Showing papers by "Lehigh University published in 2000"

Comparisons and physics basis of tokamak transport models and turbulence simulations

Abstract: The predictions of gyrokinetic and gyrofluid simulations of ion-temperature-gradient(ITG)instability and turbulence in tokamak plasmas as well as some tokamak plasma thermal transportmodels, which have been widely used for predicting the performance of the proposed International Thermonuclear Experimental Reactor (ITER) tokamak [Plasma Physics and Controlled Nuclear Fusion Research, 1996 (International Atomic Energy Agency, Vienna, 1997), Vol. 1, p. 3], are compared. These comparisons provide information on effects of differences in the physics content of the various models and on the fusion-relevant figures of merit of plasma performance predicted by the models. Many of the comparisons are undertaken for a simplified plasma model and geometry which is an idealization of the plasma conditions and geometry in a Doublet III-D [Plasma Physics and Controlled Nuclear Fusion Research, 1986 (International Atomic Energy Agency, Vienna, 1987), Vol. 1, p. 159] high confinement (H-mode) experiment. Most of the models show good agreements in their predictions and assumptions for the linear growth rates and frequencies. There are some differences associated with different equilibria. However, there are significant differences in the transport levels between the models. The causes of some of the differences are examined in some detail, with particular attention to numerical convergence in the turbulence simulations (with respect to simulation mesh size, system size and, for particle-based simulations, the particle number). The implications for predictions of fusion plasma performance are also discussed.

A phylogenetically conserved NAD+-dependent protein deacetylase activity in the Sir2 protein family.

Abstract: The yeast Sir2 protein, required for transcriptional silencing, has an NAD+-dependent histone deacetylase (HDA) activity. Yeast extracts contain a NAD+-dependent HDA activity that is eliminated in a yeast strain from which SIR2 and its four homologs have been deleted. This HDA activity is also displayed by purified yeast Sir2p and homologous Archaeal, eubacterial, and human proteins, and depends completely on NAD+ in all species tested. The yeast NPT1 gene, encoding an important NAD+ synthesis enzyme, is required for rDNA and telomeric silencing and contributes to silencing of the HM loci. Null mutants in this gene have significantly reduced intracellular NAD+ concentrations and have phenotypes similar to sir2 null mutants. Surprisingly, yeast from which all five SIR2 homologs have been deleted have relatively normal bulk histone acetylation levels. The evolutionary conservation of this regulated activity suggests that the Sir2 protein family represents a set of effector proteins in an evolutionarily conserved signal transduction pathway that monitors cellular energy and redox states.

On the go with SONOS

Abstract: Advancements in scaling gate insulators for MOS transistors permit low-voltage, silicon-oxide-nitride-silicon (SONOS) nonvolatile semiconductor memories (NVSMs) for a wide range of applications. The continued scaling of SONOS devices offers improved performance with a small cell size, single-level polysilicon with low voltage, fast erase/write, improved memory retention, increased endurance, and radiation hardness. In this article, we discuss scaled SONOS devices, SONOS memory technology, and some SONOS NVSM applications.

Investigation of Surface Structures of Supported Vanadium Oxide Catalysts by UV−vis−NIR Diffuse Reflectance Spectroscopy

Abstract: UV−vis−NIR diffuse reflectance spectroscopy (DRS) was applied to study the local structures of V(V) cations on various oxide supports (Al2O3, ZrO2 TiO2, Nb2O5, CeO2, and SiO2) under hydrated and dehydrated conditions. The edge energy (Eg) of the LMCT transitions of V(V) cations was used to elucidate the local structures of V(V) cations, and a correlation between the edge energy and the number of the covalent V−O−V bonds (CVB) around the central V(V) cations was established based on some V(V) reference compounds/oxides. For TiO2, Nb2O5, and CeO2 supported vanadia catalysts, the strong support absorption in the same region as the V(V) cations prevents a reliable determination of the local structure of the surface vanadium oxide species by either the LMCT band position or the edge energy. For Al2O3, ZrO2, and SiO2 supported vanadia catalysts, the average CVB number derived from the edge energy allows the assignment of the possible structure of the surface vanadium oxide species, which is a strong function of...

Modulation instability and pattern formation in spatially incoherent light beams.

