9,715 research outputs found
A geometric basis for the standard-model gauge group
A geometric approach to the standard model in terms of the Clifford algebra
Cl_7 is advanced. A key feature of the model is its use of an algebraic spinor
for one generation of leptons and quarks. Spinor transformations separate into
left-sided ("exterior") and right-sided ("interior") types. By definition,
Poincare transformations are exterior ones. We consider all rotations in the
seven-dimensional space that (1) conserve the spacetime components of the
particle and antiparticle currents and (2) do not couple the right-chiral
neutrino. These rotations comprise additional exterior transformations that
commute with the Poincare group and form the group SU(2)_L, interior ones that
constitute SU(3)_C, and a unique group of coupled double-sided rotations with
U(1)_Y symmetry. The spinor mediates a physical coupling of Poincare and
isotopic symmetries within the restrictions of the Coleman--Mandula theorem.
The four extra spacelike dimensions in the model form a basis for the Higgs
isodoublet field, whose symmetry requires the chirality of SU(2). The charge
assignments of both the fundamental fermions and the Higgs boson are produced
exactly.Comment: 17 pages, LaTeX requires iopart. Accepted for publication in J. Phys.
A: Math. Gen. 9 Mar 2001. Typos correcte
Feeding the fire: Tracing the mass-loading of 10^7 K galactic outflows with O VI absorption
Galactic outflows regulate the amount of gas galaxies convert into stars.
However, it is difficult to measure the mass outflows remove because they span
a large range of temperatures and phases. Here, we study the rest-frame
ultraviolet spectrum of a lensed galaxy at z~2.9 with prominent interstellar
absorption lines from O I, tracing neutral gas, up to O VI, tracing
transitional phase gas. The O VI profile mimics weak low-ionization profiles at
low velocities, and strong saturated profiles at high velocities. These trends
indicate that O VI gas is co-spatial with the low-ionization gas. Further, at
velocities blueward of -200 km/s the column density of the low-ionization
outflow rapidly drops while the O VI column density rises, suggesting that O VI
is created as the low-ionization gas is destroyed. Photoionization models do
not reproduce the observed O VI, but adequately match the low-ionization gas,
indicating that the phases have different formation mechanisms. Photoionized
outflows are more massive than O VI outflows for most of the observed
velocities, although the O VI mass outflow rate exceeds the photoionized
outflow at velocities above the galaxy's escape velocity. Therefore, most gas
capable of escaping the galaxy is in a hot outflow phase. We suggest that the O
VI absorption is a temporary by-product of conduction transferring mass from
the photoionized phase to an unobserved hot wind, and discuss how this
mass-loading impacts the observed circum-galactic medium.Comment: 17 pages, 12 figures, accepted for publication in MNRA
Development and flight test of an X-band precision approach concept for remote-area rotorcraft operations
A novel airborne radar-based precision approach concept was developed and flight tested as a part of NASA's Rotorcraft All-Weather Operations Research Program. A demonstration, transponder-based beacon landing system (BLS), incorporating state-of-the-art X-band radar technology and digital processing techniques, was built and flight tested to demonstrate the concept feasibility. The BLS airborne hardware consists of an add-on microprocessor, installed in conjunction with the aircraft weather/mapping radar, which analyzes the radar beacon receiver returns and determines range, localizer deviation, and glide slope deviation. The ground station is an inexpensive, portable unit which can be quickly deployed at a landing site. Results from the flight test program show that the BLS concept has a significant potential for providing rotorcraft with low-cost, precision, instrument approach capability in remote areas
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Astigmatism and Pseudoaccommodation in Pseudophakic Eyes
noAdvanced IOLs with circumferential zones of different power provide pseudoaccommodation. We investigated the potential for power variation with meridian, namely astigmatism, to provide pseudo-accommodation. With appropriate power and axis orientations, acceptable pseudo-accommodation can be achieved
Do actions occur inside the body?
