24,742 research outputs found
Flex flap
To provide flap with large upper surface radius as required for airplanes with over-the-wing blowing, distort upper surface of flap by actuator. Flap can be used as control surface at leading as well as trailing edges and, with minor modification, as variant of Jacobs-Hurkamp air flap
Commensurate to incommensurate magnetic phase transition in Honeycomb-lattice pyrovanadate Mn2V2O7
We have synthesized single crystalline sample of MnVO using
floating zone technique and investigated the ground state using magnetic
susceptibility, heat capacity and neutron diffraction. Our magnetic
susceptibility and heat capacity reveal two successive magnetic transitions at
19 K and 11.8 K indicating two distinct magnetically
ordered phases. The single crystal neutron diffraction study shows that in the
temperature () range 11.8 K 19 K the magnetic structure is
commensurate with propagation vector , while upon lowering
temperature below 11.8 K an incommensurate magnetic order emerges
with and the magnetic structure can be represented by
cycloidal modulation of the Mn spin in plane. We are reporting this
commensurate to incommensurate transition for the first time. We discuss the
role of the magnetic exchange interactions and spin-orbital coupling on the
stability of the observed magnetic phase transitions.Comment: 8 pages, 7 figure
A novel chromosome segregation mechanism during female meiosis.
In a wide range of eukaryotes, chromosome segregation occurs through anaphase A, in which chromosomes move toward stationary spindle poles, anaphase B, in which chromosomes move at the same velocity as outwardly moving spindle poles, or both. In contrast, Caenorhabditis elegans female meiotic spindles initially shorten in the pole-to-pole axis such that spindle poles contact the outer kinetochore before the start of anaphase chromosome separation. Once the spindle pole-to-kinetochore contact has been made, the homologues of a 4-μm-long bivalent begin to separate. The spindle shortens an additional 0.5 μm until the chromosomes are embedded in the spindle poles. Chromosomes then separate at the same velocity as the spindle poles in an anaphase B-like movement. We conclude that the majority of meiotic chromosome movement is caused by shortening of the spindle to bring poles in contact with the chromosomes, followed by separation of chromosome-bound poles by outward sliding
Nonperturbative renormalization group in a light-front three-dimensional real scalar model
The three-dimensional real scalar model, in which the symmetry
spontaneously breaks, is renormalized in a nonperturbative manner based on the
Tamm-Dancoff truncation of the Fock space. A critical line is calculated by
diagonalizing the Hamiltonian regularized with basis functions. The marginal
() coupling dependence of the critical line is weak. In the broken
phase the canonical Hamiltonian is tachyonic, so the field is shifted as
. The shifted value is determined as a function of
running mass and coupling so that the mass of the ground state vanishes.Comment: 23 pages, LaTeX, 6 Postscript figures, uses revTeX and epsbox.sty. A
slight revision of statements made, some references added, typos correcte
Magnetoelectric polarizability: A microscopic perspective
We extend a field theoretic approach for the investigation of the electronic
charge-current density response of crystalline systems to arbitrary applied
electromagnetic fields. The approach leads to the introduction of microscopic
polarization and magnetization fields, as well as free charge and current
densities, the dynamics of which are described by a lattice gauge theory. The
spatial averages of such quantities constitute the fields of macroscopic
electrodynamics. We implement this formalism to study the orbital electronic
response of a class of insulators to applied uniform dc electric and magnetic
fields at zero temperature. To first-order in the applied fields, the free
charge and current densities vanish; thus the response of the system is
characterized by the first-order modifications to the microscopic polarization
and magnetization fields. Associated with the dipole moment of the microscopic
polarization (magnetization) field is a macroscopic polarization
(magnetization), for which we extract various response tensors. We focus on the
orbital magnetoelectric polarizability (OMP) tensor, and find the accepted
expression as derived from the "modern theory of polarization and
magnetization." Since our results are based on the spatial averages of
microscopic fields, we can identify the distinct contributions to the OMP
tensor from the perspective of this microscopic theory, and we establish the
general framework in which extensions to finite frequency can be made.Comment: 24 page
From magnetoelectric response to optical activity
We apply a microscopic theory of polarization and magnetization to
crystalline insulators at zero temperature and consider the orbital electronic
contribution of the linear response to spatially varying, time-dependent
electromagnetic fields. The charge and current density expectation values
generally depend on both the microscopic polarization and magnetization fields,
and on the microscopic free charge and current densities. But contributions
from the latter vanish in linear response for the class of insulators we
consider. Thus we need only consider the former, which can be decomposed into
"site" polarization and magnetization fields, from which "site multipole
moments" can be constructed. Macroscopic polarization and magnetization fields
follow, and we identify the relevant contributions to them; for electromagnetic
fields varying little over a lattice constant these are the electric and
magnetic dipole moments per unit volume, and the electric quadrupole moment per
unit volume. A description of optical activity and related magneto-optical
phenomena follows from the response of these macroscopic quantities to the
electromagnetic field and, while in this paper we work within the independent
particle and frozen-ion approximations, both optical rotary dispersion and
circular dichroism can be described with this strategy. Earlier expressions
describing the magnetoelectric effect are recovered as the zero frequency limit
of our more general equations. Since our site quantities are introduced with
the use of Wannier functions, the site multipole moments and their macroscopic
analogs are generally gauge dependent. However, the resulting macroscopic
charge and current densities, together with the optical effects to which they
lead, are gauge invariant, as would be physically expected.Comment: 24 pages. Minor typographical errors in Eq. 5, 14, 15 of the earlier
version are correcte
Context Dependence, MOPs,WHIMs and procedures Recanati and Kaplan on Cognitive Aspects in Semantics
After presenting Kripke’s criticism to Frege’s ideas on context dependence of thoughts, I present two recent attempts of considering cognitive aspects of context dependent expressions inside a truth conditional pragmatics or semantics: Recanati’s non-descriptive modes of presentation (MOPs) and Kaplan’s ways of having in mind (WHIMs). After analysing the two attempts and verifying which answers they should give to the problem discussed by Kripke, I suggest a possible interpretation of these attempts: to insert a procedural or algorithmic level in semantic representations of indexicals. That a function may be computed by different procedures might suggest new possibilities of integrating contextual cognitive aspects in model theoretic semanti
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