Can spacetime curvature induced corrections to Lamb shift be observable?

The Lamb shift results from the coupling of an atom to vacuum fluctuations of quantum fields, so corrections are expected to arise when the spacetime is curved since the vacuum fluctuations are modified by the presence of spacetime curvature. Here, we calculate the curvature-induced correction to the Lamb shift outside a spherically symmetric object and demonstrate that this correction can be remarkably significant outside a compact massive astrophysical body. For instance, for a neutron star or a stellar mass black hole, the correction is $\sim$ 25% at a radial distance of $4GM/c^2$, $\sim$ 16% at $10GM/c^2$ and as large as $\sim$ 1.6% even at $100GM/c^2$, where $M$ is the mass of the object, $G$ the Newtonian constant, and $c$ the speed of light. In principle, we can look at the spectra from a distant compact super-massive body to find such corrections. Therefore, our results suggest a possible way of detecting fundamental quantum effects in astronomical observations.Comment: 13 pages, 3 figures, slight title change, clarifications and more discussions added, version to be published in JHE

Gravitational Microlensing Evidence for a Planet Orbiting a Binary Star System

The study of extra-solar planetary systems has emerged as a new discipline of observational astronomy in the past few years with the discovery of a number of extra-solar planets. The properties of most of these extra-solar planets were not anticipated by theoretical work on the formation of planetary systems. Here we report observations and light curve modeling of gravitational microlensing event MACHO-97-BLG-41, which indicates that the lens system consists of a planet orbiting a binary star system. According to this model, the mass ratio of the binary star system is 3.8:1 and the stars are most likely to be a late K dwarf and an M dwarf with a separation of about 1.8 AU. A planet of about 3 Jupiter masses orbits this system at a distance of about 7 AU. If our interpretation of this light curve is correct, it represents the first discovery of a planet orbiting a binary star system and the first detection of a Jovian planet via the gravitational microlensing technique. It suggests that giant planets may be common in short period binary star systems.Comment: 11 pages, with 1 color and 2 b/w Figures included (published version

Scalar soliton quantization with generic moduli

This article is distributed under the terms of the Creative Commons Attribution License (CC-BY 4.0), which permits any use, distribution and reproduction in any medium, provided the original author(s) and source are credArticle funded by SCOAP3. CP is a Royal Society Research Fellow and partly supported by the U.S. Department of Energy under grants DOE-SC0010008, DOE-ARRA-SC0003883 and DOE-DE-SC0007897. ABR is supported by the Mitchell Family Foundation. We would like to thank the Mitchell Institute at Texas A&M and the NHETC at Rutgers University respectively for hospitality during the course of this work. We would also like to acknowledge the Aspen Center for Physics and NSF grant 1066293 for a stimulating research environment which led to questions addressed in this paper

Characterization of deposits formed on diesel injectors in field test and from thermal oxidative degradation of n-hexadecane in a laboratory reactor

Solid deposits from commercially available high-pressure diesel injectors (HPDI) were analyzed to study the solid deposition from diesel fuel during engine operation. The structural and chemical properties of injector deposits were compared to those formed from the thermal oxidative stressing of a diesel fuel range model compound, n-hexadecane at 160°C and 450 psi for 2.5 h in a flow reactor. Both deposits consist of polyaromatic compounds (PAH) with oxygen moieties. The similarities in structure and composition of the injector deposits and n-hexadecane deposits suggest that laboratory experiments can simulate thermal oxidative degradation of diesel in commercial injectors. The formation of PAH from n-hexadecane showed that aromatization of straight chain alkanes and polycondensation of aromatic rings was possible at temperatures as low as 160°C in the presence of oxygen. A mechanism for an oxygen-assisted aromatization of cylcoalkanes is proposed

Calcium and Vitamin D increase mRNA levels for the growth control hIK1 channel in human epidermal keratinocytes but functional channels are not observed

