A wind-tunnel investigation of the stalling performance of two compressor cascades of different aspect ratios at low speed

Two compressor cascades of aspect ratio 2.10 and 4.83 were tested up to the stall point in a working section with solid side walls. A change in aspect ratio was obtained by changing the blade chord only. The blade section profile was the 10C4/30C50, staggered at 36 degrees with a space-chord ratio of 0.88, and there was no tip clearance. Reynolds number similarity was maintained but its value was kept above a "critical" value. Substantial difference in performance is indicated between the two aspect ratios. The high aspect ratio cascade gives more deflection at the mid-span near stall, but stalls first. The long chord, low aspect ratio blade stalls gently whilst a classical type of sudden stall occurs at the other aspect ratio. Higher pressure rise coefficient is observed at the high aspect ratio, increasing slightly with incidence up to the stall point. Substantially higher spanwise contraction is evident with the low aspect ratio. The order of magnitude of the increase in axial velocity for both cascades is remarkably high. Further tests show that the wall stall, which is present at each incidence, is different in the two cases. It appears that the flow near the wall in the long chord blade rotates further in the passage and the stall near the end wall is more along the blade than along the wall. In the case of the short chord, the separation areas along the blade and the wall are approximately equal. The results for the overall performance are generally consistent with compressor work

The effect of change in axial velocity on the potential flow in cascades

Summary. An analysis is given for the potential flow through a cascade in which a change in axial velocity occurs. An approximate solution of the derived potential equation is obtained and applied first to a flat plate cascade and then to a cascade of blades with camber and thickness. In the former application Weinig\\'s exact solution is used as a first approximation while in the latter application Schlichting\\'s analysis is used as a basic solution and then modified to account for the change in axial velocity. Calculations demonstrate the effect of change in axial velocity on the cascade performance

Sentence Repetition in Deaf Children with Specific Language Impairment in British Sign Language

Children with specific language impairment (SLI) perform poorly on sentence repetition tasks across different spoken languages, but until now, this methodology has not been investigated in children who have SLI in a signed language. Users of a natural sign language encode different sentence meanings through their choice of signs and by altering the sequence and inflections of these signs. Grammatical information is expressed through movement and configurational changes of the hands and face. The visual modality thus influences how grammatical morphology and syntax are instantiated. How would language impairment impact on the acquisition of these types of linguistic devices in child signers? We investigated sentence repetition skills in a group of 11 deaf children who display SLI in British Sign Language (BSL) and 11 deaf controls with no language impairment who were matched for age and years of BSL exposure. The SLI group was significantly less accurate on an overall accuracy score, and they repeated lexical items, overall sentence meaning, sign order, facial expressions, and verb morphological structures significantly less accurately than controls. This pattern of language deficits is consistent with the characterization of SLI in spoken languages even though expression is in a different modality. We conclude that explanations of SLI, and of poor sentence repetition by children with this disorder, must be able to account for both the spoken and signed modalities

Declining resilience of ecosystem functions under biodiversity loss

The composition of species communities is changing rapidly through drivers such as habitat loss and climate change, with potentially serious consequences for the resilience of ecosystem functions on which humans depend. To assess such changes in resilience, we analyse trends in the frequency of species in Great Britain that provide key ecosystem functions-specifically decomposition, carbon sequestration, pollination, pest control and cultural values. For 4,424 species over four decades, there have been significant net declines among animal species that provide pollination, pest control and cultural values. Groups providing decomposition and carbon sequestration remain relatively stable, as fewer species are in decline and these are offset by large numbers of new arrivals into Great Britain. While there is general concern about degradation of a wide range of ecosystem functions, our results suggest actions should focus on particular functions for which there is evidence of substantial erosion of their resilience

Preparation, spectral characterization, structural study, and evaluation of antibacterial activity of Schiff base complexes for VOII, CrIII, MnII, ZnII,CdII and CeIII

A new series of metal ions complexes of VO(II), Cr(III), Mn(II), Zn(II), Cd(II) and Ce(III) have been synthesized from the Schiff bases (4-chlorobenzylidene)-urea amine (L1) and (4-bromobenzylidene)-urea amine (L2). Structural features were obtained from their elemental microanalyses, magnetic susceptibility, molar conductance, FT-IR, UV–Vis, LC-Mass and 1HNMR spectral studies. The UV–Vis, magnetic susceptibility and molar conductance data of the complexes suggest a tetrahedral geometry around the central metal ion except, VOII complexes that has square pyramidal geometry, but CrIII and CeIII octahedral geometry. The biological activity for the ligand (L1) and its Vanadium and Cadmium complexes were studied. Structural geometries of compounds also were suggested in gas phase by using theoretical treatments, using Hyper Chem-6 program for the molecular mechanics and semi-empirical calculations. The heat of formation (?Hf ?) and binding energy (?Eb) in the temperature of 298K for the free ligand (L1) and their metal complexes were calculated by PM3 and ZINDO/I methods. The electrostatic potential of the free ligands were calculated to investigate the reactive sites of the molecules.Bacteriological evaluation of considerable number of these compounds were maintained using organisms Escherichia coli and Staphylococcus aureus,and they were found to exhibit the high effect of activity. This may be attributed to the impact of both the Schiff bases and the metal present in these complexes

Crystal structure of 2-({[5-(adamantan-2-yl)-2-sulfanylidene-1,3,4-oxadiazolidin-3-yl]methyl}amino)benzonitrile, C20H22N4OS

C20H22N4OS, triclinic, P (1) over bar (no. 2), a = 6.8528(3) angstrom, b = 11.3498(5) angstrom, c = 13.3896(9) angstrom, alpha = 114.083(5)degrees, beta = 104.326(4)degrees, gamma = 90.369(3)degrees, V = 914.38(9) angstrom(3), Z = 2, R-gt(F) = 0.0844, wR(ref)(F-2) = 0.2217, T = 160 K