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Imaging Channel Connectivity in Proton and Hydroxide Conducting Membranes for Fuel Cells
Proton exchange membrane (PEM) fuel cells offer an alternative as an efficient power source with low environmental impact. The heart of the fuel cell is the membrane, which conducts protons through an aqueous channel network. Proton transport is critically tied to the channel connectivity – disconnected channels do not participate in the overall electrochemical activity of the cell. Nafion, the current benchmark PEM, is a random statistical copolymer, characterized by a percolating network of cylindrical channels. In previous work, conductive-probe atomic force microscopy (cp-AFM) was used to image the conductance of Nafion. Although cp-AFM provides relevant information on which channels are connected, it provides no information on the disconnected “dead-end” channels at the surface. Electrostatic Force Microscopy (EFM) was used to analyze the structure and frequency of the “dead-end” channels. Applying a simple parallel plate model allowed us to assign differences in the EFM signal to particular channel shapes: connected cylindrical channels, “dead-end” cylinder channels, and bottle-neck channels. Anion exchange membranes (AEMs), which conduct hydroxide, have attracted recent interest due to improved reaction kinetics in alkaline media, yet suffer from low conductivity and easily degrade. To this end, our AFM methodology was applied to analyze the channel connectivity of a commercial FumaTech AEM was investigated in its hydroxide form over a wide range of relative humidity (RH) by combining phase imaging and cp-AFM. At high RH, our AFM data indicates significant surface swelling. Lastly, we investigated a class of phosphonium-containing diblock copolymer AEMs that formed ordered morphologies. Although channels were observed to be well-connected in the bulk by TEM, channels aligned parallel at the surface leading to many “dead-end” channels shown by EFM. Correlating these findings with bulk measurements could offer insight toward AEMs with improved conductivity and chemical stability
The phase-space density distribution of dark matter halos
High resolution N-body simulations have all but converged on a common
empirical form for the shape of the density profiles of halos, but the full
understanding of the underlying physics of halo formation has eluded them so
far. We investigate the formation and structure of dark matter halos using
analytical and semi-analytical techniques. Our halos are formed via an extended
secondary infall model (ESIM); they contain secondary perturbations and hence
random tangential and radial motions which affect the halo's evolution at it
undergoes shell-crossing and virialization. Even though the density profiles of
NFW and ESIM halos are different their phase-space density distributions are
the same: \rho/\sigma^3 ~ r^{-\alpha}, with \alpha=1.875 over ~3 decades in
radius. We use two approaches to try to explain this ``universal'' slope: (1)
The Jeans equation analysis yields many insights, however, does not answer why
\alpha=1.875. (2) The secondary infall model of the 1960's and 1970's,
augmented by ``thermal motions'' of particles does predict that halos should
have \alpha=1.875. However, this relies on assumptions of spherical symmetry
and slow accretion. While for ESIM halos these assumptions are justified, they
most certainly break down for simulated halos which forms hierarchically. We
speculate that our argument may apply to an ``on-average'' formation scenario
of halos within merger-driven numerical simulations, and thereby explain why
\alpha=1.875 for NFW halos. Thus, \rho/\sigma^3 ~ r^{-1.875} may be a generic
feature of violent relaxation.Comment: 4 pages, 1 fig. Proceedings of Science (SISSA), "Baryons in Dark
Matter Haloes", Novigrad, Croatia, 5-9 October 2004; editors: R.-J. Dettmar,
U. Klein, P. Salucci. The full paper is astro-ph/0506571 (with minus sign in
eq.(2.2) corrected
Prospectus, September 3, 2014
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Semi-analytical dark matter halos and the Jeans equation
Although N-body studies of dark matter halos show that the density profiles,
rho(r), are not simple power-laws, the quantity rho/sigma^3, where sigma(r) is
the velocity dispersion, is in fact a featureless power-law over ~3 decades in
radius. In the first part of the paper we demonstrate, using the semi-analytic
Extended Secondary Infall Model (ESIM), that the nearly scale-free nature of
rho/sigma^3 is a robust feature of virialized halos in equilibrium. By
examining the processes in common between numerical N-body and semi-analytic
approaches, we argue that the scale-free nature of rho/sigma^3 cannot be the
result of hierarchical merging, rather it must be an outcome of violent
