Jitter reduction through feedback for picosecond pulsed InGaAsPlasers

Following a comparison of picosecond-pulse generation techniques, feedback schemes are reported for the generation of picosecond pulse trains with improved jitter for both multicontact and conventional single-contact InGaAsP-InP lasers. Subpicosecond jitter is achieved for Q-switched laser sources using a novel optoelectronic feedback scheme. The use of resonant electrical feedback is shown to improve the timing jitter of gain-switched pulses by up to six times. Pulse-to-pulse timing jitter as low as 250 fs is demonstrated for a hybrid of optical and electrical feedback schemes. Limits for timing jitter in diode lasers are established for optoelectronic, electrical, and optical feedback schemes, and the key picosecond pulse generation schemes are compared in terms of timing jitter for the first time     

Atmospheric Chemistry of 2-Ethyl Acrolein

The atmospheric oxidation of the unsaturated aldehyde 2-ethyl acrolein, CH₂=C(C₂H₅)CHO, has been studied in laboratory experiments involving the reaction of ozone with 2-ethyl acrolein in the dark (with cyclohexane added to scavenge the hydroxyl radical), and the sunlight irradiation of 2-ethyl acrolein with NO in air. The major carbonyl products of the 2-ethyl acrolein reaction with ozone are formaldehyde, acetaldehyde, and the dicarbonyl ethylglyoxal, CH₃CH₂COCHO. Sunlight irradiation of 2-ethyl acrolein and NO led to the formation of three carbonyls (formaldehyde, acetaldehyde, and ethylglyoxal) and three peroxyacyl nitrates, (RC(O)OONO₂), including PAN (R = CH₃), PPN (R = C₂H₅), and the unsaturated compound EPAN (R = CH₂=C(C₂H₅)). Mechanisms are outlined for the reactions of ozone and of the hydroxyl radical with 2-ethyl acrolein. These mechanisms are consistent with the observed carbonyl and peroxyacyl nitrate products. Thermal decomposition, a major atmospheric removal process for peroxyacyl nitrates, has been studied for EPAN. The decomposition rate of EPAN relative to that of PAN is 0.59–0.73 at 292–294 K and 1 atm of air. Atmospheric implications of these results are discussed.     

Feedstock aids microPIM parts production: Tiny cogs test the imagination of powder professionals as small parts demand ever-finer materials…

With commercially available PIM feedstock reportedly unable to fulfill the requirements for the microPIM components under investigation, researchers at the Institute for Materials Research III (IMR) in Karlsruhe, Germany, have developed new binder systems for feedstock based on both nanoceramic and ultrafine metallic powders. In the case of ceramics (zirconia) the powders can be as fine as 300 nm, and for metals in the 3μm-5μm particle size range. The powders are used to develop PIM gearwheels (Figure 1) and other components for a demonstrator micro annular gear pump design (Figure 2); however, the technology is also said to be applicable to micro gears used in watches.     

On the "adiabatic approximation" for design of control laws for linear, time-varying systems

Control laws are often designed for linear time-varying processes by solving the algebraic Riccati equation for the optimum control law at each instant of time. Such designs may be called "adiabatic approximations." Although they are not optimum, they can result in closed loop systems which perform well. The stability of systems designed using the adiabatic approximation can be assessed by the "second method of Lyapunov." Stability is assured if a readily computed test matrixF, which depends on the rate of change of the parameters of the system, is negative-definite.     

Fatigue crack initiation and propagation of binder-treated powder metallurgy steels

Many of the targeted applications for powder-metallurgy materials, particularly in the automotive industry, undergo cyclic loading. It is, therefore, essential to examine the fatigue mechanisms in these materials. The mechanisms of fatigue-crack initiation and propagation in ferrous powder-metallurgy components have been investigated. The fatigue mechanisms are controlled primarily by the inherent porosity present in these materials. Since most, if not all, fatigue cracks initiate and propagate at the specimen surface, surface replication was used to determine the role of surface porosity in relation to fatigue behavior. Surface replication provides detailed information on both initiation sites and on the propagation path of fatigue cracks. The effect of microstructural features such as pore size and pore shape, as well as the heterogeneous microstructure on crack deflection, was examined and is discussed. Fracture surfaces were examined to elucidate a mechanistic understanding of fatigue processes in these materials.     

Consent to treatment by minors attending accident and emergency departments: guidelines

The absolute right to refuse medical treatment, even if the reasons are irrational, is confined to competent adults. Children under 16 years can give legal consent to treatment in the absence of consent from those with parental responsibility. Children under 18 years do not, however, have an absolute right to consent, or refuse to consent, to treatment. The views of children assume increasing importance with age and maturity. Accident and emergency medical and nursing staff may face difficult decisions when children, or those with parental responsibility, refuse to consent to medical treatment. This paper presents guidelines designed to guide the decision making process in immediately or potentially life threatening conditions and in non-life-threatening conditions.