John Dahlgren served in the U.S. Navy for nearly 35 years, sometimes in a sea-keeping capacity but mostly developing large naval artillery. To-day, his name, when recognised by students of naval ordnance, is associated with teh Dahlgren or ‘soda bottle shaped’ gun of 9 to 11 inch calibre. He designed, developed and lived to see his guns installed aboard warships and used to considerable effect, especially in the American Civil War. However, a nearly indistinguishable external design of gun was developed for the Army by T. J. Rodman, an officer now even less known than Dahlgren and whose researches and contributions are virtually forgotten. This paper and that in Ref. [1] attempt to appreciate (along with other technical questions of the period) the different ways pursued by these men towards the final development of the ‘soda bottle shaped’ gun, though it is a matter still not entirely understood.
Both names are totally omitted from several ‘classic’ books on artillery and this is a grave misfortune. Besides trying to throw factual light on the Dahlgren-Rodman controversy and the priority issue (though not one pursued with acrimony by the men themselves at the time), the paper describes Admiral Dahlgren's general career, the books he wrote, the technical problems he attacked and the problematic ordnance discussions of his day, to which he gave his life.
The work of Dahlgren and Rodman, in particular, saw the elevation of American gun design from the level of mere copying (of early Columbiads in the first decades of the century) to that which compelled attention from, and study by, the super-powers of the day, Great Britain, France and Russia. 相似文献
The effect on mechanical behavior of ZrO2 additions to a dental porcelain was investigated. The ZrO2 was introduced into the glassy matrix phase of the porcelain by refritting the all-glass porcelain constituent. X-ray diffraction indicated that a sizeable fraction of the ZrO2 was retained in the tetragonal form after the porcelain was fired. Zirconia additions to the porcelain produced substantial improvements in fracture toughness, strength, and thermal shock resistance. 相似文献
The present work investigates the efficacy and applicability of interior global orthogonal point collocation method to the axisymmetric nonlinear analysis of elastic circular plates and shallow spherical shells subjected to uniformly distributed transverse load. Spacewise discretisation has been carried out using a polynomial expansion with the zeros of a Chebyshev polynomial as collocation points. Timewise integration has been carried out with Newmark k-β scheme corresponding to average acceleration method. The static response and snap-through buckling results, as well as, the dynamic response and dynamic buckling results under a uniformly distributed step load have been obtained and found to agree closely with the available results. 相似文献
An efficient method, based on the Schwarz–Neumann alternating technique, is presented for computing weight functions of a general solid (3-D as well as 2-D), with embedded or surface-flaw configurations. The total rate of change of the crack-opening displacements, due to simple perturbations of crack-dimension characteristics, is conveniently decomposed into the infinite-domain and boundary-correction parts. The former is determined from available analytical solutions of ideal-shaped cracks, whereas the latter is computed numerically by imposing nil boundary-traction requirements for the displacement field corresponding to the weight functions. Numerical examples, with solutions for 3-D weighted-average and local stress intensity factors, indicate that the proposed method is very accurate and efficient. 相似文献
A digital signal processor-based control system for the permanent magnet-assisted reluctance synchronous machine, with the emphasis on dynamic performance, is proposed. A classical design approach is used to design the current and speed controllers for the machine. The stator current of the machine is controlled in such a way that the current angle in the dq synchronous reference frame is constant. The load-torque is estimated using a state space observer and compensation current based on the estimated load is used to improve the dynamic performance of the drive. The control system design is machine specific as it relies on data from finite-element analysis. Simulated and measured results on a 110-kW power level show that the resulting control system is stable and robust with good dynamic performance 相似文献
The structure of the recently introduced Brazilian government programme for monitoring pesticide residues in six major agricultural products is described. Residues found from the analysis of samples of tomatoes and strawberries are discussed in detail. The much greater frequency of detection of pesticide residues, many of which are not approved for use in Brazil, in produce being sold on the domestic market, as opposed to that produced for export, is of major concern. It is perceived that this new monitoring programme will become permanent and be used to underpin enforcement actions that will need to be taken to reduce the numbers of incidents of illegal residues occurring, particularly in fresh fruits and vegetables. 相似文献
Reaction models are proposed to quantify the hydration products and to determine the composition of C–S–H from alkali-activated
slags (AAS). Products of the slag hydration are first summarized from observations in literature. The main hydration products
include C–S–H, hydrotalcite, hydrogarnet, AFm phases (C4AH13 and C2ASH8) and ettringite. Then, three stoichiometric reaction models are established correlating the mineral composition of slag (the
glass part) with the hydration products. Using the proposed models, quantities of hydration products and composition of C–S–H
are determined. The models are validated with a number of experimental investigations reported in literature, yielding good
agreement, i.e., these models can successfully predict the hydration reaction of AAS. The models are furthermore applied to
calculate the retained water in the hydration products of AAS in different hydration states and a general hydration equation
of AAS is derived. As an illustration to one of the model applications, chemical shrinkage of the AAS cement paste in different
hydration states are predicted. The chemical shrinkage of AAS is shown to be remarkably higher than OPC. Furthermore, phase
distribution in the hardened AAS paste and the porosity are calculated. 相似文献
Flux pinning characteristics have been investigated for the Nbx Ti100-x/Nb(x = 65, 50 and 28) and Nb28Ti72/Nb65Ti35 superconductor(S)/superconductor(S′) multilayers. The maximum of the pinning force Fp⊥ max perpendicular to the layer plane as a function of the structure modulation length λ has a peak in the quasi-two-dimensional region (λ~20 nm). The maximum. values of the Fp⊥ max versus λ curve are proportional to the difference of the GL coherence length (ξGL) between the superconductive sublayers S and S′. The results suggest that the large Fp⊥ max in the S/S′ multilayer is caused by the repulsive pinning force due to Nb layers with larger ξGL. 相似文献