Energy deposition in different diameter sites can help characterize the incident radiation

The energy deposited by many types of radiation, including the high energy heavy ions found in galactic cosmic rays, is more damaging to biological systems than equal amounts of energy delivered by conventional X-ray irradiation. Average quantities such as dose and LET do not provide the information necessary to predict the effect of these types of irradiation at low doses. Charged particle fluence, as a function of the particle charge and velocity, is the ideal way to characterize the radiation, but in many practical situations the fluence spectrum is not known, and cannot be easily obtained. Low pressure proportional counters, simulating tissue volumes a few micrometers in diameter, provide a convenient alternative to dose and fluence measurements. Such instruments are used routinely on the space shuttle and space station to evaluate radiation exposures. However, the energy deposited does not relate directly to energy transferred because a significant amount of energy is carried away from the particle track by delta rays. Using experimental data and simple approximations we show that energy deposited in targets 0.02, 2, and in diameter differs by easily measurable amounts. These results suggest that it is possible to estimate the fraction of the events that are due only to delta rays, and, thus, the average velocity of the particles that deposited the energy, from measurements of energy imparted in different size sites.     

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Experimental limitations in impedance spectroscopy: Part VI. Four-point measurements of solid materials systems

Four-point impedance spectroscopy of solid materials systems is severely hampered by unavoidable voltage-divider effects associated with the reference electrodes. As demonstrated by test circuit studies and experiments with Pt/YSZ/Pt cells (with embedded silver reference electrodes), high impedance reference electrodes can produce distorted and erroneous impedance data. The relationships between these data and the sample properties (conductivity, dielectric constant) and instrument limitations (input impedance/capacitance) are derived. Successful four-point impedance measurements on conductive systems require large effective dielectric constants, which may be unattainable in bulk solids, but are often associated with internal interfaces.     

An explicit sieve bound and small values of σ(ф(m))

We prove an explicit sieve upper bound based on the large sieve of Montgomery and Vaughan [MV], and apply it to show that σ(ф(m)) ≥ m/39.4 for all positive integers m.