The paper offers a critical examination of Jennifer Hornsby's view that actions are internal to the body. It focuses on three of Hornsby's central claims: (P) many actions are bodily movements (in a special sense of the word âmovementâ) (Q) all actions are tryings; and (R) all actions occur inside the body. It is argued, contra Hornsby, that we may accept (P) and (Q) without accepting also the implausible (R). Two arguments are first offered in favour of the thesis (Contrary-R): that no actions occur inside the body. Three of Hornsby's arguments in favour of R are then examined. It is argued that we need to make a distinction between the causes and the causings of bodily movements (in the ordinary sense of the word âmovementâ) and that actions ought to be identified with the latter rather than the former. This distinction is then used to show how Hornsby's arguments for (R) may be resisted
Development and flight test of a helicopter compact, portable, precision landing system concept
An airborne, radar-based, precision approach concept is being developed and flight tested as a part of NASA's Rotorcraft All-Weather Operations Research Program. A transponder-based beacon landing system (BLS) applying state-of-the-art X-band radar technology and digital processing techniques, was built and is being flight tested to demonstrate the concept feasibility. The BLS airborne hardware consists of an add-on microprocessor, installed in conjunction with the aircraft weather/mapping radar, which analyzes the radar beacon receiver returns and determines range, localizer deviation, and glide-slope deviation. The ground station is an inexpensive, portable unit which can be quickly deployed at a landing site. Results from the flight test program show that the BLS concept has a significant potential for providing rotorcraft with low-cost, precision instrument approach capability in remote areas
The Frames Behind the Games: Player's Perceptions of Prisoner's Dilemma, Chicken, Dictator, and Ultimatum Games
The tension between cooperative and competitive impulses is an eternal issue for every society. But how is this problem perceived by individual participants in the context of a behavioral games experiment? We first assess individual differences in playersâ propensity to cooperate in a series of experimental games. We then use openended interviews with a subset of those players to investigate the various concepts (or âframesâ) they used when thinking about self-interested and cooperative actions. More generally, we hope to raise awareness of playerâs perceptions of experimental environments to inform both the design and interpretation of experiments and experimental data.Laboratory Experiment, Frames, Selfishness, Cooperation
Enhancing the EdTech Ecosystem in a British Columbia School District
Technology has brought significant opportunities to education, but they are largely being lost. In many cases, spending on educational technology (EdTech) has not resulted in improved student outcomes. This Organizational Improvement Plan (OIP) addresses the problem of practice (PoP) of a lack of a framework and supports for K-12 teachers to effectively utilize EdTech in classrooms in the Canadian province of British Columbia (BC). Using a BC school district as a case study, I propose strategies for how leaders can craft and implement a change plan to enhance an EdTech ecosystem that best supports teachers and learners. Establishing a framework for effective use of EdTech in schools is complex and multifaceted. Investments in technology must support best pedagogical practices, and leaders must create conditions that boost teachersâ Technological, Pedagogical and Content Knowledge (TPACK; Mishra & Koehler, 2006). Leaders must adapt to shifting power dynamics in which teachers have new roles as emergent leaders. Optimizing the impact of EdTech in education requires a confluence of three key factors: technology, pedagogy, and excellent leadership. The change process must be iterative, ongoing, stakeholder-driven, and system-wide. This OIP blends Appreciative Inquiry (Cooperrider, 1986) principles with servant leadership (Greenleaf, 1970) and incorporates the districtâs existing approaches into a hybrid transformational leadership model. I explore a three-pronged solution of EdTech capacity building for teachers, an EdTech vetting system, and a supportive leadership framework. This aims to raise TPACK, optimize EdTech usage, support wise pedagogy, and improve student outcomes
Use of derived forcing functions at Centaur main engine cutoff in predicting transient loads on Mariner Mars 1971 and Viking spacecraft
Mathematical models for prediction of acceleration responses and reaction forces and moments at base of Mariner Mars 71 and Viking spacecraft from Centaur main engine cutof
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