409 research outputs found
On the R-Matrix Formulation of Deformed Algebras and Generalized Jordan-Wigner Transformations
The deformed algebra , depending upon a Yang-Baxter R- matrix, is
considered. The conditions under which the algebra is associative are discussed
for a general number of oscillators. Four types of solutions satisfying these
conditions are constructed and two of them can be represented by generalized
Jordan-Wigner transformations.Our analysis is in some sense an extension of the
boson realization of fermions from single-mode to multimode oscillators.Comment: 10+ii pages,preprint RBI-TH-10/93,Latex,(to appear in Europhys.Lett.
Hermitian boson mapping and finite truncation
Starting from a general, microscopic fermion-to-boson mapping that preserves
Hermitian conjugation, we discuss truncations of the boson Fock space basis. We
give conditions under which the exact boson images of finite fermion operators
are also finite (e.g., a 1+2-body fermion Hamiltonian is mapped to a 1+2-body
boson Hamiltonian) in the truncated basis. For the most general case, where the
image is not necessarily exactly finite, we discuss how to make practical and
controlled approximations.Comment: 12 pages in RevTex with no figures, Los Alamos preprint #
LA-UR-94-146
2D Kagome Ordering in the 3D Frustrated Spinel Li2Mn2O4
muSR experiments on the geometrically frustrated spinel oxide, Li2Mn2O4, show
the development of spin correlations over a range of length scales with
decreasing temperature. Increased relaxation below 150 K is consistent with the
onset of spin correlations. Below 50 K, spin order on a length scale, which is
long range for the muSR probe, appears abruptly in temperature, consistent with
prior neutron diffraction results. The oscillations in the zero field asymmetry
are analyzed using a three frequency model. By locating the muon site this is
shown to be consistent with the unexpected 2D q = root 3 x root 3 structure on
the Kagome planes proposed originally from neutron data. Longitudinal field
data demonstrate that some spin dynamics persist even at 2 K. Thus, a very
complex magnetic ground state, featuring the co-existence of long length scale
2D ordering and significant spin dynamics, is proposed. This is unusual
considering the 3D topology of the Mn3+ spins in this material.Comment: 9 pages, 9 figures, to be submitted to J. Phys. Cond. Mat
Elizabeth Cary and Intersections of Catholicism and Gender in Early Modern England
Historians have analyzed the life of Elizabeth Cary, Lady Falkland, primarily in the context of her highly publicized conversion to Catholicism and her equally public separation from her Protestant husband, Henry Cary. Through this scrutiny, she has become one among many English Catholic recusant heroines. Literary critics, in contrast, have celebrated Cary\u27s literary corpus both for its challenge to traditional ideals of early modern women as chaste, silent, and obedient and for its reevaluation of women\u27s roles within marriage.1 To circumscribe our understandings of Cary in such ways obscures one of her greatest contributions. Elizabeth Cary, albeit unintentionally, provided an alternative model of Catholic woman hood that sought to negotiate a new balance between religion and gender, thus challenging assumptions about women\u27s roles in English Catholic communities and about the rigid character of Catholicism in the Reformation era
Identifying the sources driving observed PM2.5 temporal variability over Halifax, Nova Scotia, during BORTAS-B
The source attribution of observed variability of total PM<sub>2.5</sub> concentrations over Halifax, Nova Scotia was investigated between 11 Julyā26 August 2011 using measurements of PM<sub>2.5</sub> mass and PM<sub>2.5</sub> chemical composition (black carbon, organic matter, anions, cations and 33 elements). This was part of the BORTAS-B (quantifying the impact of BOReal forest fires on Tropospheric oxidants using aircraft and satellites) experiment, which investigated the atmospheric chemistry and transport of seasonal boreal wild fire emissions over eastern Canada in 2011. The US EPA Positive Matrix Factorization (PMF) receptor model was used to determine the average mass (percentage) source contribution over the 45 days, which was estimated to be: Long-Range Transport (LRT) Pollution 1.75 Ī¼g m<sup>ā3</sup> (47%), LRT Pollution Marine Mixture 1.0 Ī¼g m<sup>ā3</sup> (27.9%), Vehicles 0.49 Ī¼g m<sup>ā3</sup> (13.2%), Fugitive Dust 0.23 Ī¼g m<sup>ā3</sup> (6.3%), Ship Emissions 0.13 Ī¼g m<sup>ā3</sup> (3.4%) and Refinery 0.081 Ī¼g m<sup>ā3</sup> (2.2%). The PMF model describes 87% of the observed variability in total PM<sub>2.5</sub> mass (bias = 0.17 and RSME = 1.5 Ī¼g m<sup>ā3</sup>). The factor identifications are based on chemical markers, and they are supported by air mass back trajectory analysis and local wind direction. Biomass burning plumes, found by other surface and aircraft measurements, were not significant enough to be identified in this analysis. This paper presents the results of the PMF receptor modelling, providing valuable insight into the local and upwind sources impacting surface PM<sub>2.5</sub> in Halifax during the BORTAS-B mission
Pressure effect on the in-plane magnetic penetration depth in YBa_2Cu_4O_8
We report a study of the pressure effect (PE) on the in-plane magnetic field
penetration depth lambda_{ab} in YBa_2Cu_4O_8 by means of Meissner fraction
measurements. A pronounced PE on lambda_{ab}^{-2}(0) was observed with a
maximum relative shift of \Delta\lambda^{-2}_{ab}/\lambda^{-2}_{ab}= 44(3)% at
a pressure of 10.2 kbar. It arises from the pressure dependence of the
effective in-plane charge carrier mass and pressure induced charge carrier
transfer from the CuO chains to the superconducting CuO_2 planes. The present
results imply that the charge carriers in YBa_2Cu_4O_8 are coupled to the
lattice.Comment: 4pages 3 figure
Back-reacted saponite in Jurassic mudstones and limestones intruded by a Tertiary sill, Isle of Skye
The LĆ³n Ostatoin stream section, Trotternish Peninsula, Isle of Skye, exposes a sequence of Middle Jurassic mudstones and limestones which have been locally metasomatized by a transgressive sill of Tertiary age. Limestones in the sequence, including some previously reported as bentonite, have been altered to an unusual assemblage of grossular garnet and saponite clay. The mudstones also contain large proportions of saponite together with pyroxene and zeolites. Saponite also occurs within the basalt intrusion. Grossular and pyroxene represent artifacts of relatively high-temperature assemblages that formed during an early phase of alteration. As the intrusion and adjacent altered country rocks cooled, lower-temperature fluids flowed through a late set of contraction (micro)fractures. Back-reacted saponite, analcime and clinoptilolite were formed, possibly as alteration products of the unstable higher-temperature minerals. The lower-temperature mineral assemblage eventually sealed the late fracture system.
