Showing papers by "Lehigh University published in 1997"
TL;DR: In this article, an efficient method of synthesizing nanoscale (1−100 nm) iron and palladized iron particles is presented, which is characterized by high surface area to volume ratios and high reactivities.
Abstract: Transformation of halogenated organic compounds (HOCs) by zero-valent iron represents one of the latest innovative technologies for environmental remediation. For example, iron can be used to construct a reactive wall in the path of a contaminated groundwater plume to degrade HOCs. In this paper, an efficient method of synthesizing nanoscale (1−100 nm) iron and palladized iron particles is presented. Nanoscale particles are characterized by high surface area to volume ratios and high reactivities. BET specific surface area of the synthesized metal particles is 33.5 m2/g. In comparison, a commercially available Fe powder (<10 μm) has a specific surface area of just 0.9 m2/g. Batch studies demonstrated that these nanoscale particles can quickly and completely dechlorinate several chlorinated aliphatic compounds and a mixture of PCBs at relatively low metal to solution ratio (2−5 g/100 mL). Surface-area-normalized rate constants (KSA) are calculated to be 10−100 times higher than those of commercially availa...
1,500 citations
01 Jan 1997
TL;DR: Signal detection has developed many useful and interesting extensions of the basic concepts, resulting in new ideas of asymptotically optimum nonparametric, robust, and sequential centralized detection.
Abstract: Following the foundational work that established basic ideas for optimum distributed defection schemes using multiple sensors (as reviewed in Part I of this two-part review), further work on distributed detection has developed many useful and interesting extensions of the basic concepts. These more recent developments parallel those that arose from the early work on centralized, classical signal detection, resulting in new ideas of asymptotically optimum nonparametric, robust, and sequential centralized detection. Recent developments on these topics in the setting of distributed signal detection are reviewed in the present paper. Results in these directions are important in practice because they allow cases of modeling uncertainty to be addressed, and they provide more efficient detection schemes by optimizing more general performance criteria.
818 citations
TL;DR: In this article, a comparison of the molecular structure and reactivity information of supported vanadium oxide catalysts is presented, which provides new fundamental insights into the catalytic properties of surface vanadia species during hydrocarbon oxidation reactions.
Abstract: Supported vanadium oxide catalysts, containing surface vanadia species on oxide supports, are extensively employed as catalysts for many hydrocarbon oxidation reactions. This paper discusses the current fundamental information available about the structure and reactivity of surface vanadia species on oxide supports: monolayer surface coverage, stability of the surface vanadia monolayer, oxidation state of the surface vanadia species, molecular structures of the surface vanadia species (as a function of environment and catalyst composition), acidity of the surface vanadia species and reactivity of the surface vanadia species. Comparison of the molecular structure and reactivity information provides new fundamental insights into the catalytic properties of surface vanadia species during hydrocarbon oxidation reactions: (1) the role of terminal VO, bridging VOV and bridging VO-support bonds, (2) the number of surface vanadia sites required, (3) the influence of metal oxide additives, (4) the influence of surface acidic and basic sites, (5) the influence of preparation methods and (6) the influence of the specific oxide support phase. The unique physical and chemical characteristics of supported vanadia catalysts, compared to other supported metal oxide catalysts, for hydrocarbon oxidation reactions are also discussed.
644 citations
TL;DR: It is proposed that nocodazole acts by generating TuD subunits that then alter dynamic instability in interphase cells and in vitro with purified brain tubulin, which is similar to the effects of increasing concentrations of GDP-tubulin (TuD) subunits on microtubule assembly.
