Signal-to-noise ratio for lightwave systems using avalanchephotodiodes

An expression for the signal-to-noise ratio (SNR) at the output of an avalanche photodiode (APD) receiver is derived that includes the effects of photoinjected carriers, dark-generated carriers, and the receiver circuitry. It is found that the dark current alters both the magnitude of the SNR and the value of the mean multiplication where the SNR achieves its maximum value. The formula differs from the expression that is conventionally used (S.M. Sze, 1981) in that it makes use of different excess noise factors for photo-generated and dark-generated carriers     

A computer program for the optimization of the machining variables

In practice, the values of the machining variables (cutting speed, feed and depth of cut) are determined either by mere experience as usually done by machine tool operators or selected from the available engineering tables which is the usual practice for engineers and technologists. Both methods do not take the process constraints into consideration and merely depend on the personal experience of the employed personnel and hence lead to values which are too far from the economic values. The present paper present a technological optimization technique for turning operations. A computer program has been developed for this purpose, by means of which those optimum values of the machining variables can be obtained, which satisfy the encountered technical and technological constraints and lead to minimum manufacturing cost or maximum production rate as required.     

Relationships between teachers' presentations of classroom tasks and students' engagement in those tasks.

Correlated the presence/absence of various teacher task-presentation statements with measures of subsequent student task engagement to investigate the possibility that expectations about classroom tasks that teachers communicate to students in the process of presenting those tasks might affect student engagement in the tasks. Reading and math lessons were observed (8–25 times each) in 2 4th-grade, 2 5th-grade, and 2 6th-grade classes. Typically, each reading or math period was subdivided into 2–4 tasks. For example, a math period might begin with a review of the previous day's seatwork/homework assignment, followed by presentation of a new concept or skill, followed by presentation of a new assignment. Teacher-presentation data and student-engagement data were collected for each task observed. Contrary to expectation, student engagement was generally higher when teachers moved directly into tasks than when they began with some presentation statement. Within the subset of tasks that were begun with teacher-presentation statements, those presentation statements classified as likely to have negative effects on student engagement were associated with lower student engagement, but there was no corresponding tendency for teacher-presentation statements classified as likely to have positive effects on student engagement to be associated with high rates of student engagement. (11 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Some new negative-impedance convertors

Three new realisations of a negative impedance convertor are proposed. Two of them are of the voltage-inversion type, and the other is of the current-inversion type. In order to satisfy the necessary conditions required of a negative-impedance convertor, certain constraints are imposed on the choice of circuit elements. These conditions are briefly discussed. The proposed new circuits have not been tried out in practice.     

Effect of natural ageing on the dielectric properties of some synthetic rubber mixtures

The dielectric constant ε′ and dielectric loss ε″ have been investigated for SBR samples loaded with some white fillers and for perbunan rubber loaded with silica and carbon black in the frequency range from 60 to 10⁷ Hz at room temperature. The samples were exposed to normal weathering conditions for about five years. The results are compared with those obtained five years before and the differences are interpreted.     

On the performance of ENDF/B-VII.0 data for fast neutron fluence calculations

The newest release of the Evaluated Nuclear Data File, ENDF/B-VII.0, has recently become available, along with the announcement of its significant advances over previous versions. The older ENDF/B releases, however, have been assessed for numerous applications in the past and, as such, currently find wide application in the nuclear industry. An analysis of the influence of the recent upgrade in the data file is thus needed with respect to specific practical applications. The present technical note addresses the effects of modifications of the neutron cross-sections in the ENDF/B-VII.0 library, relative to the preceding ENDF/B-VI.8 release, on calculations of the fast neutron fluence accumulated in a PWR reactor pressure vessel, which is of direct relevance for the licensing and safe operation of nuclear power plants.     

An Accurate Indoor RSSI Localization Algorithm Based on Active RFID System with Reference Tags

Radio frequency identification technologies are popular since their cost is very low and its data transmission based upon radio-wave communications. Where, the objects that are attached to tags are located using the reference tags. However, RSSI information suffers from the multipath propagation and anisotropic interference. So, the localization accuracy will be affected severely. Also, the multipath-propagation increases whenever the reference-tags increase, and so does for the cost, and signal interference. This paper presents a boundary virtual reference label algorithm for improving the indoor-efficiency by inserting some virtual reference tags on the boundary with establishing a linear regression model that eliminates unwanted tag information from the estimation procedure. The Results show that the localisation precision of the proposed approach has significantly increased, at least 78% without adding extra reference tags or radio frequency interference which represents a significant improvement over other algorithms .