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In models, nucleation mode (1 nm < Dp < 10 nm) particle microphysics can be represented explicitly with aerosol microphysical processes or can be parameterized to obtain the growth and survival of nuclei to the model's lower size boundary. This study investigates how the representation of nucleation mode microphysics impacts aerosol number predictions in the TwO-Moment Aerosol Sectional (TOMAS) aerosol microphysics model running with the GISS GCM II-prime by varying its lowest diameter boundary: 1 nm, 3 nm, and 10 nm. The model with the 1 nm boundary simulates the nucleation mode particles with fully resolved microphysical processes, while the model with the 10 nm and 3 nm boundaries uses a nucleation mode dynamics parameterization to account for the growth of nucleated particles to 10 nm and 3 nm, respectively. We also investigate the impact of the time step for aerosol microphysical processes (a 10-min versus a 1-h time step) to aerosol number predictions in the TOMAS models with explicit dynamics for the nucleation mode particles (i.e. 3 nm and 1 nm boundary). The model with the explicit microphysics (i.e. 1 nm boundary) with the 10-min time step is used as a numerical benchmark simulation to estimate biases caused by varying the lower size cutoff and the time step. Different representations of the nucleation mode have a significant effect on the formation rate of particles larger than 10 nm from nucleated particles (J10) and the burdens and lifetimes of ultrafine mode (10 nm < Dp < 70 nm) particles but have less impact on the burdens and lifetimes of CCN-sized particles. The models using parameterized microphysics (i.e. 10 nm and 3 nm boundaries) result in higher J10 and shorter coagulation lifetimes of ultrafine mode particles than the model with explicit dynamics (i.e. 1 nm boundary). The spatial distributions of CN10 (Dp > 10 nm) and CCN(0.2%) (i.e. CCN concentrations at 0.2% supersaturation) are moderately affected, especially CN10 predictions above ~ 700 hPa where nucleation contributes most strongly to CN10 concentrations. The lowermost layer CN10 is substantially improved with the 3 nm boundary (compared to 10 nm) in most areas. The overprediction in CN10 with the 3 nm and 10 nm boundaries can be explained by the overprediction of J10 or J3 with the parameterized microphysics possibly due to the instantaneous growth rate assumption in the survival and growth parameterization. The errors in CN10 predictions are sensitive to the choice of the lower size boundary but not to the choice of the time step applied to the microphysical processes. The spatial distribution of CCN(0.2%) with the 3 nm boundary is almost identical to that with the 1 nm boundary, but that with the 10 nm boundary can differ more than 10–40% in some areas. We found that the deviation in the 10 nm simulations is partly due to the longer time step (i.e. 1-h time step used in the 10 nm simulations compared to 10-min time step used in the benchmark simulations) but, even with the same time step, the 10 nm cutoff showed noticeably higher errors than the 3 nm cutoff. In conclusion, we generally recommend using a lower diameter boundary of 3 nm for studies focused on aerosol indirect effects but down to 1 nm boundary for studies focused on CN10 predictions or nucleation.

H2SO4 vapor is important for the nucleation of atmospheric aerosols and the growth of ultrafine particles to cloud condensation nuclei (CCN) sizes. Recent studies have found that reactions of stabilized Criegee intermediates (CIs, formed from the ozonolysis of alkenes) with SO2 may be an important source of H2SO4 that has been missing from atmospheric aerosol models. In this paper, we use the chemical transport model, GEOS-Chem, with the online aerosol microphysics module, TOMAS, to estimate the possible impact of CIs on present-day H2SO4, CCN, and the cloud-albedo aerosol indirect effect (AIE). We extend the standard GEOS-Chem chemistry with CI-forming reactions (ozonolysis of isoprene, methyl vinyl ketone, methacrolein, propene, and monoterpenes) from the Master Chemical Mechanism. Using a fast rate constant for CI+SO2, we find that the addition of this chemistry increases the global production of H2SO4 by 4%. H2SO4 concentrations increase by over 100% in forested tropical boundary layers and by over 10–25% in forested NH boundary layers (up to 100% in July) due to CI + SO2 chemistry, but the change is generally negligible elsewhere. The predicted changed in CCN were strongly dampened to the CI + SO2 changes in H2SO4 in these regions: less than 15% in tropical forests and less than 2% in most mid-latitude locations. The global-mean CCN change was less than 1% both in the boundary layer and the free troposphere. The associated cloud-albedo AIE change was less than 0.03 W m−2. The model global sensitivity of CCN and the AIE to CI + SO2 chemistry is significantly (approximately one order-of-magnitude) smaller than the sensitivity of CCN and AIE to other uncertain model inputs, such as nucleation mechanisms, primary emissions, SOA and deposition. Similarly, comparisons to size-distribution measurements show that uncertainties in other model parameters dominate model biases in the model-predicted size distributions. We conclude that improvement in the modeled CI + SO2 chemistry would not likely to lead to significant improvements in present-day CCN and AIE predictions.

