Valves of High-Nickel Alloys

The practical difficulties encountered in the manufacture of high-nickel alloys have been enumerated.Some properties of the core sand , facing and backing sands used for moulding have been given. Suitable fluxes are mentioned, but only the proprietary flux acted as a degassing agent and for deoxidation. It has been noticed that despite adoption of all precautions, porosity could not be entirely eliminated. Author has invited remedial suggestions to solve difficulties

Removal of Aluminium from Copper-based Alloys to Ensure Pressure-Tight Castings

The preserce of aluminium is harmful in gunmetal particularly meant for the production of pressure-tight castings, because aluminium, if present in gunmetal even in traces, causes leakage; but the metal is sometimes introduced into the alloy along with the used scraps which may contain aluminium varying from 0.5 to 2.5 per cent., viz. naval parts, impellers, propellers, etc. The passing of dry compressed air under 100 lb./sq. in. through the melt containing different proportions of intentionally added aluminium caused .the removal of even traces of the metal practically without any loss of zinc or tin, as aluminium has the tendency for preferential oxidation. The extent of its removal has been shown to depend on its percentage in the melt and the amount of compressed air passed through it

Flux jumps, Second Magnetization Peak anomaly and the Peak Effect phenomenon in single crystals of YNi2B2CYNi_2B_2C and LuNi2B2CLuNi_2B_2C

We present magnetization measurements in single crystals of the tetragonal $YNi_2B_2C$ compound, which exhibit the phenomenon of peak effect as well as the second magnetization peak anomaly for H $>$ 0.5T (H $||$ c). At the lower field (50mT $<$ H $<$ 200mT), we have observed the presence of flux jumps, which seem to relate to a structural change in the local symmetry of the flux line lattice (a first order re-orientation transition across a local field in some parts of the sample, in the range of 100mT to 150mT). These flux jumps are also observed in a single crystal of $LuNi_2B_2C$ for H $||$ c in the field region from 2 mT to 25 mT, which are compatible with the occurrence of a re-orientation transition at a lower field in a cleaner crystal of this compound, as compared to those of $YNi_2B_2C$. Vortex phase diagrams drawn for H $||$ c in $LuNi_2B_2C$ and $YNi_2B_2C$ show that the ordered elastic glass phase spans a larger part of (H, T) space in the former as compared to latter, thereby, reaffirming the difference in the relative purity of the two samples.Comment: 11 pages, 14 figure

Vortex Phase Diagram of weakly pinned YBa2_2Cu3_3O7−δ_{7-\delta} for H ∥\parallel c

Vortex phase diagram in a weakly pinned crystal of YBCO for H $\parallel$ c is reviewed in the light of a recent elucidation of the process of `inverse melting' in a Bismuth cuprate system and the imaging of an interface between the ordered and the disordered regions across the peak effect in 2H-NbSe$_2$. In the given YBCO crystal, a clear distinction can be made between the second magnetization peak (SMP) and the peak effect (PE) between 65 K and 75 K. The field region between the peak fields of the SMP (H$^m_{smp}$) and the onset fields of the PE (H$^{on}_{pe}$)is not only continuously connected to the Bragg glass phase at lower fields but it is also sandwiched between the higher temperature vortex liquid phase and the lower temperature vortex glass phase. Thus, an ordered vortex state between H$^m_{smp}$ and H$^{on}_{pe}$ can get transformed to the (disordered) vortex liquid state on heating as well as to the (disordered) vortex glass state on cooling, a situation analogous to the thermal melting and the inverse melting phenomenon seen in a Bismuth cuprate.Comment: Presented in IWCC-200

Free flap pulse oximetry utilizing reflectance photoplethysmography

The successful salvage of a free flap is dependent on the continuous monitoring of perfusion. To date there is no widely accepted and readily available post-operative monitoring technique to reliably assess the viability of free flaps by continuously monitoring free flap blood oxygen saturation. In an attempt to overcome the limitations of the current techniques a reflectance photoplethysmographic (PPG) processing system has been developed with the capability of real-time estimation of arterial oxygen saturation (SpO2) levels implemented in LabVIEW. This system was evaluated in clinical measurements on five patients undergoing breast reconstruction using Deep Inferior Epigastric Perforator (DIEP) flap. Good quality PPG signals were obtained from the flaps and fingers simultaneously. The estimated free flap SpO2 values were in broad agreement with the oxygen saturation readings from the commercial pulse oximeter. The results suggest that reflectance free flap photoplethysmography can be used as a continuous monitoring technique to non-invasively monitor the perfusion of free flaps

Development of a Reflectance Photoplethysmographic Sensor used for the Assessment of Free Flap Perfusion

Monitoring of free flap perfusion and early identification of flap failure is an indispensable prerequisite for flap salvage. Although many methods of free flap monitoring are available, there is still no single reliable continuous non-invasive perfusion monitoring technique which will also assist in the early recognition of flap failure. In order to overcome the current technological limitations, we have developed a multi-wavelength photoplethysmographic (PPG) sensor and processing system to systematically investigate the perfusion mechanism in flaps used in reconstructive plastic microsurgery. The new prototype reflectance photoplethysmographic sensor was evaluated on three anaesthetized patients undergoing elective breast reconstructive (Deep Inferior Epigastric Perforator Flap) surgery. PPG signals were successfully obtained pre-operatively, intra-operatively and post-operatively. These preliminary results suggest that a PPG sensor may be a suitable method for evaluating the perfusion of free flap

Effects of Cooling Rate on the Formation of Kappa Phase in the Cu-Al-Ni-Fe-Mn System

Aluminium bronzes of the complex type produced by the addition of Fe, Ni, and Mn in amounts of the order of 5%, 5% and 1% respectively, with Al close to 10% find wide-spread use as naval propeller material and in other marine applications. Their excellent properties are attributed to the transformation of the high temperature beta phase to an additional phase termed kappa in the alpha matrix. As the mode of formation of the kappa` phaseis reported to be influenced by the boqing rate,- which in turn affects the mechanical properties and corrosion resistance of the alloy, an attempt has been made to study the effects of coolings rates on the types, sizes, shapes, hardness and composition of the kappa phase using, metall-ographic techniques and microprobeanalysis

The applicability of size-factor and electron concentration concepts to alloying behaviour of copper

DURING the last forty years there has been much progress in the understanding of principles governing the formation of alloys. These have been put forward in the form of empirical generalisations and schemes involving factors like valencies, size-factors, etc. and as has happened with all other branches of science empirical formulations forming the basis for advances in theory, the enunciated empirical rules have formed the basis for advances in the theory of alloys. In the formulation of these empirical generalisations it is natural that alloys of simple metals should have played a major role, for with simple metals complicating influences governing alloy formation are minimised.Copper being a simple metal1 has therefore found much favour for being chosen for understanding electronic structure of metals and it has also been used in the study of alloys for formulating empirical rules of alloy formation. These rules are due to the work of Hume-Rothery and his collaborators2a in 1930s and were advanced from a study of alloy systems of copper, silver and gold with other group B metals