Minimizing the Ground Effect for Photophoretically Levitating Disks

Photophoretic levitation is a propulsion mechanism in which lightweight objects can be lifted and controlled through their interactions with light. Since photophoretic forces on macroscopic objects are usually maximized at low pressures, they may be tested in vacuum chambers in close proximity to the chamber floor and walls. We report here experimental evidence that the terrain under levitating microflyers, including the chamber floor or the launchpad from which microflyers lift off, can greatly increase the photophoretic lift forces relative to their free-space (mid-air) values. To characterize this so-called "ground effect" during vacuum chamber tests, we introduced a new miniature launchpad composed of three J-shaped (candy-cane-like) wires that minimized a microflyer's extraneous interactions with underlying surfaces. We compared our new launchpads to previously used wire-mesh launchpads for simple levitating mylar-based disks with diameters of 2, 4, and 8 cm. Importantly, wire-mesh launchpads increased the photophoretic lift force by up to sixfold. A significant ground effect was also associated with the bottom of the vacuum chamber, particularly when the distance to the bottom surface was less than the diameter of the levitating disk. We provide guidelines to minimize the ground effect in vacuum chamber experiments, which are necessary to test photophoretic microflyers intended for high-altitude exploration and surveillance on Earth or on Mars.Comment: 7 pages, 7 figures, including the Supplemental Materia

Nucleon Charge Symmetry Breaking and Parity Violating Electron-Proton Scattering

The consequences of the charge symmetry breaking effects of the mass difference between the up and down quarks and electromagnetic effects for searches for strangeness form factors in parity violating electron scattering from the proton are investigated. The formalism necessary to identify and compute the relevant observables is developed by separating the Hamiltonian into charge symmetry conserving and breaking terms. Using a set of SU(6) non-relativistic quark models, the effects of the charge symmetry breaking Hamiltonian are considered for experimentally relevant alues of the momentum transfer and found to be less than about 1 percent. The charge symmetry breaking corrections to the Bjorken sum rule are also studied and shown to vanish in first-order perturbation theory.Comment: 35 pages, 9 figure

Expectation values of four-quark operators in pions

The values of four-quark operators averaged over pions are expressed through those averaged over vacuum. The specific values are obtained in the framework of the factorization assumption. For the condensates of the light quarks of the same flavour \bar q\Gamma q\bar q\Gamma q the scalar condensate is shown to be an order of magnitude larger than the other ones. The condensates containing the strange quarks \bar q q\bar s s appear to be only about twice smaller than those of the light quarks. The degeneracy of the ground state in the Nambu--Jona--Lasinio model is shown explicitly.Comment: 9 pages, no figures, typos correcte

Modified Quark-Meson Coupling Model for Nuclear Matter

The quark-meson coupling model for nuclear matter, which describes nuclear matter as non-overlapping MIT bags bound by the self-consistent exchange of scalar and vector mesons, is modified by introducing medium modification of the bag constant. We model the density dependence of the bag constant in two different ways: one invokes a direct coupling of the bag constant to the scalar meson field, and the other relates the bag constant to the in-medium nucleon mass. Both models feature a decreasing bag constant with increasing density. We find that when the bag constant is significantly reduced in nuclear medium with respect to its free-space value, large canceling isoscalar Lorentz scalar and vector potentials for the nucleon in nuclear matter emerge naturally. Such potentials are comparable to those suggested by relativistic nuclear phenomenology and finite-density QCD sum rules. This suggests that the reduction of bag constant in nuclear medium may play an important role in low- and medium-energy nuclear physics.Comment: Part of the text is reordered, revised version to appear in Phys. Rev. C. 19 pages, ReVTeX, 4 figures embedde

Analysis and Suggestions for Business Model of eBayEachnet

EBAY易趣网和淘宝网是目前中国电子商务中经常被提及的两个对手。2002年时，EBAY易趣曾经一枝独秀，但在淘宝网和拍拍网的竞争下，迅速丧失市场领先地位，市场份额逐步缩小，并终于与TOM集团有限公司下属的TOM在线成立了合营公司。 本文主要运用翁君奕教授的《商业模式创新》理论，以合营公司的成立为研究截止时间，尝试揭示、分析、解释EBAY易趣商务模式针对中国大陆市场而言存在的不足之处，并提出实现转机的若干建议。全文共分五章，分别如下： 第一章主要介绍论文写作的背景和研究意义所在，以及研究理论和框架。 第二章针对EBAY易趣商务模式，按照商业模式创新理论的层次，从商务模式环境、商务模式要素、...eBayEachnet and Taobao are main competitors in China’s E-commerce. eBayEachnet just took the lead in as earlier as year 2002, however, it was overwhelmed by Taobao and Paipai gradually, the leading was lost and the share market diminished very soon, as a result, it incorporated with Tom Online, a filial of Tom group limited company.Bearing in mind the theory of <Business Models Innovatio...学位：工商管理硕士院系专业：管理学院工商管理教育中心（MBA中心）_工商管理硕士(MBA)学号：20041523

Predicting outcome following mild traumatic brain injury: protocol for the longitudinal, prospective, observational Concussion Recovery (CREST) cohort study

Introduction Mild traumatic brain injury (mTBI) is a complex injury with heterogeneous physical, cognitive, emotional and functional outcomes. Many who sustain mTBI recover within 2 weeks of injury; however, approximately 10%–20% of individuals experience mTBI symptoms beyond this ‘typical’ recovery timeframe, known as persistent post-concussion symptoms (PPCS). Despite increasing interest in PPCS, uncertainty remains regarding its prevalence in community-based populations and the extent to which poor recovery may be identified using early predictive markers. Objective (1) Establish a research dataset of people who have experienced mTBI and document their recovery trajectories; (2) Evaluate a broad range of novel and established prognostic factors for inclusion in a predictive model for PPCS. Methods and analysis The Concussion Recovery Study (CREST) is a prospective, longitudinal observational cohort study conducted in Perth, Western Australia. CREST is recruiting adults aged 18–65 from medical and community-based settings with acute diagnosis of mTBI. CREST will create a state-wide research dataset of mTBI cases, with data being collected in two phases. Phase I collates data on demographics, medical background, lifestyle habits, nature of injury and acute mTBI symptomatology. In Phase II, participants undergo neuropsychological evaluation, exercise tolerance and vestibular/ocular motor screening, MRI, quantitative electroencephalography and blood-based biomarker assessment. Follow-up is conducted via telephone interview at 1, 3, 6 and 12 months after injury. Primary outcome measures are presence of PPCS and quality of life, as measured by the Post-Concussion Symptom Scale and the Quality of Life after Brain Injury questionnaires, respectively. Multivariate modelling will examine the prognostic value of promising factors. Ethics and dissemination Human Research Ethics Committees of Royal Perth Hospital (#RGS0000003024), Curtin University (HRE2019-0209), Ramsay Health Care (#2009) and St John of God Health Care (#1628) have approved this study protocol. Findings will be published in peer-reviewed journals and presented at scientific conferences