37,119 research outputs found

    Diapause in the Boll Weevil, Anthonontus grandis Boheman, As Related to Fruiting Activity in the Cotton Plant

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    Studies in Arkansas show that boll weevil diapause is related to changes in fruiting activity of the cotton plant. Generally, when larval development took place while fruiting levels were increasing or being held at a high level, diapause in resulting adults was low (0-20%). Diapause was approximately 20-50% when larval development coincided with decreasing fruiting levels, and was 50-100% as true cut-out approached. Regrowth cotton generally lowered diapause incidence and as fruiting levels decreased, diapause increased. Therefore, the boll weevil not only responds to short photoperiods that are characteristic during the fall in the temperate zone, but also may respond throughout the season to changes in fruiting activity of the cotton plant

    Origin of the Mott Gap

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    We show exactly that the only charged excitations that exist in the strong-coupling limit of the half-filled Hubbard model are gapped composite excitations generated by the dynamics of the charge 2e2e boson that appears upon explicit integration of the high-energy scale. At every momentum, such excitations have non-zero spectral weight at two distinct energy scales separated by the on-site repulsion UU. The result is a gap in the spectrum for the composite excitations accompanied by a discontinuous vanishing of the density of states at the chemical potential when UU exceeds the bandwidth. Consequently, we resolve the long-standing problem of the cause of the charge gap in a half-filled band in the absence of symmetry breaking.Comment: 6 pages, 2 figures: Expanded Published versio

    Method of forming a wick for a heat pipe

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    A method of forming a tubular wick for a heat pipe is presented. The method is characterized by the steps of forming a wick blank of a predetermined thickness comprising a plurality of superimposed layers of stainless steel mesh screen, wet rolling the blank for reducing the thickness, wrapping the blank about an inner mandrel, compressing the blank into a rigid tubular structure, removing the tubular structure from the mandrel and sintering the tubular structure

    Generalised photon sieves: fine control of complex fields with simple pinhole arrays

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    Spatial shaping of light beams has led to numerous new applications in fields such as imaging, optical communication, and micromanipulation. However, structured radiation is less well explored beyond visible optics, where methods for shaping fields are more limited. Binary amplitude filters are often used in these regimes and one such example is a photon sieve consisting of an arrangement of pinholes, the positioning of which can tightly focus incident radiation. Here, we describe a method to design generalized photon sieves: arrays of pinholes that generate arbitrary structured complex fields at their foci. We experimentally demonstrate this approach by the production of Airy and Bessel beams, and Laguerre–Gaussian and Hermite–Gaussian modes. We quantify the beam fidelity and photon sieve efficiency, and also demonstrate control over additional unwanted diffraction orders and the incorporation of aberration correction. The fact that these photon sieves are robust and simple to construct will be useful for the shaping of short- or long-wavelength radiation and eases the fabrication challenges set by more intricately patterned binary amplitude masks

    Sterilization of liquids by filtration and certification of probability

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    Sterilization of liquids by hydrosol filtratio

    From Hadrons to Nuclei: Crossing the Border

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    The study of nuclei predates by many years the theory of quantum chromodynamics. More recently, effective field theories have been used in nuclear physics to ``cross the border'' from QCD to a nuclear theory. We are now entering the second decade of efforts to develop a perturbative theory of nuclear interactions using effective field theory. This work describes the current status of these efforts.Comment: 141 pages, 58 figs, latex. To appear in the Boris Ioffe Festschrift, ed. by M. Shifman, World Scientifi

    Chiral effective theory predictions for deuteron form factor ratios at low Q^2

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    We use chiral effective theory to predict the deuteron form factor ratio G_C/G_Q as well as ratios of deuteron to nucleon form factors. These ratios are calculated to next-to-next-to-leading order. At this order the chiral expansion for the NN isoscalar charge operator (including consistently calculated 1/M corrections) is a parameter-free prediction of the effective theory. Use of this operator in conjunction with NLO and NNLO chiral effective theory wave functions produces results that are consistent with extant experimental data for Q^2 < 0.35 GeV^2. These wave functions predict a deuteron quadrupole moment G_Q(Q^2=0)=0.278-0.282 fm^2-with the variation arising from short-distance contributions to this quantity. The variation is of the same size as the discrepancy between the theoretical result and the experimental value. This motivates the renormalization of G_Q via a two-nucleon operator that couples to quadrupole photons. After that renormalization we obtain a robust prediction for the shape of G_C/G_Q at Q^2 < 0.3 GeV^2. This allows us to make precise, model-independent predictions for the values of this ratio that will be measured at the lower end of the kinematic range explored at BLAST. We also present results for the ratio G_C/G_M.Comment: 31 pages, 7 figure
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