Abstract: Previous studies demonstrated that nanomolar concentrations of nocodazole can block cells in mitosis without net microtubule disassembly and resulted in the hypothesis that this block was due to a nocodazole-induced stabilization of microtubules. We tested this hypothesis by examining the effects of nanomolar concentrations of nocodazole on microtubule dynamic instability in interphase cells and in vitro with purified brain tubulin. Newt lung epithelial cell microtubules were visualized by video-enhanced differential interference contrast microscopy and cells were perfused with solutions of nocodazole ranging in concentration from 4 to 400 nM. Microtubules showed a loss of the two-state behavior typical of dynamic instability as evidenced by the addition of a third state where they exhibited little net change in length (a paused state). Nocodazole perfusion also resulted in slower elongation and shortening velocities, increased catastrophe, and an overall decrease in microtubule turnover. Experiments performed on BSC-1 cells that were microinjected with rhodamine-labeled tubulin, incubated in nocodazole for 1 h, and visualized by using low-light-level fluorescence microscopy showed similar results except that nocodazole-treated BSC-1 cells showed a decrease in catastrophe. To gain insight into possible mechanisms responsible for changes in dynamic instability, we examined the effects of 4 nM to 12 microM nocodazole on the assembly of purified tubulin from axoneme seeds. At both microtubule plus and minus ends, perfusion with nocodazole resulted in a dose-dependent decrease in elongation and shortening velocities, increase in pause duration and catastrophe frequency, and decrease in rescue frequency. These effects, which result in an overall decrease in microtubule turnover after nocodazole treatment, suggest that the mitotic block observed is due to a reduction in microtubule dynamic turnover. In addition, the in vitro results are similar to the effects of increasing concentrations of GDP-tubulin (TuD) subunits on microtubule assembly. Given that nocodazole increases tubulin GTPase activity, we propose that nocodazole acts by generating TuD subunits that then alter dynamic instability.
472 citations
TL;DR: A meta-analysis evaluating the effects of school-based interventions for students with attention deficit hyperactivity disorder was conducted by examining 60 outcome studies between 1996 and 2010 as discussed by the authors, and the results showed that the interventions had little effect on students with ADHD.
Abstract: A meta-analysis evaluating the effects of school-based interventions for students with attention deficit hyperactivity disorder was conducted by examining 60 outcome studies between 1996 and 2010 t...
404 citations
TL;DR: In this paper, simple insights from the physics of ice, water and sediment place constraints on the possible sediment-transport behavior of glaciers and ice sheets, and several sediment-entrainment mechanisms may be active beneath a single glacier, but one process is likely to be dominant at any place and time.
358 citations
TL;DR: In this article, the authors considered the plane elasticity problem for a nonhomogeneous layer containing a crack perpendicular to the boundaries and solved the problem under three different loading conditions, namely fixed grip, membrane loading, and bending applied to the layer away from the crack region.
Abstract: In this study the plane elasticity problem for a nonhomogeneous layer containing a crack perpendicular to the boundaries is considered. It is assumed that the Young's modulus of the medium varies continuously in the thickness direction. The problem is solved under three different loading conditions, namely fixed grip, membrane loading, and bending applied to the layer away from the crack region. Mode I stress intensity factors are presented for embedded as well as edge cracks for various values of dimensionless parameters representing the size and the location of the crack and the material nonhomogeneity. Some sample results are also given for the crack-opening displacement and the stress distribution.
341 citations
TL;DR: The fit of a correlated, 2-factor structure of ADHD was examined and was confirmed for both parent and teacher ratings and was invariant across child gender, age, informant, informant gender, and language.
Abstract: Changes in the diagnostic criteria for attention-deficit/hyperactivity disorder (ADHD) have necessitated the creation of new measures for clinical assessment. The factor structure of a parent rating scale containing the 18 symptoms of ADHD was examined in this study. Factor analyses and assessment of differences in ADHD ratings across sex, age, and ethnic group were conducted using a sample of 4666 participants ranging in age from 4 to 20 years old who attended kindergarten through 12th grade in 22 school districts across the United States. Two factors (Inattention and Hyperactivity-Impulsivity) were derived and normative data for a nationally representative sample are presented. A higher frequency of ADHD symptoms was found for boys, younger children, and African-American participants. Potential uses of this scale in clinical practice and research are discussed.
300 citations
TL;DR: In this article, a theory describing propagation and self-focusing of partially spatially incoherent light beams in nonlinear media is developed, which is effectively governed by an infinite set of coupled nonlinear Schrodinger-like equations, provided they are initially appropriately weighted with respect to the incoherent angular power spectrum.
Abstract: A theory describing propagation and self-focusing of partially spatially incoherent light beams in nonlinear media is developed. It is shown that this process is effectively governed by an infinite set of coupled nonlinear Schr\"odinger-like equations, provided they are initially appropriately weighted with respect to the incoherent angular power spectrum of the source. The particular case of spatially incoherent beam propagation in biased photorefractive media is considered in detail. Numerical simulations indicate that spatial compression as well as self-trapped states are possible under appropriate conditions. Our results are in good agreement with recent experimental observations.
