Experimental study of the effects of a six-level phase mask on a digital holographic storage system

We measure the M/# and the bit-error rate of a digital holographic storage system with a 4f optical arrangement for three configurations: recording at the Fourier plane with and without a phase mask and recording outside the Fourier plane without a phase mask. Unexpectedly, no significant change in the dynamic range was observed when a phase mask was used to record in thick crystals. However, we show that a phase mask is a key component in a 4f digital holographic storage system if high-fidelity holograms with optimum volumetric density are to be stored.     

O-ring wear test machine

An abrasive wear test machine was built to study the friction and wear resistance of O-ring materials. In this test machine, two O-ring segments are held against a rotating roughened metal disc. The disc and the O-ring specimens are submerged in an abrasive fluid (drilling mud). The roughened disc surface draws the abrasive particles between the O-ring and the disc surface to produce three-body abrasive wear. Wear occurs on both the specimen and the disc. The wear of the O-ring specimen is determined by weight loss measurements. By careful design of the disc and selection of the test conditions, wear surface similarity was obtained between machine-tested O-rings and O-rings used in field-operated equipment. The testing machine is described, preliminary wear results are presented and photographs of field-worn and machine-worn specimens are shown for three materials.     

Loss detection results on simulated tank data modified by realistic effects

Solution monitoring (SM) is a type of process monitoring (PM) intended to improve nuclear safeguards in large commercial facilities that contain solutions. Typically, masses (M) and volumes (V) are estimated from frequent in-process measurements. Transfers between tanks can be identified in these data, segments of which can then be compared to generate transfer differences (TDs). A safeguards concern might then be raised if either these TDs or deviations in M or V data during “wait” modes become significant. Average M and V TDs should be 0 (perhaps following a bias adjustment) to within a historical limit that is a multiple of the standard deviation of the M or V TD, as should deviations during “wait” modes. Statistical test options can be compared on the basis of their estimated probabilities to detect various material loss scenarios. Multivariate statistical PM options have previously been applied to residuals produced from simulated SM data that had no process variation, only random and systematic measurement errors. This article examines how detection probabilities might be estimated with real data. To do this, realistic effects such as pump carryover, evaporation, condensation, and mixing/sparging, are included in simulated data. In real facilities false alarms are a concern, particularly when data need to be evaluated regularly, on a day-to-day basis. The need to widen control limits to avoid alarming on innocent process variation effects is discussed, and the consequential reduction in DPs is illustrated with numerical examples.     

Signal stability in periodically amplified fiber transmission systems using multiple quantum well saturable absorbers for regeneration

The use of multiple quantum well (MQW) saturable absorbers (SAs) for signal regeneration in periodically amplified fiber transmission systems is explored. A systematic study of signal destabilization resulting from incomplete saturation of MQW SAs used for regeneration, and of means of overcoming such destabilization, is presented. A computer model for MQW SAs, which considers the asymmetric Fabry-Pe/spl acute/rot (AFP) cavity structure commonly employed to increase the contrast of such devices, is presented. The model is used to simulate nitrogen-implanted MQW SAs with < 5 ps recovery time in a transmission system. A comparison is made with results previously obtained for a 10 Gb/s standard single-mode fiber (SMF) recirculating loop transmission experiment using MQW SAs and temporary soliton propagation for signal regeneration. The simulations allow the benefits derived from the two parts of the regenerator to be identified, as well as their contributions to the destabilization of the propagating signal. The error-free transmission distance is improved from /spl sim/ 2000 to > 7000 km when the two components are combined.     

Comparative rates of oxidation of isomeric linolenic acids and their esters

Conclusion 1. The maximum velocities of oxygen absorption as measured by the Warburg-Barcroft respirometer at 40° and expressed as mols 0₂/mol substance/100 minutes was found for a series of octadecatrienoic acids and their esters to be as follows:alpha-eleostearic acid, 2.68;beta-eleostearic acid, 1.02; pseudo-eleostearic acid, 0.64; methyl pseudo-eleostearate, 0.42; alpha-linolenic acid, 0.52; ethyl linolenate, 0.24. 2. The data showed the effect of spatial configuration as well as type of unsaturation and functional grouping on the oxidation reaction. 3. The apparently pure fatty compounds were found to have induction periods, pointing to the autocatalytic nature of the oxidation reaction. This work was aided by grants from the National Livestock and Meat Board, the Hormel Foundation, and the Graduate School of the University of Minnesota. Presented before the Chicago convention of the American Oil Chemists’ Society on October 2, 1940.     

The AMS 14C dating of Iron Age rice chaff ceramic temper from Ban Non Wat,Thailand: First results and its interpretation

Pottery tempered with rice chaff from the early Iron Age cemetery of Ban Non Wat site, northeast Thailand, has been subjected to direct AMS ¹⁴C dating, using low temperature combustion with oxygen as originally developed by authors. The carbon yield (0.2–0.5%) testifies the suitability of this pottery for dating. However, not all the results are in agreement with expected archaeological ages and other ¹⁴C dates from the studied site and neighboring site of Noen U-Loke. This calls for a thorough analysis and interpretation of pottery temper dates from the region.     

Turbo-codes: the ultimate error control codes?

Turbo-codes have attracted a great deal of interest since their discovery in 1993. This paper reviews the reasons for this, in particular their attainment of the ultimate limits of the capacity of a communication channel. The paper describes the two fundamental concepts on which they are based: concatenated coding and iterative decoding. This latter is the real `turbo-principle', which is the real secret of their remarkable performance. The paper also reviews the direction of research in this area since 1993, and shows that, far from bringing coding research to an end, turbo-codes have led to a renaissance. In particular, other applications of the `turbo-principle' have emerged, and these are discussed, along with the practical applications of turbo-codes that have appeared, from mobile radio to deep-space exploration     

Pathways to labor force exit: work transitions and work instability

The purpose of this study is to examine alternative pathways to labor force exit among older men. Based on the life course perspective, we distinguish between crisp exits from the labor force, which are characterized as being unidirectional, and blurred transition patterns, which include repeated exists, entrances, and unemployment spells. Using longitudinal data from the 1984 Survey of Income and Program Participation, we find that one-quarter of the sample of men aged 55 to 74 at first interview experienced at least one transition in labor force status over a 28-month observation period. Fewer than half of these can be characterized as crisp exists from the labor force. Our multivariate analysis suggests that blurred transition patterns are likely part of an effort to maintain economic status in later life.