9,972 research outputs found
Critical behaviour of three-dimensional Ising ferromagnets at imperfect surfaces: Bounds on the surface critical exponent
The critical behaviour of three-dimensional semi-infinite Ising ferromagnets
at planar surfaces with (i) random surface-bond disorder or (ii) a terrace of
monatomic height and macroscopic size is considered. The
Griffiths-Kelly-Sherman correlation inequalities are shown to impose
constraints on the order-parameter density at the surface, which yield upper
and lower bounds for the surface critical exponent . If the surface
bonds do not exceed the threshold for supercritical enhancement of the pure
system, these bounds force to take the value of the
latter system's ordinary transition. This explains the robustness of
to such surface imperfections observed in recent Monte Carlo
simulations.Comment: Latex, 4 pages, uses Revtex stylefiles, no figures, accepted EPJB
version, only minor additions and cosmetic change
Platinum thin film resistors as accurate and stable temperature sensors
The measurement characteristics of thin-Pt-film temperature sensors fabricated using advanced methods are discussed. The limitations of wound-wire Pt temperature sensors and the history of Pt-film development are outlined, and the commonly used film-deposition, structuring, and trimming methods are presented in a table. The development of a family of sputtered film resistors is described in detail and illustrated with photographs of the different types. The most commonly used tolerances are reported as + or - 0.3 C + 0.5 percent of the temperature measured
Critical, crossover, and correction-to-scaling exponents for isotropic Lifshitz points to order
A two-loop renormalization group analysis of the critical behaviour at an
isotropic Lifshitz point is presented. Using dimensional regularization and
minimal subtraction of poles, we obtain the expansions of the critical
exponents and , the crossover exponent , as well as the
(related) wave-vector exponent , and the correction-to-scaling
exponent to second order in . These are compared with
the authors' recent -expansion results [{\it Phys. Rev. B} {\bf 62}
(2000) 12338; {\it Nucl. Phys. B} {\bf 612} (2001) 340] for the general case of
an -axial Lifshitz point. It is shown that the expansions obtained here by a
direct calculation for the isotropic () Lifshitz point all follow from the
latter upon setting . This is so despite recent claims to the
contrary by de Albuquerque and Leite [{\it J. Phys. A} {\bf 35} (2002) 1807].Comment: 11 pages, Latex, uses iop stylefiles, some graphs are generated
automatically via texdra
Boundary critical behaviour at -axial Lifshitz points: the special transition for the case of a surface plane parallel to the modulation axes
The critical behaviour of -dimensional semi-infinite systems with
-component order parameter is studied at an -axial bulk
Lifshitz point whose wave-vector instability is isotropic in an -dimensional
subspace of . Field-theoretic renormalization group methods are
utilised to examine the special surface transition in the case where the
potential modulation axes, with , are parallel to the surface.
The resulting scaling laws for the surface critical indices are given. The
surface critical exponent , the surface crossover exponent
and related ones are determined to first order in
\epsilon=4+\case{m}{2}-d. Unlike the bulk critical exponents and the surface
critical exponents of the ordinary transition, is -dependent already
at first order in . The \Or(\epsilon) term of is
found to vanish, which implies that the difference of and
the bulk exponent is of order .Comment: 21 pages, one figure included as eps file, uses IOP style file
Notes on the design of ailerons
Recent data have shown that certain forms or types of ailerons that are in extensive use are in reality quite inefficient and entirely unsuited for the high speeds now realized. The same data indicate that two forms (both shown here) are efficient and satisfactory in every way. The most important characteristics of ailerons are effectiveness under all flight conditions, small moments about the hinge, high efficiency (small yawing moment opposing turn), and simplicity in construction. Information required for the design of ailerons is given for chord, span, area, and plan form
F-5-L Boat Seaplane : performance characteristics
Performance characteristics for the F-5-L Boat Seaplane are given. Characteristic curves for the RAF-6 airfoil and the F-5-L wings, parasite resistance and velocity data, engine and propeller characteristics, effective and maximum horsepower, and cruising performance are discussed
Comparative performance with direct and geared engines
Comprehensive tests were made to compare the performance of the F-5-L Boat Seaplane fitted with direct drive and Liberty engines. Details are given on the test conditions. The conclusions of the comparison tests follow. 1) An F-5-L with geared engines takes off in approximately 90 percent of the time required for the same airplane with standard direct drive engines. An F-5-L with geared engines climbs in 20 minutes to an altitude approximately 20 percent greater than that obtained with the standard direct drive on the same airplane. 3) There is a large difference between the climbs of the two airplanes of the same type. This difference will always be more pronounced when the climb is normally slow. In the case of the F-5-L airplanes under construction, it is of the order of a 10 percent difference in altitude on a 20 minute climb. 4) The maximum speed of an F-5-L with geared engines is about 3.5 percent greater than the maximum speed of the same airplane with standard direct drive engines (at the same engine r.p.m.). 5) The fuel consumption is probably less effected by the type of drive than by inherent differences in the performance of different airplanes
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