1,486 research outputs found
NSEG, a segmented mission analysis program for low and high speed aircraft. Volume 1: Theoretical development
A rapid mission analysis code based on the use of approximate flight path equations of motion is presented. Equation form varies with the segment type, for example, accelerations, climbs, cruises, descents, and decelerations. Realistic and detailed characteristics were specified in tabular form. The code also contains extensive flight envelope performance mapping capabilities. Approximate take off and landing analyses were performed. At high speeds, centrifugal lift effects were accounted for. Extensive turbojet and ramjet engine scaling procedures were incorporated in the code
NSEG: A segmented mission analysis program for low and high speed aircraft. Volume 3: Demonstration problems
Program NSEG is a rapid mission analysis code based on the use of approximate flight path equations of motion. Equation form varies with the segment type, for example, accelerations, climbs, cruises, descents, and decelerations. Realistic and detailed vehicle characteristics are specified in tabular form. In addition to its mission performance calculation capabilities, the code also contains extensive flight envelope performance mapping capabilities. For example, rate-of-climb, turn rates, and energy maneuverability parameter values may be mapped in the Mach-altitude plane. Approximate take off and landing analyses are also performed. At high speeds, centrifugal lift effects are accounted for. Extensive turbojet and ramjet engine scaling procedures are incorporated in the code
NSEG: A segmented mission analysis program for low and high speed aircraft. Volume 2: Program users manual
A rapid mission analysis code based on the use of approximate flight path equations of motion is described. Equation form varies with the segment type, for example, accelerations, climbs, cruises, descents, and decelerations. Realistic and detailed vehicle characteristics are specified in tabular form. In addition to its mission performance calculation capabilities, the code also contains extensive flight envelop performance mapping capabilities. Approximate take off and landing analyses can be performed. At high speeds, centrifugal lift effects are taken into account. Extensive turbojet and ramjet engine scaling procedures are incorporated in the code
Effects of lattice geometry and interaction range on polaron dynamics
We study the effects of lattice type on polaron dynamics using a
continuous-time quantum Monte-Carlo approach. Holstein and screened Froehlich
polarons are simulated on a number of different Bravais lattices. The effective
mass, isotope coefficients, ground state energy and energy spectra, phonon
numbers, and density of states are calculated. In addition, the results are
compared with weak and strong coupling perturbation theory. For the Holstein
polaron, it is found that the crossover between weak and strong coupling
results becomes sharper as the coordination number is increased. In higher
dimensions, polarons are much less mobile at strong coupling, with more phonons
contributing to the polaron. The total energy decreases monotonically with
coupling. Spectral properties of the polaron depend on the lattice type
considered, with the dimensionality contributing to the shape and the
coordination number to the bandwidth. As the range of the electron-phonon
interaction is increased, the coordination number becomes less important, with
the dimensionality taking the leading role.Comment: 16 pages, 12 figure
Unconventional pairing in bipolaronic theories
Various mechanisms have been put forward for cuprate superconductivity, which
fit largely into two camps: spin-fluctuation and electron-phonon (el-ph)
mechanisms. However, in spite of a large effort, electron-phonon interactions
are not fully understood away from clearly defined limits. To this end, we use
a numerically exact algorithm to simulate the binding of bipolarons. We present
the results of a continuous-time quantum Monte-Carlo (CTQMC) algorithm on a
tight-binding lattice, for bipolarons with arbitrary interaction range in the
presence of strong coulomb repulsion. The algorithm is sufficiently efficient
that we can discuss properties of bipolarons with various pairing symmetries.