Nucleation in coal-fired power-plant plumes can greatly contribute to particle number concentrations near source regions. The changing emissions rates of SO2 and NOx due to pollution-control technologies over recent decades may have had a significant effect on aerosol formation and growth in the plumes, with ultimate implications for climate and human health. We use the System for Atmospheric Modeling (SAM) large-eddy simulation model with the TwO-Moment Aerosol Sectional (TOMAS) microphysics algorithm to model the nucleation in plumes of coal-fired plants. We test a range of cases with varying emissions to simulate the implementation of emissions-control technologies between 1997 and 2010. For the W.A. Parish power plant (near Houston, TX) during this time period, NOx emissions were reduced by ~90%, while SO2 emissions decreased by ~30%. Increases in plume OH (due to the reduced NOx) produced enhanced SO2 oxidation and particle nucleation despite the reduction in SO2 emissions. These results suggest that NOx emissions may strongly regulate particle nucleation and growth in power-plant plumes. Comparison of model results with airborne measurements made in the W.A. Parish power-plant plume in 2000 and 2006 confirm the importance of NOx emissions on new particle formation, yet also highlight the substantial effect of background aerosol loadings on this process. A wide range of NOx and SO2 emissions were modeled to understand how they affect particle formation in the plume. Particle formation generally increases with SO2 emission, while NOx shows two different regimes: increasing particle formation with increasing NOx under low-NOx emissions and decreasing particle formation with increasing NOx under high-NOx emissions. Finally, we calculate emissions statistics of 330 coal-fired power plants in the US in 1997 and 2010, and the model results show a median decrease of 19% in particle formation ratesfrom 1997 to 2010 (whereas the W.A. Parish case study showed an increase). These results suggest that there may be important climate implications of power-plant controls due to changes in plume chemistry and microphysics. More extensive plume measurements for a range of emissions of SO2 and NOx and in varying background aerosol conditions are needed to better quantify these effects.

Twenty spinal injured wheelchair bound individuals were tested to peak VO2 on a wheelchair ergometer. Sixteen subjects were paraplegics (5 females, 11 males) and four were quadriplegic (2 females, 2 males). The level of injury ranged from C4-5 to L2-3. The mean age of the subjects was 29.9 years, with a mean weight of 63.66 kg. Prior to the peak VO2 and during the rest immediately after peak VO2, each subject was tested for the ability to discriminate touch over the skin of the thigh, leg, and foot. A chi square statistical technique was used to test for differences between pre- and postexercise sensitivity. The chi square was significant at the .003 level of significance. Because the increase in sensitivity was short, it was theorized that under peak exercise stress the body may recruit pathways that have been dormant, but not injured, explaining the increase in sensitivity.