BACKGROUND: Intermediate-conductance, calcium-activated potassium channels (IKs) modulate proliferation and differentiation in mesodermal cells by enhancing calcium influx, and they contribute to the physiology of fluid movement in certain epithelia. Previous reports suggest that IK channels stimulate proliferative growth in a keratinocyte cell line; however, because these channels indirectly promote calcium influx, a critically unique component of the keratinocyte differentiation program, an alternative hypothesis is that they would be anti-proliferative and pro-differentiating. This study addresses these hypotheses. METHODS: Real-time PCR, patch clamp electrophysiology, and proliferation assays were used to determine if human IK1 (hIK1) expression and function are correlated with either proliferation or differentiation in cultured human skin epidermal keratinocytes, and skin biopsies grown in explant culture. RESULTS: hIK1 mRNA expression in human keratinocytes and skin was increased in response to anti-proliferative/pro-differentiating stimuli (elevated calcium and Vitamin D). Correspondingly, the hIK1 agonist 1-EBIO inhibited keratinocyte proliferation suggesting that the channel could be anti-proliferative and pro-differentiating. However, this proliferative inhibition by 1-EBIO was not reversed by a panel of hIK1 blockers, calling into question the mechanism of 1-EBIO action. Subsequent patch clamp electrophysiological analysis failed to detect hIK1 channel currents in keratinocytes, even those expressing substantial hIK1 mRNA in response to calcium and Vitamin D induced differentiation. Identical electrophysiological recording conditions were then used to observe robust IK1 currents in fibroblasts which express IK1 mRNA levels comparable to those of keratinocytes. Thus, the absence of observable hIK1 currents in keratinocytes was not a function of the electrophysiological techniques. CONCLUSION: Human keratinocyte differentiation is stimulated by calcium mobilization and influx, and differentiation stimuli coordinately upregulate mRNA levels of the calcium-activated hIK1 channel. This upregulation is paradoxical in that functional hIK1 channels are not observed in cultured keratinocytes. It appears, therefore, that hIK1 does not contribute to the functional electrophysiology of primary human keratinocytes, nor intact human skin. Further, the results indicate caution is required when interpreting experiments utilizing pharmacological hIK1 modulators in human keratinocytes

Exploration of Burnout, Emotional Thriving, and Emotional Recovery in an Academic Medical Center: a Mixed Methods Quality Improvement Project

Introduction: Healthcare provider burnout, an indicator of wellbeing, impacts patient safety, provider distress, and employee turnover. In this mixed methods, multi-site quality improvement study conducted \u3c6 months prior to the start of the COVID-19 pandemic, we assessed employee wellbeing in a large clinical department. Methods: Wellbeing surveys were sent electronically to Department of Medicine clinicians, researchers, administrators, and staff from August-September 2019 assessing perceptions of Burnout, Emotional Thriving (ET), and Emotional Recovery (ER). Qualitative responses were reviewed for themes using mixed inductive-deductive analysis. The initial coding was done by small teams with consensus obtained through large group discussions. This study was IRB-approved as non-human subjects research. Results: Of the 671 respondents, 54% met criteria for burnout (Burnout+), 65% for ER (ER+), and 61% for ET (ET+). ER+ and ET+ were present in nearly half of Burnout+ respondents (53% and 43% respectively). Several themes emerged in the qualitative analysis: workload and expectations; tangible resources; work culture; and salary/benefits, with leadership influencing each of the domains. Conclusion: Burnout, ET, and ER can co-exist within the same individual. Employee wellbeing is not adequately reflected by the binary of whether or not an individual is experiencing burnout. All employees at academic medical centers, including staff, researchers, and clinicians, are vulnerable to the same workplace factors driving burnout. Our findings have been used to target areas of intervention during the COVID-19 pandemic at our institution. We propose that other academic medical centers may have similar workplace stressors that they could assess and target for improvement

Does peer learning or higher levels of e-learning improve learning abilities? A randomized controlled trial

