Experimental analysis of v-belt tensile loads

An experimental investigation was conducted to determine the magnitude of v-belt stresses in automotive drive situations. A constant tension belt test apparatus was designed and fabricated using a variable speed cradled D.C. motor for power and two automotive alternators for absorption. Free span stresses on the dynamic torque loaded belt drive were determined from the equations governing a pivoted drive system. Centrifugal stress was determined by a theoretical analysis of belt motion. Bending stresses were obtained from a static test employing strain gages mounted on the top of belts with exposed cord layers. The variation in load stress around the pulleys in a dynamic torque loaded drive was to be determined by taking time synchronized photographs of a marked belt section and measuring strain from enlarged photographic negatives. The time synchronization of high speed close-up photography was accomplished during this study, but the capability of making measurements from photographic data was not perfected. Insight gained from this work led to the advancement of ideas which may allow photographic determination of belt strain in a future study. A magnetic pickoff and timer system also failed to indicate the magnitude of dynamic belt strains. In order to complete the present analysis, the Hornung analytical solution for tensions around torque loaded pulleys was employed in a digital simulation program. A matrix of computer runs was made for the range of drive parameters studied. Finally, power losses in belt drives were experimentally obtained in order to determine the design acceptability of the drive situations tested. Superposition of bending, centrifugal and load tensions led to the conclusion that bending stress is by far the largest stress factor to be considered in automotive v-belt drives. The fact that small changes in load stress cause noticeable changes in belt fatigue life must be attributed to the creep, slip, and heat generation phenomena which accompany torque transmission --Abstract, pages ii-iii

Scale setting for Nf=3+1N_f=3+1 QCD

We present the scale setting for a new set of gauge configurations generated with $N_f=3+1$ Wilson quarks with a non-perturbatively determined clover coefficient in a massive O($a$) improvement scheme. The three light quarks are degenerate, with the sum of their masses being equal to its value in nature and the charm quark has its physical mass. We use open boundary conditions in time direction to avoid the problem of topological freezing at small lattice spacings and twisted-mass reweighting for improved stability of the simulations. The decoupling of charm at low energy allows us to set the scale by measuring the value of the low-energy quantity $t_0^\star/a^2$, which is the flow scale $t_0$ at our mass point, and comparing it to an $N_f=2+1$ result in physical units. We present the details of the algorithmic setup and tuning procedure and give the bare parameters of ensembles with two lattice spacings a=0.054 fm and a=0.043 fm. We discuss finite volume effects and lattice artifacts and present physical results for the charmonium spectrum. In particular the hyperfine splitting between the $\eta_c$ and $J/\psi$ mesons agrees very well with its physical value.Comment: 25 pages, 9 figures. Version accepted for publication in the European Physical Journal

Validation and characterisation of a novel peptide that binds monomeric and aggregated beta-amyloid and inhibits the formation of neurotoxic oligomers

Although the formation of β-amyloid (Aβ) deposits in the brain is a hallmark of Alzheimer disease (AD), the soluble oligomers rather than the mature amyloid fibrils most likely contribute to Aβ toxicity and neurodegeneration. Thus, the discovery of agents targeting soluble Aβ oligomers is highly desirable for early diagnosis prior to the manifestation of a clinical AD phenotype and also more effective therapies. We have previously reported that a novel 15-amino acid peptide (15-mer), isolated via phage display screening, targeted Aβ and attenuated its neurotoxicity (Taddei, K., Laws, S. M., Verdile, G., Munns, S., D'Costa, K., Harvey, A. R., Martins, I. J., Hill, F., Levy, E., Shaw, J. E., and Martins, R. N. (2010) Neurobiol. Aging 31, 203–214). The aim of the current study was to generate and biochemically characterize analogues of this peptide with improved stability and therapeutic potential. We demonstrated that a stable analogue of the 15-amino acid peptide (15M S.A.) retained the activity and potency of the parent peptide and demonstrated improved proteolytic resistance in vitro (stable to t = 300 min, c.f. t = 30 min for the parent peptide). This candidate reduced the formation of soluble Aβ42 oligomers, with the concurrent generation of non-toxic, insoluble aggregates measuring up to 25–30 nm diameter as determined by atomic force microscopy. The 15M S.A. candidate directly interacted with oligomeric Aβ42, as shown by coimmunoprecipitation and surface plasmon resonance/Biacore analysis, with an affinity in the low micromolar range. Furthermore, this peptide bound fibrillar Aβ42 and also stained plaques ex vivo in brain tissue from AD model mice. Given its multifaceted ability to target monomeric and aggregated Aβ42 species, this candidate holds promise for novel preclinical AD imaging and therapeutic strategies

