Search

It is widely acknowledged that the RMS (root mean square) measurement of waveforms furnishes the most accurate amplitude information. Rectify-and-average schemes, usually calibrated to a sine wave, are only accurate for one waveshape. Departures from this waveshape result in pronounced errors. Although accurate, RMS conversion often entails limited bandwidth, restricted range, complexity, and dynamic and static errors difficult to characterize. Recent developments address these issues while simultaneously improving accuracy. Monolithic RMS-to-DC converters use an implicit computation to calculate the RMS value of an input signal. The input to the lowpass filter (LPF) is the calculation from the multiplier/divider: ( V IN ) 2 / V OUT . The LPF takes the average of this to create the output. Unlike the prior generation RMS-to-DC converters, the LTC1966/LTC1967/LTC1968 computation does not use log/antilog circuits, which all have the same problems, and more, of log/antilogmultipliers/dividers, i.e., linearity is poor, the bandwidth changes with the signal amplitude and the gain drifts with temperature. LTC1966/LTC1967/LTC1968 uses a completely new topology for RMS-to-DC conversion, in which a DS modulator acts as the divider, and a simple polarity switch is used as the multiplier.

Publisher Summary Voltage drops in wiring can produce considerable load regulation errors in electrical systems. As load current increases, the voltage drop in the wiring increases and the voltage delivered to the system drops. The traditional approach to solving this problem, remote sensing, regulates the voltage at the load, increasing the power supply voltage to compensate for voltage drops in the wiring. While remote sensing works well, it does require an additional pair of wires to measure the load, which may not always be practical. LT4180 eliminates the need for a pair of remote sense wires by creating a virtual remote sense. Virtual remote sensing is achieved by measuring the incremental change in voltage that occurs with an incremental change in current in the wiring. This measurement can be used to infer the total DC voltage drop in the wiring, which can then be compensated for. The virtual remote sense (VRS) takes over control of the power supply via its feedback pin, maintaining tight regulation of load voltage. A new cycle begins when the power supply and VRS close the loop around VOUT. Both VOUT and IOUT slew and settle to a new value, and these values are stored in the VRS. The VOUT feedback loop is opened and a new feedback loop is set up commanding the power supply to deliver 90% of current. VOUT drops to a new value as the power supply reaches a new steady state, and this information is also stored in the VRS. At this point, the change in the output voltage for a –10% change in output current has been measured and is stored in the VRS. This voltage is used during the next VRS cycle to compensate for voltage drops due to wiring resistance.

A large group of fiber optic lasers are powered by DC current. Laser drive is supplied by a current source with modulation added further along the signal path. The current source, although conceptually simple, constitutes an extraordinarily tricky design problem. The key to a successful design is a thorough understanding of individual system requirements. Various approaches suit different sets of freedoms and constraints, although all must address some basic concerns. There are two basic sets of concerns for laser current sources: performance and protection. Performance issues include the current source's magnitude and stability under all conditions, output connection restrictions, voltage compliance, efficiency, programming interface, and power requirements. Protection features must be included to prevent laser and optical component damage. The laser, an expensive and delicate device, must be protected under all conditions, including supply ramp up and down, improper control input commands, open or intermittent load connections and “hot plugging.”

Medical, remote data acquisition, power monitoring, and other applications are good candidates for battery-driven, low-power operation. Micropower analog circuits for transducer-based signal conditioning present a special class of problems. Although micropower integrated circuits are available, the interconnection of these devices to form a functioning micropower circuit requires care. In particular, tradeoffs between signal levels and power dissipation become painful when performance in the 10- to 12-bit area is desirable. The most obvious way to save power is to choose components which require little energy. Circuits should be examined in terms of current flow. The best way to get low power circuit characteristics is to turn off the power. While there are some obvious problems with this approach, it does point a way toward minimizing power consumption. In many applications, continuous circuit power is not necessary. If bandwidth requirements are low, sampling techniques offer a simple way to save power. With low duty cycles, instantaneous current can be relatively high while average drain remains low. When considering a sampled approach some issues should be examined. The required circuit bandwidth dictates the minimum sampling frequency in accordance with Nyquist criteria. The sampling interval's duration is determined by circuit settling time to the required accuracy. This settling time can be considered for all circuit elements individually and together.

