Characterization of Catalyst Layer Ionomer Degradation in PEM Fuel Cells

The catalyst layer ionomer unavoidably gets involved in other components degradation processes since it is subjected to exposure to different operating effects, including the presence of the catalyst, catalyst support, and the porous nature of the electrode layer which includes 2-phase flow. PEMFC durability issues cannot be fully resolved without understanding the contribution of ionomer degradation in electrode to the performance decay in life time. However, catalyst layer ionomer is essentially chemically identical to the membrane ionomeric material, and is composed of low atomic number elements, making characterization difficult. In the present work, MEAs with different Nafion ionomer types: stabilized (S) and non-stablized (NS) ionomer in the electrode layer (Type I) and mixed membrane / ionomer MEAs (Type II) were designed to separate ionomer degradation from membrane degradation respectively. Stabilized and non stabilized ionomers were 5% Nafion ®ҏ solutions. The non-stabilized version is the typical Nafion chemical structure with carboxylic acid (-COOH) end groups; these end groups are thought to be a susceptible point of degradative peroxide attack Type I MEA fabrication follows the same procedure described as Ref Commercial Nafion ® 212 membrane was applied in Type I MEAs initially. The MEAs failed fast (< 200h) during the AST mainly due to membrane degradation. The short life time of the AST test provided limited time resolved ECSA loss data, with limited impedance characterization due to membrane thinning, which makes it difficult to unambiguously conclude much about the different ionomers' effect on the degradation process. Similar catalyst layer degradation analysis by XPS as Zhang et al The ratio of CF x /QRQ-fluorinated C decreased from 0.59 to 0.52 at the surface of NS electrodes, while that of S electrodes decreased from 0.53 to 0.49. The ratio of CF x to total carbon decreased from 0.373 to 0.345 and 0.346 to 0.331 for NS and S electrodes respectively. The higher decrease in the NS electrodes probably was due to the longer life time (~240h) compared to that of S electrodes (~192 h). The biggest change was observed for the ratio of IOXRULQDWHG &JUDSKLF LQ 16 HOHFWURGHV IURP WR 3.25, ~ 42% decrease, while the drop of S electrodes was from 3.88 to 3.63, only ~7%. This difference is not consistent with the testing time and longer durability testing may be required for better understanding of this difference. For a longer membrane life time during AST testing to obtain better time resolved analysis, MEAs were made using stabilized Nafion ® XL 100 membrane supplied by Ion Power. The MEA durability during the OCV AST test was extended over 400hr

Lattice determination of the critical point of QCD at finite T and \mu

Based on universal arguments it is believed that there is a critical point (E) in QCD on the temperature (T) versus chemical potential (\mu) plane, which is of extreme importance for heavy-ion experiments. Using finite size scaling and a recently proposed lattice method to study QCD at finite \mu we determine the location of E in QCD with n_f=2+1 dynamical staggered quarks with semi-realistic masses on $L_t=4$ lattices. Our result is T_E=160 \pm 3.5 MeV and \mu_E= 725 \pm 35 MeV. For the critical temperature at \mu=0 we obtained T_c=172 \pm 3 MeV.Comment: misprints corrected, version to appear in JHE

Quantum heat transfer through an atomic wire

We studied the phononic heat transfer through an atomic dielectric wire with both infinite and finite lengths by using a model Hamiltonian approach. At low temperature under ballistic transport, the thermal conductance contributed by each phonon branch of a uniform and harmonic chain cannot exceed the well-known value which depends linearly on temperature but is material independent. We predict that this ballistic thermal conductance will exhibit stepwise behavior as a function of temperature. By performing numerical calculations on a more realistic system, where a small atomic chain is placed between two reservoirs, we also found resonance modes, which should also lead to the stepwise behavior in the thermal conductance.Comment: 14 pages, 2 separate figure

Open-closed duality and Double Scaling

Nonperturbative terms in the free energy of Chern-Simons gauge theory play a key role in its duality to the closed topological string. We show that these terms are reproduced by performing a double scaling limit near the point where the perturbation expansion diverges. This leads to a derivation of closed string theory from this large-N gauge theory along the lines of noncritical string theories. We comment on the possible relevance of this observation to the derivation of superpotentials of asymptotically free gauge theories and its relation to infrared renormalons.Comment: 10 pages, LaTe

