4,269 research outputs found
Study of hypersonic propulsion/airframe integration technology
An assessment is done of current and potential ground facilities, and analysis and flight test techniques for establishing a hypersonic propulsion/airframe integration technology base. A mach 6 cruise prototype aircraft incorporating integrated Scramjet engines was considered the baseline configuration, and the assessment focused on the aerodynamic and configuration aspects of the integration technology. The study describes the key technology milestones that must be met to permit a decision on development of a prototype vehicle, and defines risk levels for these milestones. Capabilities and limitations of analysis techniques, current and potential ground test facilities, and flight test techniques are described in terms of the milestones and risk levels
Break in the VHE spectrum of PG 1553+113: new upper limit on its redshift?
PG 1553+113 is a known BL Lac object, newly detected in the GeV-TeV energy
range by H.E.S.S and MAGIC. The redshift of this source is unknown and a lower
limit of was recently estimated. The very high energy (VHE) spectrum
of PG 1553+113 is attenuated due to the absorption by the low energy photon
field of the extragalactic background light (EBL). Here we correct the combined
H.E.S.S and MAGIC spectrum of PG 1553+113 for this absorption assuming a
minimum density of the evolving EBL. We use an argument that the intrinsic
photon index cannot be harder than and derive an upper limit on
the redshift of . Moreover, we find that a redshift above
implies a possible break of the intrinsic spectrum at about 200 GeV. Assuming
that such a break is absent, we derive a much stronger upper limit of . Alternatively, this break might be attributed to an additional emission
component in the jet of PG 1553+113. This would be the first evidence for a
second component is detected in the VHE spectrum of a blazar.Comment: revised version submitted to Ap
Local lipschitzness of reachability maps for hybrid systems with applications to safety
Motivated by the safety problem, several definitions of reachability maps, for hybrid dynamical systems, are introduced. It is well established that, under certain conditions, the solutions to continuous-time systems depend continuously with respect to initial conditions. In such setting, the reachability maps considered in this paper are locally Lipschitz (in the Lipschitz sense for set-valued maps) when the right-hand side of the continuous-time system is locally Lipschitz. However, guaranteeing similar properties for reachability maps for hybrid systems is much more challenging. Examples of hybrid systems for which the reachability maps do not depend nicely with respect to their arguments, in the Lipschitz sense, are introduced. With such pathological cases properly identified, sufficient conditions involving the data defining a hybrid system assuring Lipschitzness of the reachability maps are formulated. As an application, the proposed conditions are shown to be useful to significantly improve an existing converse theorem for safety given in terms of barrier functions. Namely, for a class of safe hybrid systems, we show that safety is equivalent to the existence of a locally Lipschitz barrier function. Examples throughout the paper illustrate the results
Non-prescription dispensing of emergency oral contraceptives: Recommendations from the German Federal Chamber of Pharmacists [Bundesapothekerkammer].
BACKGROUND: Emergency hormonal contraceptives (EHC) are contraceptives used to prevent unintended pregnancy following unprotected sexual intercourse (USI) or contraceptive failure. The EHCs available without a prescription include medicines containing levonorgestrel (LNG) in more than 80 countries and, recently, based on an EU-switch ellaOne®, which contains ulipristal acetate (UPA). EHCs work by stopping or delaying ovulation. Those containing LNG can be used up to 72 hours after USI or contraceptive failure, while UPA can be used up to 120 hours. In the context of the UPA implementation process, Germany switched LNG to non-prescription status as well. OBJECTIVES: To develop recommendations, a protocol, and a continuing education program for pharmacists to assure quality when giving advice and dispensing EHCs in community pharmacies without a medical prescription. METHODS: The recommendations were developed by an iterative process of drafting, recognizing, and discussing comments and proposals for amendments as well a seeking agreement with a number of stakeholders such as the Federal Ministry of Health (BMG), Federal Institute for Drugs and Medical Devices (BfArM), Federal Chamber of Physicians (BÄK), Drug Commission of German Physicians (AkdÄ), professional organizations/associations of gynaecologists, pharmaceutical OTC-industry as well as government-controlled, private, and church-based organizations and centres providing advice on sex education and family planning. RESULTS: The recommendations were eventually endorsed by the BMG in consultation with the BfArM. CONCLUSIONS: The recommendations were made public, published in the professional journal and used in an uncounted number of continuing education programs based on the curriculum and provided by the State Chambers of Pharmacists
MAGIC observations of Mkn 421 in 2008, and related optical/X-ray/TeV MWL study
The HBL-type blazar Markarian 421 is one of the brightest TeV gamma-ray
sources of the Northern sky. From December 2007 until June 2008 it was
intensively observed in the VHE (E>100 GeV) band by the MAGIC gamma-ray
telescope. The source showed intense and prolonged activity during the whole
period. In some nights the integral flux rose up to 3.6 Crab units (E>200 GeV).
Intra-night rapid flux variations were observed. We compared the optical (KVA)
and X-ray (RXTE-ASM, Swift-XRT) data with the MAGIC VHE data, investigating the
correlations between different energy bands.Comment: 4 pages,4figures, Contribution to the 31st ICRC, Lodz, Poland, July
200
The value function of an asymptotic exit-time optimal control problem
We consider a class of exit--time control problems for nonlinear systems with
a nonnegative vanishing Lagrangian. In general, the associated PDE may have
multiple solutions, and known regularity and stability properties do not hold.
In this paper we obtain such properties and a uniqueness result under some
explicit sufficient conditions. We briefly investigate also the infinite
horizon problem
Joint Spectral Radius and Path-Complete Graph Lyapunov Functions
We introduce the framework of path-complete graph Lyapunov functions for
approximation of the joint spectral radius. The approach is based on the
analysis of the underlying switched system via inequalities imposed among
multiple Lyapunov functions associated to a labeled directed graph. Inspired by
concepts in automata theory and symbolic dynamics, we define a class of graphs
called path-complete graphs, and show that any such graph gives rise to a
method for proving stability of the switched system. This enables us to derive
several asymptotically tight hierarchies of semidefinite programming
relaxations that unify and generalize many existing techniques such as common
quadratic, common sum of squares, and maximum/minimum-of-quadratics Lyapunov
functions. We compare the quality of approximation obtained by certain classes
of path-complete graphs including a family of dual graphs and all path-complete
graphs with two nodes on an alphabet of two matrices. We provide approximation
guarantees for several families of path-complete graphs, such as the De Bruijn
graphs, establishing as a byproduct a constructive converse Lyapunov theorem
for maximum/minimum-of-quadratics Lyapunov functions.Comment: To appear in SIAM Journal on Control and Optimization. Version 2 has
gone through two major rounds of revision. In particular, a section on the
performance of our algorithm on application-motivated problems has been added
and a more comprehensive literature review is presente
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