Resistive Magnetohydrodynamic Equilibria in a Torus

It was recently demonstrated that static, resistive, magnetohydrodynamic equilibria, in the presence of spatially-uniform electrical conductivity, do not exist in a torus under a standard set of assumed symmetries and boundary conditions. The difficulty, which goes away in the ``periodic straight cylinder approximation,'' is associated with the necessarily non-vanishing character of the curl of the Lorentz force, j x B. Here, we ask if there exists a spatial profile of electrical conductivity that permits the existence of zero-flow, axisymmetric r esistive equilibria in a torus, and answer the question in the affirmative. However, the physical properties of the conductivity profile are unusual (the conductivity cannot be constant on a magnetic surface, for example) and whether such equilibria are to be considered physically possible remains an open question.Comment: 17 pages, 4 figure

Toroidal Vortices in Resistive Magnetohydrodynamic Equilibria

Resistive steady states in toroidal magnetohydrodynamics (MHD), where Ohm's law must be taken into account, differ considerably from ideal ones. Only for special (and probably unphysical) resistivity profiles can the Lorentz force, in the static force-balance equation, be expressed as the gradient of a scalar and thus cancel the gradient of a scalar pressure. In general, the Lorentz force has a curl directed so as to generate toroidal vorticity. Here, we calculate, for a collisional, highly viscous magnetofluid, the flows that are required for an axisymmetric toroidal steady state, assuming uniform scalar resistivity and viscosity. The flows originate from paired toroidal vortices (in what might be called a ``double smoke ring'' configuration), and are thought likely to be ubiquitous in the interior of toroidally driven magnetofluids of this type. The existence of such vortices is conjectured to characterize magnetofluids beyond the high-viscosity limit in which they are readily calculable.Comment: 17 pages, 4 figure

Noise kernel for a quantum field in Schwarzschild spacetime under the Gaussian approximation

A method is given to compute an approximation to the noise kernel, defined as the symmetrized connected 2-point function of the stress tensor, for the conformally invariant scalar field in any spacetime conformal to an ultra-static spacetime for the case in which the field is in a thermal state at an arbitrary temperature. The most useful applications of the method are flat space where the approximation is exact and Schwarzschild spacetime where the approximation is better than it is in most other spacetimes. The two points are assumed to be separated in a timelike or spacelike direction. The method involves the use of a Gaussian approximation which is of the same type as that used by Page to compute an approximate form of the stress tensor for this field in Schwarzschild spacetime. All components of the noise kernel have been computed exactly for hot flat space and one component is explicitly displayed. Several components have also been computed for Schwarzschild spacetime and again one component is explicitly displayed.Comment: 34 pages, no figures. Substantial revisions in Secs. I, IV, and V; minor revisions elsewhere; new results include computation of the exact noise kernel for hot flat space and an approximate computation of the noise kernel for a thermal state at an arbitrary temperature in Schwarzschild spacetime when the points are split in the time directio

Biodiversity loss underlies the dilution effect of biodiversity

The dilution effect predicts increasing biodiversity to reduce the risk of infection, but the generality of this effect remains unresolved. Because biodiversity loss generates predictable changes in host community competence, we hypothesised that biodiversity loss might drive the dilution effect. We tested this hypothesis by reanalysing four previously published meta-analyses that came to contradictory conclusions regarding generality of the dilution effect. In the context of biodiversity loss, our analyses revealed a unifying pattern: dilution effects were inconsistently observed for natural biodiversity gradients, but were commonly observed for biodiversity gradients generated by disturbances causing losses of biodiversity. Incorporating biodiversity loss into tests of generality of the dilution effect further indicated that scale-dependency may strengthen the dilution effect only when biodiversity gradients are driven by biodiversity loss. Together, these results help to resolve one of the most contentious issues in disease ecology: the generality of the dilution effect.Non peer reviewe

Development and Evaluation of a Connective Tissue Phantom Model for Subsurface Visualization of Cancers Requiring Wide Local Excision

Wide local excision (WLE) of tumors with negative margins remains a challenge because surgeons cannot directly visualize the mass. Fluorescence-guided surgery (FGS) may improve surgical accuracy; however, conventional methods with direct surface tumor visualization are not immediately applicable, and properties of tissues surrounding the cancer must be considered. We developed a phantom model for sarcoma resection with the near-infrared fluorophore IRDye 800CW and used it to iteratively define the properties of connective tissues that typically surround sarcoma tumors. We then tested the ability of a blinded surgeon to resect fluorescent tumor-simulating inclusions with ∼1-cm margins using predetermined target fluorescence intensities and a Solaris open-air fluorescence imaging system. In connective tissue-simulating phantoms, fluorescence intensity decreased with increasing blood concentration and increased with increasing intralipid concentrations. Fluorescent inclusions could be resolved at ≥1-cm depth in all inclusion concentrations and sizes tested. When inclusion depth was held constant, fluorescence intensity decreased with decreasing volume. Using targeted fluorescence intensities, a blinded surgeon was able to successfully excise inclusions with ∼1-cm margins from fat- and muscle-simulating phantoms with inclusion-to-background contrast ratios as low as 2∶1. Indirect, subsurface FGS is a promising tool for surgical resection of cancers requiring WLE

