet is then repopulated, because the cells on the fringe of the damage, which are no longer contact-inhibited, move into the available space. This mechanical disruption is often done deliberately in a "wound-healing" assay as a means to assess the migration of the cells. In such assays, a scrape is made in the cell layer followed by microscopy to monitor the advance of the cells into the wound. We have found that these types of assays can also be accomplished electrically. In this approach, cells growing on small electrodes and monitored by using electric cell-substrate impedance sensing are subjected to currents, resulting in severe electroporation and subsequent cell death. After this invasive treatment, the electrode's impedance is again monitored to chart the migration and ultimate healing of the wound. We report here that this procedure to study cell behavior is both highly reproducible, quantitative, and provides data similar to that acquired with traditional measurements.

Journal ArticleDOI
TL;DR: This work uses a recursive set-partitioning procedure to sort subsets of wavelet coefficients by maximum magnitude with respect to thresholds that are integer powers of two, and concludes that this algorithm retains all the desirable features of these algorithms and is highly competitive to them in compression efficiency.
Abstract: We propose an embedded, block-based, image wavelet transform coding algorithm of low complexity. It uses a recursive set-partitioning procedure to sort subsets of wavelet coefficients by maximum magnitude with respect to thresholds that are integer powers of two. It exploits two fundamental characteristics of an image transform-the well-defined hierarchical structure, and energy clustering in frequency and in space. The two partition strategies allow for versatile and efficient coding of several image transform structures, including dyadic, blocks inside subbands, wavelet packets, and discrete cosine transform (DCT). We describe the use of this coding algorithm in several implementations, including reversible (lossless) coding and its adaptation for color images, and show extensive comparisons with other state-of-the-art coders, such as set partitioning in hierarchical trees (SPIHT) and JPEG2000. We conclude that this algorithm, in addition to being very flexible, retains all the desirable features of these algorithms and is highly competitive to them in compression efficiency.