Modified two-potential approach to tunneling problems

One-body quantum tunneling to continuum is treated via the two-potential approach, dividing the tunneling potential into external and internal parts. We show that corrections to this approach can be minimized by taking the separation radius inside the interval determined by simple expressions. The resulting two-potential approach reproduces the resonance energy and its width, both for narrow and wide resonances. We also demonstrate that, without losing its accuracy, the two-potential approach can be modified to a form resembling the R-matrix theory, yet without any uncertainties of the latter related to the choice of the matching radius.Comment: 7 two-column pages, 3 figures, extra-explanation added, Phys. Rev. A, in pres

Superconductivity and crystalline electric field effects in the filled skutterudite series Pr(Os1−x_{1-x}Rux_x)4_4Sb12_{12}

X-ray powder diffraction, magnetic susceptibility $\chi(T)$, and electrical resistivity $\rho(T)$ measurements were made on single crystals of the filled skutterudite series Pr(Os$_{1-x}$Ru$_x$)$_4$Sb$_{12}$. One end of the series ($x = 0$) is a heavy fermion superconductor with a superconducting critical temperature $T_{c} = 1.85$ K, while the other end ($x = 1$) is a conventional superconductor with $T_{c} \approx 1$ K. The lattice constant $a$ decreases approximately linearly with increasing Ru concentration $x$. As Ru (Os) is substituted for Os (Ru), $T_{c}$ decreases nearly linearly with substituent concentration and exhibits a minimum with a value of $T_{c} = 0.75$ K at $x = 0.6$, suggesting that the two types of superconductivity compete with one another. Crystalline electric field (CEF) effects in $\chi_\mathrm{dc}(T)$ and $\rho(T)$ due to the splitting of the Pr$^{3+}$ nine-fold degenerate Hund's rule $J = 4$ multiplet are observed throughout the series, with the splitting between the ground state and the first excited state increasing monotonically as $x$ increases. The fits to the $\chi_\mathrm{dc}(T)$ and $\rho(T)$ data are consistent with a $\Gamma_{3}$ doublet ground state for all values of x, although reasonable fits can be obtained for a $\Gamma_{1}$ ground state for $x$ values near the end member compounds ($x = 0$ or $x = 1$).Comment: 10 pages, 8 figures, submitted to Phys. Rev.

Space-time versus particle-hole symmetry in quantum Enskog equations

The non-local scattering-in and -out integrals of the Enskog equation have reversed displacements of colliding particles reflecting that the -in and -out processes are conjugated by the space and time inversions. Generalisations of the Enskog equation to Fermi liquid systems are hindered by a request of the particle-hole symmetry which contradicts the reversed displacements. We resolve this problem with the help of the optical theorem. It is found that space-time and particle-hole symmetry can only be fulfilled simultaneously for the Bruckner-type of internal Pauli-blocking while the Feynman-Galitskii form allows only for particle-hole symmetry but not for space-time symmetry due to a stimulated emission of Bosons

Kinetic Properties of a Bose-Einstein Gas at Finite Temperature

We study, in the framework of the Boltzmann-Nordheim equation (BNE), the kinetic properties of a boson gas above the Bose-Einstein transition temperature $T_c$. The BNE is solved numerically within a new algorithm, that has been tested with exact analytical results for the collision rate of an homogeneous system in thermal equilibrium. In the classical regime ($T > 6~ T_c$), the relaxation time of a quadrupolar deformation in momentum space is proportional to the mean free collision time $\tau_{relax} \sim T^{-1/2}$. Approaching the critical temperature ($T_c < T < 2.7~ T_c$), quantum statistic effects in BNE become dominant, and the collision rate increases dramatically. Nevertheless, this does not affect the relaxation properties of the gas that depend only on the spontaneous collision term in BNE. The relaxation time $\tau_{relax}$ is proportional to $(T - T_c)^{-1/2}$, exhibiting a critical slowing down. These phenomena can be experimentally confirmed looking at the damping properties of collective motions induced on trapped atoms. The possibility to observe a transition from collisionless (zero-sound) to hydrodynamic (first-sound) is finally discussed.Comment: RevTeX, 5 figures. Submitted to Phys. Rev.

Observations of a Solar Energetic Particle Event From Inside and Outside the Coma of Comet 67P

Publisher Copyright: ©2022. The Authors.We analyze observations of a solar energetic particle (SEP) event at Rosetta's target comet 67P/Churyumov-Gerasimenko during 6–10 March 2015. The comet was 2.15 AU from the Sun, with the Rosetta spacecraft approximately 70 km from the nucleus placing it deep inside the comet's coma and allowing us to study its response. The Eastern flank of an interplanetary coronal mass ejection (ICME) also encountered Rosetta on 6 and 7 March. Rosetta Plasma Consortium data indicate increases in ionization rates, and cometary water group pickup ions exceeding 1 keV. Increased charge exchange reactions between solar wind ions and cometary neutrals also indicate increased upstream neutral populations consistent with enhanced SEP induced surface activity. In addition, the most intense parts of the event coincide with observations interpreted as an infant cometary bow shock, indicating that the SEPs may have enhanced the formation and/or intensified the observations. These solar transient events may also have pushed the cometopause closer to the nucleus. We track and discuss characteristics of the SEP event using remote observations by SOHO, WIND, and GOES at the Sun, in situ measurements at Solar Terrestrial Relations Observatory Ahead, Mars and Rosetta, and ENLIL modeling. Based on its relatively prolonged duration, gradual and anisotropic nature, and broad angular spread in the heliosphere, we determine the main particle acceleration source to be a distant ICME which emerged from the Sun on 6 March 2015 and was detected locally in the Martian ionosphere but was never encountered by 67P directly. The ICME's shock produced SEPs for several days which traveled to the in situ observation sites via magnetic field line connections.Peer reviewe

