21,667 research outputs found

    Coherent Amplification of Optical Pulses in Metamaterials

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    In this paper we theoretically study propagation of steady state ultrashort pulse in dissipative medium. We considered two cases (i) medium consists of lossy metallic nanostructures embedded into a gain material and (ii) the gain material is embedded directly into the nanostructures. We found the shape and velocity of an optical pulse coupled with the polarization wave.Comment: 9 pages, 5 figures, submitted to IEEE Tran

    Methyl 2-amino-5-iso­propyl-1,3-thia­zole-4-carboxyl­ate

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    The title compound, C8H12N2O2S, forms a supramolecular network based on N-HN hydrogen-bonded centrosymmetric dimers that are linked in turn by N-HO contacts

    Postcard: Optometrists Advertisement

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    This black and white printed postcard features an advertisement for an optometrist. There is an illustration of an eye and eyebrow in the top right corner. A photographic portrait of E.R. Kennedy is on the left side of the card. Printed text fills the card. Handwriting is on the back of the card.https://scholars.fhsu.edu/tj_postcards/1660/thumbnail.jp

    Phase Diagram of the Spin-One Heisenberg System with Dimerization and Frustration

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    We use the density matrix renormalization group method to study the ground state properties of an antiferromagnetic spin-11 chain with a next-nearest neighbor exchange J2 J_2 ~ and an alternation δ\delta of the nearest neighbor exchanges. We find a line running from a gapless point at (J2,δ)=(0,0.25±0.01)(J_2 , \delta) = (0, 0.25 \pm 0.01) upto an almost gapless point at (0.725±0.01,0(0.725 \pm 0.01, 0 such that the open chain ground state is 44-fold degenerate below the line and is unique above it. A disorder line 2J2+δ=12 J_2 + \delta = 1 runs from δ=0\delta =0 to about δ=0.136\delta =0.136. To the left of this line, the peak in the structure factor S(q)S(q) is at π\pi, while to the right of the line, it is at less than π\pi.Comment: 11 pages, plain TeX, 3 figures available on reques

    Fabrication and properties of gallium phosphide variable colour displays

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    The unique properties of single-junction gallium phosphide devices incorporating both red and green radiative recombination centers were investigated in application to the fabrication of monolithic 5 x 7 displays capable of displaying symbolic and alphanumeric information in a multicolor format. A number of potentially suitable material preparation techniques were evaluated in terms of both material properties and device performance. Optimum results were obtained for double liquid-phase-epitaxial process in which an open-tube dipping technique was used for n-layer growth and a sealed tipping procedure for subsequent p-layer growth. It was demonstrated that to prepare devices exhibiting a satisfactory range of dominant wavelengths which can be perceived as distinct emission colors extending from the red through green region of the visible spectrum involves a compromise between the material properties necessary for efficient red emission and those considered optimum for efficient green emission

    Thermodynamic limit of the density matrix renormalization for the spin-1 Heisenberg chain

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    The density matrix renormalization group (``DMRG'') discovered by White has shown to be a powerful method to understand the properties of many one dimensional quantum systems. In the case where renormalization eventually converges to a fixed point we show that quantum states in the thermodynamic limit with periodic boundary conditions can be simply represented by a special type of product ground state with a natural description of Bloch states of elementary excitations that are spin-1 solitons. We then observe that these states can be rederived through a simple variational ansatz making no reference to a renormalization construction. The method is tested on the spin-1 Heisenberg model.Comment: 13 pages uuencoded compressed postscript including figure

    The superconducting phase transition and gauge dependence

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    The gauge dependence of the renormalization group functions of the Ginzburg-Landau model is investigated. The analysis is done by means of the Ward-Takahashi identities. After defining the local superconducting order parameter, it is shown that its exponent β\beta is in fact gauge independent. This happens because in d=3d=3 the Landau gauge is the only gauge having a physical meaning, a property not shared by the four-dimensional model where any gauge choice is possible. The analysis is done in both the context of the ϵ\epsilon-expansion and in the fixed dimension approach. It is pointed out the differences that arise in both of these approaches concerning the gauge dependence.Comment: RevTex, 3 pages, no figures; accepted for publication in PRB; this paper is a short version of cond-mat/990527

    Magnetization plateaus in spin chains: ``Haldane gap'' for half-integer spins

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    We discuss zero-temperature quantum spin chains in a uniform magnetic field, with axial symmetry. For integer or half-integer spin, SS, the magnetization curve can have plateaus and we argue that the magnetization per site mm is topologically quantized as q(Sm)=integerq (S - m)= integer at the plateaus, where qq is the period of the groundstate. We also discuss conditions for the presence of the plateau at those quantized values. For S=3/2S=3/2 and m=1/2m=1/2, we study several models and find two distinct types of massive phases at the plateau. One of them is argued to be a ``Haldane gap phase'' for half-integer SS.Comment: Revised version, to appear in Phys. Rev. Lett. (no changes in main conclusions); 5 pages, REVTEX with 2 figures in ep
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