Background and aims : The fast development of e-learning and social forums demands us to update our understanding of e-learning and peer learning. We aimed to investigate if higher, pre-defined levels of e-learning or social interaction in web forums improved students’ learning ability. Methods : One hundred and twenty Danish medical students were randomized to six groups all with 20 students (eCases level 1, eCases level 2, eCases level 2+, eTextbook level 1, eTextbook level 2, and eTextbook level 2+). All students participated in a pre-test, Group 1 participated in an interactive case-based e-learning program, while Group 2 was presented with textbook material electronically. The 2+ groups were able to discuss the material between themselves in a web forum. The subject was head injury and associated treatment and observation guidelines in the emergency room. Following the e-learning, all students completed a post-test. Pre- and post-tests both consisted of 25 questions randomly chosen from a pool of 50 different questions. Results : All students concluded the study with comparable pre-test results. Students at Level 2 (in both groups) improved statistically significant compared to students at level 1 (p>0.05). There was no statistically significant difference between level 2 and level 2+. However, level 2+ was associated with statistically significant greater student's satisfaction than the rest of the students (p>0.05). Conclusions : This study applies a new way of comparing different types of e-learning using a pre-defined level division and the possibility of peer learning. Our findings show that higher levels of e-learning does in fact provide better results when compared with the same type of e-learning at lower levels. While social interaction in web forums increase student satisfaction, learning ability does not seem to change. Both findings are relevant when designing new e-learning materials

Unbalanced Holographic Superconductors and Spintronics

We present a minimal holographic model for s-wave superconductivity with unbalanced Fermi mixtures, in 2+1 dimensions at strong coupling. The breaking of a U(1)_A "charge" symmetry is driven by a non-trivial profile for a charged scalar field in a charged asymptotically AdS_4 black hole. The chemical potential imbalance is implemented by turning on the temporal component of a U(1)_B "spin" field under which the scalar field is uncharged. We study the phase diagram of the model and comment on the eventual (non) occurrence of LOFF-like inhomogeneous superconducting phases. Moreover, we study "charge" and "spin" transport, implementing a holographic realization (and a generalization thereof to superconducting setups) of Mott's two-current model which provides the theoretical basis of modern spintronics. Finally we comment on possible string or M-theory embeddings of our model and its higher dimensional generalizations, within consistent Kaluza-Klein truncations and brane-anti brane setups.Comment: 45 pages, 15 figures; v2: two paragraphs below eq. (3.1) slightly modified, figure 5 (left) replaced, references added; v3: typos corrected, comments added, figure 12 replace

Agent based modelling helps in understanding the rules by which fibroblasts support keratinocyte colony formation

Background: Autologous keratincoytes are routinely expanded using irradiated mouse fibroblasts and bovine serum for clinical use. With growing concerns about the safety of these xenobiotic materials, it is desirable to culture keratinocytes in media without animal derived products. An improved understanding of epithelial/mesenchymal interactions could assist in this. Methodology/Principal Findings: A keratincyte/fibroblast o-culture model was developed by extending an agent-based keratinocyte colony formation model to include the response of keratinocytes to both fibroblasts and serum. The model was validated by comparison of the in virtuo and in vitro multicellular behaviour of keratinocytes and fibroblasts in single and co-culture in Greens medium. To test the robustness of the model, several properties of the fibroblasts were changed to investigate their influence on the multicellular morphogenesis of keratinocyes and fibroblasts. The model was then used to generate hypotheses to explore the interactions of both proliferative and growth arrested fibroblasts with keratinocytes. The key predictions arising from the model which were confirmed by in vitro experiments were that 1) the ratio of fibroblasts to keratinocytes would critically influence keratinocyte colony expansion, 2) this ratio needed to be optimum at the beginning of the co-culture, 3) proliferative fibroblasts would be more effective than irradiated cells in expanding keratinocytes and 4) in the presence of an adequate number of fibroblasts, keratinocyte expansion would be independent of serum. Conclusions: A closely associated computational and biological approach is a powerful tool for understanding complex biological systems such as the interactions between keratinocytes and fibroblasts. The key outcome of this study is the finding that the early addition of a critical ratio of proliferative fibroblasts can give rapid keratinocyte expansion without the use of irradiated mouse fibroblasts and bovine serum