Loss of ELK1 has differential effects on age-dependent organ fibrosis and integrin expression

ETS domain-containing protein-1 (ELK1) is a transcription factor important in regulating αvβ6 integrin expression. αvβ6 integrins activate the profibrotic cytokine Transforming Growth Factor β1 (TGFβ1) and are increased in the alveolar epithelium in idiopathic pulmonary fibrosis (IPF). IPF is a disease associated with aging and therefore we hypothesised that aged animals lacking Elk1 globally would develop spontaneous fibrosis in organs where αvβ6 mediated TGFβ activation has been implicated. Here we identify that Elk1-knockout (Elk1−/0) mice aged to one year developed spontaneous fibrosis in the absence of injury in both the lung and the liver but not in the heart or kidneys. The lungs of Elk1−/0 aged mice demonstrated increased collagen deposition, in particular collagen 3α1, located in small fibrotic foci and thickened alveolar walls. Despite the liver having relatively low global levels of ELK1 expression, Elk1−/0 animals developed hepatosteatosis and fibrosis. The loss of Elk1 also had differential effects on Itgb1, Itgb5 and Itgb6 expression in the four organs potentially explaining the phenotypic differences in these organs. To understand the potential causes of reduced ELK1 in human disease we exposed human lung epithelial cells and murine lung slices to cigarette smoke extract, which lead to reduced ELK1 expression andmay explain the loss of ELK1 in human disease. These data support a fundamental role for ELK1 in protecting against the development of progressive fibrosis via transcriptional regulation of beta integrin subunit genes, and demonstrate that loss of ELK1 can be caused by cigarette smoke

Quantum Kinetic Theory I: A Quantum Kinetic Master Equation for Condensation of a weakly interacting Bose gas without a trapping potential

A Quantum Kinetic Master Equation (QKME) for bosonic atoms is formulated. It is a quantum stochastic equation for the kinetics of a dilute quantum Bose gas, and describes the behavior and formation of Bose condensation. The key assumption in deriving the QKME is a Markov approximation for the atomic collision terms. In the present paper the basic structure of the theory is developed, and approximations are stated and justified to delineate the region of validity of the theory. Limiting cases of the QKME include the Quantum Boltzmann master equation and the Uehling-Uhlenbeck equation, as well as an equation analogous to the Gross-Pitaevskii equation.Comment: 37 pages, 4 figure

Establishing a library of resources to help people understand key concepts in assessing treatment claims—The “Critical thinking and Appraisal Resource Library” (CARL)

Background People are frequently confronted with untrustworthy claims about the effects of treatments. Uncritical acceptance of these claims can lead to poor, and sometimes dangerous, treatment decisions, and wasted time and money. Resources to help people learn to think critically about treatment claims are scarce, and they are widely scattered. Furthermore, very few learning-resources have been assessed to see if they improve knowledge and behavior. Objectives Our objectives were to develop the Critical thinking and Appraisal Resource Library (CARL). This library was to be in the form of a database containing learning resources for those who are responsible for encouraging critical thinking about treatment claims, and was to be made available online. We wished to include resources for groups we identified as ‘intermediaries’ of knowledge, i.e. teachers of schoolchildren, undergraduates and graduates, for example those teaching evidence-based medicine, or those communicating treatment claims to the public. In selecting resources, we wished to draw particular attention to those resources that had been formally evaluated, for example, by the creators of the resource or independent research groups. Methods CARL was populated with learning-resources identified from a variety of sources—two previously developed but unmaintained inventories; systematic reviews of learning-interventions; online and database searches; and recommendations by members of the project group and its advisors. The learning-resources in CARL were organised by ‘Key Concepts’ needed to judge the trustworthiness of treatment claims, and were made available online by the James Lind Initiative in Testing Treatments interactive (TTi) English (www.testingtreatments.org/category/learning-resources).TTi English also incorporated the database of Key Concepts and the Claim Evaluation Tools developed through the Informed Healthcare Choices (IHC) project (informedhealthchoices.org). Results We have created a database of resources called CARL, which currently contains over 500 open-access learning-resources in a variety of formats: text, audio, video, webpages, cartoons, and lesson materials. These are aimed primarily at ‘Intermediaries’, that is, ‘teachers’, ‘communicators’, ‘advisors’, ‘researchers’, as well as for independent ‘learners’. The resources included in CARL are currently accessible at www.testingtreatments.org/category/learning-resources Conclusions We hope that ready access to CARL will help to promote the critical thinking about treatment claims, needed to help improve healthcare choices