2,011 research outputs found
Fe adatoms along Bi lines on H/Si(001): Patterning atomic magnetic chains
The stability, electronic and magnetic properties of Fe atoms adsorbed on the
self-assembled Bi-dimer lines nanostructure on the H/Si(001) surface are
addressed by spin-density functional calculations. Our results show that Fe
adatoms are much more stable on sites closer to the Bi nanolines being able to
form one-dimensional atomic arrays. The most stable structure occurs on a
missing dimer line aside the Bi dimers, which corresponds to an array with
distances between Fe adatoms of about 8 Ang. In this array the irons are
coupled antiferromagnetically with spin magnetic moment of about 1.5 Bohr
magnetons per Fe atom, whereas the coupling exchange interactions is found to
be of 14.4 meV. We also estimate a large magnetic anisotropy energy for the Fe
adatom of about 3 meV/atom. In addition, the electronic band structure of the
Fe array at the most stable structure shows a magnetic half-metal behavior.Comment: 5 pages, 5 figures, accepted in AP
Hydrogenated grain boundaries in graphene
We have investigated by means of first principles calculations the structural
and electronic properties of hydrogenated graphene structures with distinct
grain boundary defects. Our total energy results reveal that the adsorption of
a single H is more stable at grain boundary defect. The electronic structure of
the grains boundaries upon hydrogen adsorption have been examined. Further
total energy calculations indicate that the adsorption of two H on two neighbor
carbons, forming a basic unit of graphane, is more stable at the defect region.
Therefore, we expect that these extended defects would work as a nucleation
region for the formation of a narrow graphane strip embedded in graphene
region
Parallel generation of quadripartite cluster entanglement in the optical frequency comb
Scalability and coherence are two essential requirements for the experimental
implementation of quantum information and quantum computing. Here, we report a
breakthrough toward scalability: the simultaneous generation of a record 15
quadripartite entangled cluster states over 60 consecutive cavity modes
(Qmodes), in the optical frequency comb of a single optical parametric
oscillator. The amount of observed entanglement was constant over the 60
Qmodes, thereby proving the intrnisic scalability of this system. The number of
observable Qmodes was restricted by technical limitations, and we
conservatively estimate the actual number of similar clusters to be at least
three times larger. This result paves the way to the realization of large
entangled states for scalable quantum information and quantum computing.Comment: 4 pages + 7 supplemental-info pages, 6+1 figures, accepted by
Physical Review Letters. One minor revision to main text. One error corrected
in Eq. (18) of Supplemental informatio
Simultaneous conduction and valence band quantisation in ultra-shallow, high density doping profiles in semiconductors
We demonstrate simultaneous quantisation of conduction band (CB) and valence
band (VB) states in silicon using ultra-shallow, high density, phosphorus
doping profiles (so-called Si:P -layers). We show that, in addition to
the well known quantisation of CB states within the dopant plane, the
confinement of VB-derived states between the sub-surface P dopant layer and the
Si surface gives rise to a simultaneous quantisation of VB states in this
narrow region. We also show that the VB quantisation can be explained using a
simple particle-in-a-box model, and that the number and energy separation of
the quantised VB states depend on the depth of the P dopant layer beneath the
Si surface. Since the quantised CB states do not show a strong dependence on
the dopant depth (but rather on the dopant density), it is straightforward to
exhibit control over the properties of the quantised CB and VB states
independently of each other by choosing the dopant density and depth
accordingly, thus offering new possibilities for engineering quantum matter.Comment: 5 pages, 2 figures and supplementary materia
Total reaction cross section on a deuteron target and the eclipse effect of the constituent neutron and proton
Background: Eclipse effect of the neutron and proton in a deuteron target is
essential to correctly describe high-energy deuteron scattering. The
nucleus-deuteron scattering needs information not only on the nucleus-proton
but also the nucleus-neutron interaction, for which no direct measurement of
the nucleus-neutron cross sections is available for unstable nuclei.
Purpose: We systematically evaluated the total reaction cross sections by a
deuteron target to explore the feasibility of extracting the nucleus-neutron
interaction from measurable cross sections.
Methods: High-energy nucleus-deuteron collision is described by the Glauber
model, in which the proton and neutron configuration of the deuteron is
explicitly taken into account.
Results: Our calculation reproduces available experimental total reaction
cross section data on the nucleus-deuteron scattering. The possibility of
extracting the nucleus-neutron total reaction cross section from
nucleus-deuteron and nucleus-proton total reaction cross sections is explored.
The total reaction cross sections of a nucleus by proton, neutron, and deuteron
targets can be expressed, to good accuracy, in terms of the nuclear matter
radius and neutron skin thickness. Incident-energy dependence of the total
reaction cross sections is examined.