The Use of Phage-Displayed Peptide Libraries to Develop Tumor-Targeting Drugs

Monoclonal antibodies have been successfully utilized as cancer-targeting therapeutics and diagnostics, but the efficacies of these treatments are limited in part by the size of the molecules and non-specific uptake by the reticuloendothelial system. Peptides are much smaller molecules that can specifically target cancer cells and as such may alleviate complications with antibody therapy. Although many endogenous and exogenous peptides have been developed into clinical therapeutics, only a subset of these consists of cancer-targeting peptides. Combinatorial biological libraries such as bacteriophage-displayed peptide libraries are a resource of potential ligands for various cancer-related molecular targets. Target-binding peptides can be affinity selected from complex mixtures of billions of displayed peptides on phage and further enriched through the biopanning process. Various cancer-specific ligands have been isolated by in vitro, in vivo, and ex vivo screening methods. As several peptides derived from phage-displayed peptide library screenings have been developed into therapeutics in current clinical trials, which validates peptide-targeting potential, the use of phage display to identify cancer-targeting therapeutics should be further exploited

Structure-Based Design of Non-Natural Amino Acid Inhibitors of Amyloid Fibrillation

Many globular and natively disordered proteins can convert into amyloid fibers. These fibers are associated with numerous pathologies1 as well as with normal cellular functions2,3, and frequently form during protein denaturation4,5. Inhibitors of pathological amyloid fibers could serve as leads for therapeutics, provided the inhibitors were specific enough to avoid interfering with normal processes. Here we show that computer-aided, structure-based design can yield highly specific peptide inhibitors of amyloid formation. Using known atomic structures of segments of amyloid fibers as templates, we have designed and characterized an all D-amino acid inhibitor of fibrillation of the tau protein found in Alzheimer’s disease, and a non-natural L-amino acid inhibitor of an amyloid fiber that enhances sexual transmission of HIV. Our results indicate that peptides from structure-based designs can disrupt the fibrillation of full-length proteins, including those like tau that lack fully ordered native structures.We thank M.I. Ivanova, J. Corn, T. Kortemme, D. Anderson, M.R. Sawaya, M. Phillips, S. Sambashivan, J. Park, M. Landau, Q. Zhang, R. Clubb, F. Guo, T. Yeates, J. Nowick, J. Zheng, and M.J. Thompson for discussions, HHMI, NIH, NSF, the GATES foundation, and the Joint Center for Translational Medicine for support, R. Peterson for help with NMR experiments, E. Mandelkow for providing tau constructs, R. Riek for providing amyloid beta, J. Stroud for amyloid beta preparation. Support for JK was from the Damon Runyon Cancer Research Foundation, for HWC by the Ruth L. Kirschstein National Research Service Award, for JM from the programme for junior-professors by the ministry of science, Baden-Württemberg, and for SAS by a UCLA-IGERT bioinformatics traineeship

Small molecule inhibitors of Aβ-aggregation and neurotoxicity

Alzheimer disease (AD) is characterized pathologically by extracellular amyloid deposits composed of Aβ peptide, neurofibrillary tangles (NFTs) made up of hyperphosphorylated tau, and a deficit of cholinergic neurons in the basal forebrain. Presently, only symptomatic therapies are available for the treatment of AD and these therapies have a limited time frame of utility. Amyloid disorders represent the effects of chronic Aβ production and are not a secondary pathological effect caused by a distant trigger; therefore targeting Aβ is a viable pursuit. In this review, we will discuss the various small molecule anti-aggregation inhibitors that have been reported in the literature, with emphasis on compounds that are presently being investigated in clinical trials

Identifizierung und Charakterisierung eines spezifischen Liganden für das Alzheimer Amyloidβ\beta-Peptid (Aβ\beta)

