Spectroscopic exploration of conformal heterogeneity in an amorphous polyphenylene-vinylene derivative

Photoluminescence and Resonant Raman spectroscopy were performed on the conjugated polymer MDMO-PPV (Poly[2-methoxy-5-(3\u2032,7\u2032-dimethyloctyloxy)-1,4-phenylenevinylene]), both in its pure form and in blends with electron acceptors, in order to understand how conformations are affected by interactions with neighboring polymer chains and small molecules. Thermal and solvent annealing are used to tune these interactions, and the resulting changes in the electronic structure and processes of the polymer are inferred through interpretation of spectroscopic signatures. Optical absorption and emission spectra were measured for MDMO-PPV in several solvents, in thin films processed under various conditions, and in nanoparticle form. These different environments and processing conditions can encourage the polymer to coil (bad solvent), extend (good solvent), strongly interact with neighboring molecules (nanoparticles), or interact weakly (dilute solution), and feature the polymer in a more glassy (spin-cast) or more ordered (thermally annealed) state. We can then interrogate a defind conformation of the polymer, and correlate the spectroscopic and structural changes. Analysis of the lineshape parameters of emission and absorption spectra reveal a relationship between the intensity and spacing of vibronic sidebands, and planarity of the conjugated backbone. Planarity is extremely important in conjugated polymers, as it defines the extent of electron delocalization and has serious consequences on every electronic process in the polymer. As well, solvatochromic shifts in the emission spectrum reveal information about the relative polarities of the ground and excited states. Resonant Raman spectroscopy was used to identify the vibrational modes coupled to electronic excitation, and mode-specific displacements were estimated by modeling the photoluminescence spectra using a time-dependent quantum mechanical simulation to reproduce experimental observations. Coupling of electronic processes to vibrational modes in organic photovoltaics both helps and hinders function. It broadens absorption and emission spectra, increasing the ability to absorb light and transport energy, but can provide a structural barrier to some electronic processes. However, here we use it to investigate changes in the planarity of a conjugated polymer. Spectra of polymer/C60 blend films show increased displacement of a symmetry-forbidden out-of-plane vibrational mode with increasing fullerene doping, indicating a loss of planarity. We also use photoluminescence spectroscopy to confirm this, as the electronic origin of emission blue-shifts with fullerene loading which indicates decreased conjugation length and thus molecular planarity. Ground state charge transfer complexes of MDMO-PPV and several electron acceptors were studied using linear absorption and Resonant Raman spectroscopy to better understand the nuclear rearrangements that the polymer undergoes upon loss of an electron. Any bonds displaced upon the movement of charge will make it more difficult to move and separate charge in the material, processes essential for the function of a solar cell. Thin films of blended MDMO-PPV:DDQ, MDMO-PPV:TCNQ, and MDMO-PPV:PCBM blends show several orders of Raman overtones. We use the intensity of these Resonant Raman overtones and the framework of time-dependant spectroscopic theory, to estimate vibrational-mode displacements and the reorganizational barriers to charge transfer and transport

Chiral Perturbation Theory for phi -> rho gamma gamma and phi -> omega gamma gamma

We predict differential decay distributions for phi->rho gamma gamma and phi -> omega gamma gamma using chiral perturbation theory. We also consider the isospin violating decay phi -> omega pi^0. Experimental information on these decays can be used to determine couplings in the heavy vector meson chiral Lagrangian.Comment: It was shown by P. Ko et al., hep-ph/9510205 (Phys. Lett. B366 (1996) 287), that there is a etaprime pole contribution that dominates over what we calculate

Transcript Profiling in Host–Pathogen Interactions

Using genomic technologies, it is now possible to address research hypotheses in the context of entire developmental or biochemical pathways, gene networks, and chromosomal location of relevant genes and their inferred evolutionary history. Through a range of platforms, researchers can survey an entire transcriptome under a variety of experimental and field conditions. Interpretation of such data has led to new insights and revealed previously undescribed phenomena. In the area of plant-pathogen interactions, transcript profiling has provided unparalleled perception into the mechanisms underlying gene-for-gene resistance and basal defense, host vs nonhost resistance, biotrophy vs necrotrophy, and pathogenicity of vascular vs nonvascular pathogens, among many others. In this way, genomic technologies have facilitated a system-wide approach to unifying themes and unique features in the interactions of hosts and pathogens