Abstract: We report on the experimental observation of modulation instability of partially spatially incoherent light beams in noninstantaneous nonlinear media and show that in such systems patterns can form spontaneously from noise. Incoherent modulation instability occurs above a specific threshold that depends on the coherence properties (correlation distance) of the wave packet and leads to a periodic train of one-dimensional filaments. At a higher value of nonlinearity, the incoherent one-dimensional filaments display a two-dimensional instability and break up into self-ordered arrays of light spots. This discovery of incoherent pattern formation reflects on many other nonlinear systems beyond optics. It implies that patterns can form spontaneously (from noise) in diverse nonlinear many-body systems involving weakly correlated particles, such as atomic gases at (or near) Bose-Einstein condensation temperatures and electrons in semiconductors at the vicinity of the quantum Hall regime.

CHAPTER 9 – Feeding in Snakes

Abstract: Body elongation and limblessness have evolved significantly within Tetrapoda, typically associated with aquatic, fossorial, crevice dwelling, or grass-swimming lifestyles. Some lineages of secondarily elongate vertebrates (for example, limbless skinks) have solved the concomitant problem of reduction in size of the feeding apparatus by eating many tiny items, whereas others (for example, some caecilians) shear ingestible chunks out of large prey. Many advanced snakes achieved a third solution by radically restructuring their heads and feeding infrequently on large items; perhaps not coincidentally. Among limbless squamate reptiles, only Serpentes has achieved substantial adaptive radiation and high species richness. More than 2,500 species of living snakes inhabit most temperate and tropical land masses, and they often are prominent predators in terrestrial, arboreal, fossorial, aquatic, and even marine faunas. Snakes eat prey as different as onycophorans, fish eggs, centipedes, cormorants, and porcupines; many species commonly consume individual items weighing 20% of their own mass, and some venomous species occasionally subdue and eat prey that exceed their own mass by as much as 50%. This chapter first briefly surveys snake diversity and then examines in detail the functional and morphological aspects of capturing, swallowing, and processing prey that generally characterize relatively derived subgroups. It only touches on sensory aspects of feeding.

Shape-adaptive discrete wavelet transforms for arbitrarily shaped visual object coding

Abstract: This paper presents a shape-adaptive wavelet coding technique for coding arbitrarily shaped still texture. This technique includes shape-adaptive discrete wavelet transforms (SA-DWTs) and extensions of zerotree entropy (ZTE) coding and embedded zerotree wavelet (EZW) coding. Shape-adaptive wavelet coding is needed for efficiently coding arbitrarily shaped visual objects, which is essential for object-oriented multimedia applications. The challenge is to achieve high coding efficiency while satisfying the functionality of representing arbitrarily shaped visual texture. One of the features of the SA-DWTs is that the number of coefficients after SA-DWTs is identical to the number of pixels in the original arbitrarily shaped visual object. Another feature of the SA-DWT is that the spatial correlation, locality properties of wavelet transforms, and self-similarity across subbands are well preserved in the SA-DWT. Also, for a rectangular region, the SA-DWT becomes identical to the conventional wavelet transforms. For the same reason, the extentions of ZTE and EZW to coding arbitrarily shaped visual objects carefully treat "don't care" nodes in the wavelet trees. Comparison of shape-adaptive wavelet coding with other coding schemes for arbitrarily shaped visual objects shows that shape-adaptive wavelet coding always achieves better coding efficiency than other schemes. One implementation of the shape-adaptive wavelet coding technique has been included in the new multimedia coding standard MPEG-4 for coding arbitrarily shaped still texture. Software implementation is also available.

The good, bad and ugly: distributed detection of a known signal in dependent Gaussian noise

Abstract: Most results about quantized detection rely strongly on an assumption of independence among random variables. With this assumption removed, little is known. Thus, in this paper, Bayes-optimal binary quantization for the detection of a shift in mean in a pair of dependent Gaussian random variables is studied. This is arguably the simplest meaningful problem one could consider. If results and rules are to be found, they ought to make themselves plain in this problem. For certain problem parametrizations (meaning the signals and correlation coefficient), optimal quantization is achievable via a single threshold applied to each observation-the same as under independence. In other cases, one observation is best ignored or is quantized with two thresholds; neither behavior is seen under independence. Further, and again in distinction from the case of independence, it is seen that in certain situations, an XOR fusion rule is optimal, and in these cases, the implied decision rule is bizarre. The analysis is extended to the multivariate Gaussian problem.