Alzheimer's Disease (AD) is a progressive neurodegenerative disorder. Extracellular amyloid plaques in the brain are one of the main histopathological hallmarks of this disease. The amyloid-cascade-hypothesis" assigns the amyloid-$\beta$-peptide (A$\beta$) a central role in the pathogenesis of AD. lt is assumed that progressive accumulation of A$\beta$ initiates a complex multicellular cascade that includes neuritic dystrophy, microgliosis, astrocytosis, neuronal dysfunction and loss of synapsis. The consequences ofthis multicellular cascade are impaired amnestic and cognitive functions of patients suffered by AD. Based an this hypothesis, diagnostic and therapeutic strategies targeting A$\beta$ and A$\beta$ fibrils are being pursued. In the present dissertation peptides consisting of D-amino acids (D-peptides) should be identified that bind to A$\beta$ with high specifity. D-peptides are thought to be protease-resistant and less immunogenic than the respective L-enantimer (Schumacher et al., 1996). A screening of a randomized 12mer peptide library presented an bacteriophage M13 for binding to A$\beta_{l-42}$ consisting of D-amino acids as target was performed. After four rounds of selection and amplification different peptides were selected. The amino acid sequence of Q S H Y R H I S P A Q V (all amino acids in one-letter-code) was obtained in 20 of 39 selected peptides. The mirror image of this dominating peptide (D-peptide) binds to synthetic A$\beta_{1-42}$ consisting of L-amino acids as shown by fluorescence spectroscopy titration experiments. An estimation of the dissociation equilibrium constant (KD) with non-linear regression produced a value in the micromolar range. Binding of D-Pepl to natural A$\beta$ was verified through in-vitro-targeting of A$\beta$ precipitations in tissue sections derived from patients that suffered from AD. Amyloid precipitations in tissue sections of patients that suffered from other amyloidosis disorders were not marked by D-Pepl. In cytotoxicity tests, it has been demonstrated that the D-peptide has a positive effect an the cytotoxicity of A$\beta$. The influence depends an the concentration of the D-peptide and the fibril formation state of A$\beta$. The results of the cytotoxicity assays could not be explained based an the nucleations-elongations-modell by Lansbury et al. (consisting of two steps: building of a aggregation nucleus and elongation of fibrils) (Jarrett et al., 1993 ; Jarrett and Lansbury, 1993; Harper and Lansbury, 1997). An interpretation of all results of the cytotoxicity tests becomes possible by consideration of an extended model by Harper et al. which adjuLansbury, 1993; Harper and Lansbury, 1997). An interpretation of all results of the cytotoxicity tests becomes possible by consideration of an extended model by Harper et al.. which adjusts protofilaments (Harper et al., 1999). Thereby an influence of D-Pepl to the aggregation of ALansbury, 1993; Harper and Lansbury, 1997). An interpretation of all results of the cytotoxicity tests becomes possible by consideration of an extended model by Harper et al.. which adjusts protofilaments (Harper et al., 1999). Thereby an influence of D-Pepl to the aggregation of $\beta$ as well as different mechanisms for toxicity of protofilaments and fibrils was assumed

Reproducibility of Effects of Vibrational Strong Coupling on Chemical Reaction Rates

The ability to conduct new chemical reactions, or to control known reactions in new ways, is a key area of academic and societal interest. In recent years, developments in the field of photonics have revealed phenomena that occur when molecules strongly interact with light. One area of interest is in vibrational strong coupling, which occurs when molecular bond vibrations strongly interact with electromagnetic fields in the mid-infrared regime. In a fascinating series of experiments, reactions were performed under vibrational strong coupling and observed to be dramatically modified. Given the impact that these findings imply, independent verification and a thorough understanding of the underlying mechanisms is critical. One such reaction, where the ester para-nitrophenyl acetate is hydrolyzed by tetrabutylammonium fluoride in ethyl acetate, reportedly accelerated by an order of magnitude. An attempt to reproduce these findings with the goal of further investigating the mechanism of reaction modification is presented. While experimental procedures and conditions were performed closely to those of the original work, no reaction modification was observed. Furthermore, no significant change in reaction rate with detuning was found. An analysis of the reaction system was performed using Jaynes-Cummings coupled oscillator and transfer matrix method models to confirm vibrational strong coupling and investigate the lack of observed reaction modification. The potential of vibrational strong coupling as new tool for reaction control is tantalizing and may usher in a new era of chemical synthesis, however a robust understanding of the underlying mechanisms involved are crucial to its realization