Short-range Magnetic interactions in the Spin-Ice compound Ho2_{2}Ti2_{2}O7_{7}

Magnetization and susceptibility studies on single crystals of the pyrochlore Ho$_{2}$Ti$_{2}$O$_{7}$ are reported for the first time. Magnetization isotherms are shown to be qualitatively similar to that predicted by the nearest neighbor spin-ice model. Below the lock-in temperature, $T^{\ast }\simeq 1.97$ K, magnetization is consistent with the locking of spins along [111] directions in a specific two-spins-in, two-spins-out arrangement. Below $T^{\ast}$ the magnetization for $B||[111]$ displays a two step behavior signalling the breaking of the ice rules.Comment: 4 pages, 3 figure

Heating and cooling system

A heating and cooling apparatus capable of cyclic heating and cooling of a test specimen undergoing fatigue testing is discussed. Cryogenic fluid is passed through a block clamped to the speciment to cool the block and the specimen. Heating cartridges penetrate the block to heat the block and the specimen to very hot temperaures. Control apparatus is provided to alternatively activate the cooling and heating modes to effect cyclic heating and cooling between very hot and very cold temperatures. The block is constructed of minimal mass to facilitate the rapid temperature changes

Fiber-optic push-pull sensor systems

Fiber-optic push-pull sensors are those which exploit the intrinsically differential nature of an interferometer with concommitant benefits in common-mode rejection of undesired effects. Several fiber-optic accelerometer and hydrophone designs are described. Additionally, the recent development at the Naval Postgraduate School of a passive low-cost interferometric signal demodulator permits the development of economical fiber-optic sensor systems

AN ECONOMIC EVALUATION OF THE COLORADO RIVER BASIN SALINITY CONTROL PROGRAM

Dissolved salts (salinity) adversely affect numerous urban and agricultural users of Colorado River water in California and Arizona. Congress in 1974 authorized a major salinity control program. Studies of general economic benefits from salinity abatement and the cost per unit of salinity reduction expected from specific proposed projects have been developed by the responsible federal agencies, but no project-by-project evaluation has been published. We find a conceptual basis for a substantial downward revision of prospective economic benefits of salinity abatement. Revised benefits are compared with estimated costs, and only for five of the nineteen projects do economic benefits appear to exceed costs.Resource /Energy Economics and Policy,

Vibrational intensity distributions for continuum photoionization of oxygen

Results from measurements of vibrational intensity distributions for continuum photoionization of O2 are reported. Measurements were made using the 584 and 304 A He lines. The photoionization cross section of O2 shows a substantial dip in magnitude over a 20 A band centered about 590 A; thus the possibility exists that a 584 A photoelectron spectrum of O2 includes an autoionized contribution and the vibrational intensity distributions may not correspond to those of continuum ionization. Oxygen photoionization cross section shows no structure around 304 A and purley continuum ionization is expected

On the ionization potential of molecular oxygen

The ionization potential of O2 was measured by the technique of high resolution photoelectron spectroscopy taking into account the influence of rotational structure on the shape of the vibrational bands. A value of 12.071 + or - .001 eV (1027.1 + or - 0.1 A) was found for the ionization potential. A lowering of the ionization potential caused by a branch-head when delta N = -2 gave an appearance potential for ionization of 12.068 + or - .001 eV (1027.4 + or - 0.1 A)

Vibrational intensity distributions in the photoelectron spectrum of hydrogen

The intensity distribution over the H2(+) vibrational levels up to a quantum number of 15 was measured for H2 photoelectron spectra at a photon wavelength of 584 A. The data show reasonable agreement with recent calculations only in the quantum number of 0 through 8. The higher levels are populated significantly lower than predicted by theory

Photoionization branching ratios and vibrational intensity distribution for N2, CO; and CO2 between 53 and 75 nm

The probability of radiation producing ions in specific electronic and vibrational levels was documented. For example, when a narrow band-pass of solar ionizing photons is incident on an atmospheric species it is now possible to describe, accurately, how the radiant energy is shared among the various electronic states of the ions produced. The molecules studied were N2, CO, and CO2. These molecules were photoionized by radiation between 53 and 75 nm. The effects of autoionization are discussed and continuum vibrational intensities are tabulated and compared with theoretical Franck-Condon factors where available. The branching ratios and partial cross sections for ionization into various electronic states are tabulated

Collecting efficiency of a cylindrical mirror electron energy analyzer with preretarding lens

The electron collecting efficiency of a cylindrical mirror energy analyzer incorporating retardation of the electrons prior to analysis has been determined over the range 0 to 30 eV by two methods. The first method requires the use of a vacuum ultraviolet monochromator to produce monoenergetic electrons of different energies; the second method involves measuring the energy-brightness relationship of the retarding optics and should be applicable to any deflection analyzer with pre-retarding optics. The results of the two methods are compared and the limitations of the latter method are discussed

Interference between postural control and mental task performance in patients with vestibular disorder and healthy controls

OBJECTIVES - To determine whether interference between postural control and mental task performance in patients with balance system impairment and healthy subjects is due to general capacity limitations, motor control interference, competition for spatial processing resources, or a combination of these.METHOD - Postural stability was assessed in 48 patients with vestibular disorder and 24 healthy controls while they were standing with eyes closed on (a) a stable and (b) a moving platform. Mental task performance was measured by accuracy and reaction time on mental tasks, comprising high and low load, spatial and non-spatial tasks. Interference between balancing and performing mental tasks was assessed by comparing baseline (single task) levels of sway and mental task performance with levels while concurrently balancing and carrying out mental tasks.RESULTS - As the balancing task increased in difficulty, reaction times on both low load mental tasks grew progressively longer and accuracy on both high load tasks declined in patients and controls. Postural sway was essentially unaffected by mental activity in patients and controls.CONCLUSIONS - It is unlikely that dual task interference between balancing and mental activity is due to competition for spatial processing resources, as levels of interference were similar in patients with vestibular disorder and healthy controls, and were also similar for spatial and non-spatial tasks. Moreover, the finding that accuracy declined on the high load tasks when balancing cannot be attributed to motor control interference, as no motor control processing is involved in maintaining accuracy of responses. Therefore, interference between mental activity and postural control can be attributed principally to general capacity limitations, and is hence proportional to the attentional demands of both tasks