34,324 research outputs found
Sun angle calculator
A circular computer and system is disclosed for determining the sun angle relative to the horizon from any given place and at any time. The computer includes transparent, rotatably mounted discs on both sides of the circular disc member. Printed on one side of the circular disc member are outer and inner circular sets of indicia respectively representative of site longitude and Greenwich Mean Time. Printed on an associated one of the rotatable discs is a set of indicia representative of Solar Time. Printed on the other side of the circular disc member are parallel lines representative of latitude between diametral representations of North and South poles. Elliptical lines extending between the North and South poles are proportionally disposed on the surface to scale Solar Time in hours
Killian-Jamieson diverticulum mimicking a suspicious thyroid lesion
Killian-Jamieson diverticulum represents a rare form of esophageal diverticulum originating on the anterolateral wall of the cervical esophagus. Despite its rarity, it is crucial to recognize this entity, with such specific imaging findings, to avoid unnecessary invasive procedures such as fine-needle aspiration or even surgery.info:eu-repo/semantics/publishedVersio
High-speed T-38A landing gear extension loads
Testing of T-38A landing gear extension at high speed and high altitude is described. The mechanisms are shown together with peak hydraulic pressure data during landing gear deployment with active and inactive strut door flaps. Results of strain gage measurements of stress on various structural members are included
Abundances of trace elements Na, Sc, Cr, Mn, Fe, Co, and Cu in chondrules and meteorites in IN meteorites and terrestrial matter and U in type I carbonaceous chondrites Quarterly progress report, 1 Mar. - 15 Jun. 1966
Abundances of sodium, scandium, chromium, iron, manganese, cobalt, copper, indium, and uranium in chondrules, chondrites, and meteorites determined by neutron activation analysi
Harmonic equiangular tight frames comprised of regular simplices
An equiangular tight frame (ETF) is a sequence of unit-norm vectors in a
Euclidean space whose coherence achieves equality in the Welch bound, and thus
yields an optimal packing in a projective space. A regular simplex is a simple
type of ETF in which the number of vectors is one more than the dimension of
the underlying space. More sophisticated examples include harmonic ETFs which
equate to difference sets in finite abelian groups. Recently, it was shown that
some harmonic ETFs are comprised of regular simplices. In this paper, we
continue the investigation into these special harmonic ETFs. We begin by
characterizing when the subspaces that are spanned by the ETF's regular
simplices form an equi-isoclinic tight fusion frame (EITFF), which is a type of
optimal packing in a Grassmannian space. We shall see that every difference set
that produces an EITFF in this way also yields a complex circulant conference
matrix. Next, we consider a subclass of these difference sets that can be
factored in terms of a smaller difference set and a relative difference set. It
turns out that these relative difference sets lend themselves to a second,
related and yet distinct, construction of complex circulant conference
matrices. Finally, we provide explicit infinite families of ETFs to which this
theory applies
Large quantum fluctuations in the strongly coupled spin-1/2 chains of green dioptase: a hidden message from birds and trees
The green mineral dioptase Cu6Si6O18(H2O)6 has been known since centuries and
plays an important role in esoteric doctrines. In particular, the green
dioptase is supposed to grant the skill to speak with trees and to understand
the language of birds. Armed with natural samples of dioptase, we were able to
unravel the magnetic nature of the mineral (presumably with hidden support from
birds and trees) and show that strong quantum fluctuations can be realized in
an essentially framework-type spin lattice of coupled chains, thus neither
frustration nor low-dimensionality are prerequisites. We present a microscopic
magnetic model for the green dioptase. Based on full-potential DFT
calculations, we find two relevant couplings in this system: an
antiferromagnetic coupling J_c, forming spiral chains along the hexagonal c
axis, and an inter-chain ferromagnetic coupling J_d within structural Cu2O6
dimers. To refine the J_c and J_d values and to confirm the proposed spin
model, we perform quantum Monte-Carlo simulations for the dioptase spin
lattice. The derived magnetic susceptibility, the magnetic ground state, and
the sublattice magnetization are in remarkably good agreement with the
experimental data. The refined model parameters are J_c = 78 K and J_d = -37 K
with J_d/J_c ~ -0.5. Despite the apparent three-dimensional features of the
spin lattice and the lack of frustration, strong quantum fluctuations in the
system are evidenced by a broad maximum in the magnetic susceptibility, a
reduced value of the Neel temperature T_N ~ 15 K >> J_c, and a low value of the
sublattice magnetization m = 0.55 Bohr magneton. All these features should be
ascribed to the low coordination number of 3 that outbalances the
three-dimensional nature of the spin lattice.Comment: Dedicated to Stefan-Ludwig Drechsler on the occasion of his 60th
birthday (9 pages, 6 figures
- …