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It has often been suggested that actual or anticipated final grades may influence the ratings given by students in student experience surveys but few studies have been able to test this using actual grades. A study was carried out involving six courses over all four year levels of an undergraduate engineering programme, where students were asked to identify themselves in an experience survey by providing their student ID on the survey form. The aim of the study was to investigate a number of questions related to the readiness of students to identify themselves, and to examine any correlation between final examination grades, ratings of student satisfaction and the students’ perception of their level of understanding of material in their courses. Students were discovered to have a poor idea of how well they understand the concepts presented in their courses. This lack of an accurate idea of their own understanding is particularly important because ‘student understanding’ correlated to the ratings they gave...

The concept of a teacher profile, determined from student evaluations of his or her teaching, is well established in the literature. A complementary concept, that of the student profile, has not been investigated to the same extent, and this may be partly due to the lack of identifiable evaluation returns from the students from most surveys of learning and teaching. In the current study several cohorts of students who undertook evaluations of teaching had the opportunity to include their Student ID on the survey form. This meant that it was possible to investigate returns from individual students to more than one course and teacher, and to see if there was any characteristic pattern in the evaluation. The results show that while not strong, there was evidence of students having a characteristic profile that affected the way they filled out the survey forms in each of their classes. Although the effect was statistically significant for both classes surveyed in the study, the correlation was stronger for the higher year level students. The results are important as they show that the teacher profiles are partly due to the student profiles, and this should be recognised by those reacting to student feedback.

Tilt-rotor aircraft combine the advantages of helicopters (i.e. ability to take-off and land in confined spaces and to hover and loiter at low speed) with the high speed and economy of turbo-props. The paper reports on the modelling and longitudinal control of a large tilt-rotor aircraft. The aim is to improve the handling qualities, which are characterized by poor predictability due to pitch drop-back, and to suppress key structural loads.

We developed a simple vitrification technique for bovine embryos that could permit direct transfer. Embryos were produced in-vitro by standard procedures. The base medium for cryopreservation was a chemically defined medium similar to SOF + 25 mM Hepes and 0.25% fatty acid free bovine serum albumin (FAF-BSA) (HCDM2). In experiment 1, embryos were first exposed to 3.5M ethylene glycol (V1) for 1, 2 or 3 min at room temperature (20-24 degrees C), and then moved to 7 M ethylene glycol (V2) at 4 or 20-24 degrees C and loaded in 0.25-mL straws. After 45 s in 7 M ethylene glycol, straws were placed in liquid nitrogen. Embryos that were loaded at 20-24 degrees C had higher survival rates than those loaded at 4 degrees C (P0.05). Exposure for 1 min was best for morulae, while 3 min was best for blastocysts. In experiment 2, blastocysts were handled at 24 degrees C and exposed to two concentrations of ethylene glycol in V1 (3.5 or 5 M) followed by V2 as in experiment 1, two warming temperatures (20 or 37 degrees C) and two post-warming holding times until culture (5 or 15 min). Exposure to 5 M ethylene glycol and warming at 37 degrees C was the optimal combination of procedures, and embryos survived well after 15 min in straws if warmed at 37 degrees C. In experiment 3, ethylene glycol concentration (3, 4 or 5 M) and exposure time (0.5 or 1 min) during two-step addition of cryoprotectant were studied for bovine morulae. In experiment 4, morulae were exposed to V2 for 30 or 45 s in HCDM2 or Vigro holding medium and then held in 22-24 degrees C air or 37 degrees C water post-warming. Experiment 5 was like experiment 4 except blastocysts were used. Overall survival rates of blastocysts in experiment 5 averaged 80% of non-vitrified controls after 48 h culture. The survival rates with in vitro-produced morulae in experiments 1, 3 and 4 were unacceptable. Vitrification solutions based on Vigro tended to result in higher survival than HCDM2 for blastocysts, but not morulae. In experiment 6, the survival rate in vitro of in vivo-produced morulae and blastocysts after two-step vitrification was nearly 100%. Our vitrification technique was very effective for in vitro produced blastocysts, but not for in vitro-produced morulae.

This paper describes the design and flight-testing of a multivariable helicopter flight control system. The system consisted of separate longitudinal and lateral controllers, each designed using H-infinity optimization. The design was based on a low-order aircraft model. The system was successfully flight-tested on a fly-by-wire research helicopter. It was considerably simpler than other H-infinity controllers tested during the same research program. It also outperformed them in most respects, achieving bandwidths of 3.7 rad/s in roll, 2.5 rad/s in pitch and 1.5 rad/s in yaw, and virtually eliminating pitch–roll coupling.