This paper explores the impacts of carbonaceous aerosol on cloud condensation nuclei (CCN) concentrations in a global climate model with size-resolved aerosol microphysics. Organic matter (OM) and elemental carbon (EC) from two emissions inventories were incorporated into a preexisting model with sulfate and sea-salt aerosol. The addition of carbonaceous aerosol increased CCN(0.2%) concentrations by 65–90% in the globally averaged surface layer depending on the carbonaceous emissions inventory used. Sensitivity studies were performed to determine the relative importance of the organic "solute effect", in which CCN concentrations increase because of the added soluble carbonaceous material, versus the "seeding effect", in which CCN concentrations increase because of increased particle number concentrations. In a sensitivity study where carbonaceous aerosol was assumed to be completely insoluble, concentrations of CCN(0.2%) still increased by 40–50% globally over the no carbonaceous simulation because primary carbonaceous emissions were able to become CCN via condensation of sulfuric acid. This shows that approximately half of the contribution of carbonaceous particles to CCN comes from the "seeding effect" and half from the "solute effect". The solute effect tends to dominate more in areas where there is less inorganic aerosol than organic aerosol and the seeding effect tends to dominate in areas where is more inorganic aerosol than organic aerosol. It was found that an accurate simulation of the number size distribution is necessary to predict the CCN concentration but assuming an average chemical composition will generally give a CCN concentration within a factor of 2. If a "typical" size distribution is assumed for each species when calculating CCN, such as is done in bulk aerosol models, the mean error relative to a simulation with size resolved microphysics is on the order of 35%. Predicted values of carbonaceous aerosol mass and aerosol number were compared to observations and the model showed average errors of a factor of 3 for carbonaceous mass and a factor of 4 for total aerosol number. These errors may be reduced by improving the emission size distributions of both primary sulfate and primary carbonaceous aerosol.

The Department of Defense has embraced utilization management (UM) as an important tool to control and possibly decrease medical costs. Budgetary withholds have been taken by the Office of the Assistant Secretary of Defense (Health Affairs) to encourage the military services to implement UM programs. In response, Walter Reed Army Medical Center implemented a UM program along with other initiatives to effect changes in the delivery of inpatient care. This paper describes this UM program and other organizational initiatives, such as the introduction of new levels of care in an attempt to effect reductions in length of stay and unnecessary admissions. We demonstrate the use of a diversity of databases and analytical methods to quantify improved utilization and management of resources. The initiatives described significantly reduced hospital length of stay and inappropriate inpatient days. Without solid command and clinical leadership support and empowerment of the professional staffs, these significant changes and improvements could not have occurred.

OBJECTIVE: To assess the rate of tuberculosis infection among Hispanic students enrolled in English-as-a-Second-Language classes compared with Hispanic and non-Hispanic students not enrolled in such classes. METHODS: Using Mantoux tuberculin skin tests, the authors screened 720 students--out of 844 eligible--in two schools with predominantly Hispanic populations. Ethnicity and enrollment in the English-as-a-Second Language classes were recorded for each student. The rate of skin test positivity was compared for students enrolled and not enrolled in these classes. RESULTS: The incidence of positive tests among Hispanic students enrolled in an English-as-a-Second-Language class was 10.6%, compared with 1.3% for Hispanic students not enrolled (relative risk 8.3, 95% confidence interval 2.92, 23.8). There was no statistically significant difference in incidence rates for non-Hispanic students (0.5%) and Hispanic students (1.3%) who were not enrolled in English-as-a-Second-Language class (relative risk 2.4, 95% confidence interval 0.27, 20.9). CONCLUSION: School-based tuberculin screening programs targeted at students enrolled in English-as-a-Second-Language classes can be effective and are not racially discriminatory.

The professional activities and experiences of Army active component pediatricians deployed to Southwest Asia in support of Operations Desert Shield, Desert Storm, and Provide Comfort are reported. The 37 pediatricians who served in Southwest Asia were surveyed by a voluntary questionnaire. The survey revealed that Army pediatricians played an important role in these operations and in supporting the combat forces in Southwest Asia. They also played a critical role in caring for children displaced by the war and its aftermath in southern and northern Iraq. Pediatricians played an equally important role in continuing to provide care and support for the family members left behind in the United States and Europe.

The United States Army is committed to providing quality health care for active-duty service members, their dependents, and retired service members. Historically, the Army has never had enough active-duty physicians to provide care for all its beneficiaries. Alternatives utilizing civilian health care providers have been established to provide the balance of the medical services. In this review, the cost of each of the civilian health care providers in the Ft. Hood, Texas area is compared to that of the Army pediatrician. The Army pediatrician proves to be the least expensive of the health care providers.