Chiral bosonization for non-commutative fields

A model of chiral bosons on a non-commutative field space is constructed and new generalized bosonization (fermionization) rules for these fields are given. The conformal structure of the theory is characterized by a level of the Kac-Moody algebra equal to $(1+ \theta^2)$ where $\theta$ is the non-commutativity parameter and chiral bosons living in a non-commutative fields space are described by a rational conformal field theory with the central charge of the Virasoro algebra equal to 1. The non-commutative chiral bosons are shown to correspond to a free fermion moving with a speed equal to $c^{\prime} = c \sqrt{1+\theta^2}$ where $c$ is the speed of light. Lorentz invariance remains intact if $c$ is rescaled by $c \to c^{\prime}$. The dispersion relation for bosons and fermions, in this case, is given by $\omega = c^{\prime} | k|$.Comment: 16 pages, JHEP style, version published in JHE

R Symmetries in the Landscape

In the landscape, states with $R$ symmetries at the classical level form a distinct branch, with a potentially interesting phenomenology. Some preliminary analyses suggested that the population of these states would be significantly suppressed. We survey orientifolds of IIB theories compactified on Calabi-Yau spaces based on vanishing polynomials in weighted projective spaces, and find that the suppression is quite substantial. On the other hand, we find that a $Z_2$ R-parity is a common feature in the landscape. We discuss whether the cosmological constant and proton decay or cosmology might select the low energy branch. We include also some remarks on split supersymmetry.Comment: 13 page

Uplifting and Inflation with D3 Branes

Back-reaction effects can modify the dynamics of mobile D3 branes moving within type IIB vacua, in a way which has recently become calculable. We identify some of the ways these effects can alter inflationary scenarios, with the following three results: (1) By examining how the forces on the brane due to moduli-stabilizing interactions modify the angular motion of D3 branes moving in Klebanov-Strassler type throats, we show how previous slow-roll analyses can remain unchanged for some brane trajectories, while being modified for other trajectories. These forces cause the D3 brane to sink to the bottom of the throat except in a narrow region close to the D7 brane, and do not ameliorate the \eta-problem of slow roll inflation in these throats; (2) We argue that a recently-proposed back-reaction on the dilaton field can be used to provide an alternative way of uplifting these compactifications to Minkowski or De Sitter vacua, without the need for a supersymmetry-breaking anti-D3 brane; and (3) by including also the D-term forces which arise when supersymmetry-breaking fluxes are included on D7 branes we identify the 4D supergravity interactions which capture the dynamics of D3 motion in D3/D7 inflationary scenarios. The form of these potentials sheds some light on recent discussions of how symmetries constrain D term interactions in the low-energy theory.Comment: JHEP.cls, 35 pages, 3 .eps figure