Oscillators are fundamental circuit building blocks. A substantial percentage of electronic apparatus utilizes oscillators, either as timekeeping references, clock sources, for excitation or other tasks. The most obvious oscillator application is a clock source in digital systems. A second area is instrumentation. Transducer circuitry, carrier-based amplifiers, sine wave formation, filters, interval generators, and data converters all utilize different forms of oscillators. Commonly employed oscillators are resonant element based or resistor–capacitor (RC) types. Quartz crystals and ceramic resonators offer high initial accuracy and low drift but are essentially untuneable over any significant range. Typical RC types have lower initial accuracy and increased drift but are easily tuned over broad ranges. A problem with conventional RC oscillators is that considerable design effort is required to achieve good specifications. A new device, LTC1799, is also an RC type but fills the need for a simply applied, broadly tuneable, accurate oscillator. Its accuracy and drift specifications fit between resonator-based types and typical RC oscillators. Additionally, its board footprint, a 5-pin SOT-23 package and a single resistor, is notably small.

This chapter discusses a monolithic approach, which is broadly used over a range of magnetics and applications. Size, output flexibility, and efficiency advantages have made switching regulators common in electronic apparatus. The continued emphasis on these attributes has resulted in circuitry with 95% efficiency that requires a minimal board area. Something commonly referred to as noise is a primary concern. The switched mode power creates wideband harmonic energy. This undesirable energy appears as radiated and conducted components commonly labeled as noise. Actually, switching regulator output noise is not really noise at all, but coherent, high frequency residue directly related to the regulator's switching. The key to an inherently low noise regulator is to minimize the harmonic content in the switching transitions. Slowing down the switching interval does this, although power dissipated during the transition causes some efficiency loss. Reducing the switch repetition rate can largely offset the losses, resulting in a reasonably efficient design with small magnetics and the desired low noise. Noise reduction by restricting harmonic generation has been employed before, although the implementations were complex and narrowly applicable.

Significant progress in high precision, instrumentation grade digital-to-analog conversion has recently occurred. Ten years ago 12-bit digital-to-analog converters (DACs) were considered premium devices. Today, 16-bit DACs are available and increasingly common in system design. These are true precision devices with less than 1 least significant bit linearity error and 1 ppm/ ° C drift. Nonetheless, there are DAC applications that require even higher performance. Automatic test equipment, instruments, calibration apparatus, laser trimmers, medical electronics, and other applications often require DAC accuracy beyond 16 bits. 18-bit DACs have been produced in circuit assembly form, although they are expensive and require frequent calibration. Twenty and even 23+ bit DACs are represented by manually switched Kelvin–Varley dividers. In practice, the slave 20-bit DAC's output is monitored by the “master” LTC2400 analog-to-digital (A-to-D), which feeds digital information to a code comparator. The code comparator differences the user input word with the LTC2400 output, presenting a corrected code to the slave DAC. In this fashion, the slave DAC's drifts and nonlinearity are continuously corrected by the loop to an accuracy determined by the A-to-D converter and V REF . The sole DAC requirement is that it be monotonic. No other components in the loop need to be stable. This loop has a number of desirable attributes. As mentioned, accuracy limitations are set by the A-to-D converter and its reference. No other components need be stable. Additionally, loop behavior averages low-order bit indexing and jitter, obviating the loop's inherent small-signal instability. Finally, classical remote sensing may be used, or digitally based sensing is possible by placing the A-to-D converter at the load. The A-to-D's SO-8 package and lack of external components make this digitally incarnated Kelvin-sensing scheme practical.