268 citations
TL;DR: In this article, the role of photochemical degradation of dissolved organic carbon (DOC) on UV transparency (280-400 nm) was investigated in three Pocono Plateau lakes.
Abstract: The role of photochemical degradation of dissolved organic carbon (DOC) on UV transparency (280–400 nm) was investigated in three Pocono Plateau lakes. Diffuse attenuation coefficients (KdUV) in the epilimnia of these lakes varied seasonally (39–81% decline from maximum Kd320nm), with minimum KdUV values occurring near summer solstice. Declines in KdUV corresponded to reductions in UV absorbance by dissolved material (adUV), caused by declines in both DOC concentration and UV (ad : [DOC]). The seasonal decline in KdUV was also accompanied by substantial increases in an absorption coefficient ratio (ad250nm : ad365nm) and decreases in spectral slopes (S).
Experimental studies of photochemical degradation were also performed using filtered lake water and natural sunlight. Exposure to solar radiation produced a number of changes in optical parameters and DOC that resembled those observed in the water column: adUV (−35 to −52%), UV absorptivity (−31 to −48%), ad250nm : ad365nm (0 to +39%), spectral slope, S (0 to −27%), and DOC concentration (0 to −20%).
Changes in adUV were correlated with absorbed UV dose. The derived rate constants were used in a model to estimate the contribution of photochemical degradation of DOC to water column declines in KdUV. Results suggest that rates of photochemical degradation were sufficient to account for the summer reductions in KdUV observed in the three lakes.
253 citations
TL;DR: In this paper, the authors show that extensive Neogene Patagonian plateau lavas are syncollisional or postcollisional in age, with eruptions of both sequences migrating northeastward at 50 to 70 km/Ma.
Abstract: Extensive Neogene Patagonian plateau lavas (46.5° to 49.5°S) southeast of the modern Chile Triple Junction can be related to opening of asthenospheric “slab windows” associated with collisions of Chile Rise segments with the Chile Trench at ≈ 12 Ma and 6 Ma. Support comes from 26 new total-fusion, whole rock 40Ar/39Ar ages and geochemical data from back arc plateau lavas. In most localities, plateau lava sequences consist of voluminous, tholeiitic main-plateau flows overlain by less voluminous, 2 to 5 million year younger, alkalic postplateau flows. Northeast of where the ridge collided at ≈12 Ma, most lavas are syncollisional or postcollisional in age, with eruptions of both sequences migrating northeastward at 50 to 70 km/Ma. Plateau lavas have ages from 12 to 7 Ma in the western back arc and from 5 to 2 Ma farther to the northeast. Trace element and isotopic data indicate main-plateau lavas formed as larger percentage melts of a garnet-bearing, oceanic island basalt (OIB) -like mantle than postplateau lavas. The highest percentage melts erupted in the western and central plateaus. In a migrating slab window model, main-plateau lavas can be explained as melts that formed as upwelling, subslab asthenosphere which flowed around the trailing edge of the descending Nazca Plate and then interacted with subduction-altered asthenospheric wedge and continental lithosphere. Alkaline, postplateau lavas can be explained as melts generated by weaker upwelling of subslab asthenosphere through the open slab window. Thermal problems of high-pressure melt generation of anhydrous mantle can be explained by volatiles (H2O and CO2) introduced by the subduction process into slab window source region(s). An OIB-like, rather than a mid-ocean ridge basalt (MORB) -like source region, and the lack of magmatism northeast of where ridge collision occurred at ≈13 to 14 Ma can be explained by entrainment of “weak” plume(s) or regional variations in an ambient, OIB-like asthenosphere.
TL;DR: For multivariate data sets, the relationship between the connectivity of a mutual k-nearest-neighbor graph, and the presence of clustering structure and outliers in the data is studied.
TL;DR: The authors examined work and family influences on the decision to leave the field of public accounting and found that women were more likely than men to leave public accounting, and the reason for the sex difference in departure rate was not because women experienced greater family pressures than men, but rather women had less of a desire to be promoted to partner than men.
TL;DR: In this paper, a survey of building pounding caused by the 1989 Loma Prieta earthquake is presented, which contains more than 200 building pounding occurrences involving more than 500 building structures over a wide geographical area including the cities of San Francisco, Oakland, Santa Cruz and Watsonville.
