7,700 research outputs found
Trajectory control sensor engineering model detailed test objective
The concept employed in an existing Trajectory Control Sensor (TCS) breadboard is being developed into an engineering model to be considered for flight on the Shuttle as a Detailed Test Objective (DTO). The sensor design addresses the needs of Shuttle/SSF docking/berthing by providing relative range and range rate to 1500 meters as well as the perceived needs of AR&C by relative attitude measurement over the last 100 meters. Range measurement is determined using a four-tone ranging technique. The Doppler shift on the highest frequency tone will be used to provide direct measurement of range rate. Bearing rate and attitude rates will be determined through back differencing of bearing and attitude, respectively. The target consists of an isosceles triangle configuration of three optical retroreflectors, roughly one meter and one-half meter in size. After target acquisition, the sensor continually updates the positions of the three retros at a rate of about one hertz. The engineering model is expected to weigh about 25 pounds, consume 25-30 watts, and have an envelope of about 1.25 cubic feet. The following concerns were addressed during the presentation: are there any concerns with differentiating attitude and bearing to get attitude and bearing rates? Since the docking scenario has low data bandwidth, back differencing is a sufficient approximation of a perfect differentiator for this application. Could range data be obtained if there were no retroreflectors on the target vehicle? Possibly, but only at close range. It would be dependent on target characteristics
Semi-immersive space mission design and visualization: case study of the "terrestrial planet finder" mission
The paper addresses visualization issues of the Terrestrial Planet Finder Mission (C.A. Beichman et al., 1999). The goal of this mission is to search for chemical signatures of life in distant solar systems using five satellites flying in formation to simulate a large telescope. To design and visually verify such a delicate mission, one has to analyze and interact with many different 3D spacecraft trajectories, which is often difficult in 2D. We employ a novel trajectory design approach using invariant manifold theory, which is best understood and utilized in an immersive setting. The visualization also addresses multi-scale issues related to the vast differences in distance, velocity, and time at different phases of the mission. Additionally, the parameterization and coordinate frames used for numerical simulations may not be suitable for direct visualization. Relative motion presents a more serious problem where the patterns of the trajectories can only be viewed in particular rotating frames. Some of these problems are greatly relieved by using interactive, animated stereo 3D visualization in a semi-immersive environment such as a Responsive Workbench. Others were solved using standard techniques such as a stratify approach with multiple windows to address the multiscale issues, re-parameterizations of trajectories and associated 2D manifolds and relative motion of the camera to "evoke" the desired patterns
Tensor envelopes of regular categories
We extend the calculus of relations to embed a regular category A into a
family of pseudo-abelian tensor categories T(A,d) depending on a degree
function d. Under the condition that all objects of A have only finitely many
subobjects, our main results are as follows:
1. Let N be the maximal proper tensor ideal of T(A,d). We show that T(A,d)/N
is semisimple provided that A is exact and Mal'cev. Thereby, we produce many
new semisimple, hence abelian, tensor categories.
2. Using lattice theory, we give a simple numerical criterion for the
vanishing of N.
3. We determine all degree functions for which T(A,d) is Tannakian. As a
result, we are able to interpolate the representation categories of many series
of profinite groups such as the symmetric groups S_n, the hyperoctahedral
groups S_n\semidir Z_2^n, or the general linear groups GL(n,F_q) over a fixed
finite field.
This paper generalizes work of Deligne, who first constructed the
interpolating category for the symmetric groups S_n. It also extends (and
provides proofs for) a previous paper math.CT/0605126 on the special case of
abelian categories.Comment: v1: 52 pages; v2: 52 pages, proof of Lemma 7.2 fixed, otherwise minor
change
Gradually Guiding Nursing Students through Their Capstone Course: Registered Nurse Preceptors Share Their Experiences
Professional precepted immersion courses (capstone) have become the standard as a means to prepare senior nursing students to enter the workforce. Preceptors have a significant role in developing the student nurse, yet exactly how to prepare preceptors for this role has been an ongoing discussion. This qualitative inquiry explored the educational needs of clinical registered nurse (RN) preceptors who work directly with senior nursing students in a professional precepted immersion (capstone) course. A descriptive qualitative design was used to examine preceptors responses to a prepared set of questions about their educational needs. Results showed that preceptors have three distinct sets of learning needs: the need to know the expectations of their role, wanting to know how best to role model for the student, and knowing how to socialize the student into the profession of nursing. Overall, preceptors communicated their desire and commitment to doing the best job possible. They also clearly stated their expectation of faculty to have a physical presence on the nursing unit that included being proactive in resolving mismatches and exposing the student to the roles of provider of care, leader and manager of care, and member of profession
Vascular endothelial growth factor is an autocrine survival factor for breast tumour cells under hypoxia.
Vascular endothelial growth factor (VEGF) is produced by most tumour types and stimulates the growth of new blood vessels in the tumour. The expansion of a solid tumour ultimately leads to the development of hypoxic regions, which increases VEGF production and further angiogenesis. In this study, we examined the role of VEGF in the survival of breast tumour cells under hypoxia. Murine 4T1 and human MDA-MB-231 tumour cells were cultured under normoxic and hypoxic growth conditions in the presence or absence of VEGF neutralising antibodies. Apoptosis was assessed in addition to changes in expression of the anti- and pro-apoptotic proteins, Bcl-2 and Bad, respectively. The effect of hypoxia on the novel VEGF receptor, NP1 (neuropilin-1) and the role of the PI3K (phosphatidylinositol-3-kinase) signalling pathway in response to VEGF were examined. VEGF blockade resulted in direct tumour cell apoptosis of both tumour cell lines under normoxia and hypoxia. While blocking VEGF resulted in a downregulation of hypoxia-induced Bcl-2 expression, there was a significant increase in the pro-apoptotic protein Bad relative to cells cultured under hypoxia alone. Both hypoxia and VEGF phosphorylated Akt. Neutralising antibodies to VEGF abrogated this effect, implicating the PI3K pathway in VEGF-mediated cell survival of mammary adenocarcinoma cells. This study demonstrates that VEGF acts as a survival factor not only for endothelial cells as previously thought, but also for some breast tumour cells, protecting them from apoptosis, particularly under hypoxic stress. The data presented provide an additional rationale for combining anti-VEGF strategies with conventional anti-cancer therapies such as chemotherapy and radiotherapy
Solving the strong CP problem with supersymmetry
We propose a new solution to the strong CP problem based on supersymmetric
non-renormalization theorems. CP is broken spontaneously and it's breaking is
communicated to the MSSM by radiative corrections. The strong CP phase is
protected by a susy non-renormalization theorem and remains exactly zero while
loops can generate a large CKM phase from wave function renormalization. We
present a concrete model as an example but stress that our framework is
general. We also discuss constraints on susy breaking and point out
experimental signatures.Comment: 12 pages, 2 figures, references adde
A Comment on the Strong Interactions of Color-Neutral Technibaryons
We estimate the cross section for the scattering of a slow, color-neutral
technibaryon made of colored constituents with nuclei. We find a cross section
of order cm, where is the atomic number of the nucleus.
Even if technibaryons constitute the dark matter in the galactic halo, this is
too small to be detected in future underground detectors.Comment: 6 pages, BUHEP-92-36 and UCSD/PTH 92-3
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