Multiplicative Operator Splittings in Nonlinear Diffusion: From Spatial Splitting to Multiple Timesteps

Operator splitting is a powerful concept used in many diversed fields of applied mathematics for the design of effective numerical schemes. Following the success of the additive operator splitting (AOS) in performing an efficient nonlinear diffusion filtering on digital images, we analyze the possibility of using multiplicative operator splittings to process images from different perspectives.We start by examining the potential of using fractional step methods to design a multiplicative operator splitting as an alternative to AOS schemes. By means of a Strang splitting, we attempt to use numerical schemes that are known to be more accurate in linear diffusion processes and apply them on images. Initially we implement the Crank-Nicolson and DuFort-Frankel schemes to diffuse noisy signals in one dimension and devise a simple extrapolation that enables the Crank-Nicolson to be used with high accuracy on these signals. We then combine the Crank-Nicolson in 1D with various multiplicative operator splittings to process images. Based on these ideas we obtain some interesting results. However, from the practical standpoint, due to the computational expenses associated with these schemes and the questionable benefits in applying them to perform nonlinear diffusion filtering when using long timesteps, we conclude that AOS schemes are simple and efficient compared to these alternatives.We then examine the potential utility of using multiple timestep methods combined with AOS schemes, as means to expedite the diffusion process. These methods were developed for molecular dynamics applications and are used efficiently in biomolecular simulations. The idea is to split the forces exerted on atoms into different classes according to their behavior in time, and assign longer timesteps to nonlocal, slowly-varying forces such as the Coulomb and van der Waals interactions, whereas the local forces like bond and angle are treated with smaller timesteps. Multiple timestep integrators can be derived from the Trotter factorization, a decomposition that bears a strong resemblance to a Strang splitting. Both formulations decompose the time propagator into trilateral products to construct multiplicative operator splittings which are second order in time, with the possibility of extending the factorization to higher order expansions. While a Strang splitting is a decomposition across spatial dimensions, where each dimension is subsequently treated with a fractional step, the multiple timestep method is a decomposition across scales. Thus, multiple timestep methods are a realization of the multiplicative operator splitting idea. For certain nonlinear diffusion coefficients with favorable properties, we show that a simple multiple timestep method can improve the diffusion process.     

Directionality from anisotropic phonon production in solid state dark matter detection

We present results from computer simulations of the events immediately following the scattering of a dark matter particle off a nucleus in a crystal detector. Our simulations show that with NaF as the target, the recoil produces solitary waves that decay slowly, resulting in a narrow wake of phonons. The phonon wake allows a determination of direction of the nuclear recoil.     

Reducing the Health and Digital Divides: A Model for Using Community‐Based Participatory Research Approach to E‐Health Interventions in Low‐Income Hispanic Communities

Low‐income Hispanics are the most digitally underserved population in the U.S. This article examines the potential of community‐based participatory research approach to e‐health to decrease the disparities in access to technology and health information in low‐income Hispanic communities. To demonstrate this framework, we describe the process of designing a community‐based e‐health intervention to increase knowledge and parental self‐efficacy in coping with young children's mental health problems including mental health service utilization. Our model incorporates utilizing promotoras de salud (lay community health educators) and community media principles to create the content of e‐health interventions and train community members in using the technology. This case study illustrates the processes involved in using this approach, barriers for participatory e‐health interventions in bridging the Digital Divide, and lessons learned.     

Orthographic Structure Versus Morphological Structure: Principles of Lexical Organization in a Given Language.

Most models of visual word recognition in alphabetic orthographies assume that words are lexically organized according to orthographic similarity. Support for this is provided by form-priming experiments that demonstrate robust facilitation when primes and targets share similar sequences of letters. The authors examined form-orthographic priming effects in Hebrew, Arabic, and English. Hebrew and Arabic have an alphabetic writing system but a Semitic morphological structure. Hebrew morphemic units are composed of noncontiguous phonemic (and letter) sequences in a given word. Results demonstrate that form-priming effects in Hebrew or Arabic are unreliable, whereas morphological priming effects with minimal letter overlap are robust. Hebrew bilingual subjects, by contrast, showed robust form-priming effects with English material, suggesting that Semitic words are lexically organized by morphological rather than orthographic principles. The authors conclude that morphology can constrain lexical organization even in alphabetic orthographies and that visual processing of words is first determined by morphological characteristics. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Myo-Inositol Limits Kainic Acid-Induced Epileptogenesis in Rats

Epilepsy is a severe neurological disease characterized by spontaneous recurrent seizures (SRS). A complex pathophysiological process referred to as epileptogenesis transforms a normal brain into an epileptic one. Prevention of epileptogenesis is a subject of intensive research. Currently, there are no clinically approved drugs that can act as preventive medication. Our previous studies have revealed highly promising antiepileptogenic properties of a compound–myo-inositol (MI) and the present research broadens previous results and demonstrates the long-term disease-modifying effect of this drug, as well as the amelioration of cognitive comorbidities. For the first time, we show that long-term treatment with MI: (i) decreases the frequency and duration of electrographic SRS in the hippocampus; (ii) has an ameliorating effect on spatial learning and memory deficit associated with epileptogenesis, and (iii) attenuates cell loss in the hippocampus. MI treatment also alters the expression of the glial fibrillary acidic protein, LRRC8A subunit of volume-regulated anion channels, and protein tyrosine phosphatase receptor type R, all expected to counteract the epileptogenesis. All these effects are still present even 4 weeks after MI treatment ceased. This suggests that MI may exert multiple actions on various epileptogenesis-associated changes in the brain and, therefore, could be considered as a candidate target for prevention of epileptogenesis.     