Behavioral preorders based on the idea of bisimulation equivalence and providing explicit treatments of the phenomenon of divergence in communicating systems are investigated. Particular study is made of those preorders in the context of R. Milner's (1980) calculus of communicating systems. The precongruence relations generated by the preorders are characterized and axiomated on the classes of finite closed terms and sequential terms. A compositional verification technique based on the theory of the preorders is introduced and illustrated. >

A new, mechanical fluid loss control system, integral to the base pipe of gravel pack screens, has been developed for ‘smart’ completions. This system allows for positive fluid loss control through all phases of well work once the gravel/frac pack is in place including the running of the isolation tubing stinger through the upper screen assembly of stacked completions. The isolation valves are opened for production without wireline intervention by hydraulically opening the zonal isolation sleeve of the ‘smart’ completion and applying pressure down the tubing. A new screen coupling system has also been developed to allow fluid returns during gravel/frac pack operations when the pressure actuated valves are run. To date, this system has been designed, tested, and successfully run in two deepwater subsea completions (3200’ WD).

The freezing tolerance of populations of the fodder species Atriplex halimus L. and Atriplex canescens (Pursh.) Nutt (Chenopodiaceae) from different locations in Algeria was investigated, in relation to plant provenance and leaf cation concentrations. For two populations of A. halimus, the effect of increased soil salinity (addition of NaCl) on tolerance was determined. Tolerance was determined in leaf electrolyte leakage assays and by assessment of visual damage, after exposure to temperatures between -5 and -25 C deg. There was significant correlation (P Se ha investigado la tolerancia a la congelación de distintas poblaciones de las especies forrajeras Atriplex halimus L. y Atriplex canescens (Pursh.) Nutt (Chenopodiaceae) de diversos lugares en Argelia, en relación con las concentraciones de cationes en la hoja y con la distinta procedencia de la plantas. Se determinó el efecto de la salinidad del suelo (adición de NaCl) sobre la tolerancia al frío para dos poblaciones de A. halimus. La tolerancia a la congelación fue determinada por análisis del contenido de electrólitos en las hojas y por el gravamen del daño visual, tras la exposición a temperaturas entre -5 y -25 grados C. Existió una correlación significativa (P

In vitro fertilization in the horse does not work reliably. Several methods of capacitating sperm in other species fail in the horse. The goal of this experiment was to develop a method to capacitate equine spermatozoa using calcium ionophore A23187 or phosphatidylcholine 12 (PC12). We also studied effects of maturing bovine oocytes for 24 or 28 h on fertilizability by capacitated equine sperm, hypothesizing that longer maturation would yield oocytes more easily fertilized by equine spermatozoa. Two sets of bovine oocytes were aspirated from 3 to 8 mm follicles of abattoir ovaries 4 h apart, but fertilized at the same time. On the day of fertilization, semen from 1 of 3 stallions was collected, evaluated, and centrifuged through 33% Percoll to remove seminal plasma. The resultant pellet was extended to 5 × 107 cells mL–1 in M199 containing 0.6% BSA, 2 mm caffeine, and 5 mm CaCl2. Sperm were treated with A23187 (1 or 3 μm) or PC12 (40 or 70 μm) or both A23187 and PC12 (1 μm/40 μm) in 500- μL aliquots. Sperm were incubated at 39°C for 10 min (for A23187 and combination treatments) or 15 min (for PC12 treatments), and then diluted 1:20 for fertilization. Oocytes from each maturation time were fertilized using the same semen preparation for each treatment. Oocytes and sperm were incubated together for 18 h in FCDM in 5% CO2 at 39°C (De La Torre-Sanchez et al. 2006 Reprod. Fertil. Devel. 18, 585–596). Presumptive zygotes were cultured for 30 h in CDM-1, vortexed to remove cumulus cells, and evaluated for cleavage. Oocytes were also co-incubated with killed sperm to determine the level of parthenogenesis. Cleaved embryos were stained with orcein to ensure that each cell had a nucleus. Number of cell divisions were recorded as 0 for a 1-cell, 1 for a 2-cell, 1.5 for a 3-cell, etc. More oocytes cleaved after 28 h (18%) than 24 h (14%) maturation (P < 0.01). Sperm of Stallion 1 resulted in higher overall cleavage (24%) than Stallions 2 or 3 (11 and 12%; P < 0.01). Highest cleavage was seen with 28 h maturation and 70 μm PC12 and 3 μm A23187 (27 and 24%, respectively). The most cell divisions were seen with 28 h maturation and 70 μm PC12 (0.48); 28 of the 49 cleaved in this treatment reached ≥4-cell stage. In conclusion, both A23187 and PC12 were able to capacitate equine sperm in a dose-dependent manner as determined from cleavage of bovine oocytes matured for 28 h; maturation for the conventional 24 h was an inferior model for this purpose. Table 1. Mean responses of bovine oocytes fertilized by equine sperm