Abstract Because Floating Production, Storage, and Offloading (FPSO) modules experience significant deflections from wave motion as well as hog/ sag, on board piping must be analyzed to assure that it is suitably designed for high cycle fatigue. This is done by keeping accumulated damage to a value less than 1.0 using the Palmgren-Miner rule. In order to simplify the acceptance criteria, a method must be developed to convert allowable accumulated damage into an allowable stress range that pipe stress engineers are accustomed to evaluating. This is done by combining methods from PD5500, DVN publications and the Fatigue Handbook: Offshore Steel Structures Probabilistic Fracture Mechanics; Tapir 1985. To consider the effects of deck bending and module sway, displacements must be calculated from the naval architects hull data for every restraint in the pipe stress analysis model. Multiple loading cases require this process to be repeated for each loading case being considered. Most engineering companies have developed a technique for automating the computation of module and/or deck displacements. These values once computed must be entered into the pipe stress analysis software. This task normally requires 8 to 24 hours per calculation depending on size and complexity of the piping system being analyzed. Since the data has been manually entered it must also be checked, which requires another 4 to 12 hours. If a method can be found to calculate displacements and then automatically load them into the pipe stress analysis software, significant cost savings can be realized through reduced engineering work hours. On a project requiring 100 calculations, the potential savings using a reduction of 25 hours per calculation will be 2500 hours. This will result in a cost savings of $225,000 using $90/ hour as the cost basis. Savings could range as high as $700,000 on large FPSO's. By using the Caesar II neutral file writer to import/ export input data, it is possible to automate this process. An engineer, after entering the piping geometry into Caesar II and assigning restraints at the applicable nodes, can export a neutral file which can be read into displacement generating software (this is a company proprietary tool) where the displacements and rotations are applied to each restraint node. This enhanced neutral file can be re-imported into Caesar II ready for analysis complete with displacements and rotations. The most complex calculations can be processed in less than 30 minutes. By automating this process it may be possible to reduce FPSO pipe stress analysis time by as much as 40%.

• Northwest Flight 188 — carrying 144 people and five crew members — flew past the Minneapolis airport during a mysterious 78 minutes of radio silence beginning about 7:56 p.m. ET Wednesday night. • The Airbus A320 was carrying 147 passengers and an unknown number of crew members, according to the National Transportation Safety Board. • Air traffic controllers re-established radio contact after the plane had flown about 150 miles past its destination.

A case of leiomyoma of the urinary bladder, a rare benign tumor, in a 56-year-old female first seen with bilateral flank pain radiating to both groins, is reported. Examination showed a well developed female with obesity (260 pounds) and elevated blood pressure (132/90 mmHg). Evaluation with ultrasound, cystoscopy, urodynamics, and cytology contributed to the diagnosis of urinary bladder leiomyoma. Ultrasound detected a mass in the urinary bladder, and it was confirmed by cystoscopy to be a 5 cm to 6 cm bladder mass on the anterior bladder wall. The mass was prolapsing as a ball valve into the urethra at the level of the bladder neck. Frozen section of the mass showed it to be leiomyoma.

Circuit startup or overdrive causes the circuit's AC-coupled feedback to latch. If this occurs, C1 's output goes high. C2 , detecting this via the inverters and the 2.7 M–0.1 μF lag also goes high. This lifts C1 's negative input and grounds the positive input with Q7 , initiating normal circuit action. Because the charge pump is directly coupled to C1 's output, response is fast. This scheme promises both lower temperature drift and lower power. Assuming ideal junction compensation, the remaining uncompensated drift terms are C1 's–120 ppm temperature coefficient and the input resistor. This configuration does nothing to fix the PSRR problem. The only realistic fix for that is to replace R1 with a current source. The current source doesn't have to be very stable but must run with only 2 V of headroom because the circuit has to work down to 6.5 V. The simplest alternative is the monolithic LM134. This three-terminal, resistor-programmable device will function with only 800 mV across it, although it does have a 0.33%/°C temperature coefficient.