relaxation. The empirical results of the first part of the paper motivate the
analytical work of the second part of the paper, where we use rho/sigma^3
proportional to r^{-alpha} as an additional constraint in the isotropic Jeans
equation of hydrostatic equilibrium. Our analysis shows that the constrained
Jeans equation has different types of solutions, and in particular, it admits a
unique ``periodic'' solution with alpha=1.9444. We derive the analytic
expression for this density profile, which asymptotes to inner and outer
profiles of rho ~ r^{-0.78}, and rho ~ r^{-3.44}, respectively.Comment: 37 pg, 14 fig. Accepted to ApJ: added two figures and extended
discussion. Note that an earlier related paper (conference proceedings)
astro-ph/0412442 has a mistake in eq.(2.2); the correct version is eq.(5) of
the present submissio
Effect of Selected Herbicides on Italian Ryegrass (Lolium multiflorum) and Returns from Hard Red Winter Wheat (Triticum aestivum)
Field experiments were conducted to evaluate the effects of selected herbicides on Italian ryegrass, forage production, and returns from hard red winter wheat grain. Herbicides included BAY FOE 5043 + metribuzin (4:1 w/w premix), BAY MKH 6562, chlorsulfuron, chlorsulfuron + metsulfuron (5:1 w/w premix), clodinafop, diclofop, MON 37560, pendimethalin, tralkoxydim, and triasulfuron. Italian ryegrass was controlled greater than 90 % by 27 of 39 treatments at one site, and by 20 of 39 treatments at a second site. Grain dockage was reduced by 38 and 36 treatments at the two sites, and grain yield was improved by 35 and 36 treatments. Forage yield was frequently decreased by controlling Italian ryegrass. No treatment decreased forage protein content. Gross returns from wheat grain were not improved over the untreated check by seven treatments at Site 1, and by one treatment at Site 2. resulted in a negative gross retum at Site 1. All treatments other than pendimethalin at 840 g/ha applied 3 days after seeding improved gross returns at both sites
The Effects of Endophyte-Infected KY 31 Tall Fescue Seed on Northern Bobwhite Reproduction
We assessed the impact of feeding an endophyte-free, endophyte-infected (Acremonium coenophialum), KY 31 tall fescue (Festuca arundinacea Schreb.) and a control diet on northern bobwhite (Colinus virginianus) reproduction. The birds consumed significantly more of the tall fescue diets compared to the control diet. There was no difference in female body weights at the end of the experiment. Male birds lost significantly more weight on the tall fescue diets than the control diet. The birds were in positive nutritional balances on all diets. There were no treatment effects on egg production, fertility, embryo mortality, hatch ability, or number of chicks per hen. Significantly more birds died eating endophyte-infected tall fescue seed compared to endophyte-free and control diets. These results indicate that tall fescue does not affect quail reproduction as indicated by previous authors. However, the endophyte does affect the weight gain of male birds and caused high mortality in these birds. We propose the alkaloids created by the endophyte caused a swelling of the cloaca which elicited a behavioral response in the birds causing them to become cannibalistic. These data support the idea that tall fescue does not provide quality nutritional habitat for northern bobwhite
Combinations of isoform-targeted histone deacetylase inhibitors and bryostatin analogues display remarkable potency to activate latent HIV without global T-cell activation
AbstractCurrent antiretroviral therapy (ART) for HIV/AIDS slows disease progression by reducing viral loads and increasing CD4 counts. Yet ART is not curative due to the persistence of CD4+ T-cell proviral reservoirs that chronically resupply active virus. Elimination of these reservoirs through the administration of synergistic combinations of latency reversing agents (LRAs), such as histone deacetylase (HDAC) inhibitors and protein kinase C (PKC) modulators, provides a promising strategy to reduce if not eradicate the viral reservoir. Here, we demonstrate that largazole and its analogues are isoform-targeted histone deacetylase inhibitors and potent LRAs. Significantly, these isoform-targeted HDAC inhibitors synergize with PKC modulators, namely bryostatin-1 analogues (bryologs). Implementation of this unprecedented LRA combination induces HIV-1 reactivation to unparalleled levels and avoids global T-cell activation within resting CD4+ T-cells.</jats:p
The Role of the Radial Orbit Instability in Dark Matter Halo Formation and Structure
For a decade, N-body simulations have revealed a nearly universal dark matter
density profile, which appears to be robust to changes in the overall density
of the universe and the underlying power spectrum. Despite its universality,
the physical origin of this profile has not yet been well understood.
