Optimizing the use of dry cutting in rough turning steel operations

The main objective of using cutting fluids in machining operations is the reduction of temperature in the cutting region to increase tool life. However, the advantages offered by cutting fluids have been strongly debated because of their negative effects on the economic aspect, the environment and the health of workers using them. A trend to solve these problems is cutting without fluid, a method named dry cutting, which has been made possible due to technological innovations. This work aims to seek conditions in which dry cutting is satisfactory compared with the flood of fluid (called here wet cutting) usually used. Aiming at this goal, several experiments were carried out varying parameters such as cutting speed, feed, depth of cut and tool material in rough turning of ABNT 1045 steel in dry and wet cutting. The analysis of the results showed that wet turning is, as expected, better for tool life. The second conclusion is that dry cutting cannot be used with large depth of cut. But the main conclusion is that, if the tool material is changed to a more wear resistant one, dry cutting can be used with results very similar to those obtained with a flood of fluid.     

Production and characterization of Si-N films obtained by r.f. magnetron sputtering

Si-N films were deposited by sputtering from an Si₃N₄ target with different deposition pressures and negative substrate bias. The films were amorphous and showed a “featureless” morphology. A high oxygen content was detected in unbiased films. For these films the Si/N ratio was very high compared with the target composition, whereas for biased films the opposite was observed. Si-N films presented cohesive failures for loads as high as 21 N and adhesive failure at 45 N when they were analysed by scratch test. Very high hardness (45 GPa) was obtained, particularly for biased films. Unbiased films were softer, which is attributed to the formation of silicon oxide and/or to a lower compressive stress level.     

Ni/Al Intermetallics Plasma Transferred Arc Processing

TAILORING COMPONENT SUFACES for elevatedtemperature operations has been a goal of researchersduring the last century.Process and material selectionare the key factors for this development.In particularlythe latter can be described to have started with thedevelopment of stainless steels.Ni and Co based alloys,the superalloys,attended the increasing technologicaldemands for higher service temperatures(1).Morerecently the higher operating temperatures ofequipments,such as gas turbines,r…     

Corrosion protection of NdFeB magnets by phosphating with tungstate incorporation

In this investigation the effect of surface treatments on the corrosion resistance of a commercial NdFeB sintered magnet has been investigated. A solution of 10 g L^− 1 NaH₂PO₄, acidified to pH 3.8 has been used for phosphating this magnet. The corrosion resistance of the phosphated magnet was investigated in a 0.10 mol L^− 1 Na₂SO₄ solution by electrochemical impedance spectroscopy and cyclic voltammetry with rotating disc electrode. The obtained results reveal that the resistance decreases with exposure time due to the development of pores and/or defects in the conversion coating exposing the substrate to corrosive attack. The effect of tungstate incorporation into the phosphate conversion coating resulting from a phosphating treatment prior to immersion in the tungstate solution was evaluated. The proposed treatment consists of re-immersing the phosphated samples in a 0.1 mol L^− 1 Na₂WO₄ solution during 72 h at the open circuit potential (OCP). Under these conditions, the corrosion resistance of the magnet was improved and this was attributed to the formation of a protective layer due to the adsorption of tungstate anions at the metallic substrate exposed in the coating, decreasing metal dissolution.     

A linear algebra approach to OLAP

Inspired by the relational algebra of data processing, this paper addresses the foundations of data analytical processing from a linear algebra perspective. The paper investigates, in particular, how aggregation operations such as cross tabulations and data cubes essential to quantitative analysis of data can be expressed solely in terms of matrix multiplication, transposition and the Khatri–Rao variant of the Kronecker product. The approach offers a basis for deriving an algebraic theory of data consolidation, handling the quantitative as well as qualitative sides of data science in a natural, elegant and typed way. It also shows potential for parallel analytical processing, as the parallelization theory of such matrix operations is well acknowledged.     

Factors of low individual degree polynomials

Kaltofen (Randomness in computation, vol 5, pp 375–412, 1989) proved the remarkable fact that multivariate polynomial factorization can be done efficiently, in randomized polynomial time. Still, more than twenty years after Kaltofen’s work, many questions remain unanswered regarding the complexity aspects of polynomial factorization, such as the question of whether factors of polynomials efficiently computed by arithmetic formulas also have small arithmetic formulas, asked in Kopparty et al. (2014), and the question of bounding the depth of the circuits computing the factors of a polynomial. We are able to answer these questions in the affirmative for the interesting class of polynomials of bounded individual degrees, which contains polynomials such as the determinant and the permanent. We show that if \({P(x_{1},\ldots,x_{n})}\) is a polynomial with individual degrees bounded by r that can be computed by a formula of size s and depth d, then any factor \({f(x_{1},\ldots, x_{n})}\) of \({P(x_{1},\ldots,x_{n})}\) can be computed by a formula of size \({\textsf{poly}((rn)^{r},s)}\) and depth d + 5. This partially answers the question above posed in Kopparty et al. (2014), who asked if this result holds without the dependence on r. Our work generalizes the main factorization theorem from Dvir et al. (SIAM J Comput 39(4):1279–1293, 2009), who proved it for the special case when the factors are of the form \({f(x_{1}, \ldots, x_{n}) \equiv x_{n} - g(x_{1}, \ldots, x_{n-1})}\). Along the way, we introduce several new technical ideas that could be of independent interest when studying arithmetic circuits (or formulas).