The goal of this program was to develop a revolutionary solid-state gamma-ray detector suitable for use in down-hole gas and oil exploration. This advanced detector would employ wide-bandgap semiconductor technology to extend the gamma sensor's temperature capability up to 200 C as well as extended reliability, which significantly exceeds current designs based on photomultiplier tubes. In Phase II, project tasks were focused on optimization of the final APD design, growing and characterizing the full scintillator crystals of the selected composition, arranging the APD device packaging, developing the needed optical coupling between scintillator and APD, and characterizing the combined elements as a full detector system preparing for commercialization. What follows is a summary report from the second 18-month phase of this program.

The project proposal was approved for only the phase I period. The goal for this Phase I project was to develop an industrial model that can perform continuous and efficient dewatering of fine coal slurries of the previous flotation process to fine coal cake of {approx}15% water content from 50-70%. The feasibility of this model should be demonstrated experimentally using a lab scale setup. The Phase I project was originally for one year, from May 2005 to May 2006. With DOE approval, the project was extended to Dec. 2006 without additional cost from DOE to accomplish the work. Water has been used in mining for a number of purposes such as a carrier, washing liquid, dust-catching media, fire-retardation media, temperature-control media, and solvent. When coal is cleaned in wet-processing circuits, waste streams containing water, fine coal, and noncombustible particles (ash-forming minerals) are produced. In many coal preparation plants, the fine waste stream is fed into a series of selection processes where fine coal particles are recovered from the mixture to form diluted coal fine slurries. A dewatering process is then needed to reduce the water content to about 15%-20% so that the product is marketable. However, in the dewatering processmore » currently used in coal preparation plants, coal fines smaller than 45 micrometers are lost, and in many other plants, coal fines up to 100 micrometers are also wasted. These not-recovered coal fines are mixed with water and mineral particles of the similar particle size range and discharged to impoundment. The wasted water from coal preparation plants containing unrecoverable coal fine and mineral particles are called tailings. With time the amount of wastewater accumulates occupying vast land space while it appears as threat to the environment. This project developed a special extruder and demonstrated its application in solid-liquid separation of coal slurry, tailings containing coal fines mostly less than 50 micron. The extruder is special because all of its auger surface and the internal barrier surface are covered with the membranes allowing water to drain and solid particles retained. It is believed that there are four mechanisms working together in the dewatering process. They are hydrophilic diffusion flow, pressure flow, agitation and air purging. Hydrophilic diffusion flow is effective with hydrophilic membrane. Pressure flow is due to the difference of hydraulic pressure between the two sides of the membrane. Agitation is provided by the rotation of the auger. Purging is achieved with the air blow from the near bottom of the extruder, which is in vertical direction.« less

In this paper we propose a Particle Filter-based approach for the segmentation of coronary arteries. To this end, successive planes of the vessel are modeled as unknown states of a sequential process. Such states consist of the orientation, position, shape model and appearance (in statistical terms) of the vessel that are recovered in an incremental fashion, using a sequential Bayesian filter (Particle Filter). In order to account for bifurcations and branchings, we consider a Monte Carlo sampling rule that propagates in parallel multiple hypotheses. Promising results on the segmentation of coronary arteries demonstrate the potential of the proposed approach.

Publisher Summary This chapter presents a narrative by Jim Williams about how he successfully designed a valuable circuit using liquid crystal display (LCDs). Around Christmas, Jim's boss, Bob Dobkin, asked him if he ever thought about the liquid crystal display (LCD) backlights used in portable computers. He got started by getting a bunch of portable computers and taking them apart. The AC high-voltage output was often about 50 kHz and approximately sinusoidal. The circuits seemed to operate on the assumption that a constant voltage input to the DC-AC inverter would produce a fixed, high voltage output. Jim removed lamps from the displays. They all appeared to have been installed by the display vendor, as opposed to being selected and purchased by the computer manufacturer. A good place to start was to reconsider the lamps. The “Cold Cathode Fluorescent Lamps” (CCFL) provide the highest available efficiency for converting electrical energy to light. The physical layout of the lamp, its leads, the display housing, and other high voltage components, is an integral part of the circuit. Poor layout can easily degrade efficiency by 25% and higher layout induced losses have been observed.