We investigate the effective mass and binding energies of singlet and triplet
real-space bipolarons for the first time, and discuss the extensions necessary
to investigate -symmetric pairs.Comment: Submitted to M2S-HTSC VIII, Dresden 2006, 2 page
Highly sensitive alkane odour sensors based on functionalised gold nanoparticles
We deposit dense, ordered, thin films of Au-dodecanethiol core/shell nanoparticles by the Langmuir-Schafer (LS) printing method, and find that their resistance at ambient temperature responds selectively and sensitively to alkane odours. Response is a rapid resistance increase due to swelling, and is strongest for alkane odours where the alkane chain is similar in length to the dodecane shell. For decane odours, we find a response to concentrations as low as 15 ppm, about 600 times below the lower explosive limit. Response is weaker, but still significant, to aromatic odours (e.g. Toluene, Xylene), while potential interferants such as polar and/or hydrogen-bonding odours (e.g. alcohols, ketones, water vapour) are somewhat rejected. Resistance is weakly dependent on temperature, and recovers rapidly and completely to its original value within the error margin of measurement. (C) 2011 Elsevier B.V. All rights reserved
Program user's manual for optimizing the design of a liquid or gaseous propellant rocket engine with the automated combustor design code AUTOCOM
This computer program manual describes in two parts the automated combustor design optimization code AUTOCOM. The program code is written in the FORTRAN 4 language. The input data setup and the program outputs are described, and a sample engine case is discussed. The program structure and programming techniques are also described, along with AUTOCOM program analysis
Superlight small bipolarons
Recent angle-resolved photoemission spectroscopy (ARPES) has identified that
a finite-range Fr\"ohlich electron-phonon interaction (EPI) with c-axis
polarized optical phonons is important in cuprate superconductors, in agreement
with an earlier proposal by Alexandrov and Kornilovitch. The estimated
unscreened EPI is so strong that it could easily transform doped holes into
mobile lattice bipolarons in narrow-band Mott insulators such as cuprates.
Applying a continuous-time quantum Monte-Carlo algorithm (CTQMC) we compute the
total energy, effective mass, pair radius, number of phonons and isotope
exponent of lattice bipolarons in the region of parameters where any
approximation might fail taking into account the Coulomb repulsion and the
finite-range EPI. The effects of modifying the interaction range and different
lattice geometries are discussed with regards to analytical
strong-coupling/non-adiabatic results. We demonstrate that bipolarons can be
simultaneously small and light, provided suitable conditions on the
electron-phonon and electron-electron interaction are satisfied. Such light
small bipolarons are a necessary precursor to high-temperature Bose-Einstein
condensation in solids. The light bipolaron mass is shown to be universal in
systems made of triangular plaquettes, due to a novel crab-like motion. Another
surprising result is that the triplet-singlet exchange energy is of the first
order in the hopping integral and triplet bipolarons are heavier than singlets
in certain lattice structures at variance with intuitive expectations. Finally,
we identify a range of lattices where superlight small bipolarons may be
formed, and give estimates for their masses in the anti-adiabatic
approximation.Comment: 31 pages. To appear in J. Phys.: Condens. Matter, Special Issue
'Mott's Physics
Whiteness, multiculturalism and nationalist appropriation of Celtic culture: the case of the League of the South and the Lega Nord
The League of the South (USA) and Lega Nord (Italy), formed in 1994 and 1991 respectively, are nationalist organizations that have utilized claims to Celtic ethnicity to further their appeal. In this article we explore these claims, made in relation to the southern United States and northern Italy, and argue that they are used by these organizations to justify exclusionary politics. By claiming a privileged status for Celtic culture, heritage and genealogy, the League of the South and Lega Nord envision their putative nation-states as accommodating other ethnic groups in subordinate roles. We argue that claiming Celtic ethnicity is an implicit appeal to white privilege. In the proposed nation-states of the Confederate States of America and Padania, white authority would be sustained. Further, the way these groups use Celticness allows them to make links to specific historical and material geographies. Claiming Celtic origins enables northern Italians to distinguish themselves from southern Italians, and to make an associated historical-geographical connection between themselves and northern Europe, enabling disassociation from the Mediterranean. The League of the South claim to ‘Anglo-Celtic’ ethnicity enables their membership to distinguish themselves from other residents of the United States, be these non-white residents of the southern states or other white people within the USA. Finally, we suggest that some dominant political commitments to multiculturalism facilitate precisely such claims to Celtic origins, however tenuous, to be made in the name of recognizing and protecting cultural difference
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