This paper highlights an important concept for the study of analogue sites used to investigate thermal effects on engineered liners or barrier host rocks for the landfill and radioactive-waste industries. This is that the original thermally altered mineral assemblage may be overprinted by later, lower-temperature back-reactions. A detailed understanding of both processes is necessary in order to construct a sensible model for the thermal and mineralogical evolution of the site
Lattice-switch Monte Carlo
We present a Monte Carlo method for the direct evaluation of the difference
between the free energies of two crystal structures. The method is built on a
lattice-switch transformation that maps a configuration of one structure onto a
candidate configuration of the other by `switching' one set of lattice vectors
for the other, while keeping the displacements with respect to the lattice
sites constant. The sampling of the displacement configurations is biased,
multicanonically, to favor paths leading to `gateway' arrangements for which
the Monte Carlo switch to the candidate configuration will be accepted. The
configurations of both structures can then be efficiently sampled in a single
process, and the difference between their free energies evaluated from their
measured probabilities. We explore and exploit the method in the context of
extensive studies of systems of hard spheres. We show that the efficiency of
the method is controlled by the extent to which the switch conserves correlated
microstructure. We also show how, microscopically, the procedure works: the
system finds gateway arrangements which fulfill the sampling bias
intelligently. We establish, with high precision, the differences between the
free energies of the two close packed structures (fcc and hcp) in both the
constant density and the constant pressure ensembles.Comment: 34 pages, 9 figures, RevTeX. To appear in Phys. Rev.
Back-reacted saponite in Jurassic mudstones and limestones intruded by a Tertiary sill, Isle of Skye
The reductive activation of CO2 across a TiāTi double bond: synthetic, structural, and mechanistic studies
[Image: see text] The reactivity of the bis(pentalene)dititanium double-sandwich compound Ti(2)Pn(ā )(2) (1) (Pn(ā ) = 1,4-{Si(i)Pr(3)}(2)C(8)H(4)) with CO(2) is investigated in detail using spectroscopic, X-ray crystallographic, and computational studies. When the CO(2) reaction is performed at ā78 Ā°C, the 1:1 adduct 4 is formed, and low-temperature spectroscopic measurements are consistent with a CO(2) molecule bound symmetrically to the two Ti centers in a Ī¼:Ī·(2),Ī·(2) binding mode, a structure also indicated by theory. Upon warming to room temperature the coordinated CO(2) is quantitatively reduced over a period of minutes to give the bis(oxo)-bridged dimer 2 and the dicarbonyl complex 3. In situ NMR studies indicated that this decomposition proceeds in a stepwise process via monooxo (5) and monocarbonyl (7) double-sandwich complexes, which have been independently synthesized and structurally characterized. 5 is thermally unstable with respect to a Ī¼-O dimer in which the TiāTi bond has been cleaved and one pentalene ligand binds in an Ī·(8) fashion to each of the formally Ti(III) centers. The molecular structure of 7 shows a āside-onā bound carbonyl ligand. Bonding of the double-sandwich species Ti(2)Pn(2) (Pn = C(8)H(6)) to other fragments has been investigated by density functional theory calculations and fragment analysis, providing insight into the CO(2) reaction pathway consistent with the experimentally observed intermediates. A key step in the proposed mechanism is disproportionation of a mono(oxo) di-Ti(III) species to yield di-Ti(II) and di-Ti(IV) products. 1 forms a structurally characterized, thermally stable CS(2) adduct 8 that shows symmetrical binding to the Ti(2) unit and supports the formulation of 4. The reaction of 1 with COS forms a thermally unstable complex 9 that undergoes scission to give mono(Ī¼-S) mono(CO) species 10. Ph(3)PS is an effective sulfur transfer agent for 1, enabling the synthesis of mono(Ī¼-S) complex 11 with a double-sandwich structure and bis(Ī¼-S) dimer 12 in which the TiāTi bond has been cleaved
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