Publisher Summary This chapter describes the usefulness of a laboratory in an electronics engineer's home. The enormous productivity advantage provided by a home laboratory is unmatched by anything. The magic of a home laboratory is that it effectively creates time. The ability to grab a few hours here and there combined with occasional marathon 5–20 hour sessions produces a huge accumulated time benefit. The easy and instant availability of laboratory time makes even small amounts of time practical. Everything is undisturbed and just as it was left after the last session because no one else uses the laboratory at home. Nothing is missing or broken and all test equipment is familiar. The oscilloscope is probably the most important instrument in the analog laboratory. Tektronix oscilloscopes manufactured between 1964 and 1969 are the favorites. Brilliantly conceived and stunning in their execution, they define excellence. Laboratory needs a variety of signal sources. The Hewlett-Packard 200 series sine wave oscillators are excellent, cheap, and easily repaired. The later versions are solid state and quite small.

Publisher Summary This chapter presents a narrative by a research student, Jim Williams, at MIT about his experience of fixing laboratory equipment that developed faults. Eminent physicist, Jerrold R. Zacharias, rejected Jim's equipment repair and calibration budget, and asked him to fix the equipment on his own. The first thing that developed fault was a high sensitivity, a differential ‘scope plug-in,’ a Tektronix 1A7. The problem was not particularly difficult to find once he took the time to understand how the thing worked. Hours after the thing was fixed, he continued to probe and puzzle through its subtleties. Jim started enjoying equipment repair so much that he found himself continually drifting away from his research project, taking apart test equipment to see how it worked. He started offering free repair services to other students, who would bring him instruments to fix. He paid people to deliberately disable his test equipment so that he could fix it. Whether the instrument is three months or 30 years old has no beating on the quality of the thinking that went into it.

We describe mission requirements, standards-based techniques, and advanced techniques for multimedia data compression in a military C41 environment. We describe compression techniques used in the National Imagery Transmission Format Standiuds. We descrihe losslcss compression results using the new JBIG International Standard upon military image types. We report on a comp;rr;ltive study of the PEG and MPEG International Standards with wavelet-based subband compression when ;rpplied l o v;uious military sensor data sets. We also predict future directions in this dynamic field. The complcssion technologies outlined herein will form an integral part of future 4 multimedia architectures for C I systms.

Spacecraft materials selection is based on an upward flammability test conducted in a quiescent environment in the highest-expected oxygen-concentration environment. However, NASA s advanced space exploration program is anticipating using various habitable environments. Because limited data is available to support current program requirements, a different test logic is suggested to address these expanded atmospheric environments through the determination of materials self-extinguishment limits. This paper provides additional pressure effects data on oxygen concentration and partial pressure self-extinguishment limits under quiescent conditions. For the range of total pressures tested, the oxygen concentration and oxygen partial pressure flammability thresholds show a near linear function of total pressure. The oxygen concentration/oxygen partial pressure flammability thresholds depend on the total pressure and appear to increase with increasing oxygen concentration (and oxygen partial pressure). For the Constellation Program, the flammability threshold information will allow NASA to identify materials with increased flammability risk because of oxygen concentration and total pressure changes, minimize potential impacts, and allow for development of sound requirements for new spacecraft and extraterrestrial landers and habitats.

Orimulsion-400® is a novel bitumen-emulsion power plant fuel. We exposed Atlantic herring (Clupea harengus L.) eggs to 0, 0.1, 1.0, 10, 100, and 1,000 mg/L concentrations of an oil-in-water dispersion of Orimulsion-400 for a 24-h period. No significant differences were found in daily mortality or percent hatch. The 1,000 mg/L exposure resulted in a significantly higher incidence of premature hatch, indicated by significantly shorter incubation time, significantly smaller total length and notochord length, and significantly greater yolk sac depth. The larvae exposed to the 1,000 mg/L treatment also had a significantly higher incidence of abnormalities than all other treatments.