Slaughtered bovine females have different characteristics including age, nutritional status, breed, and management system, all of which may affect the results obtained in in vitro embryo production. Another key consideration is that early embryos move from the oviduct to a slightly different environment in the uterus, which has led to development of sequential embryo culture media (e.g. Lane M et al. 2003 Theriogenology 60, 407–419). However, the benefits and importance of using sequential media are not fully known. Therefore, the aim of the present study was to compare developmental rates of oocytes obtained from slaughterhouse-derived ovaries from cows or heifers after culture in sequential media (CDM-1, CDM-2) or in a continuous medium (C-CDM). The experiment was a 3 × 2 × 2 factorial design [bulls (A, B, or C), source (cows or heifers), and medium (sequential or continuous)]. Cumulus–oocyte complexes were aspirated, within 5 h of slaughter, from 3- to 8-mm ovarian follicles of cows (1482 oocytes) and fattened heifers usually fed melengesterol acetate (2818 oocytes). Embryos were produced in vitro as described by De La Torre-Sanchez et al. 2006 Reprod. Fertil. Devel. 18, 585–596, with slight modifications. Presumptive zygotes were vortexed to remove cumulus cells and cultured for 2.5 d in C-CDM (CDM supplemented with 5.0 mm L-lactate, essential and nonessential amino acids, and 0.5% FAF-BSA, or in CDM-1 (De La Torre-Sanchez et al. 2006 Reprod. Fertil. Devel. 18, 585–596) at 39°C in a humidified incubator under 5% CO2, 5% O2, and 90% N2. Cleavage was assessed after 2.5 d; 2- to 6-cell embryos were considered as cleaved, but were not cultured further. Embryos at the 7- to 8-cell stage were cultured for an additional 4.5 d in fresh C-CDM or CDM-2. The percentage blastocysts per oocyte was assessed after 7 and 8 days of culture. Data were arcsin-transformed and evaluated by ANOVA. There was a significant interaction between bull and ovary source for both 8-cell embryos and cleavage rate (P < 0.05); however, this interaction was no longer significant for blastocysts. No other interactions were significant nor a source of ovaries. Culturing embryos in CDM-C refreshed after cleavage evaluation (continuous) or culturing embryos in CDM-1 early and CDM-2 after cleavage evaluation (sequential) resulted in similar cleavage and blastocyst rates (Table 1). We conclude that bovine embryos can be produced using a single chemically defined medium (+BSA) with similar efficacy as a system using 2 sequential media. Table 1. Effects of media on embryonic development (mean ± SE)

An approach to solving the two most serious shortcomings of previous artificial neural network implementations is discussed. A flexible architecture that permits the realization of arbitrary network topologies and dimensions is presented. Furthermore, the performance of this architecture is independent of the size of the network and permits the processing of typically 100000 patterns per second. The key innovation is the representation of neuron activations and synaptic weights as stochastic functions of time, leading to efficient implementations of the synapses. High densities of synapses per silicon area, exceeding even analog implementations, have been achieved. Finally, the neuron activations are represented digitally, as are the synaptic computations, thereby permitting fabrication of digital neural network architectures using a variety of standard, low-cost semiconductor processes. A pair of general-purpose chips (SU3232 and NU32) that permit post facto construction of neural networks of arbitrary topology and virtually unlimited dimensions is presented