Strong Decays of Excited Heavy Mesons In Chiral Perturbation Theory

We construct an effective Lagrangian describing the interaction of soft pions and kaons with mesons containing a heavy quark and light degrees of freedom in an orbital $p$ wave. The formalism is easily extended to heavy mesons and baryons in arbitrary excited states. We calculate the leading contributions to the strong decays \dtwo\to\d\pi, \dtwo\to\dstar\pi and \done\to\dstar\pi. We confirm the relations between the rates previously obtained by Isgur and Wise using heavy quark symmetry, and find that the absolute widths are consistent with na\"\i ve power counting. We also estimate the branching ratios for the two pion decays \dtwo\to\dstar\pi\pi, \done\to\dstar\pi\pi and \done\to\d\pi\pi, which are dominated by pole graphs. Our predictions depend on the masses and widths of the as yet unseen scalar-pseudovector $p$-wave doublet. Heavy quark spin symmetry predicts \Gamma(\dtwo\to\dstar\pi\pi): \Gamma(\done\to\dstar\pi\pi):\Gamma(\done\to\d\pi\pi)=3:1:2, but this relation is badly violated in practice because $1/M$ effects arising purely from kinematics are large.Comment: (14 pages, 2 figures available from the authors, harvmac.tex required), SLAC-PUB-5812, UCSD/PTH 92-1

Heavy Quark Fragmentation to Baryons Containing Two Heavy Quarks

We discuss the fragmentation of a heavy quark to a baryon containing two heavy quarks of mass $m_Q\gg\Lambda_{\rm QCD}$. In this limit the heavy quarks first combine perturbatively into a compact diquark with a radius small compared to $1/\Lambda_{\rm QCD}$, which interacts with the light hadronic degrees of freedom exactly as does a heavy antiquark. The subsequent evolution of this $QQ$ diquark to a $QQq$ baryon is identical to the fragmentation of a heavy antiquark to a meson. We apply this analysis to the production of baryons of the form $ccq$, $bbq$, and $bcq$.Comment: 9 pages, 1 figure included, uses harvmac.tex and epsf.tex, UCSD/PTH 93-11, CALT-68-1868, SLAC-PUB-622

Analyticity and the Isgur-Wise Function

We reconsider the recent derivation by de Rafael and Taron of bounds on the slope of the Isgur-Wise function. We argue that one must be careful to include cuts starting below the heavy meson pair production threshold, arising from heavy quark-antiquark bound states, and that if such cuts are properly accounted for then no constraints may be derived.Comment: 8 pages, uses harvmac, SLAC-PUB-5956, UCSD/PTH 92-35, CALT-68-183

PTEN protein phosphatase activity is not required for tumour suppression in the mouse prostate

Loss PTEN function is one of the most common events driving aggressive prostate cancers and biochemically, PTEN is a lipid phosphatase which opposes the activation of the oncogenic PI3K-AKT signalling network. However, PTEN also has additional potential mechanisms of action, including protein phosphatase activity. Using a mutant enzyme, PTEN Y138L, which selectively lacks protein phosphatase activity, we characterised genetically modified mice lacking either the full function of PTEN in the prostate gland or only lacking protein phosphatase activity. The phenotypes of mice carrying a single allele of either wild-type Pten or Pten(Y138L) in the prostate were similar, with common prostatic intraepithelial neoplasia (PIN) and similar gene expression profiles. However, the latter group, lacking PTEN protein phosphatase activity additionally showed lymphocyte infiltration around PIN and an increased immune cell gene expression signature. Prostate adenocarcinoma, elevated proliferation and AKT activation were only frequently observed when PTEN was fully deleted. We also identify a common gene expression signature of PTEN loss conserved in other studies (including Nkx3.1, Tnf and Cd44). We provide further insight into tumour development in the prostate driven by loss of PTEN function and show that PTEN protein phosphatase activity is not required for tumour suppression

Progress on Gust Load Alleviation Wind Tunnel Experiment and Aeroservoelastic Model Validation for a Flexible Wing with Variable Camber Continuous Trailing Edge Flap System

This paper discusses a wind tunnel experiment of active gust load alleviation of a flexible wing which took place at University of Washington (UW) in 2019. The experiment performed under a NASA SBIR contract with Scientific Systems Company, Inc (SSCI). The objective of the experiment is to demonstrate active controls of the Variable Camber Continuous Trailing Edge Flap (VCCTEF) system for gust load alleviation and real-time drag optimization. The wind tunnel model is a 8.2% sub-scale Common Research Model (CRM) wing. The wing structure is designed to provide a substantial degree of flexibility to represent that of a modern high-aspect ratio wing. Eight active control surfaces are employed in the VCCTEF. A new gust generator system was designed and installed by UW under a sub-contract with SSCI. The first test entry started in July 2019 and ended in September 2019. During this test entry, many significant issues were found with the hardware and software. The significant issues with the servos prevented the test objective from being completed. A follow-up second test entry in 2020 is being planned. The wing system is being repaired by SSCI. This paper reports on the progress of this experimental effort and the aeroservoelastic (ASE) model validation which was conducted during the test entry

Preparing Youths for Careers in Agriculture Through State Crop Scouting Competitions

State crop scouting competitions (CSCs) promote agriculture by introducing youths in Indiana, Iowa, and Nebraska to various agricultural disciplines while focusing on integrated pest management (IPM). High school students compete as teams to address crop management issues at various stations. Each station is led by university representatives. Two surveys were conducted to determine the impacts of the competition on students. Results indicate that students improved in skills key to future careers and that they learned about aspects of IPM. CSCs can serve as models for states that wish to improve ties between university-based Extension specialists and state high schools