Ecosystem decay of Amazonian forest fragments: a 22-year investigation

P E R M A N E N T G E N E T I C R E S O U R C E S N O T E 1265 Cell/Tissue Genomic DNA extraction kit (TianGen) and digested with MboI (Takara). Fragments of 400-1000bp were collected by TianGen Gel DNA Extraction Kit. Doublestranded MboI adapters, Linker A (5′-GATCGTCGACGG-TACCGAATTCT-3′) and Linker B (3′-CAGCTGCCAT-GGCTTAAGAACTG-5′) (250 pmol, excess) were ligated to DNA fragments with T4 DNA ligase (Takara) at 16°C overnight. Excess adapters were removed by washing on an Ultrafree column (Pall). DNA fragments were amplified 10 cycles with linker B and purified. The products were denatured and hybridized to biotin-labelled (CA) 12 , (GA) 12 , (ACA) 8 , (AGA) 8 , (GACA) 6 and (GATA) 6 oligo-nucleotides (mixed in advance at the ratio of 3:1:1:1:2:2) in 0.5X SSC at 68°C for 1 h. DNA fragments bound to these probes were captured with Promega Streptavidin MagneSphere® Paramagnetic Particles and eluted by DNase-free water after being washed four times in 0.1× SSC at room temperature, and then amplified for 10 cycles with Linker B. The enriched fragments were ligated to pGEM-T-easy vector (Promega) at 4°C overnight, and then transformed into Promega high-efficiency competent Escherichia coli cells (Dh5α), which were cultured on Luria-Bertani solid medium containing 100mg/mL ampicillin. One-hundred and ninety-nine white positive clones were picked and sequenced with the T7 primer on ABI 3730xl DNA analysers at the Shanghai Sangon Biological Engineering Technology & Services Co., Ltd. Sequences were screened for microsatellites containing at least six di-, five tri-, five tetra-, four penta-, three hexa-and three octa-nucleotide repeats using the software misa (http:/ /pgrc.ipk-gatersleben.de/misa/). One-hundred and twenty-six (excluding five duplicates) microsatellite-containing sequences were identified and consisted of 28.1% di-, 7.8% tri-, 22.7% tetra-, 6.3% penta-, 1.6% hexa-, 4.7% octa-nucleotide and 35.2% compound microsatellite repeats. Fifty-seven good sequences with sufficient flanking regions were selected for primer design with Primer 3 (http:/ /biotools.umassmed.edu/bioapps/ primer3_www.cgi). An M13 (-21) universal leading sequence (18bp) 5′-TGTAAAACGACGGCCAGT was added to the 5′ end of each forward primer listed in Observed (H O ) and expected (H E ) heterozygosities were calculated with arlequin 3.0 Three primer pairs RUSS33, RUSS47 and RUSS57 amplified more than two fragments per individual, suggesting that they belong to duplicated loci. RUSS33 amplified three to six fragments per individual with well-defined patterns. It can be explained by the amplification of a tandem mini-satellite repeat in a model of Fprimer-25bp-Fprimer75bp-Fprimer-(18bp)n-Rprimer. RUSS47 (and RUSS45, not presented here) had clusters of fragments that differed by 8bp, with a cluster-to-cluster distance of 145bp: Fprimer-[(8bp)n]N-Rprimer-145bp-Rprimer-145-Rprimer. RUSS57 amplified one monomorphic locus at 152 bp and another polymorphic locus. This is the first time that microsatellite markers have been developed for S. solidissima. Most of the markers developed here are highly polymorphic and in HWE. They should be useful in genetic studies on this important model and fishery species. Acknowledgemen

Warped Tachyonic Inflation in Type IIB Flux Compactifications and the Open-String Completeness Conjecture

We consider a cosmological scenario within the KKLT framework for moduli stabilization in string theory. The universal open string tachyon of decaying non-BPS D-brane configurations is proposed to drive eternal topological inflation. Flux-induced `warping' can provide the small slow-roll parameters needed for successful inflation. Constraints on the parameter space leading to sufficient number of e-folds, exit from inflation, density perturbations and stabilization of the Kahler modulus are investigated. The conditions are difficult to satisfy in Klebanov-Strassler throats but can be satisfied in T^3 fibrations and other generic Calabi-Yau manifolds. This requires large volume and magnetic fluxes on the D-brane. The end of inflation may or may not lead to cosmic strings depending on the original non-BPS configuration. A careful investigation of initial conditions leading to a phenomenologically viable model for inflation is carried out. The initial conditions are chosen on the basis of Sen's open string completeness conjecture. We find time symmetrical bounce solutions without initial singularities for k=1 FRW models which are correlated with an inflationary period. Singular big-bang/big-crunch solutions also exist but do not lead to inflation. There is an intriguing correlation between having an inflationary universe in 4 dimensions and 6 compact dimensions or a big-crunch singularity and decompactification.Comment: 43 pages, 9 figures. v3: Typos correcte

Generating Optimal Topologies in Structural Design Using a Homogenization Method,"

This paper proposes a basic method for designing light and rigid structures that have a maximum natural frequency for a designated mode. A design variable "density," related to the material properties of a three-dimensional solid element, is introduced into the finite element method ( FEM ). Thus, a structure is expressed as a density distribution inside its design domain, and the optimal structure is obtained by searching for the most suitable such distribution