1,793 research outputs found
Redetermination of para-aminopyridine (fampridine, EL-970) at 150 K
The structure of fampridine (EL-970) or 4-aminopyridine, Câ
HâNâ, has been redetermined at 150 K. The room-temperature structure has been reported previously [Chao & Schempp (1977). Acta Cryst. B33, 1557-1564]. Pyramidalization at the amine N atom occurs in fampridine, with the N atom 0.133 (11) Ă
from the plane of the three C/H/H atoms to which it is bonded; the interplanar angle between the pyridyl ring and NH2 group is 21 (2)°. Aggregation in the solid state occurs by N-H...N and N-H...[pi](pyridine) interactions with N...N and N...[pi](centroid) distances of 2.9829 (18) and 3.3954 (15) Ă
, respectively; a C-H...[pi](pyridine) contact completes the intermolecular interactions [C...[pi](centroid) = 3.6360 (16) Ă
]
Ethyl and isopropyl 4-ferrocenylbenzoate.
The title compounds, [Fe(C5H5)(C14H13O2)] and [Fe(C5H5)-
(C15H15O2)], respectively, contain the ferrocenyl 5(C5H4) and
phenylene ±C6H4± rings in a nearly coplanar arrangement,
with interplanar angles of 6.88 (12) and 10.5 (2), respectively.
Molecules of the ethyl ester form dimers through 5(C5H5)CĂ
H O C hydrogen bonds, with graph set R22
(20), and,
together with Csp3ĂH (C5H5) interactions, generate a
one-dimensional column (irregular ladder). Molecules of the
isopropyl ester aggregate through 5(C5H5)CĂH (C6H4)
interactions
An explicit height bound for the classical modular polynomial
For a prime m, let Phi_m be the classical modular polynomial, and let
h(Phi_m) denote its logarithmic height. By specializing a theorem of Cohen, we
prove that h(Phi_m) <= 6 m log m + 16 m + 14 sqrt m log m. As a corollary, we
find that h(Phi_m) <= 6 m log m + 18 m also holds. A table of h(Phi_m) values
is provided for m <= 3607.Comment: Minor correction to the constants in Theorem 1 and Corollary 9. To
appear in the Ramanujan Journal. 17 pages
Are Student Self-Assessments a Valid Proxy for Direct Assessments in Efforts to Improve Information Systems Courses and Programs? An Empirical Study
Accrediting agencies in the United States require business schools to conduct ongoing assessment directed at continuous improvement of their instruction. Because direct assessment efforts are usually more time consuming and resource-intensive than indirect assessment, it would be helpful if indirect assessment could be used as an effective alternative, at least on occasion. The validity of one indirect method, student self-assessment, has been debated in the research literature. This study compares results of direct measures and student self-assessments for learning outcomes in an Information Systems course. We find student self-assessments are valid proxies for direct assessment when used with some types of learning outcomes but not others. We discuss possible reasons for the difference and the implications for assessment in Information System programs
Resonant magnetic mode in superconducting 2-leg ladders
The spin dynamics of a doped 2-leg spin ladder is investigated by numerical
techniques. We show that a hole pair-magnon boundstate evolves at finite hole
doping into a sharp magnetic excitation below the two-particle continuum. This
is supported by a field theory argument based on a SO(6)-symmetric ladder.
Similarities and differences with the resonant mode of the high-T cuprates
are discussed.Comment: 5 pages, 5 figure
Implementing Direct and Indirect Assessment in the MIS Curriculum
Assessment and continuous improvement have become focus areas for accrediting agencies. The process used to develop assessment plans within a sequence of MIS courses at a major midwestern university is described. The process includes establishing student outcomes, developing assignments that tap into these outcomes, and utilizing both direct and indirect assessment measures. Actionable insights that can be gleaned to improve pedagogy from the use of both direct and indirect measures are described
H I ABSORPTION TOWARD H II REGIONS AT SMALL GALACTIC LONGITUDES
We make a comprehensive study of H I absorption toward H II regions located within |l| < 10°. Structures in the extreme inner Galaxy are traced using the longitude-velocity space distribution of this absorption. We find significant H I absorption associated with the Near and Far 3 kpc Arms, the Connecting Arm, Bania's Clump 1, and the H I Tilted Disk. We also constrain the line-of-sight distances to H II regions, by using H I absorption spectra together with the H II region velocities measured by radio recombination lines
Black holes as mirrors: quantum information in random subsystems
We study information retrieval from evaporating black holes, assuming that
the internal dynamics of a black hole is unitary and rapidly mixing, and
assuming that the retriever has unlimited control over the emitted Hawking
radiation. If the evaporation of the black hole has already proceeded past the
"half-way" point, where half of the initial entropy has been radiated away,
then additional quantum information deposited in the black hole is revealed in
the Hawking radiation very rapidly. Information deposited prior to the half-way
point remains concealed until the half-way point, and then emerges quickly.
These conclusions hold because typical local quantum circuits are efficient
encoders for quantum error-correcting codes that nearly achieve the capacity of
the quantum erasure channel. Our estimate of a black hole's information
retention time, based on speculative dynamical assumptions, is just barely
compatible with the black hole complementarity hypothesis.Comment: 18 pages, 2 figures. (v2): discussion of decoding complexity
clarifie
Order of Two-Dimensional Isotropic Dipolar Antiferromagnets
The question of the existence of order in two-dimensional isotropic dipolar
Heisenberg antiferromagnets is studied. It is shown that the dipolar
interaction leads to a gap in the spin-wave energy and a nonvanishing order
parameter. The resulting finite N\'eel-temperature is calculated for a square
lattice by means of linear spin-wave theory.Comment: 10 pages, REVTEX, 1 figure available upon request, TUM-CP-93-0
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