An Alternative Approach to Aldol Reactions: Gold-Catalyzed Formation of Boron Enolates from Alkynes

A new method for enolate generation via the gold-catalyzed addition of boronic acids to alkynes is reported. The formation of boron enolates from readily accessible ortho-alkynylbenzeneboronic acids proceeds rapidly with 2 mol % PPh3AuNTf2 at ambient temperature. The enolates undergo aldol reaction with an aldehyde present in the reaction mixture to give cyclic boronate esters, which can be subsequently transformed into phenols, biaryls, or dihydrobenzofurans via oxidation, Suzuki-Miyaura, or intramolecular Chan-Lam coupling, respectively. A combined gold/boronic acid catalyzed aldol condensation reaction of an alkynyl aldehyde was also successfully achieved

Study of the semileptonic decay \Lambda_b^0 \to \Lambda_c^+ l^- \bar{\nu}_l

Within the framework of a nonrelativistic quark model we evaluate the six form factors associated to the \Lambda_b^0 \to \Lambda_c^+ l^- \bar{\nu}_l semileptonic decay. The baryon wave functions were evaluated using a variational approach applied to a family of trial functions constrained by Heavy Quark Symmetry (HQS). We use a spectator model with only one-body current operators. For these operators we keep up to first order terms on the internal (small) heavy quark momentum, but all orders on the transferred (large) momentum. Our result for the partially integrated decay width is in good agreement with lattice calculations. Comparison of our total decay width to experiment allows us to extract the V_{cb} Cabbibo-Kobayashi-Maskawa matrix element for which we obtain a value of |V_{cb}|=0.047\pm 0.005 in agreement with a recent determination by the DELPHI Collaboration. Furthermore, we obtain the universal Isgur-Wise function with a slope parameter \rho^2=0.98 in agreement with lattice results.Comment: 4 pages, 3 figures. Presented at 6th International Conference on Hyperons, Charm and Beauty Hadrons (BEACH 2004), Chicago, Illinois, 27 Jun - 3 Jul 200

Exploring patterns of recurrent melanoma in Northeast Scotland to inform the introduction a digital self-examination intervention

Peer reviewedPublisher PD

A nonlinear beam model of photomotile structures

Actuation remains a significant challenge in soft robotics. Actuation by light has important advantages: Objects can be actuated from a distance, distinct frequencies can be used to actuate and control distinct modes with minimal interference, and significant power can be transmitted over long distances through corrosion-free, lightweight fiber optic cables. Photochemical processes that directly convert photons to configurational changes are particularly attractive for actuation. Various works have reported light-induced actuation with liquid crystal elastomers combined with azobenzene photochromes. We present a simple modeling framework and a series of examples that study actuation by light. Of particular interest is the generation of cyclic or periodic motion under steady illumination. We show that this emerges as a result of a coupling between light absorption and deformation. As the structure absorbs light and deforms, the conditions of illumination change, and this, in turn, changes the nature of further deformation. This coupling can be exploited in either closed structures or with structural instabilities to generate cyclic motion

Bounds on Heavy-to-Heavy Mesonic Form Factors

We provide upper and lower bounds on the form factors for B -> D, D^* by utilizing inclusive heavy quark effective theory sum rules. These bounds are calculated to leading order in Lambda_QCD/m_Q and alpha_s. The O(alpha_s^2 beta_0) corrections to the bounds at zero recoil are also presented. We compare our bounds with some of the form factor models used in the literature. All the models we investigated failed to fall within the bounds for the combination of form factors (omega^2 - 1)/(4 omega)|omega h_{A2}+h_{A3}|^2.Comment: 27 pages, 10 figure

Spectral fluctuation characterization of random matrix ensembles through wavelets

A recently developed wavelet based approach is employed to characterize the scaling behavior of spectral fluctuations of random matrix ensembles, as well as complex atomic systems. Our study clearly reveals anti-persistent behavior and supports the Fourier power spectral analysis. It also finds evidence for multi-fractal nature in the atomic spectra. The multi-resolution and localization nature of the discrete wavelets ideally characterizes the fluctuations in these time series, some of which are not stationary.Comment: 7 pages, 2 eps figure

Form-factor-independent test of lepton universality in semileptonic heavy meson and baryon decays

In the semileptonic decays of heavy mesons and baryons, the lepton-mass dependence factors out in the quadratic cos2θ coefficient of the differential cosθ distribution. We call the corresponding normalized coefficient the convexity parameter. This observation opens the path to a test of lepton universality in semileptonic heavy meson and baryon decays that is independent of form-factor effects. By projecting out the quadratic rate coefficient, dividing out the lepton-mass-dependent factor, and restricting the phase space integration to the τ lepton phase space, one can define optimized partial rates which, in the Standard Model, are the same for all three (e,μ,τ) modes in a given semileptonic decay process. We discuss how the identity is spoiled by new physics effects. We discuss semileptonic heavy meson decays such as B¯0→D(∗)+ℓ-ν¯ℓ and Bc-→J/ψ(ηc)ℓ-ν¯ℓ and semileptonic heavy baryon decays such as Λb→Λcℓ-ν¯ℓ for each ℓ=e, μ, τ

Importance of Tests for the Complete Lorentz Structure of the t --> W+ b vertex at Hadron Colliders

The most general Lorentz-invariant decay-density-matrix for $t\to W^{+}b\to (l^{+}\nu)b$, or for $t\to W^{+}b\to (j_{\bar d}j_u)b$, is expressed in terms of eight helicity parameters. The parameters are physically defined in terms of partial-width-intensities for polarized-final-states in $t\to W^{+}b$ decay. The parameters are the partial width, the $b$ quark's chirality parameter $\xi$, the $W^+$ polarimetry parameter $\sigma$, a "pre-SSB" test parameter $\zeta$, and four $W_{L}$-$W_{T}$ interference parameters $\eta$, $\eta^{'}$, $\omega$, $\omega^{'}$ which test for $\tilde T_{FS}$ violation. They can be used to test for non-CKM-type CP violation, anomalous $\Gamma_{L,T}$'s, top weak magnetism, weak electricity, and second-class currents. By stage-two spin-correlation techniques, percent level statistical uncertainites are typical for measurements at the Tevatron, and several mill level uncertainites are typical at the LHC.Comment: Minor clarifications. Expression for r_{+-} corrected. 19 pages LaTex + Tables + 1 Figur