An 80-year-old man had acute pancreatitis during the fourth week of antibiotic therapy for enterococcal endocarditis and 12 days after initiation of ketoprofen therapy for osteoarthritis of the hip. Pancreatitis resolved after discontinuance of ketoprofen therapy and while continuing antibiotic therapy for endocarditis. Common causes of pancreatitis were excluded by laboratory testing. Ketoprofen may have been the cause of pancreatitis in this case; we have suggested two possible mechanisms related to prostaglandin inhibition.

Data on time response in the nervous system are available for animals. Rate‐matching data for humam subjects with implanted electrodes are available. These data do not tell us with certainty up to what rate people with normal hearing utilize time information directly. In many experiments an attempt to measure time response is confused by the presence of spectral clues. Short‐term spectral clues exist in stochastic sequences of positive and negative pulses and in modulated white noise, both of which have a white long‐term spectrum. These clues are periodicity (with a period equal to the pulse or modulation rate) and symmetry (about frequencies equal to integer multiples of half this rate), differences at different frequencies in the peak‐ or rms‐voltage distribution function of the output of a narrow‐band filter and, in the case of stochastic pulse sequences, differences in extreme intensity at different frequencies. It may be that the ability to match at high rates and the perception of tonal quality that subjects with excellent and trained hearing, such as musicians, exhibit for white‐spectrum stochastic pulse sequences or gated noise is due to the residue phenomenon or to spectral clues discussed in this paper.

Twenty spinal-cord-injured subjects (4 quadriplegics and 16 paraplegics) were maximally stress tested on the Arizona State University wheelchair ergometer. Physiological data for each individual were collected as follows: (a) blood flow in the left leg by a photoelectric plethysmograph before exercise, during exercise, and postexercise, and (b) blood lactates before exercise and post-exercise. Eleven subjects had increased leg blood flow and vasodilation during exercise, but vasoconstriction postexercise. The lactate readings, in comparison to able-bodied individuals, were higher at rest but lower at maximal exercise.

We examined the mechanism by which hypertriglyceridemia interferes with the Roche Diagnostics "Amylochrome" procedure for measurement of amylase in lactescent samples with normal and above-normal amylase activity. The serum blank recommended in the Amylochrome protocol to compensate for lactescence remains inappropriately turbid, compared with the test, and is partly responsible for the underestimation of amylase activity. Other major interference is seen when lipoprotein in hyperlipemic samples with above-normal amylase activity reacts with the soluble oligosaccharide-triazinyl dye product of the Amylochrome assay to form a flocculent blue precipitate. The formation of this precipitate in the test, and its removal, diminish lactescence due to lipemia, an effect that cannot be matched by any manipulation of a serum blank procedure. Oligosaccharide-dye product is removed as a component of the precipitate.

SUMMARY: The fepA gene of Escherichia coli encodes the outer-membrane receptor protein for ferrienterobactin. Previous genetic studies indicated that fepA mutations occur frequently and suggested that most of the mutations were deletions. In this work seven spontaneous fepA mutations were analysed by enzyme assay (enterobactin synthase and enterobactin esterase) and by DNA hybridization studies. In two strains, UT500 and UT700, the mutations were confined to the fepA gene. In the remaining mutants, the mutations were large deletions; in several cases, 27 kb or more of DNA had been lost. The deletions, all of which eliminated approximately the left half of the enterobactin gene cluster, extended from the vicinity of the fepC gene counterclockwise into the chromosome. A minimum of three clockwise endpoints were identified and at least two counterclockwise endpoints were detected. The variation in endpoints among the deletions argues against the involvement of a normal transposon in their formation. Also, unexpected homology was found between enterobactin gene cluster DNA and lacPOZ and pSC101.

The equations for low amplitude space‐charge waves in an electron stream containing heavy positive ions are considered. At frequencies a little below the ion plasma frequency there should be a wave which increases in amplitude as it travels (negative attenuation). Ion motion tends to limit the rate of increase. In a beam filling a conducting cylinder and confined by a uniform magnetic field there should be an increasing wave at frequencies near the ion cyclotron frequency. Such waves might explain observed fluctuations in long electron beams.

