arXiv subjects

T. Stein

Publications and source records attributed to T. Stein.

5 recordsLinked to original sources

arXiv2019

Penetrating particle ANalyzer (PAN)

PAN is a scientific instrument suitable for deep space and interplanetary missions. It can precisely measure and monitor the flux, composition, and direction of highly penetrating particles ($> \sim$100 MeV/nucleon) in deep space, over at least one full solar cycle (~11 years). The science program of PAN is multi- and cross-disciplinary, covering cosmic ray physics, solar physics, space weather and space travel. PAN will fill an observation gap of galactic cosmic rays in the GeV region, and provide precise information of the spectrum, composition and emission time of energetic particle originated from the Sun. The precise measurement and monitoring of the energetic particles is also a unique contribution to space weather studies. PAN will map the flux and composition of penetrating particles, which cannot be shielded effectively, precisely and continuously, providing valuable input for the assessment of the related health risk, and for the development of an adequate mitigation strategy. PAN has the potential to become a standard on-board instrument for deep space human travel. PAN is based on the proven detection principle of a magnetic spectrometer, but with novel layout and detection concept. It will adopt advanced particle detection technologies and industrial processes optimized for deep space application. The device will require limited mass (~20 kg) and power (~20 W) budget. Dipole magnet sectors built from high field permanent magnet Halbach arrays, instrumented in a modular fashion with high resolution silicon strip detectors, allow to reach an energy resolution better than 10\% for nuclei from H to Fe at 1 GeV/n.

physics.space-ph↗

arXiv2008

The Nature of the Vector and Scalar Potentials and Gauge Invariance in the Context of Gauge Theory

Modern undergraduate textbooks in electricity and magnetism typically focus on a force representation of electrodynamics with an emphasis on Maxwell's Equations and the Lorentz Force Law. The vector potential $\mathbf{A}$ and scalar potential $Φ$ play a secondary role mainly as quantities used to calculate the electric and magnetic fields. However, quantum mechanics including quantum electrodynamics (QED) and other gauge theories demands a potential ($Φ$,$\mathbf{A}$) oriented representation where the potentials are the more fundamental quantities. Here, we help bridge that gap by showing that the homogeneous Maxwell's equations together with the Lorentz Force Law can be derived from assuming that the potentials represent potential energy and momentum per unit charge. Furthermore, we enumerate the additional assumptions that are needed to derive the inhomogeneous Maxwell's equations. As part of this work we demonstrate the physical nature and importance of gauge invariance.

physics.gen-ph↗

arXiv1999

Dynamics of Flux Creep in Underdoped Single Crystals of Y_1-xPr_xBa_2Cu_3O_7-d

Transport as well as magnetic relaxation properties of the mixed state were studied on strongly underdoped Y_1-xPr_xBa_2Cu_3O_7-d crystals. We observed two correlated phenomena - a coupling transition and a transition to quantum creep. The distribution of transport current below the coupling transition is highly nonuniform, which facilitates quantum creep. We speculate that in the mixed state below the coupling transition, where dissipation is nonohmic, the current distribution may be unstable with respect to self-channeling resulting in the formation of very thin current-carrying layers.

cond-mat.supr-con↗

arXiv1999

Relationship Between Conductivity and Phase Coherence Length in Cuprates

The large ($10^2 - 10^5$) and strongly temperature dependent resistive anisotropy $η= (σ_{ab}/σ_c)^{1/2}$ of cuprates perhaps holds the key to understanding their normal state in-plane $σ_{ab}$ and out-of-plane $σ_{c}$ conductivities. It can be shown that $η$ is determined by the ratio of the phase coherence lengths $\ell_i$ in the respective directions: $σ_{ab}/σ_c = \ell_{ab}^2/\ell_{c}^2$. In layered crystals in which the out-of-plane transport is incoherent, $\ell_{c}$ is fixed, equal to the interlayer spacing. As a result, the T-dependence of $η$ is determined by that of $\ell_{ab}$, and vice versa, the in-plane phase coherence length can be obtained directly by measuring the resistive anisotropy. We present data for hole-doped $YBa_2Cu_3O_y$ ($6.3 < y < 6.9$) and $Y_{1-x}Pr_xBa_2Cu_3O_{7-δ}$ ($0 < x \leq 0.55$) and show that $σ_{ab}$ of crystals with different doping levels can be well described by a two parameter universal function of the in-plane phase coherence length. In the electron-doped $Nd_{2-x}Ce_{x}CuO_{4-y}$, the dependence $σ_{ab}(η)$ indicates a crossover from incoherent to coherent transport in the c-direction.

cond-mat.supr-con↗

arXiv1999

Quantum Creep in Y_{1-x}Pr_{x}Ba_{2}Cu_{3}O_{7}$ Crystals: Magnetic Relaxation and Transport

We report transport and magnetic relaxation measurements in the mixed state of strongly underdoped Y_{1-x}Pr_{x}Ba_{2}Cu_{3}O_{7} crystals. A transition from thermally activated flux creep to temperature independent quantum flux creep is observed in both transport and magnetic relaxation at temperatures T * 5 K. Flux transformer measurements indicate that the crossover to quantum creep is preceded by a coupling transition. Based on these observations we argue that below the coupling transition the current is confined within a very narrow layer beneath the current contacts.

cond-mat.supr-con↗