Quantification of levels of cytochrome P4501A (CYP1A) gene expression in sentinel species of fishes has been proposed as a management tool to evaluate contamination of aquatic systems. Based on preliminary studies, we hypothesized that differences in CYP1A mRNA inducibility among individuals, populations, or species might lead to spurious conclusions when using this approach in environmental monitoring programs. To address this possibility, we quantitated and compared CYP1A mRNA induction levels in four species of common Atlantic Coast estuarine fish: smooth flounder, hogchoker, striped bass, and Atlantic tomcod, which were treated with model chemicals (beta naphthoflavone (β-NF), or benzo[a]pyrene at 10 ppm) known to induce CYP1A mRNA, or were exposed to contaminated environments. Species-specific CYP1A DNA probes were generated from PCR (polymerase chain reaction) amplification of genomic DNA using conserved oligonucleotide primers, and, along with cloned rainbow trout and Atlantic tomcod CYP1A cDNA probes were used to quantify CYP1A mRNA levels in northern blot analyses. Successful PCR amplification of CYP1A hybridizable DNA fragments was observed for all four species. Results from northern blot analyses showed large differences in CYP1A mRNA induction among species; only Atlantic tomcod exhibited significant induction of CYP1A mRNA for both chemically treated (97-fold) and environmentally exposed fish (34-fold). Significant, although lower, levels of induction were observed in β-NF treated (14-fold) smooth flounder, but not in environmentally exposed smooth flounder. Only low levels (not significant) of CYP1A gene induction were detected in hogchokers and striped bass. We conclude that CYP1A mRNA inducibility differed significantly among fish taxa perhaps due to differences in regulation of gene expression, suggesting that careful selection of sentinel species should be exercised prior to the use of CYP1A mRNA induction in environmental monitoring programs. However, the significance of differences in CYP1A mRNA inducibility in relation to higher level biological endpoints has yet to be determined.

Specific fragments of Adenovirus 5 DNA were produced by digestion of intact, 32P-labeled viral DNA with restriction endonucleases Eco R1 and and Hpa 1. The kinetics of renaturation of each fragment and of complete Adenovirus 5 DNA were measured in the presence of DNA extracted from four lines of Adenovirus 5-transformed rodent cells and from nontransformed control cells. All four transformed cell lines contained sequences homologous to the Hpa 1 fragment comprising the left 4% of the viral genome, but varied in the other Adenovirus 5 DNA sequences which were present: three lines of transformed cells contain segments of DNA extending from the left hand end to points 35, 40, and 12% along the viral genome and carry no other Adenovirus 5 DNA sequences. The fourth line also contains sequences homologous to the left half of the viral genome, but these could not be precisely defined. Therefore, the gene(s) encoded by the left end of Adenovirus 5 DNA must specify any viral gene functions expressed in transformed cells. Separated strands of the three Eco R1 fragments and certain Hpa 1 fragments of 32P-labeled Adenovirus 5 DNA were hybridized with unlabeled, cytoplasmic RNA extracted from each of the four transformed cell lines. In each case, about 10% only of the r strand sequences of the largest Eco R1 fragment were complementary to transformed cell RNA. These sequences have been mapped to the left end of the viral genome using Hpa 1 fragment strands. The same sequences are shown to be expressed as mRNA during the early phase of an Adenovirus 5 lytic infection.

For pt.II see ibid., vol.8, no.10, p.1683 (1975). Absolute differential elastic cross sections have been measured for the scattering of electrons from atomic hydrogen over the electron energy range from 20 to 680 eV and over the angular range from 10 to 140 degrees. The experimental techniques and method are those associated with crossed electron and modulated atom beams with momentum analysis of the incident and scattered electrons. The measured relative angular distributions were made absolute within 11% by means of the following sequence of measurements, (i) a phaseshift analysis around the (1s2s2)2S resonance elastic scattering in helium, (ii) relative beam densities of helium and hydrogen beams and (iii) absolute calibration of all apparatus functions.