This paper treats propagation of slaw waves in two-dimensional neutralized electron. flow in which all electrons have the same velocity in the direction of propagation but in which there are streams of two or more velocities normal to the direction of propagation. In a finite beam in which electrons are reflected elastically at the boundaries and in which equal dc currents are carried by electrons with transverse velocities

While orbital radio relays probably could not compete with microwave radio relay for communication over land, they might be useful in transoceanic communication. Three sorts of repeaters appear to be consistent with microwave art: (a) 100-ft reflecting spheres at an altitude of around 2200 miles; (b) a 100-ft oriented plane mirror in a 24-hr orbit, at an altitude of 22,000 miles; (c) an active repeater in a 24-hr orbit. Cases (a) and (b) require at 10cm wavelength 250-ft-diam antennas and 100-kw and 50kw power, respectively; in case (c), using 250-ft antennas on the ground and 10-ft antennas on the repeater, only 100 watts on the ground and 0.03 watt on the repeater would be required; in this case one should probably use smaller antennas on the ground. In cases (b) and (c) the problem of maintaining the correct orientation and position of the repeater is critical; perturbations by the moon and sun might cause the satellite to rock or wander prohibitively.

This paper describes a new amplifier in which use is made of an electron flow consisting of two streams of electrons having different average velocities. When the currents or charge densities of tie two streams are sufficient, the streams interact to give an increasing wave. Conditions for an increasing wave and the gain of the increasing wave are evaluated for a particular geometry of flow.

Many microwave tubes make use of a long electron beam. The radio frequency excitation on such a beam can be expressed in terms of two space-charge waves, one of which has negative energy and negative power flow. The electron beam may pass through resonators, through lossy surroundings, through slow-wave circuits. In this paper the low-level operation of klystrons, resistive-wall amplifiers, easitrons, space-charge-wave amplifiers, traveling-wave tubes and double-stream amplifiers is explained in terms of waves on electron beams and on circuits. Noise is discussed in terms of such waves.

An earlier paper presented equations for increasing waves in the presence of two streams of charged particles having different velocities, and solved the equations assuming the velocity of one group of particles to be zero or small. Numerical solutions giving the rate of increase and the phase velocity of the increasing wave for a wide range of parameters, covering cases of ion oscillation and double‐stream amplification, are presented here.

Many ideas important to microwave tubes, including the interaction of electrons with waves, occurred very early. An orderly understanding came much later. The RF diode equation (1933-1944) gave quantitative results concerning microwave tubes rather than insight. The klystron and the concept of velocity modulation and phase focusing (1938-1939) led to a clear picture of important phenomena as well as to powerful microwave devices. Insight and performance were extended by the traveling-wave tube and the wave analysis of its behavior (1946-1947). This led to explorations in terms of the behavior of coupled circuits (1951, 1954) and negative-energy waves (1951). Backward-wave oscillators provided further understanding and a new tool (1952-1953). This background of understanding which grew up concerning microwave tubes led to analysis of and improvement in noise behavior (1950-1959). Finally, the invention of the parametric amplifier led to very-low-noise microwave tubes (1959-1961). Crossed-field tubes have always been highly effective but difficult to analyze and design. Nonetheless, useful high-power amplifiers and oscillators have been built.

Propagation on a. helix as a function of frequency is characterized by ranges in which there is a slow wave which can be explained as very nearly a transverse electromagnetic wave traveling along the wire, and ranges in which the helix does not propagate; these are associated with "forbidden regions" of propagation constant pointed out by Sensiper. Each mode of propagation consists of an infinite number of spatial Fourier components called spatial harmonics. The complicated behavior with frequency of the modes of a helix is explained as an effect of the coupling through spatial harmonics of the slow wave which travels with about the velocity of light along the wire to fast free-space or waveguide waves which travel with about the velocity of light along the axis. The qualitative effects of such coupling agree with a tape-helix analysis of helixes in free space and helixes surrounded by a conducting tube. The case of the bifflar helix is also treated.

