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Hexavalent chromium, Cr(VI), is a toxic, mutagenic and carcinogenic species. We report here the semiconductor-based, photocatalytic reduction of Cr(VI) to trivalent chromium, Cr(III), using CdS nanorods (NRs) as the photocatalyst under visible light illumination. The CdS NRs were synthesized by a facile and scalable solvothermal method in which ethylenediamine acts as solvent and morphology controller. The CdS NRs produced were studied by PXRD, Raman, FESEM, EDX, XPS, PL, UV-visible DRS and BET techniques in order to investigate their structural, morphological and optical properties, as well as their porosity. The photoreduction of Cr(VI) to Cr(III) under visible light illumination was performed under a variety of conditions, i.e., varying the irradiation time, pH, substrate concentration, and the amount of photocatalyst. The maximum photoreduction of Cr(VI) to Cr(III) (99%) was achieved using 60 min of irradiation under acidic conditions (pH 4). The excellent photoreduction ability of the CdS NRs can be attributed to their rod-like structure together with their small particle size, large surface area, and clean surfaces. These properties enhanced separation of the photo-generated electron-hole pairs, which was confirmed by the XRD, BET, and PL measurements. In addition, the results of a kinetic study indicated that the photoreduction of Cr(VI) to Cr(III) follows a pseudo-first-order kinetic model. A possible mechanism for the photocatalytic reduction of Cr(VI) to Cr(III) is also proposed in this paper.

The development of a scalable and facile method for the synthesis of visible light driven photocatalytic materials to degrade toxic organic dyes is highly challenging and essential. In this regards, cadmium sulfide (CdS) nanorods and nanowires with controlled aspect ratio, grain size, surface area, and bandgap were synthesized by a simple solvothermal method, and their photocatalytic performances were exploited for the photo-degradation of methylene blue (MB) under simulated solar light. Extensive structural characterizations to identify the origin of the activities were performed. The photocatalytic activity measurements showed that the degradation of MB was 94.41%, 97.24%, 97.88%, and 99.82% for CdS prepared by following four different synthesis routes and increasing trend showed a correlation with the nanostructure morphology changing from nanorod and nanowires with increasing aspect ratio. It has been found that CdS nanowires show more pronounced photocatalytic activity due to the efficient separation of photo-generated electron-hole pairs induced by increased the aspect ratio and higher active surface area.

Massively parallel architectures are gaining momentum thanks to the opportunities for both high performance and low-power consumption. After being a matter for experiments in academia, manycores are now in production and industries with products that rely on high performance, for example, in the field of telecom and radar, are in the process of adopting them. In order to encourage adoption, there is a need for compiler technologies that can make appropriate use of the opportunities of these architectures. Programming languages with constructs that the compiler can easily identify as parallel are a reasonable starting point for these technologies. For example, in CAL (Caltrop Actor Language) [1], a program is organized as a network of actors and these actors can be executed in parallel. As a first approach, if there were enough processors for all actors in the network, each actor could be mapped on to one processor. Writing a compiler is a comprehensive software engineering project and there are a number of tools, data structures and algorithms that have to be chosen and that facilitate the task. Some tools are lexer and parser generators, some data structures are abstract syntax trees and intermediate representations for code generation, some of the algorithms are for analyzing properties of the program and for translating between different data structures. LLVM (Low Level Virtual Machine) [7] is a compiler infrastructure that offers a well defined language and target independent intermediate representation for programs. LLVM also provides compile-time, link-time and run-time optimization. This report discusses the front end of a compiler for CAL, including generation of code to LLVM. The work described in this report translates CAL programs into LLVM's intermediate representation and includes a runtime system that handles intercommunication links between actors and actor scheduling. This is an intermediate step in generating LLVM code for parallel architectures. With this compiler, application developers that need to evaluate different parallel platforms will be able to have their applications written in CAL and only the back-end, form LLVM to the platform, will need to be re-programmed.