Composite quasiparticle formation and the low-energy effective Hamiltonians of the one- and two-dimensional Hubbard Model

We investigate the effect of hole doping on the strong-coupling Hubbard model at half-filling in spatial dimensions $D\ge 1$. We start with an antiferromagnetic mean-field description of the insulating state, and show that doping creates solitons in the antiferromagnetic background. In one dimension, the soliton is topological, spinless, and decoupled from the background antiferromagnetic fluctuations at low energies. In two dimensions and above, the soliton is non-topological, has spin quantum number 1/2, and is strongly coupled to the antiferromagnetic fluctuations. We derive the effective action governing the quasiparticle motion, study the properties of a single carrier, and comment on a possible description at finite concentration.Comment: REVTEX 3.0, 22 pages with 14 figures in the PostScript format compressed using uufile. Submitted to Phys. Rev. B. The complete PostScript file including figures can be obtained via ftp at ftp://serval.berkeley.edu/hubbard.ps . It is also available via www at http://roemer.fys.ku.dk/recent.ht

Quasiparticle structure and coherent propagation in the t−Jz−J⊥t-J_{z}-J_{\perp} model

Numerical studies, from variational calculation to exact diagonalization, all indicate that the quasiparticle generated by introducing one hole into a two-dimensional quantum antiferromagnet has the same nature as a string state in the $t-J_{z}$ model. Based on this observation, we attempt to visualize the quasiparticle formation and subsequent coherent propagation at low energy by studying the generalized $t-J_{z}-J_{\perp}$ model in which we first diagonalize the $t-J_{z}$ model and then perform a {\em degenerate} perturbation in $J_{\perp}$. We construct the quasiparticle state and derive an effective Hamiltonian describing the coherent propagation of the quasiparticle and its interaction with the spin wave excitations in the presence of the N\'{e}el order. We expect that qualitative properties of the quasiparticle remain intact when analytically continuing $J_{\perp}$ from the anisotropic $J_{\perp} < J_{z}$ to the isotropic $J_{\perp} = J_{z}$ limit, despite the fact that the spin wave excitations change from gapful to gapless. Extrapolating to $J_{\perp}=J_{z}$, our quasiparticle dispersion and spectral weight compare well with the exact numerical results for small clusters.Comment: Revised with minor changes and references updated. To appear in Phys. Rev. B., Jan. 1996. 10 pages, The complete PostScript file including figures can be obtained via ftp at ftp://serval.berkeley.edu/tjzjp.ps . It is also posted in the WEB site of Niels Bohr Institute at http://roemer.fys.ku.dk/recent.ht

A global view of porcine transcriptome in three tissues from a full-sib pair with extreme phenotypes in growth and fat deposition by paired-end RNA sequencing

<p>Abstract</p> <p>Background</p> <p>Elucidation of the pig transcriptome is essential for interpreting functional elements of the genome and understanding the genetic architecture of complex traits such as fat deposition, metabolism and growth.</p> <p>Results</p> <p>Here we used massive parallel high-throughput RNA sequencing to generate a high-resolution map of the porcine mRNA and miRNA transcriptome in liver, longissimus dorsi and abdominal fat from two full-sib F₂hybrid pigs with segregated phenotypes on growth, blood physiological and biochemical parameters, and fat deposition. We obtained 8,508,418-10,219,332 uniquely mapped reads that covered 78.0% of the current annotated transcripts and identified 48,045-122,931 novel transcript fragments, which constituted 17,085-29,499 novel transcriptional active regions in six tested samples. We found that about 18.8% of the annotated genes showed alternative splicing patterns, and alternative 3' splicing is the most common type of alternative splicing events in pigs. Cross-tissue comparison revealed that many transcriptional events are tissue-differential and related to important biological functions in their corresponding tissues. We also detected a total of 164 potential novel miRNAs, most of which were tissue-specifically identified. Integrated analysis of genome-wide association study and differential gene expression revealed interesting candidate genes for complex traits, such as <it>IGF2, CYP1A1, CKM </it>and <it>CES1 </it>for heart weight, hemoglobin, pork pH value and serum cholesterol, respectively.</p> <p>Conclusions</p> <p>This study provides a global view of the complexity of the pig transcriptome, and gives an extensive new knowledge about alternative splicing, gene boundaries and miRNAs in pigs. Integrated analysis of genome wide association study and differential gene expression allows us to find important candidate genes for porcine complex traits.</p

A laboratory GTEM cell design for electromagnetic exposure study on biological system

International audienceIn this paper, a Gigaherz Transverse Electromagnetic (GTEM) cell is designed for laboratory use electromagnetic fields exposure study on biological system. Once the total volume and the area of exposure have been defined, a first calculation will be made to deduce the initial values of the parameters of the GTEM cell. The use of a fullwave electromagnetic simulation software will allow these parameters to be adjusted to obtain a low reflection on a frequency band around 915 MHz, and a fairly homogeneous electric field in the test zone... The effect of the biological medium on the distribution of the electromagnetic field will also be analyzed and the Specific Absorption Rate (SAR) estimation will be made with different parameters of the biological media

