June 20th, 2019

лошадь, диаграмма, Фейнман

Компактный циклотрон с редкоземельным магнитом

В начале статьи - обзор по циклотронам.

Compact Rare-Earth Superconducting Cyclotron: https://arxiv.org/abs/1906.07642

The use of superconductivity is well-known as a method to increase the average field of a cyclotron and thereby to allow a substantial reduction of its size and mass. We present a compact high-field design for the first superconducting cyclotron with rare-earth (holmium) poles. Our design supports stable acceleration of protons to Ek = 70 MeV with no significant limit in beam current, suitable for wide applications in ocular therapy, isotope production, radiobiological studies and nuclear physics.

14 pages, 18 figures
лошадь, диаграмма, Фейнман

Парочка педагогически полезных статеек с матфизическим содержанием

A Unified View of Transport Equations: https://arxiv.org/abs/1906.06541

Distribution functions of many static transport equations are found using the Maximum Entropy Principle. The equations of constraint which contain the relevant dynamical information are simply the low-lying moments of the distributions. Systems subject to conservative forces have also been considered.

Why pushing a bell does not produce a sound: https://arxiv.org/abs/1906.06837

The difference between "beating" and "pushing" results in the perception that a push just makes the object move as a whole, while a beat produces also a sound. Through a detailed analysis of the physics underlying such everyday experiences, we identify the \emph{strength}, the \emph{duration} and the \emph{softness} of the applied contact force, as the main (measurable) characteristics that mark such difference. The strength determines the final velocity Δv achieved by the body. The duration 2τ compares to the time τℓ the sound takes to cross the body. The softness γ (a positive exponent) results from the shape in time of the contact force. Those three elements enter the formula for the intensity of the sound produced. The relevant role of the softness is stressed and specific values are calculated for a thin metallic bar, chosen as the simplest possible model system.
лошадь, диаграмма, Фейнман

Новое по дозиметрическим единицам

Conversion Coefficients from Kerma to Ambient Dose and Personal Dose for X-Ray Spectra: https://arxiv.org/abs/1906.05411

In radiation protection, the protection quantity for whole-body exposure is effective dose E. Effective dose cannot be measured and operational quantities have been introduced for dose measurement and calibration of dosimeters and survey instruments. To overcome some shortcomings of the presently used operational quantities, ICRU Report Committee 26 introduces two new quantities for whole body exposure, ambient dose H∗ for prospective dose assessment and personal dose Hp(α) for retrospective measurements with personal dosimeters. Dosimeters and survey instruments are calibrated in reference fields, realised with radioisotopes and with well-defined x-ray spectra. In this paper, the spectrum-averaged conversion coefficients from kerma in air Ka to the new quantities ambient dose and personal dose are calculated and compared with the published coefficients for the present operational quantities. Especially at low energies (Eph < 40 keV), the new quantities are significantly lower than the present ones, thus correcting a strong overestimate of effective dose.

14 pages, 5 tables, 8 figures
лошадь, диаграмма, Фейнман


Bosons, Fermions, Spin, Gravity, and the Spin-Statistics Connection: https://arxiv.org/abs/1906.07656

Invited article written for the S. N. Bose 125-birth anniversary commemorative issue of Physics News (Indian Physics Association), 22 pages

Catching Gravitational Waves With A Galaxy-sized Net Of Pulsars: https://arxiv.org/abs/1906.07568

Pedagogical article on gravitational-waves and pulsar-timing arrays written for a young audience