Semi--analytic models by Barnes et al. (2005) have suggested that the density
structure of dark matter halos is determined by the onset of the radial orbit
instability (ROI). We have tested this hypothesis using N-body simulations of
collapsing dark matter halos with a variety of initial conditions. For
dynamically cold initial conditions, the resulting halo structures are triaxial
in shape, due to the mild aspect of the instability. We examine how variations
in initial velocity dispersion affect the onset of the instability, and find
that an isotropic velocity dispersion can suppress the ROI entirely, while a
purely radial dispersion does not. The quantity sigma^2/vc^2 is a criterion for
instability, where regions with sigma^2/vc^2 <~1 become triaxial due to the ROI
or other perturbations. We also find that the radial orbit instability sets a
scale length at which the velocity dispersion changes rapidly from isotropic to
radially anisotropic. This scale length is proportional to the radius at which
the density profile changes shape, as is the case in the semi--analytic models;
however, the coefficient of proportionality is different by a factor of ~2.5.
We conclude that the radial orbit instability is likely to be a key physical
mechanism responsible for the nearly universal profiles of simulated dark
matter halos.Comment: 13 pages, 12 figures, accepted to Ap
Evolution of the Dark Matter Phase-Space Density Distributions of LCDM Halos
We study the evolution of phase-space density during the hierarchical
structure formation of LCDM halos. We compute both a spherically-averaged
surrogate for phase-space density (Q) and the coarse-grained distribution
function f(x,v) for dark matter particles that lie within~2 virial radii of
four Milky-Way-sized dark matter halos. The estimated f(x,v) spans over four
decades at any radius. Dark matter particles that end up within two virial
radii of a Milky-Way-sized DM halo at have an approximately Gaussian
distribution in log(f) at early redshifts, but the distribution becomes
increasingly skewed at lower redshifts. The value corresponding to the peak of
the Gaussian decreases as the evolution progresses and is well described by a
power-law in (1+z). The highest values of f are found at the centers of dark
matter halos and subhalos, where f can be an order of magnitude higher than in
the center of the main halo. The power-law Q(r) profile likely reflects the
distribution of entropy (K = sigma^2/rho^{2/3} \propto r^{1.2}), which dark
matter acquires as it is accreted onto a growing halo. The estimated f(x, v),
on the other hand, exhibits a more complicated behavior. Although the median
coarse-grained phase-space density profile F(r) can be approximated by a
power-law in the inner regions of halos and at larger radii the profile
flattens significantly. This is because phase-space density averaged on small
scales is sensitive to the high-f material associated with surviving subhalos,
as well as relatively unmixed material (probably in streams) resulting from
disrupted subhalos, which contribute a sizable fraction of matter at large
radii. (ABRIDGED)Comment: Closely matches version accepted for publicatio
Rapid Detection and Quantification of Triacylglycerol by HPLC–ELSD in \u3ci\u3eChlamydomonas reinhardtii\u3c/i\u3e and \u3ci\u3eChlorella\u3c/i\u3e Strains
Triacylglycerol (TAG) analysis and quantification are commonly performed by first obtaining a purified TAG fraction from a total neutral lipid extract using thinlayer chromatography (TLC), and then analyzing the fatty
acid composition of the purified TAG fraction by gas chromatography (GC). This process is time-consuming, labor
intensive and is not suitable for analysis of small sample sizes or large numbers. A rapid and efficient method for monitoring oil accumulation in algae using high performance liquid chromatography for separation of all lipid classes combined with detection by evaporative light scattering (HPLC–ELSD) was developed and compared to the conventional TLC/GC method. TAG accumulation in two Chlamydomonas reinhardtii (21 gr and CC503) and three
Chlorella strains (UTEX 1230, CS01 and UTEX 2229) grown under conditions of nitrogen depletion was measured. The TAG levels were found to be 3–6 % DW (Chlamydomonas strains) and 7–12 % DW (Chlorella strains) respectively by both HPLC–ELSD and TLC/GC methods. HPLC–ELSD resolved the major lipid classes such as carotenoids, TAG, diacylglycerol (DAG), free fatty acids, phospholipids, and galactolipids in a 15-min run. Quantitation of TAG content was based on comparison to calibration curves of trihexadecanoin (16:0 TAG) and trioctadecadienoin (18:2 TAG) and showed linearity from 0.2 to 10 lg. Algal TAG levels \u3e0.5 lg/g DW were detectable by this method. Furthermore TAG content in Chlorella kessleri UTEX 2229 could be detected. TAG as well as DAG and TAG content were estimated at 1.6 % DWby HPLC–ELSD, while it was undetectable by TLC/GC method
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