Conclusions: The total reaction cross section on a deuteron target includes
information on both the nucleus-neutron and nucleus-proton profile functions.
Measuring the cross sections by deuteron and proton targets is a promising tool
to extract the nuclear size properties.Comment: 9 pages, 5 figures, to appear in Phys. Rev.
The Bloch-Okounkov correlation functions, a classical half-integral case
Bloch and Okounkov's correlation function on the infinite wedge space has
connections to Gromov-Witten theory, Hilbert schemes, symmetric groups, and
certain character functions of \hgl_\infty-modules of level one. Recent works
have calculated these character functions for higher levels for \hgl_\infty
and its Lie subalgebras of classical type. Here we obtain these functions for
the subalgebra of type of half-integral levels and as a byproduct, obtain
-dimension formulas for integral modules of type at half-integral level.Comment: v2: minor changes to the introduction; accepted for publication in
Letters in Mathematical Physic
Exact 1/4 BPS Loop - Chiral Primary Correlator
Correlation functions of 1/4 BPS Wilson loops with the infinite family of 1/2
BPS chiral primary operators are computed in super Yang-Mills
theory by summing planar ladder diagrams. Leading loop corrections to the sum
are shown to vanish. The correlation functions are also computed in the
strong-coupling limit by examining the supergravity dual of the loop-loop
correlator. The strong coupling result is found to agree with the extrapolation
of the planar ladders. The result is related to known correlators of 1/2 BPS
Wilson loops and 1/2 BPS chiral primaries by a simple re-scaling of the
coupling constant, similar to an observation of Drukker, hep-th/0605151, for
the case of the 1/4 BPS loop vacuum expectation value.Comment: 17 pages, 4 figures, a few minor typos correcte
Symmetry and Integrability of Non-Singlet Sectors in Matrix Quantum Mechanics
We study the non-singlet sectors of matrix quantum mechanics (MQM) through an
operator algebra which generates the spectrum. The algebra is a nonlinear
extension of the W_\infty algebra where the nonlinearity comes from the angular
part of the matrix which can not be neglected in the non-singlet sector. The
algebra contains an infinite set of commuting generators which can be regarded
as the conserved currents of MQM. We derive the spectrum and the eigenfunctions
of these conserved quantities by a group theoretical method. An interesting
feature of the spectrum of these charges in the non-singlet sectors is that
they are identical to those of the singlet sector except for the
multiplicities. We also derive the explicit form of these commuting charges in
terms of the eigenvalues of the matrix and show that the interaction terms
which are typical in Calogero-Sutherland system appear. Finally we discuss the
bosonization and rewrite the commuting charges in terms of a free boson
together with a finite number of extra degrees of freedom for the non-singlet
sectors.Comment: 34 pages, 4 figure
Construction of Integrals of Higher-Order Mappings
We find that certain higher-order mappings arise as reductions of the
integrable discrete A-type KP (AKP) and B-type KP (BKP) equations. We find
conservation laws for the AKP and BKP equations, then we use these conservation
laws to derive integrals of the associated reduced maps.Comment: appear to Journal of the Physical Society of Japa
Electrochemical degradation of the dye reactive orange 16 using electrochemical flow-cell
Electrochemical removals of color and organic load from solutions containing the dye reactive orange 16 (RO16) were performed in an electrochemical flow-cell, using a platinum working electrode. The influence of the process variables flow-rate, such as NaCl concentration, applied potential and solution pH, were studied. The best color removal achieved was 93% (λ = 493 nm) after 60 min at 2.2 V vs. RHE electrolysis, using 1.00 g L-1 NaCl as supporting electrolyte. The rises in the concentration of NaCl and applied potential increased the color removal rate. The best total organic carbon removal (57%) was obtained at 1.8 V, without the separating membrane, indicating that the ideal conditions for the color removal are not necessarily the same as those to remove the total organic carbon. The degradation efficiency decreased with the solution pH decrease.As remoções eletroquímicas de cor e do conteúdo orgânico de soluções do corante laranja reativo 16 (RO16) foram efetuadas usando uma célula em fluxo e um eletrodo de trabalho de Pt. As influências das variáveis do sistema, tais como fluxo, concentração de NaCl, potencial aplicado e pH da solução, foram estudadas. A melhor remoção de cor foi de 93% (λ = 493 nm) após 60 min de eletrólise potentiostática a 2,2 V vs. ERH, usando 1,00 g L-1 NaCl como eletrólito suporte. Os aumentos na concentração de NaCl e do potencial aumentam a velocidade de remoção de cor. A melhor remoção de carbono orgânico total (57%) foi obtida com a aplicação de 1,8 V, sem membrana de separação, indicando que as melhores condições para remoção de cor não são necessariamente as melhores para remover conteúdo orgânico. A eficiência de degradação diminui com a diminuição do pH da solução.Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)FAPES
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