Machining of NiTi-shape memory alloys-A review

The emerging trends in the development of advanced smart materials with better unique properties under different environments for a particular application fascinate the researchers and industrialists. Nickel-Titanium based shape memory alloys are exotic materials due to their unique properties such as SME, SE, high damping characteristics, high corrosion and wear resistance and biocompatibility. This article presents an overview of machining processes that can be used to machine the NiTi and its surface induced characteristics such as microhardness, surface roughness, topography, induced layer, residual stress, fatigue and phase transformation. The surface integrity characteristics are discussed for machining of NiTi-SMAs under the category of traditional, non-traditional and micro-machining with the effect of input parameters such as cutting speed, feed, depth of cut, type of lubricant and type of coating material on cutting tool. The conventional machining of NiTi alloys are quite complicated due to high toughness, severe strain hardening, fatigue hardening and distinctive property of NiTi-SMAs such as pseudoelastic and shape memory effect. From this study, non-traditional process is significantly used to machine the NiTi-SMAs due to its better results on surface integrity characteristics. Consequently, future trends are also identified for machining the NiTi-SMAs and to improve the surface integrity characteristics.     

Exact solutions to differential-difference heat and mass transfer equations with a finite relaxation time

Certain exact solutions to the linear differential-difference heat and mass transfer equations with a finite relaxation time are specified. The exact solution to the one-dimensional Stokes problem with the periodic boundary condition when a first-order volume chemical reaction occurs is given. A wide class of exact solutions to the nonlinear differential-difference heat-conduction equation with the following source is described: $$\Theta _t = div[f(T)\nabla T] + g(\Theta ), = T(r,t + \tau ),$$ where T = T(r, t) is temperature and τ is the relaxation time. Certain more complex heat conduction models with a variable relaxation time that can depend on time and a temperature gradient are also considered.     

Crosslinking effect on polydimethylsiloxane elastic modulus measured by custom‐built compression instrument

A macroscopic compression test utilizing a simple custom‐built instrument was employed to measure polydimethylsiloxane (PDMS) elastic modulus. PDMS samples with varying crosslinking density were prepared with the elastomer base to the curing agent ratio ranging from 5 : 1 to 33 : 1. The PDMS network elastic modulus varied linearly with the amount of crosslinker, ranging from 0.57 MPa to 3.7 MPa for the samples tested. PDMS elastic modulus in MPa can be expressed as 20 MPa/PDMS base to curing agent ratio. This article describes a simple method for measuring elastic properties of soft polymeric materials. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 41050.     

Nanostructured Guidance for Peripheral Nerve Injuries: A Review with a Perspective in the Oral and Maxillofacial Area

Injury to peripheral nerves can occur as a result of various surgical procedures, including oral and maxillofacial surgery. In the case of nerve transaction, the gold standard treatment is the end-to-end reconnection of the two nerve stumps. When it cannot be performed, the actual strategies consist of the positioning of a nerve graft between the two stumps. Guided nerve regeneration using nano-structured scaffolds is a promising strategy to promote axon regeneration. Biodegradable electrospun conduits composed of aligned nanofibers is a new class of devices used to improve neurite extension and axon outgrowth. Self assembled peptide nanofibrous scaffolds (SAPNSs) demonstrated promising results in animal models for central nervous system injuries, and, more recently, for peripheral nerve injury. Aims of this work are (1) to review electrospun and self-assembled nanofibrous scaffolds use in vitro and in vivo for peripheral nerve regeneration; and (2) its application in peripheral nerve injuries treatment. The review focused on nanofibrous scaffolds with a diameter of less than approximately 250 nm. The conjugation in a nano scale of a natural bioactive factor with a resorbable synthetic or natural material may represent the best compromise providing both biological and mechanical cues for guided nerve regeneration. Injured peripheral nerves, such as trigeminal and facial, may benefit from these treatments.     

Climate Change, “Grid Neutrality,” and Electricity Distributors

My late colleague and friend Alfred Kahn relayed how President Jimmy Carter hired him in 1977 to head the Civil Aeronautics Board to reform and ultimately deregulate the US airline industry. Accepting the job, he told a group of airline executives (to their fury), “I really don't know one plane from the other. To me they are all marginal costs with wings.” He used that term to signal his intention of reforming the industry in keeping with economic principles, uninfluenced by the romance of air travel.     

Electricity Deregulation Under Siege

It has not been a good few years for the advance of competition in electricity supply in a number of places in the world.     

Benzophenone vs. Copper/Benzophenone in Light‐Promoted Atom Transfer Radical Additions (ATRAs): Highly Effective Iodoperfluoroalkylation of Alkenes/Alkynes and Mechanistic Studies

Iodoperfluooralkylation of terminal alkenes and alkynes is effectively photo‐promoted by benzophenone 2 (BP) or the photoreducible copper(II) complex 1 . In particular, BP at 1 mol% in methanol upon 365 nm irradiation with a low‐pressure mercury lamp (type TLC=thin layer chromatography, 6 W) results in a fast reaction with excellent reaction yields. Complex 1 and BP 2 exhibited very similar reactivity, suggesting that the reactions involving 1 are likely to be governed by the benzophenone photoactivation processes, rather than copper(I)/(II) redox processes. Mechanistic investigations using transient absorption spectroscopy revealed that a deactivation pathway of the benzophenone triplet (³BP*) is via its reaction with the methanol solvent. We propose that the generated radicals, in particular ^.CH₂OH, play a key role in the initiation step forming R_f^. by reacting with R_fI, R_f^. then entering a radical chain cycle. ¹H NMR studies provided evidence that a substantial amount (∼7% NMR yield) of the hemiacetal CH₃OCH₂OH is formed, i.e., the possible by‐product of the reaction between ^.CH₂OH and R_fI. Finally, DFT calculations indicate that a triplet‐triplet energy transfer (TTET) process from ³BP* to perfluorooctyl iodide (C₈F₁₇I) is unlikely or should be rather slow under the reaction conditions, consistent with the transient absorption studies.

     

Exploring the Biosynthesized Metal Nanoparticles for their Catalytic Degradation of Toxic Water Wastes and Antimicrobial Potential

Journal of Inorganic and Organometallic Polymers and Materials - In recent decades, the analysis of nanoparticles is of greater importance for their applications in various fields. This present...