In electron beam devices the thermal velocities of the electrons leaving the cathode limit the current density which can be attained with given cathode current density, cathode temperature, potential, and angular spread of arriving electrons. By using Liouville's theorem, limiting expressions are obtained which are valid for any point focus or line focus concentrating system using steady electric and magnetic fields. Current densities in perfectly focused beams are also evaluated. Curves are presented which relate the nearness of approach to the maximum attainable current density with the fraction of cathode current necessarily lost in the concentrating system. Use of the expressions obtained is illustrated by applying them to cathode ray tubes and electron multipliers.

In Chapter VI we have expressed the properties of a circuit in terms of its normal modes of propagation rather than its physical dimensions. In this chapter we shall use this representation in justifying the circuit equation of Chapter II and in adding to it a term to take into account the local fields produced by a-c space charge. Then, a combined circuit and ballistical equation will be obtained, which will be used in the following chapters in deducing various properties of traveling-wave tubes.

This paper discusses the operation and characteristics of electrostatic photo‐multipliers, using the Western Electric D‐159076 photo‐multiplier as an example to illustrate specific points. The following subjects are discussed: description of operation, advantages and applications, typical operating conditions, variation of sensitivity with voltage, hum due to ripple in power supply, effect of unequal voltage division, output impedance, linearity of response and fluctuation noises.

The voltage and current modulation of ideal cylindrical electron beams in Brillouin flow, as well as beams in zero magnetic field, are studied by means of Laplace transform. With a large-diameter beam of this class, suddenly accelerated from a temperature-limited cathode and without transverse velocities, the minimum noise figure of an amplifier is found to be smaller than it would be for a narrow, essentially one-dimensional (filament or sheet) beam, or for a confined-flow beam with the same diameter, longitudinal velocity and direct current. Certain space-charge wave solutions obtained in field analyses of beams from shielded diodes, which have never been detected experimentally, are found to be nonexistent in the sense that no phenomenon taking place in a vacuum tube excites them.

Elementary arguments of conservation of energy and momentum are used to derive expressions for what Sturrock terms the ``formal'' momentum, angular momentum, and energy of a plane wave in a moving medium. If E is the energy per unit length, p the momentum per unit length, q the angular momentum per unit length, vf the phase velocity, and if the angular variation of a circulatory polarized wave is as exp(—jnθ), p=E/vf,q=nE/ω. If E0 is the energy per unit length observed moving with the medium, and then if the medium moves past the observer with a velocity u and the observer measures a phase velocity vf, he observes an energy per unit length E, E=E0/(1−u/vf). When p, q, and E are not the physical momenta and energy, they lead to the correct power and force for sinusoidal sources moving with respect to the medium.

Traveling-wave tubes will have gain even if the r-f field at the mean position of the electron stream is purely transverse. The addition of a longitudinal magnetic focusing field reduces the gain due to transverse fields and increases the electron velocity for optimum gain.

The operation of a wave‐type parametric amplifier may be thought of in terms of the force exerted by traveling discontinuities or reflecting elements on the waves present in the device. By invoking the principles of conservation of energy and momentum it is possible to understand in very simple terms certain limitations on the operation of such devices and to arrive very easily at certain general relations governing their behavior, including the Manley‐Rowe relation. It is proposed that for a guided wave the momentum per unit distance is the power divided by the product of the group and phase velocities.

Technically correct results in a field are achieved initially in diverse and often confusing and complicated ways. Sometimes, such results are later brought together to give them a more unified form and a sounder basis; such critical summary and exposition is of great value. In quite another way, a worker who uses results established in a field will discover many plausible reasons for believing the results, and he will find eventually that an air of inevitability and “understanding” pervades the subject. Such “understanding” is not to be confused with the process of rigorous proof carried out step by step, but it can help in organizing and making use of a body of related material.

The limitation on the rate at which information can be transmitted over an ordinary telephone channel is a human one. In this study people read words as fast as they were able to; from these results some deductions are made about the capacity of a human being as an information channel. The discrepancy between human channel capacity measured thus (40–50 bits/sec) and telephone and television channel capacity (about 50,000 bits/sec and 50,000,000 bits/sec respectively) is provocative.