Les Lieux de Reverdy

Le concept de lieu intéresse l analyse littéraire non seulement dans une acception thématique mais aussi en ce qu il traduit et symbolise la relation du sujet lyrique au monde et au langage, que l œuvre de Reverdy reconstruit de manière originale. On se propose, dans une première partie, de décrire la structuration du monde imaginaire de Reverdy, ce paysage au sens où le définit Michel Collot que son œuvre instaure, construit, recompose. S il est riche de lieux qui se distribuent de manière polysémique, il rend également compte d une expérience originale de l existence, en traduit les données les plus personnelles, celles d un je poétique immergé dans un monde qu il recompose par des lois imaginaires et dont il éprouve l instabilité essentielle. Ce monde éminemment subjectif nous sommes, rappelle Jean-Pierre Richard, en poésie et par là-même lacunaire et mouvant, présuppose une place du sujet ancré au monde, et donc lieu exclu du monde tel un point aveugle. Une seconde partie étudie le travail de l écriture poétique reverdyenne qui conteste et subvertit cette relation. Sous l influence du cubisme, elle entre en lutte contre l unité/unicité d un sujet dont elle mine la vérité, détruit la cohésion, dont elle rêve la diffraction et la dispersion dans un paysage qu elle investit de manière massive, jusqu à l y confondre. L écriture poétique est donc un moyen privilégié de repenser le lieu, ce Dasein qui concrétise l existence, et apparaît ainsi comme un lieu de nouage, de fusion, un carrefour où sujet et monde imaginaires se constituent en un lieu de l œuvre, véritable figure du sujet lyrique, territoire au sens où l entend Jean-Marie Gleize et dont une troisième partie expose l essence. C est là l occasion de comprendre comment fonctionne l écriture reverdyenne, quelles sont les grandes forces de l imaginaire qui s y met en œuvre, pour en tirer des conclusions sur sa spécificité.The concept of place is of special interest for literary analysis not only thematically but also in so far as it translates and symbolizes the relation of the lyrical subject to the world and to language, which is reconstructed by Reverdy s literary work in an original way. The first part of this thesis is devoted to the structuration of Reverdy s imaginary world, this landscape as defined by Michel Collot elaborated, built and recombined. This landscape, made of polysemous places, also translates an original existential experiment, through most personal data, the data of a poetical I submerged in a reconstructed world based on imaginary laws and experienced by the author as essentially unstable. This extremely subjective world we are, as Jean-Pierre Richard reminds us, in poesy thus on a land of gap and constant change, is based on the principle of a subject rooted in the world and thus a place excluded from the world like a blind spot. The second part studies the work of the Reverdian poetic writing that rejects and subverts this relation. Under the spell of Cubism, it fights against the unity/uniqueness of a subject by distorting reality, destructing coherence and dreaming of its diffraction and blurring into a landscape it massively invests in, till melting. Poetic writing is thus a privileged way of rethinking the concept of place, this Dasein materializing existence, and is revealed as a place of binding, of fusion, a crossroad where the subject and the imaginary world are intertwined in a place of the work, true self of the lyrical subject, territory as defined by Jean-Marie Gleize and whose third part presents the essence. We have the opportunity to understand the way the Reverdian writing works, the great forces of the imagination at work in it, so as to be able to conclude on its specificity.BORDEAUX3-Bib. électronique (335229906) / SudocSudocFranceF

A test of empirical and semi-analytical algorithms for euphotic zone depth with SeaWifs data off southeastern China

This study employs SeaWiFS data over the waters off the southeastern China to evaluate a semi-analytical algorithm for euphotic zone depth (Ze). This algorithm is based on water's inherent optical properties (IOPs), which can be near-analytically calculated from spectral remote-sensing reflectance, where remote-sensing reflectance can be derived from the normalized water-leaving radiance provided by SeaWiFS. In the Taiwan Strait, compared with in situ Z(e) (+/- 3 hour within SeaWiFS collection), average error (c) is 15.0 % and root mean square error (RMSE) is 0.074, with Ze in a range of 14-34 in from field measurements. In the South China Sea, compared with in situ Ze ( 48 hour within SeaWiFS collection),epsilon is 5.1 % in summer and 22.6 in winter, while RMSE is 0.032 in summer and 0.129 in winter, with Z(e) in a range of 10-82 in from field measurements. For comparison, we also evaluate the performance of the empirical Ze algorithm that is based on chlorophyll concentration. It is found that the IOP-centered approach has higher accuracy, compared to the chlorophyll-a centered approach (e.g. in the South China Sea in winter, epsilon is 55.3 % and RMSE is 0.219). The new algorithm is thus found not only worked well with waters of the Gulf of Mexico, Monterey Bay and the Arabian Sea, but also worked well with waters of the China Sea