Vitrification combined with in-straw dilution may replace conventional cryopreservation of bovine embryos, but this requires further study for practicality. Our objectives were to compare three ethylene glycol concentrations (6, 7, and 8M) and two equilibration times (2.5 and 3.5min) for one-step addition of cryoprotectant. In vitro-matured oocytes from slaughterhouse ovaries, fertilized using sperm of 3 bulls, were cultured in chemically defined medium (CDM-1/CDM-2) plus FAF-BSA to produce 420 blastocysts. Day 7.5 embryos were placed into HCDM-2 (HEPES-buffered medium) and then transferred to a 6μL drop of vitrification solution (V) (6, 7, or 8M ethylene glycol, 0.5M galactose, and 18% w/v Ficoll 70 in HCDM-2). Immediately thereafter, 1cm column of DHCDM (0.5M galactose in HCDM-2) was drawn into a 0.25mL straw, followed by a 0.5cm column of air and another 7cm of DHCDM. Another 0.5cm column of air was aspirated before the 6μL of V (0.5cm) containing the embryos were aspirated; then 0.5cm of air followed. Finally, DHCDM was drawn until the first column came into contact with the cotton plug. Straws were then heat-sealed and plunged into liquid nitrogen slightly above the embryos after 2.5 or 3.5min equilibration. The rest of the straw was then submerged slowly. Straws were thawed in air for 10s and then in 37°C water for 20s. Straws were held at room temperature (24°C) for 4min before being expelled into HCDM-2. They were then placed into CDM-2+5% FCS for culture. Quality score (1=excellent, 2=fair, 3=poor), survival (S) as determined by expansion of blastocysts, and hatching (H) were assessed at 24 and 48h post-thaw. Data from 6 replicates (2/bull) were analyzed by ANOVA after arc sin transformation of percentage data. S and H responses were calculated as a percentage of non-frozen controls in the same replicate. Control survival and hatching rates were: 24S: 90%, 24H: 50%, 48S: 90%, 48H: 72%. Quality scores at both 24 and 48h were higher (P0.1). Neither ethylene glycol concentration nor exposure time affected survival or hatching at 24 or 48h (P>0.1). Survival rates (as a % of control) at 48h were: 8M: 57%, 7M: 55%, 6M: 36% and hatching: 8M: 39%, 7M: 30%, and 6M: 21%; 2.5min tended to be better than 3.5min for survival at 24h, hatching at 24h, survival at 48h, but not hatching at 48h (56% and 43%, 30% and 26%, 55% and 44%, 28% and 32% respectively). Higher concentrations of ethylene glycol proved beneficial in terms of embryo quality, with the same trend for survival and hatching rates. One-step addition of cryoprotectant for vitrification shows potential for simplifying embryo cryopreservation. However, further research is needed to produce more acceptable survival rates and to study vitrification of in vivo-produced embryos.

Slow-cooling techniques are widely used in cryopreservation of bovine embryos. We have previously developed a simple, two-step vitrification technique for direct transfer in the field; however, simplification to one-step vitrification would be attractive. Therefore, factorial combinations of two techniques (one-step and two-step) and two post-thaw temperatures until culture (24 and 37°C) were studied. Blastocysts (n=220) sired by two bulls were obtained in vitro in four replicates. Briefly, oocytes were aspirated from 2–8-mm follicles of ovaries obtained at a slaughterhouse, matured, fertilized and cultured in vitro with standard procedures using chemically defined media (CDM1/2 or G1/2). Two-step embryos were transferred in 1μL into 1mL of V1-CDM (5M ethylene glycol (EG) in HEPES-buffered holding medium (HCDM2)), and one-step embryos into a 7-μL droplet of V2-CDM (7M EG, 0.5M galactose and 18% w/v Ficoll 70 in HCDM2) for 3min at 24°C. Next, embryos for the two-step method were moved in 1μL into a 7μL droplet of V2-CDM at 24°C. Droplets containing embryos (one or two-step) were loaded into 0.25-mL straws preloaded with a 1-cm column of D-HCDM (0.5M galactose in HCDM2), then 0.5cm air, and then 7cm of D-HCDM followed by 0.5cm air. The column containing the embryos (0.5cm (7μL)) was followed with 0.5cm air and 1cm of D-HCDM. Straws were heat-sealed and plunged vertically, sealed end first, into liquid nitrogen just covering the embryo, and the rest of the straw was then slowly immersed. The time from loading to plunging was 40–50s. Straws were thawed in air (24°C) for 10s and then in water horizontally at 37°C until ice disappeared. Straws were gently shaken to mix the columns; then, after 5min at 24 or 37°C, embryos were expelled and cultured in CDM2+5% FCS. Re-expansion and hatching rates were evaluated 48 h post thaw. Data (Table 1) were calculated as a percentage of non-vitrified controls for respective replicates (control means: re-expansion 87%; hatching 74%) and analyzed by ANOVA. There were no main effects of post-thawing temperature (P>0.1), indicating that, after thawing, embryos can be kept at room or body temperature. Also, main effect means for re-expansion and hatching for one-step or two-step addition of cryoprotectant were similar (P>0.1), but there was a tendency for higher survival for the two-step procedure. Further refinements of the one-step technique including EG concentrations, embryological stages and equilibration times should be studied. Table 1 Main effect means (least-square means±SEM) of vitrified embryos (% of non-vitrified controls)