TL;DR: In this paper, the authors test the hypothesis that supervisees' multicultural case conceptualization ability and self-reported multicultural competence are functions of their racial identity and their supervisors' instruction to focus on multicultural issues.
Abstract: The purpose of this investigation was to test the hypothesis that supervisees' multicultural case conceptualization ability and self-reported multicultural competence are functions of their racial identity and their supervisors' instruction to focus on multicultural issues. Results from 116 supervisees, both Persons of Color and White persons, indicated that their racial identity was significantly related to self-reported multicultural competence. However, racial identity for both groups was not significantly related to multicultural case conceptualization ability. Furthermore, self-reported multicultural competence was not found to be significantly related to multicultural case conceptualization ability. However, supervisors' instruction to focus on multicultural issues was significantly related to conceptualizations of a multicultural treatment strategy. Theoretical, empirical, and practical implications for multicultural counselor supervision are addressed.
TL;DR: In this article, a general heuristic design procedure is presented that generates an effective plantwide control structure for an entire complex process flowsheet and not simply individual units, based on energy management, production rate, product quality, operational, environmental and safety constraints, liquid-level and gas-pressure inventories, makeup of reactants, component balances, and economic or process optimization.
Abstract: Plantwide control involves the systems and strategies required to control an entire chemical plant consisting of many interconnected unit operations. A general heuristic design procedure is presented that generates an effective plantwide control structure for an entire complex process flowsheet and not simply individual units. The nine steps of the proposed procedure center around the fundamental principles of plantwide control: energy management; production rate; product quality; operational, environmental and safety constraints; liquid-level and gas-pressure inventories; makeup of reactants; component balances; and economic or process optimization. Application of the procedure is illustrated with three industrial examples: the vinyl acetate monomer process, the Eastman plantwide-control process, and the HDA process.
TL;DR: In this article, the authors present a modal theory of self-trapping spatially incoherent light beams in any general nonlinear media, and find that a selftrapped incoherent beam induces a multimode waveguide which guides the beam itself by multiply populating the guided modes.
Abstract: We present a modal theory of self-trapping spatially incoherent light beams in any general nonlinear media. We find that a self-trapped incoherent beam induces a multimode waveguide which guides the beam itself by multiply populating the guided modes. The self-trapping process alters the statistics of the incoherent beam, rendering it localized. We find the conditions for self-trapping (``existence region'' in parameter space) and the correlation function of the incoherent self-trapped beam.
TL;DR: In this article, the utility of differential scanning calorimetry for investigating the thermodynamics and kinetics of a broad range of thin film reactions is demonstrated, including enthalpies of crystallization, heats of formation and interfaces of interfaces.
Abstract: In this paper we demonstrate the utility of differential scanning calorimetry for investigating the thermodynamics and kinetics of a broad range of thin film reactions. We begin by describing differential scanning calorimeters and the preparation of thin film samples. We then cite a number of examples that illustrate how enthalpies of crystallization, heats of formation and enthalpies of interfaces can be measured using layered thin films of Ni/Al, Cu/Zr and Zr/Al and homogeneous thin films of Co-Si, Nb-Cu, Cr-Cu and Ge-Sn. Following these examples of thermodynamic measurements, we show how kinetic parameters of nucleation, growth and coarsening can also be determined from differential scanning calorimetry traces using layered thin films of Ni/Al, Ti/Al and Nb/Al and homogenous thin films of Co-Si and Ge-Sn. The thermodynamic and kinetic investigations highlighted in these examples demonstrate that one can characterize phase transformations that are relevant to commercial applications and scientific studies both of thin films and of bulk materials.
TL;DR: The authors found that supervisee-supervisor racial identity interactions were related to the supervisory alliance, and racial identity interaction and racial matching influenced supervisees' development of multicultural competence.
Abstract: Data from 105 counselor trainees indicated that supervisee–supervisor racial identity interactions were related to the supervisory alliance, and racial identity interactions and racial matching influenced supervisees' development of multicultural competence
TL;DR: In this paper, the authors measured cosmogenic 36 Cl in 56 samples from boulders on moraines and fluvial terraces in the vicinity of the Wind River Range, Wyoming.