An analysis of the patterns and amplitudes of the precordial movements is presented. Normal young adult subjects had three types of patterns. Type I occurred in 78 per cent, type II in 14 per cent, and type III in 8 per cent of the subjects studied. The variations of the kinetocardiogram from apex cardiograms and pneumocardiograms are discussed.

In working on the theory of electron beam devices such as travelling-wave tubes and klystrons, it has been necessary to consider a number of knotty problems, some at least of which occur in mathematical formulation of other plasma problems. Among these is the matter of multi-velocity flow. Here there are two mathematically equivalent approaches. In one, the electron flow is divided into streams according to the initial unperturbed velocities of the electrons; the variables are the densities and velocities in the various streams. In the other, velocity is regarded as a co-ordinate of phase space and the variable is the density in phase space. These approaches give different appreciations of the phenomena involved and lead to different mathematical difficulties, but are the same in content. Each demonstrates the non-existence of wave-type solutions in many infinite velocity distributions. Only a few specialized solutions of multi-velocity problems exist. As different velocity co-ordinates can be used, so different spatial co-ordinates can be used. The Eulerian approach is common and leads to no difficulties if boundary conditions are met at fluctuating boundaries. In the case of thin beams, it is sometimes useful to use displacements from the mean position of the particles as variables. Some workers have made mistakes by mixing co-ordinate systems. In dealing with power flow in electron beams, one can either replace the actual physical system with a linear system and find an expression for power in this system, or try to deal with the power flow in the true non-linear system. The former alternative is much simpler. Kinetic power, as well as electromagnetic power, is important in considering the orthogonality of wave-type components. In solving an actual physical problem, one can either assemble various wave-type components so as to satisfy the boundary conditions, or solve the problem by transform or perhaps by other means. Components of the solution must be regarded as merely a part of the solution of an actual problem, but they can sometimes be given a reasonable physical interpretation. Thus, one finds waves with positive and negative powers. When two unattenuated waves having powers of the same sign are coupled together, one observes beats. When two unattenuated waves having powers of opposite signs are coupled together, one observes growing and decaying waves. Growing waves can also be produced when a moving discontinuity couples two unattenuated waves together (parametric amplification).

This is a review paper which discusses in simple terms high-power klystrons, double-tuned circuits for reflex klystrons, noise in traveling-wave tubes and its reduction by velocity-jump or space-charge-wave deamplification, periodic magnetic focusing of electron beams, and the backward-wave oscillator.

In the sense of adapting a system to people, the study of biological and psychological phenomena can be very important. However, the author is opposed to the whole concept of designing machines to imitate biological systems. A more sensible approach is to study the abilities and needs of humans for the purpose of designing machines to serve them

The existence of artificial earth satellites and of very low-noise maser amplifiers makes microwave links using spherical satellites as passive reflectors seem an interesting alternative to cable or tropospheric scatter for broad-band transatlantic communication. A satellite in a polar orbit at a height of 3000 miles would be mutually visible from Newfoundland and the Hebrides for 22.0 per cent of the time and would be over 7.25° above the horizon at each point for 17.7 per cent of the time. Out of 24 such satellites, some would be mutually visible over 7.25° above the horizon 99 per cent of the time. With 100-foot diameter spheres, 150-foot diameter antennas, and a noise temperature of 20°K, 85 kw at 2000 mc or 9.5 kw at 6000 mc, could provide a 5-mc base band with a 40-db signal-to-noise ratio. The same system of satellites could be used to provide further communication at other frequencies or over other paths

Electrodes are devised by means of which rectilinear electron flow according to well‐known space charge equations can be realized in beams surrounded by charge‐free space. It is shown how these electrodes can be used in the design of electron guns having desirable characteristics.

This paper describes a possible sort of data network for the transmission of addressed blocks of data between data terminals. The network consists of a number of closed rings or loops around which data blocks circulate. Data terminals on local loops can read data into empty blocks and read data addressed to them from full blocks. Buffered devices transfer data between local and regional loops and between regional loops and a national loop. Loops so interconnected need not be synchronized; they need not even operate at the same bit rate. Provisions are made for a “busy” signal, for special loops to carry heavy traffic between particular local loops, and for alternate routing.