Estimation of radiation-source coordinates from satellite-observation data

An algorithm is developed for precision evaluation of optical-radiation-source coordinates from satellite-observation data. The results of a numerical experiment confirm its effectiveness and possibility of use in space metrology. Translated from Izmeritel'naya Tekhnika, No. 7, pp. 3–8, July, 2000.     

Modeling TCP SACK performance over wireless channels with semi-reliable ARQ/FEC

Providing reliable data communications over wireless channels is a challenging task because time-varying wireless channel characteristics often lead to bit errors. These errors result in loss of IP packets and, consequently, TCP segments encapsulated into these packets. Since TCP cannot distinguish packet losses due to bit corruption from those due to network congestion, any packet loss caused by wireless channel impairments leads to unnecessary execution of the TCP congestion control algorithms and, hence, sub-optimal performance. Automatic Repeat reQuest (ARQ) and Forward Error Correction (FEC) try to improve communication reliability and reduce packet losses by detecting and recovering corrupted bits. Most analytical models that studied the effect of ARQ and FEC on TCP performance assumed that the ARQ scheme is perfectly persistent (i.e., completely reliable), thus a frame is always successfully transmitted irrespective of the number of transmission attempts it takes. In this paper, we develop an analytical cross-layer model for a TCP connection running over a wireless channel with a semi-reliable ARQ scheme, where the amount of transmission attempts is limited by some number. The model allows to evaluate the joint effect of stochastic properties of the wireless channel characteristics and various implementation-specific parameters on TCP performance, which makes it suitable for performance optimization studies. The input parameters include the bit error rate, the value of the normalized autocorrelation function of bit error observations at lag 1, the strength of the FEC code, the persistency of ARQ, the size of protocol data units at different layers, the raw data rate of the wireless channel, and the bottleneck link buffer size.     

Space-based information measurement system for locating optical radiation sources. (Some aspects of space metrology)

It is proposed to consider artificial-satellite global observation systems providing remote probing of the Earth from space as space-based information measurement systems performing indirect measurements of some particular property of the observed object, utilizing mathematical modeling and information-processing algorithms. The models and algorithms are integral parts of space-based information measurement systems and to a considerable extent determine the accuracy and confidence in the results obtained. After it has processed the data, the system records an estimate of the parameters of the observed object and the covariance matrix of the estimation errors. The present article analyzes the metrological aspects of the operation of space-based information measurement systems as applied to the particular but practically important problem of locating sources of electromagnetic radiation. Translated from Izmeritel’naya Tekhnika, No. 7, pp. 8–13, July, 1999.     

Convective diffusion in a parallel plate duct with one catalytic wall—laminar flow—first order reaction: Part II: Experimental

The catalytic reaction rate of combustion of hydrogen in air on platinized alumina was measured in a flat rectangular flow reactor with one catalytic wall in laminar flow. Since the rate of reaction is very high, this measurement normally must be made in turbulent flow. However, with the aid of the measured concentration profiles and the analysis presented in Part I, it was possible to ascertain the reaction rate in the laminar flow regime. The rate constants compare well with literature values which were measured in the turbulent flow regime. Average Nusselt numbers for mass transfer calculated for the diffusionally limited cases were in good agreement with those obtained from Part I. A narrow rectangular channel (aspect ratio = 8:1) with 16-in. of one wall comprising the reactive section was constructed for this investigation. The channel has a long preheat section, an adiabatic section with multiple heaters, and thermocouples for maintaining isothermal conditions. Two micrometer mounted probes are inserted through the wall opposite the replaceable catalytic section. Concentrations are measured at the inlet, inside the reactive section, and at the outlet in a mixing chamber.     

DUAL-TEMPERATURE ION EXCHANGE FRACTIONATION

ABSTRACT

This paper reviews the results obtained by studying the dual-temperature ion-exchange fractionation (DTIXF) technique. The DTIXF is based on the use of different affinity at different temperatures of ion exchangers towards ions to be separated. This technique allows to design absolutely reagentless and, as a result, wasteless fractionation technology. The review considers the temperature dependencies of selectivity of commercially available ion-exchange (LX) resins towards components of ionic mixtures of different complexity starting from binary model systems up to naturally existing nonacomponent effluents. A novel approach for predicting the temperature sensitivity of a given LX system is presented and discussed. The same approach has been shown to be applicable for the design of IX resins with temperature-dependent selectivity. The paper also reports the results obtained in the practical application of DTIXF technique for concentration of magnesium from seawater and copper from acidic mine waters. The flowsheets of DTLXF processes are proposed and discussed.     