Abstract: We measured cosmogenic 36 Cl in 56 samples from boulders on moraines and fluvial terraces in the vicinity of the Wind River Range, Wyoming. We also measured 10 Be in 10 of the same samples. Most of the 10 Be ages were in good agreement with the 36 Cl ages, indicating that rock-surface erosion rates were very low. The oldest moraine investigated, the type Sacagewea Ridge site, yielded only a limiting minimum age of >232 ka. The oldest moraines in the type Bull Lake complex also could be constrained only to >130 ka. The main sequence of type Bull Lake moraines yielded age distributions indicating deposition within the intervals 130 to 100 ka and 120 to 100 ka; the best estimates are closer to the upper limits of these ranges, and associated uncertainties are in the range of 10% to 15%. These uncertainties could permit deposition in either marine isotope stage 6 or stage 5d. We found no evidence of glacial deposits dating to marine isotope stage 4. Both Bull Lake–age moraines from Fremont Lake, on the opposite side of the Wind River Range, and boulders on a fluvial terrace above the Wind River, gave age distributions very similar to that of the second oldest Bull Lake advance (ca. 130 to 100 ka). The distribution of boulder ages for Pinedale moraines at Bull Lake indicated deposition between 23 and 16 ka, nearly identical to the distribution of 10 Be ages previously reported for the type Pinedale moraines at Fremont Lake.
TL;DR: This paper examined the use of diatom-inferred salinity as a climate proxy, with examples taken from both modern waterbodies and sedimentary profiles, and evaluated the potential non-linearities in the salinity/climate relationship through comparison with other proxy records of hydrochemical change, historical documents where they exist.
TL;DR: In this article, the authors review the evidence for climatic change that demonstrates the historical importance of extremes in north-south differences in summer temperatures and east-west differences in aridity across four large subregions.
Abstract: The Great Plains landscape is less topographically complex than most other regions within North America, but diverse aquatic ecosystems, such as playas, pothole lakes, ox-bow lakes, springs, groundwater aquifers, intermittent and ephemeral streams, as well as large rivers and wetlands, are highly dynamic and responsive to extreme climatic fluctuations. We review the evidence for climatic change that demonstrates the historical importance of extremes in north-south differences in summer temperatures and east-west differences in aridity across four large subregions. These physical driving forces alter density stratification, deoxygenation, decomposition and salinity. Biotic community composition and associated ecosystem processes of productivity and nutrient cycling respond rapidly to these climatically driven dynamics. Ecosystem processes also respond to cultural effects such as dams and diversions of water for irrigation, waste dilution and urban demands for drinking water and industrial uses. Distinguishing climatic from cultural effects in future models of aquatic ecosystem functioning will require more refinement in both climatic and economic forecasting. There is a need, for example, to predict how long-term climatic forecasts (based on both ENSO and global warming simulations) relate to the permanence and productivity of shallow water ecosystems. Aquatic ecologists, hydrologists, climatologists and geographers have much to discuss regarding the synthesis of available data and the design of future interdisciplinary research.
TL;DR: In this paper, the roles of risk attitude and tolerance for ambiguity in predicting choice were assessed by examining the effects of these variables on decisions made in four different scenarios, and the role of these individual attitudes depend on the levels of the two treatment variables of risk and ambiguity.
Abstract: This paper extends prior research by jointly assessing the roles of risk attitude and tolerance for ambiguity in predicting choice. An experiment examined the effects of these variables on decisions made in four different scenarios. The four scenarios (treatment combinations) were generated by manipulating risk and ambiguity into two levels (high and low). The context was defined in terms of a sample size selection problem. The second issue explored was the effect of attitudes toward risk and ambiguity on decision confidence.
The results indicate that (1) both risk attitude and ambiguity intolerance determined choice behavior, (2) the roles of these individual attitudes depend on the levels of the two treatment variables of risk and ambiguity, (3) the presence of ambiguity accentuates the perception of risk in individual subjects, and (4) decision makers who are less risk averse, and have more tolerance for ambiguity, display greater confidence in their choice. The paper discusses some of the managerial implications of the results.
TL;DR: In this paper, it is shown that the instantaneous vorticity flux on either side of this jet is rapidly balanced immediately after the onset of separation from the free surface, and that the jet-like flow can be formed by small-scale breaking of a free-surface wave.
