An overview of impact printing
This paper gives an overview of impact printing and reviews some of the more recent advances made in this printing technology. Matrix and fully-formed-character impact-printing technologies are discussed for both serial printers and line printers. The critical electromechanical subassemblies that are described are the hammer unit, the paper-handling system, the inking system, and the type-element system. The mathematics describing printer performance and the operation of some of the subassemblies are presented. The relative simplicity of the impact printer still allows it to be the most economical form of text printing. Its other advantages are reliability, general insensitivity to environment, and the ability to print on the greatest variety of print media.
Inkjet Print Engines
Piezoelectric, thermal, continuous, mechanical, and electrostatic drop ejectors are used in nonimpact digital printers for consumer, office, commercial, and industrial applications. Continuous inkjet generates a stream of droplets that are selectively used for printing. Drop on demand technologies use deflection of a piezoelectric material, superheating of a fluid, pressurized ink controlled by mechanical valves, or electrostatic forces to eject ink. An inkjet print engine consists of the printhead, ink supply, carriage, and service station. Essential components of an inkjet printer are the print engine, media transport, carriage motion, power supply, and data input. Consumer and office printers use piezoelectric or thermal inkjet technology to print with aqueous inks on office papers, whereas large format printers use a range of ink types to print across a wide media set. Continuous and mechanical inkjet are used in industrial applications. Continuous, piezoelectric, and thermal inkjet page wide arrays have recently been incorporated in high speed, single pass, web press configurations. 
 
 
Keywords: 
 
inkjet; 
piezoelectric; 
thermal; 
continuous; 
mechanical; 
electrostatic; 
printhead; 
print engine
The National PKI of Peru: a new certification hierarchy
In order to guarantee secure transactions through the Internet and to generate strong evidence that could be used in case of future legal disputes, several countries around the world have promoted and regulated the use of digital signatures based on Public Key Infrastructure (PKI). However, despite the high expectations, its implementation has achieved neither the desired results nor its globalization. Many of the reasons were discovered years ago, but they are still open problems for the scientific community nowadays. In order to consider the case of the national PKI of the Peruvian state as empirical evidence for studies that address the open problems, this article describes the details about a new certification hierarchy which is expected to overcome some of its predecessors’ limitations. It is also expected that the information disclosed in this article could be useful to other countries for making a preliminary assessment for possible cross-border recognition of Peruvian digital signatures.