An algorithm has been developed for the reconstruction of the transmission function of a weakly scattering object from a digitized in-line hologram such as a shadow image obtained in a scanning transmission electron microscope with a field emission gun. Tests of the reconstruction process, made on computed holograms of simple one-dimensional objects calculated for conditions representative of those in contemporary instruments, suggest that considerable improvements of resolution for small specimens areas may be possible.

The incidence of diapause in larvae of Ephestia elutella and Plodia interpunctella under two light systems operated by solar switches was observed at 25°C. Both switches gave progressively shortening daylength, as would be experienced from early July onwards at a latitude of 52°N. One of the light systems incorporated a device, which took 60 min to change to, or from, full light to near darkness, giving a dawn and a dusk with the photophase. The other was controlled directly by the time switch itself, without any extended periods of changing intensity. Maximal percentages of E. elutella larvae entering diapause under the two systems were obtained with photoperiods half way through development of less than 13 hr 25 min and 13 hr 10 min respectively, measurements of photoperiod in the dawn-dusk system including the 1 hr dawn and 1 hr dusk. The mean critical photoperiod, here defined as that photoperiod giving half the maximum percentage of insects that enter diapause in response to photoperiod at a fixed temperature, was found to be 14 hr 15 min under the dawn-dusk system, and 14 hr 5 min under the other shortening daylength system. Comparison of the above results with the incidence of diapause under a series of fixed daylengths confirmed that the principal sensitive phase in E. elutella occurred early in the last larval instar. Over 70 per cent emergence occurred in batches of P. interpunctella within 7 weeks of egg laying under all lighting conditions tested. Maximal percentages of larvae entered diapause after rearing in total darkness, continual light, or photoperiods of 13 hr or less. The sensitive phase occurred around 8 days after hatching at 25°C, and the mean critical photoperiod was found to be about 13 hr 15 min under both shortening daylength systems, and under fixed photoperiods. Photoperiods of over 13 hr, or increased temperature, appeared to inhibit diapause in P. interpunctella . Light intensities below 1 lux influenced diapause in both species.

Concern by the public and others exists about the health, economic, and resource conservation aspects of nitrate leaching into ground water supplies. An examination of these topics as they relate to nitrogen (N) management and ground water protection is made. During the past 10 years, annual N fertilizer consumption has increased about 25 percent in Developed Countries and about 160 percent in Developing Countries of the World. The public is concerned about toxicity and health effects of nitrate that may be entering ground water supplies used for drinking water. Of special concern are methemoglobinemia and cancer. Both are discussed as they relate to the possible effects of nitrate ingestion and public health. The economic importance of N for crop production is well known. However, practices to minimize N losses are important to protection of ground water. Benefits of decreasing nitrate pollution in ground water are diffuse, enjoyed by all users of the aquifer, while costs of improving ground water quality are relatively concentrated among farmers who must alter their farming practices to reduce nitrate leaching. Therefore, some form of government intervention is needed to allign the interests of the individual farmer with the broader social interest. Several public policy options are discussed. Finally, the relationship on N fertilizer use, and modern technology in general, to resource conservation is addressed. Generally, increased crop yields allow more erosive or poorer land to be removed from production, thus decreasing soil erosion and production costs. The relationship of various management, land use, and soil factors to ground water nitrate concentrations are also discussed.

