729 research outputs found
Er:Yb:glass Coherent Laser Radar
No full textQ-switched Er:glass lasers that are injection seeded by a cw master laser are useful for eye-safe (1.535μm)coherent laser radars (CLR). Previously, we used an injection seeded, Q-switched, lamp-pumped Er:glass laser, obtaining velocity measurements of a hard target with a single shot resolution of about 1ms–1 [1]. The transmitted pulse energy was only about 1mJ however, which severely restricted the range of the radar. We shall describe the development and performance of a new, Q-switched, diode-pumped Er:Yb:glass slab laser that can produce gain-switched, transform limited, TEM00 pulses. The spectral content of the laser output, suitable for CLR will be discussed. [1] A.McGrath, et al.: Injection-seeded, single frequency, Q-switched Er:glass laser for remote sensing, Appl. Optics 37, 5706–5709, 1998Matthew C. Heintze, Jesper Munch and Peter J. Veitchhttp://aipcongress2005.anu.edu.au/pdf/AIPC_Handbook_V2.pd
On the Diophantine equation
No full textLet be a fixed linear recurrence sequence defined
over the integers (with some technical restrictions). We prove that there exist
effectively computable constants and such that for any with the equation has at most two distinct
solutions with and . Moreover, we
apply our result to the special case of Tribonacci numbers given by , and for . By means of
the LLL-algorithm and continued fraction reduction we are able to prove
and . The corresponding reduction algorithm
is implemented in Sage.Comment: 34 page
On area comparison and rigidity involving the scalar curvature
No full textIn this thesis we study the effects of lower bounds for the curvature of a Riemannian
manifold M on the geometry and topology of closed, minimal hypersurfaces. We will
prove an area comparison theorem for totally geodesic surfaces which is an optimal
analogue of the Heintze-Karcher-Maeada Theorem in the context of 3-manifolds
with lower bounds on scalar curvature (Theorem 3.8). The optimality of this result
will be addressed by explicitly constructing several counterexamples in dimensions
n ≥ 4. This area comparison theorem turns out that it provides a unified proof of
three splitting and rigidity theorems for 3-manifolds with lower bounds on the scalar
curvature that were first proved, independently, by Cai-Galloway, Bray-Brendle-
Neves and Nunes (Theorem 4.7 (a)-(c)). In the final part of this thesis we will address
some natural higher dimensional generalisations of these splitting and rigidity results
and emphasise some connections with the Yamabe problem
Holonomy and submanifold geometry
No full textWe survey applications of holonomic methods to the study of submanifold geometry, showing the consequences of some sort of extrinsic version of de Rham decomposition and Berger's Theorem, the so-called Normal Holonomy Theorem. At the same time, from geometric methods in submanifold theory we sketch very strong applications to the holonomy of Lorentzian manifolds. Moreover we give a conceptual modern proof of a result of Kostant for homogeneous space
Single-pulse measurement of wind velocities using an Er:Yb:glass coherent laser radar
No full textMany wind-field mapping applications require range-resolved atmospheric velocity measurements at long range and/or with a temporal resolution sufficient to investigate turbulence. We argue that this capability can be achieved only by coherent laser radar systems that transmit energetic (>1 mJ) pulses. We describe such a system and describe single-pulse measurement of the range-resolved line-of-sight velocities, and show that the instrument-limited reproducibility of the measurements is 0.4 ms−1.Matthew C. Heintze, Nick W. H. Chang, Francois Jeanneret, Jesper Munch, David J. Ottaway and Peter J. Veitc
On the size of a linear combination of two linear recurrence sequences over function fields
No full textLet and be two non-degenerate linear recurrence sequences
defined over a function field in one variable over , and
let be a valuation on . We prove that under suitable conditions
there are effectively computable constants and such that the
bound \begin{equation*}
\mu(G_n - H_m) \leq \mu(G_n) + C' \end{equation*} holds for .Comment: 10 page
Wie wirken Notfallsituationen nach? Retrospektive Bewertung der Akutversorgung und longitudinale Versorgungs-Trends bei Notaufnahmepatient*innen aus einer multizentrischen Berliner Kohorte
No full textAcademy of Dental Materials Guidance—Resin Composites: Part II— Technique Sensitivity (Handling, Polymerization, Dimensional Changes)
No full textObjective: The objective of this work, commissioned by the Academy of Dental Materials, was to review and critically appraise test methods to characterize properties related to critical issues for dental resin composites, including technique sensitivity and handling, polymerization, and dimensional stability, in order to provide specific guidance to investigators planning studies of these properties. Methods: The properties that relate to each of the main clinical issues identified were ranked in terms of their priority for testing, and the specific test methods within each property were ranked. An attempt was made to focus on the tests and methods likely to be the most useful, applicable, and supported by the literature, and where possible, those showing a correlation with clinical outcomes. Certain methods are only briefly mentioned to be all-inclusive. When a standard test method exists, whether from dentistry or another field, this test has been identified. Specific examples from the literature are included for each test method. Results: The properties for evaluating resin composites were ranked in the priority of measurement as follows: (1) Porosity, Radiopacity, Sensitivity to Ambient Light, Degree of Conversion, Polymerization Kinetics, Depth of Cure, Polymerization Shrinkage and Rate, Polymerization Stress, and Hygroscopic Expansion; (2) Stickiness, Slump Resistance, and Viscosity; and (3) Thermal Expansion. Significance: The following guidance is meant to aid the researcher in choosing the most appropriate test methods when planning studies designed to assess certain key properties and characteristics of dental resin composites, specifically technique sensitivity and handling during placement, polymerization, and dimensional stability
Academy of Dental Materials guidance—Resin composites: Part I—Mechanical properties
No full textObjectiveThe objective of this project, which was initiated from the Academy of Dental Materials, was to review and critically appraise methods to determine fracture, deformation and wear resistance of dental resin composites, in an attempt to provide guidance for investigators endeavoring to study these properties for these materials.MethodsTest methods have been ranked in the priority of the specific property being tested, as well as of the specific test methods for evaluating that property. Focus was placed on the tests that are considered to be of the highest priority in terms of being the most useful, applicable, supported by the literature, and which show a correlation with clinical findings. Others are mentioned briefly for the purpose of being inclusive. When a standard test method exists, including those used in other fields, these have been identified in the beginning of each section. Also, some examples from the resin composite literature are included for each test method.ResultsThe properties for evaluating resin composites were ranked in the priority of measurement as following: (1) Strength, Elastic Modulus, Fracture toughness, Fatigue, Indentation Hardness, Wear—abrasion (third body) and Wear—attrition (contact/two body), (2) Toughness, Edge strength (chipping) and (3) Wear determined by toothbrush.SignificanceThe following guidance is meant to aid the researcher in choosing the proper method to assess key properties of dental resin composites with regard to their fracture, deformation and wear resistance
On Pillai's Problem involving Lucas sequences of the second kind
No full textIn this paper we consider the Diophantine equation for
given integers with , whereas varies among
Lucas-Lehmer sequences of the second kind. We prove under some technical
conditions that if the considered equation has at least three solutions , then there is an upper bound on the size of the solutions as well as on the
size of the coefficients in the characteristic polynomial of .Comment: 24 page
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