Deactivation of Sn-Beta zeolites caused by structural transformation of hydrophobic to hydrophilic micropores during aqueous-phase glucose isomerization

The structural changes underlying the deactivation of Sn-Beta zeolites under aqueous-phase reaction conditions at elevated temperatures (373 K) are investigated using spectroscopic characterization and site titration techniques together with turnover rates for glucose isomerization, a well-understood probe reaction for which changes in measured rates can be ascribed to specific changes in catalyst structure. In the case of hydrophobic, low-defect Sn-Beta zeolites (Sn-Beta-F), treatment in hot liquid water (373 K) for short times (3 h) to hot liquid water causes turnover rates to decrease and approach values characteristic of hydrophilic, defect-rich Sn-Beta zeolites (Sn-Beta-OH). In contrast, turnover rates on hydrophilic Sn-Beta-OH zeolites are insensitive to the duration of hot liquid water exposure prior to reaction. Activation and deactivation phenomena on Sn-Beta-F zeolites occur concomitantly with the formation of silanol defects (by ∼2–10×) with increasing durations (0–24 h) of hot water treatment, despite negligible differences in open and closed Sn site speciation as quantified ex situ by CD_3CN IR spectra. Mechanistic interpretations of these phenomena suggest that silanol groups present at low densities serve as binding sites for water molecules and clusters, which confer enthalpic stability to kinetically-relevant hydride-shift transition states and increase turnover rates, while silanol groups present in higher densities stabilize extended hydrogen-bonded water networks, which entropically destabilize kinetically-relevant transition states and decrease turnover rates. Intraporous voids within hydrophobic Sn-Beta-F zeolites become increasingly hydrophilic as silanol groups are formed by hydrolysis of framework siloxane bridges with increasing durations of water treatment, thereby decreasing aqueous-phase glucose isomerization turnover rates (per open Sn site). These findings suggest design strategies that suppress framework hydrolysis would attenuate the deactivation of Lewis acid zeolites in aqueous media

Deactivation of Sn-Beta zeolites caused by structural transformation of hydrophobic to hydrophilic micropores during aqueous-phase glucose isomerization

The structural changes underlying the deactivation of Sn-Beta zeolites under aqueous-phase reaction conditions at elevated temperatures (373 K) are investigated using spectroscopic characterization and site titration techniques together with turnover rates for glucose isomerization, a well-understood probe reaction for which changes in measured rates can be ascribed to specific changes in catalyst structure. In the case of hydrophobic, low-defect Sn-Beta zeolites (Sn-Beta-F), treatment in hot liquid water (373 K) for short times (3 h) to hot liquid water causes turnover rates to decrease and approach values characteristic of hydrophilic, defect-rich Sn-Beta zeolites (Sn-Beta-OH). In contrast, turnover rates on hydrophilic Sn-Beta-OH zeolites are insensitive to the duration of hot liquid water exposure prior to reaction. Activation and deactivation phenomena on Sn-Beta-F zeolites occur concomitantly with the formation of silanol defects (by ∼2–10×) with increasing durations (0–24 h) of hot water treatment, despite negligible differences in open and closed Sn site speciation as quantified ex situ by CD_3CN IR spectra. Mechanistic interpretations of these phenomena suggest that silanol groups present at low densities serve as binding sites for water molecules and clusters, which confer enthalpic stability to kinetically-relevant hydride-shift transition states and increase turnover rates, while silanol groups present in higher densities stabilize extended hydrogen-bonded water networks, which entropically destabilize kinetically-relevant transition states and decrease turnover rates. Intraporous voids within hydrophobic Sn-Beta-F zeolites become increasingly hydrophilic as silanol groups are formed by hydrolysis of framework siloxane bridges with increasing durations of water treatment, thereby decreasing aqueous-phase glucose isomerization turnover rates (per open Sn site). These findings suggest design strategies that suppress framework hydrolysis would attenuate the deactivation of Lewis acid zeolites in aqueous media

Application of Fluorescence-Guided Surgery to Subsurface Cancers Requiring Wide Local Excision: Literature Review and Novel Developments Toward Indirect Visualization.

The excision of tumors by wide local excision is challenging because the mass must be removed entirely without ever viewing it directly. Positive margin rates in sarcoma resection remain in the range of 20% to 35% and are associated with increased recurrence and decreased survival. Fluorescence-guided surgery (FGS) may improve surgical accuracy and has been utilized in other surgical specialties. ABY-029, an anti-epidermal growth factor receptor Affibody molecule covalently bound to the near-infrared fluorophore IRDye 800CW, is an excellent candidate for future FGS applications in sarcoma resection; however, conventional methods with direct surface tumor visualization are not immediately applicable. A novel technique involving imaging through a margin of normal tissue is needed. We review the past and present applications of FGS and present a novel concept of indirect FGS for visualizing tumor through a margin of normal tissue and aiding in excising the entire lesion as a single, complete mass with tumor-free margins

No-Boundary Thinking in Bioinformatics Research

Currently there are definitions from many agencies and research societies defining bioinformatics as deriving knowledge from computational analysis of large volumes of biological and biomedical data. Should this be the bioinformatics research focus? We will discuss this issue in this review article. We would like to promote the idea of supporting human-infrastructure (HI) with no-boundary thinking (NT) in bioinformatics (HINT)