Bias against research on gender bias

The bias against women in academia is a documented phenomenon that has had detrimental consequences, not only for women, but also for the quality of science. First, gender bias in academia affects female scientists, resulting in their underrepresentation in academic institutions, particularly in higher ranks. The second type of gender bias in science relates to some findings applying only to male participants, which produces biased knowledge. Here, we identify a third potentially powerful source of gender bias in academia: the bias against research on gender bias. In a bibliometric investigation covering a broad range of social sciences, we analyzed published articles on gender bias and race bias and established that articles on gender bias are funded less often and published in journals with a lower Impact Factor than articles on comparable instances of social discrimination. This result suggests the possibility of an underappreciation of the phenomenon of gender bias and related research within the academic community. Addressing this meta-bias is crucial for the further examination of gender inequality, which severely affects many women across the world.     

Molecular Formation upon Ionization of van der Waals Clusters and Implication to Astrochemistry

The presence and formation of a large variety of organic molecules in the interstellar medium is evident from both astronomical data of absorption and emission bands at different regions of the spectrum. Specifically, polycyclic aromatic hydrocarbons (PAHs) are ubiquitous in the interstellar medium (ISM). The mechanism for their formation in ISM‘s low temperature environment is, as of yet, a mystery nonetheless. Understanding the mechanism of formation of complex molecules such as PAHs and nitrogen-based PAHs (PANH) in the ISM is a long-standing challenge which has been drawing a growing attention for the past several decades. In this review we wish to emphasize two things: Firstly, the essential role quantum chemistry can play in the study of astrochemical reactions. Secondly, we wish to demonstrate that said variety of possibilities for chemical reaction, starting upon ionization of van der Waals clusters. The potential for different chemical reactions to occur within a cluster environment arises from the fact that such processes can take place at low temperatures as the systems pose large amounts of energy upon ionization. Moreover, the spectator molecules in the cluster can provide a dissipation route for energy by detachment from the cluster, thus the system can stabilize efficiently even at low densities. The spectator molecules can also change the potential energy surface, by which it will pose a catalytic effect for certain reactions. We will demonstrate this by presenting Ab Initio Molecular Dynamic results on ionization of small acetylene clusters.     

Investigation of the inhibitory effect of silica on the degradation of 1,1,1-trichloroethane by granular iron

Although iron-based permeable reactive barriers are gaining importance for treating groundwater contaminants, little is currently known about the effect of cosolutes on barrier longevity. Because of their corrosion inhibiting properties, dissolved silica species are of particular concern. This research investigates the effect of silica on the reduction of 1,1,1-trichloroethane by granular iron as a function of added silica concentration, pH, and duration of iron exposure to dissolved silica. Batch studies reveal that, at pH 8.5 and above, added silica concentrations as low as 0.17 mM cause a 30% reduction in the reactivity of iron. At higher silica concentrations, reactivity decreases by 65-75%. The inhibitory effect is greater at higher pH: 0.83 mM silica has no apparent adverse effect at pH 7.5, but leads to a 46% decrease in reaction rate at pH 8 and 90% at pH 9. This corresponds to observed trends in silica adsorption onto iron, which is low at pH 7.3 but increases at higher pH. Extending the duration of iron exposure to silica solutions also leads to a more pronounced inhibitory effect. This is in good agreement with the increase in silica coverage on the iron surface as revealed by X-ray photoelectron spectroscopy.     

Role of temperature and Suwannee River natural organic matter on inactivation kinetics of rotavirus and bacteriophage MS2 by solar irradiation

Although the sunlight-mediated inactivation of viruses has been recognized as an important process that controls surface water quality, the mechanisms of virus inactivation by sunlight are not yet clearly understood. We investigated the synergistic role of temperature and Suwannee River natural organic matter (SRNOM), an exogenous sensitizer, for sunlight-mediated inactivation of porcine rotavirus and MS2 bacteriophage. Upon irradiation by a full spectrum of simulated sunlight in the absence of SRNOM and in the temperature range of 14-42 °C, high inactivation rate constants, k(obs), of MS2 (k(obs) ≤ 3.8 h(-1) or 1-log(10) over 0.6 h) and rotavirus (k(obs) ≤ 11.8 h(-1) or ～1-log(10) over 0.2 h) were measured. A weak temperature (14-42 °C) dependence of k(obs) values was observed for both viruses irradiated by the full sunlight spectrum. Under the same irradiation condition, the presence of SRNOM reduced the inactivation of both viruses due to attenuation of lower wavelengths of the simulated sunlight. For rotavirus and MS2 solutions irradiated by only UVA and visible light in the absence of SRNOM, inactivation kinetics were slow (k(obs) < 0.3 h(-1) or <1-log(10) unit reduction over 7 h) and temperature-independent for the range considered. Conversely, under UVA and visible light irradiation and in the presence of SRNOM, temperature-dependent inactivation of MS2 was observed. For rotavirus, the SRNOM-mediated exogenous inactivation was only important at temperatures >33 °C, with low rotavirus k(obs) values (k(obs) ≈ 0.2 h(-1); 1-log(10) unit reduction over 12 h) for the temperature range of 14-33 °C. These k(obs) values increased to 0.5 h(-1) at 43 °C and 1.5 h(-1) (1-log(10) reduction over 1.6 h) at 50 °C. While SRNOM-mediated exogenous inactivation of MS2 was triggered by singlet oxygen, the presence of hydrogen peroxide was important for rotavirus inactivation in the 40-50 °C range.