The electrical delivery of a sublimable II–VI compound by vapor transport in carbon nanotubes

Progress in the field of femtogram (10⁻¹⁵ g) mass delivery relies on finding dependable transport vehicles and uncomplicated methods to tailor the deposition of active substances. Here, current-conductive containers consisting of turbostratic carbon nanotubes were used to store a light-emitting ternary alloy and guide its delivery on demand. We found that the electrically-activated delivery process of this sublimable compound, performed inside a transmission electron microscope, was highly dependent on factors such as the substrate type and current injection mode. Furthermore, our observations suggest that the alleged “missing matter” problem is not solely due to surface migration. Besides extending the field of electrical delivery to the realm of functional materials, the extrusion and mass transport of a sublimable II–VI compound demonstrates that it is possible to guide vapor migration using a carbon nanotube support.     

Internal geometry evaluation of non-crimp 3D orthogonal woven carbon fabric composite

Measurements of the internal geometry of a carbon fiber non-crimp 3D orthogonal woven composite are presented, including: waviness of the yarns, cross sections of the yarns, dimensions of the yarn cross sections, and local fiber volume fraction. The measured waviness of warp and fill yarns are well below 0.1%, which shows that the fabric termed here “non-crimp” has nearly straight in-plane fibers as-produced, and this feature is maintained after going through all steps of fabric handling and composite manufacturing. The variability of dimensions of the yarns is in the range of 4–8% for warp and fill directions, while the variability of the yarn spacing is in the range of 3–4%. These variability parameters are lower than respective ranges of variability of the yarn waviness and the cross-sectional dimensions in typical carbon 2D weave and 3D interlock weave composites, which are also illustrated in this work for comparison.     

Reactor technology options for distributed hydrogen generation via ammonia decomposition: A review

Hydrogen (H₂) fuel obtained via thermo-catalytic ammonia (NH₃) decomposition is rapidly attracting considerable interest for portable and distributed power generation systems. Consequently, a variety of reactor technologies are being developed in view of the current lack of infrastructure to generate H₂ for proton exchange membrane (PEM) fuel cells. This paper provides an extensive review of the state-of-the-art reactor technology (also referred to as reactor infrastructure) for pure NH₃ decomposition. The review strategy is to survey the open literature and present reactor technology developments in a chronological order. The primary objective of this paper is to provide a condensed viewpoint and basis for future advances in reactor technology for generating H₂ via NH₃ decomposition. Also, this review highlights the prominent issues and prevailing challenges that are yet to be overcome for possible market entry and subsequent commercialization of various reactor technologies. To our knowledge, this work presents for the first time a review of reactor infrastructure for distributed H₂ generation via NH₃ decomposition. Despite commendable research and development progress, substantial effort is still required if commercialization of NH₃ decomposition reactor infrastructure is to be realized.     

Concept of Effective Strain Rate: Different Approaches

The term “effective strain rate” is frequently encountered in literature devoted to the ice-structure interaction problem. As a rule, it is defined as a ratio between indentation velocity and structure width, multiplied by a certain nondimensional factor (αV∕d). Usually this parameter is used to separate different interaction regimes or different types of ice behavior during the indentation process. The concept of an effective strain rate, (esr) seems to be quite useful because it allows the comparison of the results of experiments conducted at different scales if esr is properly defined. What is more, the correct definition of esr may help to apply the results obtained on the basis of small-scale laboratory tests to real ice-resistant structures. On the other hand, the overall concept of an effective strain rate definitely lacks a fundamental basis and there is no consensus on the value of the nondimensional factor α. The present paper discusses various approaches to the definition of esr and gives a few analytical expressions for esr derived for different indentation problems.