Abstract: Flow past a cylinder beneath a free surface gives rise to fundamental classes of nearwake structure that are distinctly different from the wake of a completely submerged cylinder. A central feature is the generation of a vorticity layer from the free surface due to: localized separation, in the form of small-scale breaking of a free-surface wave; or complete separation from the free surface. This vorticity layer appears adjacent to a layer from the surface of the cylinder, thereby forming a jet-like flow. It is shown that the instantaneous vorticity flux on either side of this jet is rapidly balanced immediately after the onset of separation from the free surface.
TL;DR: The dimensionless tensile strength σd/α of wet granular materials with saturation levels in the plateau region of the pendular state was correlated with the void fraction of the agglomerate as mentioned in this paper.
TL;DR: In this article, the authors provided a comprehensive experimental and theoretical study of incoherently coupled photorefractive spatial-soliton pairs in all three possible realizations: bright-bright, dark-dark, and dark-bright.
Abstract: We provide a comprehensive experimental and theoretical study of incoherently coupled photorefractive spatial-soliton pairs in all three possible realizations: bright–bright, dark–dark, and dark–bright. We also show that when the total intensity of two coupled solitons is much lower than the effective dark irradiance, the coupled soliton pair is reduced to Manakov solitons. In all cases, mutual trapping of both components in the coupled soliton pair is verified by analyzing, experimentally and numerically, the beam evolution after decoupling.
TL;DR: In this article, the authors investigated the oxidation of n -butane to maleic anhydride over a series of model-supported vanadia catalyst, where the vanadia phase was present as a two-dimensional metal oxideoverlayer on the different oxide supports.
TL;DR: In this paper, the authors used photoluminescence spectra and IR spectra of NO adsorbed on Cu 2+ in ion exchanged Cu-ZSM-5 of various Cu/Al and Si/Al ratios to identify two main Cu sites (denoted as Cu α and Cu β ) and their redox properties.
TL;DR: It is reported that high UVR levels in low-DOC lakes also may modify the spawning depth, hatching success, and thus recruitment of certain freshwater fishes, suggesting that these disturbances may have consequences for the spawning habitat of fish.
Abstract: Dissolved organic carbon (DOC) strongly influences the underwater levels of potentially damaging solar ultraviolet radiation (UVR) in freshwater lakes. Even so, little is known about how DOC-related variation in UVR may influence natural populations and communities in lakes. Past studies of fish recruitment have emphasized the importance of temperature, food limitation, and predation in controlling year-class strength in fish. Here we report that high UVR levels in low-DOC lakes also may modify the spawning depth, hatching success, and thus recruitment of certain freshwater fishes. We examined how UVR influences the spawning habitat and hatching success of yellow perch (Perca flavescens) eggs in two lakes with different DOC levels and thus different UVR environ- ments. Yellow perch eggs were incubated at the same depth (0.8 m) in quartz tubes (with mesh ends for water exchange) in both lakes in a modified reciprocal transplant experiment. Solar radiation was manipulated to provide three treatments that included exposure to full solar radiation (quartz alone), shielding from UV-B with wavelength selective filters (Mylar D), and dark controls that removed all wavelengths of solar radiation. All eggs in the light treatments in the high-UVR lake perished, whereas survival to hatching of eggs in all treatments in the low-UVR lake and in the dark controls in the high-UVR lake were ?96%. Survival time in the high-UVR lake was longer in UV-B-shielded than in fully exposed (quartz) treatments, and eggs collected from the high-UVR lake survived longer than those collected from the low-UVR lake in identical UVR treatments. A survey of natural spawning depths in the two lakes revealed a much deeper spawning depth in the high-UVR lake (median = 3.2 m) than in the low-UVR lake (median = 0.4 m). Deeper spawning depths in the high-UVR lake suggest that yellow perch can avoid direct UVR damage in low- DOC lakes. DOC and hence UVR in lakes may be altered by both anthropogenic and natural disturbances in the surrounding watershed, suggesting that these disturbances may have consequences for the spawning habitat of fish.
TL;DR: In this paper, a momentum-based method for determining the instantaneous force on a body is formulated for application to quantitative imaging of vortex shedding from a cylinder, which involves a control volume that is fixed to the reference frame of an accelerating body and requires only the instantaneous velocity within the control volume and derivatives of velocity along the control surface.