Summary Oil displacement experiments are reported which were performed in stratified rectilinear systems consisting of two lower permeability sandstone slabs, enclosing a central high permeability layer made of unconsolidated glass ballotini. The adjacent layers were in good flow communication, except for a very small region close to the outlet. This arrangement allows the crossflow mechanisms that occur when the viscosity of the displacing brine is increased by adding a water soluble polymer. These mechanisms cannot be assessed by performing experiments in one-dimensional cores or packs. Results of oil displacement experiments are presented for different mobility driving fluids, in which glycerol is used to viscosify the aqueous phase. carbon-I 4 and chlorine are used as radioactive tracers in the experiments. The effluent fluids from each layer were collected and analysed to produce data on the cumulative oil recovery, watercuts, flow rates in each layer, viscosities and concentrations of radioactive tracers. The results of these oil displacement experiments were modelled using computer simulation, and a very good match to the experiments was obtained. This simulation work confirms the flow mechanisms involved when water soluble polymers are used to increase the oil production from stratified reservoirs. Introduction In stratified reservoirs with high permeability contrasts between layers, early water breakthrough can occur during a waterflood, causing low vertical sweep efficiencies. The use of water soluble polymers to increase the water viscosity has been shown to be an effective way of improving the sweep efficiency and hence increasing the oil recovery. Earlier theoretical work has shown that the mechanism of increasing the recovery of oil in this way involves the crossflow of fluids between the various layers, as well as increasing the velocities in the lower permeability layers adjacent to the high viscosity polymer solution). A large number of papers have been published which investigate oil displacement using polymer solution in one-dimensional cores. Some experiments have also been performed in two-dimensional systems, but most of these used multiple radial or linear cores in parallel, with no contact between the cores except at the inlet. In the early literature, waterflooding experiments in communicating layered systems were reported, generally from the viewpoint of investigating scaling laws, or recovery mechanisms. More recently, polymer displacement experiments have been performed in stratified systems, with crossflow between layers. Whilst these have provided valuable information on the displacement processes, they have not provided sufficient data to allow a theoretical analysis of the flow mechanisms. In our laboratory, we are performing experiments which provide detailed information on the oil recovery, watercuts, flow rates and tracer concentrations produced from individual layers. The results of these experiments are being analysed using numerical simulation, in order to reproduce the flow mechanisms quantitatively. Earlier work performed at Winfrith used a heterogeneous core made from a sandstone cylinder with the centre removed and replaced with a pack of glass ballotini. This work has recently been extended using a rectilinear core assembly, and the results of these later studies are discussed in this paper. P. 823^

SUMMARY We describe a patient with multicentric reticulohistiocytosis (MR) who demonstrated Koebner's phenomenon and had unusually large skin nodules. OKT3 and OKT4 lymphocyte markers were demonstrated on histiocyte membranes, which have not been previously reported in this disease.

An attempt has been made to identify and review everyone who was admitted to hospital in the Northern Region between the years 1971 and 1978, and was diagnosed as having aplastic anaemia. The hospital activity analysis scheme was used as the source of the patients. Of the 537 cases recorded, the notes of 404 (75%) were traced and reviewed. We considered that 230 (57%) had been mis-classified. The incidence of aplastic anaemia was fairly constant with an average of 25 cases per year. Prognosis in the 174 cases of aplastic anaemia remaining was found to be poor with a 5-year survival of 39%. Mortality was similar in cases with an apparent cause, and those without. A follow up study of 27 long term (greater than 3 years) survivors is also reported. Seventeen (63%) had normal blood counts. There was very poor correlation between anterior iliac crest trephine findings and peripheral blood count.

Publisher Summary Microbes, depending on the milieu in which they exist, use widely varying synthetic mechanisms for maintenance and growth. Such synthetic reactions are either energy-requiring or involve the use of metabolic intermediates, which otherwise could be further degraded in energy-yielding reactions The energy requirement of a living cell can be couched in terms of adenosine triphosphate (ATP) as this compound is responsible for coupling the energy-yielding reactions of metabolism to provide the bond-forming power necessary for many synthetic reactions. A common feature of chemolithotsrophs is that the ATP required for cellular metabolism is derived by oxidative phosphorylation. Green sulphur bacteria (or Chlorobacteriaceae) are strictly anaerobic and fix carbon dioxide into cell material whilst oxidizing hydrogen sulphide to free sulphur, which transitorily accumulates in the medium. Like the green sulphur bacteria, the purple sulphur bacteria, or Thiorhodacene, oxidize sulphur compounds in the light with concomitant fixation of carbon dioxide. Athiorhodaccae, or non-sulphur purple bacteria, chiefly use organic compounds as hydrogen donors, although a number of strains can use molecular hydrogen for direct reduction of carbon dioxide in the light. Organisms growing heterotrophically obtain their energy and carbon for growth from organic substrates more reduced than carbon dioxide. This does not necessarily mean that carbon dioxide fixation does not occur;it is an essential feature of the metabolism in many heterotroph, but carbon dioxide is fixed only during the synthesis of certain essential compounds.

The particulars of a miniature crt display for helicopter aircrews are discussed. The crt clips onto a helmet and with the aid of optics creates a virtual image for the pilot.