TENNIS RACKET BIOMECHANICS - AN EMPIRICAL APPROACH

Stiffness of a racket frame, geometry of the racket head, string arrangement and string tension all contribute to the accuracy of play as well as tennis ball velocity. Mechanical racket characteristics can well be described by the laws of physics. However, empirical studies are necessary in evaluating the effect of tennis racket construction features on stress to the body as well as playing performance. Using accelerometers, grip force transducers, and a measuring matrix on the tennis racket strings allow an in depth analysis of the tennis stroke. Through several experiments it could be shown that shock and vibration transfer to the arm is influenced by ball impact location on the racket head, racket stiffness, and grip force. Playing performance of a racket, as one might predict from its mechanical characteristics, is often not reflected by its functioning in a game situation

Milk Handling in the Supply Chains: The Case of Smallholder Retail Outlets In Nakuru, Kenya

This paper characterises smallholder milk outlets in Nakuru district one of the major milk producing Districts in Kenya, and also analyses factors that influence their current operating and handling capacities. Data comes from four divisions of the district. A sample of 137 smallholder milk retail outlets was made using systematic random sampling methodology. Both descriptive and ordinary regression methods were used in the analysis. A characterisation of the retail outlets is brought out and the factors that affect their current operating capacities presented. Results show that a unit change in education, experience and selling prices leads to 0.29, 0.18 and 0.23 significant changes in milk handling capacities by the retail outlets respectively. These imply that there is an efficiency gain from education and better prices through higher consumer incomes in the industry. Enhancement of milk retailers' value addition through provision of physical facilities such as cooling equipment and stability in prices should be encouraged through policy intervention to promote informal sector investments in the sub-sector.milk supply chain, smallholder retail outlets, Kenya, Industrial Organization, Marketing,

Localization Properties of Electronic States in Polaron Model of poly(dG)-poly(dC) and poly(dA)-poly(dT) DNA polymers

We numerically investigate localization properties of electronic states in a static model of poly(dG)-poly(dC) and poly(dA)-poly(dT) DNA polymers with realistic parameters obtained by quantum-chemical calculation. The randomness in the on-site energies caused by the electron-phonon coupling are completely correlated to the off-diagonal parts. In the single electron model, the effect of the hydrogen-bond stretchings, the twist angles between the base pairs and the finite system size effects on the energy dependence of the localization length and on the Lyapunov exponent are given. The localization length is reduced by the influence of the fluctuations in the hydrogen bond stretchings. It is also shown that the helical twist angle affects the localization length in the poly(dG)-poly(dC) DNA polymer more strongly than in the poly(dA)-poly(dT) one. Furthermore, we show resonance structures in the energy dependence of the localization length when the system size is relatively small.Comment: 6 pages, 6 figure

Are plasma concentrations of tamoxifen active metabolites sufficient to ensure therapeutic efficacy for tamoxifen treated women with breast cancer in Poland?

Tamoxifen is the most commonly used drug for treating those patients with breast cancer who are oestrogen receptor positive. The main active metabolite of tamoxifen is (Z)-endoxifen whose therapeutic efficacy depends on its plasma concentration. A therapeutically effective threshold level has indeed been defined for (Z)-endoxifen above which the breast cancer relapse rate is significantly reduced. Such steady-state concentrations are conditional on gene polymorphism, principally cytochrome P450 2D6 (CYP2D6), that modulates the activity of the encoded enzymes that convert tamoxifen to its active metabolites. This drug’s metabolism however may become significantly altered when other medication is concomitantly taken, such as selective serotonin reuptake inhibitors, which inhibit CYP2D6. A recent study have demonstrated that the majority of tamoxifen treated women with breast cancer in Poland, may not in fact attain the therapeutic threshold levels of (Z)-endoxifen. In such cases, personalising optimal treatment should be based on direct monitoring of steady-state plasma concentrations of tamoxifen and its metabolites, which can thereby significantly improve therapeutic efficacy

Charge transport in poly(dG)-poly(dC) and poly(dA)-poly(dT) DNA polymers

We investigate the charge transport in synthetic DNA polymers built up from single types of base pairs. In the context of a polaron-like model, for which an electronic tight-binding system and bond vibrations of the double helix are coupled, we present estimates for the electron-vibration coupling strengths utilizing a quantum-chemical procedure. Subsequent studies concerning the mobility of polaron solutions, representing the state of a localized charge in unison with its associated helix deformation, show that the system for poly(dG)-poly(dC) and poly(dA)-poly(dT) DNA polymers, respectively possess quantitatively distinct transport properties. While the former supports unidirectionally moving electron breathers attributed to highly efficient long-range conductivity the breather mobility in the latter case is comparatively restrained inhibiting charge transport. Our results are in agreement with recent experimental results demonstrating that poly(dG)-poly(dC) DNA molecules acts as a semiconducting nanowire and exhibits better conductance than poly(dA)-poly(dT) ones.Comment: 11 pages, 5 figure

Investigation of "Courses of study in the use of libraries" in high schools.

Thesis (M.A.)--Boston Universit

Magnetic Phase Diagrams of Manganites-like Local-Moment Systems with Jahn-Teller distortions

We use an extended two-band Kondo lattice model (KLM) to investigate the occurrence of different (anti-)ferromagnetic phases or phase separation depending on several model parameters. With regard to CMR-materials like the manganites we have added a Jahn-Teller term, direct antiferromagnetic coupling and Coulomb interaction to the KLM. The electronic properties are self-consistently calculated in an interpolating self-energy approach with no restriction to classical spins and going beyond mean-field treatments. Further on we do not have to limit the Hund's coupling to low or infinite values. Zero-temperature phase diagrams are presented for large parameter intervals. There are strong influences of the type of Coulomb interaction (intraband, interband) and of the important parameters (Hund's coupling, direct antiferromagnetic exchange, Jahn-Teller distortion), especially at intermediate couplings.Comment: 11 pages, 9 figures. Accepted for publication in Phys. Rev.

Protein dynamics in the reductive activation of a B12-containing enzyme

B12-dependent proteins are involved in methyl transfer reactions ranging from the biosynthesis of methionine in humans to the formation of acetyl-CoA in anaerobic bacteria. During their catalytic cycle, they undergo large conformational changes to interact with various proteins. Recently, the crystal structure of the B12-containing corrinoid iron–sulfur protein (CoFeSP) in complex with its reductive activator (RACo) was determined, providing a first glimpse of how energy is transduced in the ATP-dependent reductive activation of corrinoid-containing methyltransferases. The thermodynamically uphill electron transfer from RACo to CoFeSP is accompanied by large movements of the cofactor-binding domains of CoFeSP. To refine the structure-based mechanism, we analyzed the conformational change of the B12-binding domain of CoFeSP by pulsed electron–electron double resonance and Förster resonance energy transfer spectroscopy. We show that the site-specific labels on the flexible B12-binding domain and the small subunit of CoFeSP move within 11 Å in the RACo:CoFeSP complex, consistent with the recent crystal structures. By analyzing the transient kinetics of formation and dissociation of the RACo:CoFeSP complex, we determined values of 0.75 μM–1 s–1 and 0.33 s–1 for rate constants kon and koff, respectively. Our results indicate that the large movement observed in crystals also occurs in solution and that neither the formation of the protein encounter complex nor the large movement of the B12-binding domain is rate-limiting for the ATP-dependent reductive activation of CoFeSP by RACo