In situ IR, Raman, and UV-Vis DRS spectroscopy of supported vanadium oxide catalysts during methanol oxidation

Abstract: The application of in situ Raman, IR, and UV-Vis DRS spectroscopies during steady-state methanol oxidation has demonstrated that the molecular structures of surface vanadium oxide species supported on metal oxides are very sensitive to the coordination and H-bonding effects of adsorbed methoxy surface species. Specifically, a decrease in the intensity of spectral bands associated with the fully oxidized surface (V5+) vanadia active phase occurred in all three studied spectroscopies during methanol oxidation. The terminal V = O (∼1030 cm−1) and bridging V–O–V (∼900–940 cm−1) vibrational bands also shifted toward lower frequency, while the in situ UV-Vis DRS spectra exhibited shifts in the surface V5+ LMCT band (>25,000 cm−1) to higher edge energies. The magnitude of these distortions correlates with the concentration of adsorbed methoxy intermediates and is most severe at lower temperatures and higher methanol partial pressures, where the surface methoxy concentrations are greatest. Conversely, spectral changes caused by actual reductions in surface vanadia (V5+) species to reduced phases (V3+/V4+) would have been more severe at higher temperatures. Moreover, the catalyst (vanadia/silica) exhibiting the greatest shift in UV-Vis DRS edge energy did not exhibit any bands from reduced V3+/V4+ phases in the d–d transition region (10,000–30,000 cm−1), even though d–d transitions were detected in vanadia/alumina and vanadia/zirconia catalysts. Therefore, V5+ spectral signals are generally not representative of the percent vanadia reduction during the methanol oxidation redox cycle, although estimates made from the high temperature, low methoxy surface coverage IR spectra suggest that the catalyst surfaces remain mostly oxidized during steady-state methanol oxidation (15–25% vanadia reduction). Finally, adsorbed surface methoxy intermediate species were easily detected with in situ IR spectroscopy during methanol oxidation in the C–H stretching region (2800–3000 cm−1) for all studied catalysts, the vibrations occurring at different frequencies depending on the specific metal oxide upon which they chemisorb. However, methoxy bands were only found in a few cases using in situ Raman spectroscopy due to the sensitivity of the Raman scattering cross-sections to the specific substrate onto which the surface methoxy species are adsorbed.

Subcolloidal Fe/Ag particles for reductive dehalogenation of chlorinated benzenes

Abstract: Subcolloidal (<0.1 μm) iron−silver (1% Ag) particles were synthesized for the transformation of chlorinated benzenes in aqueous solution. Hexachlorobenzene (HCB) (4 mg/L) was dechlorinated to tetra...

Modulation instability of incoherent beams in noninstantaneous nonlinear media

Abstract: We show that modulation instability can exist with partially spatially incoherent light beams in a noninstantaneous nonlinear environment For such incoherent modulation instability to occur, the value of the nonlinearity has to exceed a threshold imposed by the degree of spatial coherence

Charge retention of scaled SONOS nonvolatile memory devices at elevated temperatures

Abstract: The charge retention characteristics in scaled SONOS nonvolatile memory devices with an effective gate oxide thickness of 94 A and a tunnel oxide of 15 A are investigated in a temperature range from room temperature to 175°C. Electron charge decay rate is sensitive to the temperature, whereas hole charge decay rate remains essentially constant. Based on experimental observations and an amphoteric trap model for nitride traps, an analytical model for charge retention of the excess electron state is developed. Using this thermal activated electron retention model, the trap distribution in energy within the nitride film is extracted.

Enhancing Main Idea Comprehension for Students with Learning Problems: The Role of a Summarization Strategy and Self-Monitoring Instruction

Abstract: This study investigated the effectiveness of a main idea strategy and self-monitoring instructional procedure for improving comprehension of textual material in students with high-incidence (e.g., learning and behavioral) disabilities. Thirty-three middle school students with disabilities were randomly assigned to experimental and control groups. Students in the experimental condition were trained to identify and generate main idea statements using main idea strategy instruction and a self-monitoring procedure. Results indicated that the instructional procedures led to increased reading comprehension of students in the experimental group on the training measure, which was maintained over time. On near and far transfer measures, the experimental group statistically outperformed students in the control group on posttest and delayed posttest items requiring selection responses. Students in the experimental group maintained strategy usage 6 weeks later on selection type responses on the near transfer measure ...