The excitation of the 2P and 2S states of atomic hydrogen by electron impact has been studied by observing separately the prompt ( approximately 10-9 s) Lyman- alpha photons from the decay of the 2P state, the delayed Lyman- alpha photons from the quenched 2S state and the 10.2 eV energy-loss scattered electrons. Observations of these channels indicate the presence of at least four resonant states at 11.74, 11.85, 11.94 and 12.05 eV (+or-0.080 eV). These energies agree within the experimental error with the positions of the 1S, 1D, 1P and 1S(3P) resonance states predicted by six-state close-coupling theory. Over the first 0.5 eV above threshold, the measured values of the absolute cross section for separate excitation of the 2S and 2P states agree, within the experimental errors of +17% and -15%, with the three-state (1s,2s,2p) plus twenty-correlation-term close-coupling predictions of Taylor and Burke (1967). At incident electron energies of 13.87, 16.46 and 19.58 eV the first low-energy measurements are reported of the differential cross sections for exciting the n=2 states.

Host-range mutants of adenovirus type 5 have been selected on human embryo kidney cells transformed by sheared adeno 5 DNA (293 cells). These mutants grow well on 293 cells, but are restricted on HeLa cells. By complementation tests on HeLa cells, these mutants were classified into two groups, neither of which was found to correspond to any of the 17 temperature-sensitive complementation groups. Members of the two complementation groups of host-range mutants differ in their host range on other cell types: Members of one group grow only on 293 cells, while those of the other group on both normal and transformed human embryo kidney cells. In the second group, cell-associated adeno gene functions are not needed for mutant growth, but, with the other group, it is possible that an adeno gene product made in the transformed cell complements the growth of the mutants. Recombination tests carried out with the host-range mutants and Ad5 temperature-sensitive mutants indicate that the host-range mutations map within the left half of the genetic map and that some (hr 1 and hr 2) probably lie very close to the left end of the map. The results presented in this communication are briefly discussed in relation to recent unpublished work concerning the biochemical characteristics of the mutants and the transformed 293 cells and to the role of adeno genes in transformation.

Temperature-sensitive mutants of the adenovirus 2-simian virus 40 hybrid, Ad2+ ND1‡, were isolated and crossed with temperature-sensitive mutants of adenovirus type 5 (Ad5). Forty-five wild type recombinants were selected and their DNAs were separately digested with five restriction endonucleases, EcoRI, HpaI, BamI, HindIII and SmaI. There are 15 sites cleaved by these enzymes that are unique to one parental DNA or the other. The fragments obtained by digestion of each of the recombinant DNAs were separated by gel electrophoresis and compared with those obtained from the parental genomes. The recombinant DNAs were found to consist of sequences derived both from Ad5 and from Ad2+ND1. Knowing the positions at which the five restriction enzymes cleave the genomes of the parental serotypes, it was possible to decide which regions of each recombinant DNA are composed of Ad5 and which of Ad2+ND1 sequences. In this way the cross-over events that generated the recombinants were mapped and the physical locations of the ts mutations in the parental genomes were determined.

Absolute values of the angular differential cross sections for the elastic scattering of electrons from atomic hydrogen have been measured for incident electron energies of 3.4 eV and 8.7 eV and over the angular range of 30 to 150 degrees. The experimental method was bascd upon the standard crossed electron, modulated atom beam method with high resolution (0.07 eV) energy analysis of the incident and scattered electrons. The accuracy of the present measurements is 6 % which permits distinctions to be made between thevarious theoreticalapproximations. It is shownthat the variational calculated values and the pseudo-state close coupling approximation values (Burke et aZ1969) are in good agreement with measured values over the complete angular and energy range. The three-state close coupling and one-state static exchange approximation values agree with experimental values only at 8.7 eV for scattering angles greater than 90".