Encapsulation of inorganic particles via miniemulsion polymerization. I. Dispersion of titanium dioxide particles in organic media using OLOA 370 as stabilizer

Abstract: The dispersion of hydrophilic and hydrophobic titanium dioxide (TiO2) particles in organic media (styrene and cyclohexane) was studied to evaluate the effect of dispersion quality (i.e., size and stability) on the encapsulation efficiencies of subsequent miniemulsion polymerizations. Through screening studies of various block copolymers, OLOA 370 (polybutene–succinimide pentamine) was chosen as the stabilizer for detailed dispersion studies on both types of TiO2 particles. As a result of strong interactions between the amine end group of the OLOA 370 stabilizer and the hydroxyl groups on the surface of the hydrophilic TiO2 particles, a good dispersion stability and small particle size (Dv = 39–45 nm) was obtained using 1.0 wt % stabilizer and 20 min of sonification. The dispersions of the hydrophobic TiO2 particles resulted in a larger average particle size (Dv = 60 nm) and poorer stability. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 4419–4430, 2000

Meniscus instability in a thin elastic film

Abstract: A new kind of meniscus instability leading to the formation of stationary fingers with a well-defined spacing has been observed in experiments with elastomeric films confined between a plane rigid glass and a thin curved glass plate. The wavelength of the instability increases linearly with the thickness of the confined film, but it is remarkably insensitive to the compliance and the energetics of the system. However, lateral amplitude (length) of the fingers depends on the compliance of the system and on the radius of curvature of the glass plate. A simple linear stability analysis is used to explain the underlying physics and the key observed features of the instability.

Redshirting and Early Retention: Who Gets the "Gift of Time" and What Are Its Outcomes?

Abstract: This paper describes the results of a study that examined the prevalence of the delay of kindergarten entry, also known as academic redshirting. Utilizing a representative sample of Wisconsin school district, the authors examined the school records of more than 8,000 students to depict patterns of school entry, promotion, subsequent special services, and student achievement. Results indicate that approximately 7% of the sample bad delayed school entry and that those children were primarily boys with birthdates immediately before the entrance cutoff. Redshirts and retainees are more likely to receive special education services than their peers who enter and are promoted on time. The achievement of redshirts is comparable to their normally entered peers; whereas retainees perform at lower levels. Although the interpretations of these results depend on the perspective taken on extra-year interventions, they can be read in the context of other literature on extra-year interventions. We suggest next steps for ...

Level control in the steam generator of a nuclear power plant

Abstract: Poor control of the steam generator water level in the secondary circuit of a nuclear power plant can lead to frequent reactor shutdowns. Such shutdowns are caused by violation of safety limits on the water level and are common at low operating power where the plant exhibits strong nonminimum phase characteristics and flow measurements are unreliable. There is, therefore, a need to systematically investigate the problem of controlling the water level in the steam generator in order to prevent such costly reactor shutdowns. The paper presents a framework for addressing this problem based on an extension of the standard linear model predictive control algorithm to linear parameter varying systems.

Interfacial Rate Processes in Adhesion and Friction

Abstract: Adhesion between solid materials results from intermolecular interactions The fracture resistance of an adhesive joint is, however, determined jointly by the mechanical deformation in the bulk material and the strength of the interfacial bond The force needed to break an interfacial bond does not have a fixed value; it depends on the thermal state of the system and the rate at which the force is transmitted to the bond The concomitant energy dissipation arising from the extension and the relaxation of the interfacial bonds contributes a significant resistance to fracture, which is clearly evident in elastomeric polymers This issue of interfacial dissipation and its relationship to the length of the interfacial bridges and the rate of crack propagation are addressed with the kinetic theory of bond rupture in the tradition of the models developed by Eyring, Tobolsky, Zhurkov, Bueche, Schallamach, Kausch, and more recently, by Evans and Ritchie Next, the method is extended to address the velocity-depend

Encapsulation of inorganic particles via miniemulsion polymerization. II. Preparation and characterization of styrene miniemulsion droplets containing TiO2 particles

Abstract: The encapsulation of titanium dioxide (TiO2) particles via styrene miniemulsion polymerization requires two successive dispersion steps. First, the TiO2 particles must be successfully dispersed in the monomer phase. Second, this phase must be dispersed in an aqueous surfactant solution to form stable submicron droplets. The oil/water interface between the droplets and the aqueous phase can be affected not only by the surfactant used but also the components present in the oil phase. Interfacial tensions between the phases were measured. The presence of insufficient or excess stabilizer both reduced the interfacial tensions. This was attributed to migration of the partially covered hydrophilic TiO2 particles or the excess OLOA 370 stabilizer (polybutene–succinimide pentamine) to the oil/water interface. The free surfactant in the aqueous phase and the average droplet size of the miniemulsions were characterized as a function of the process variables. The presence of TiO2 particles within the droplets limited the ability of the process to reduce the droplet size although miniemulsion droplets in the size range of 150–200 nm were still obtained for subsequent polymerizations. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 4431–4440, 2000