4,690 research outputs found
Optical enhancement of photomultiplier sensitivity
Transmission and reflection light losses are reduced by introducing light into end-window of device at an angle large enough to normal so total internal reflection occurs at both photocathode-vacuum and window-air interfaces
Nondispersive infrared analyzer for specific gases in complex mixtures
Analyzer identifies and measures particular diatomic or polyatomic gases in complex gas mixtures. Mixing of absorption effects on light energy passing through gases to photodetector produces a signal component that is related to the absorption caused by reference-gas component in unknown gas mixture
Optical enhancement of sensitivity in laser Doppler velocity systems
Utilization of optical enhancement techniques prevents loss of light by reflections at the photocathode of a photomultiplier and increases signal detection sensitivity
Laser velocimeter for simultaneous two-dimensional velocity measurements
Laser velocimeter provides simultaneous orthogonal measurements in manner which minimizes many problems attending prior systems, and allows spatial traversing of flowfield in order to obtain velocity profiles. Velocimeter permits rapid interrogation of unsteady flows where area of interest is of the order of one meter in extent and flow does not vary appreciably over time of about one second
Dual mode laser velocimeter
Described is a laser Doppler velocimeter (LDV) which is capable of operating with a small focus diameter for analyzing fluid flows at low velocity with high spatial resolution, or with a larger focus diameter to measure fluid flows at higher velocities accurately. More particularly, this is an LDV in which a simple reversal of a lens pair will allow it to operate in the two focus diameter modes
âMining the materialsâ: A framework for student-led self-study task creation
Meaningful independent learning is rightly viewed as a central component of successful study in L2. Given that the considerable majority of learnersâ time is spent outside the classroom, the self-study space has become a source of great intrigue for English language teachers (Benson and Reinders, 2011). However, precisely because self-directed learning lies beyond the typical boundaries of the teacherâs gaze, it is influenced by a variety of factors, not least learnersâ familiarity with effective independent learning practices. This summary article traces and evaluates the implementation of a framework for student-led self-study task creation with a group of 14 foundation pre-sessional students making the transition from secondary to tertiary study at the University of Glasgow with little or no existing concept of effective self-study practices. The trial aimed to provide a space for students to evaluate their strengths and weaknesses in English and establish independent learning priorities, as well as a more critical awareness (âminingâ) of regular classroom tasks as potential models for independent learning activities. Obtaining feedback at regular intervals, coupled with data from weekly reflection cycles, the investigation tracked developments in self-study practices while highlighting obstacles to enhanced independent learning. The trial also presented plentiful opportunities to reflect on the definition of effectiveness with regard to independent learning
Asymmetric polarity reversals, bimodal field distribution, and coherence resonance in a spherically symmetric mean-field dynamo model
Using a mean-field dynamo model with a spherically symmetric helical
turbulence parameter alpha which is dynamically quenched and disturbed by
additional noise, the basic features of geomagnetic polarity reversals are
shown to be generic consequences of the dynamo action in the vicinity of
exceptional points of the spectrum. This simple paradigmatic model yields long
periods of constant polarity which are interrupted by self-accelerating field
decays leading to asymmetric polarity reversals. It shows the recently
discovered bimodal field distribution, and it gives a natural explanation of
the correlation between polarity persistence time and field strength. In
addition, we find typical features of coherence resonance in the dependence of
the persistence time on the noise.Comment: 5 pages, 7 figure
Quasi-normal modes of charged, dilaton black holes
In this paper we study the perturbations of the charged, dilaton black hole,
described by the solution of the low energy limit of the superstring action
found by Garfinkle, Horowitz and Strominger. We compute the complex frequencies
of the quasi-normal modes of this black hole, and compare the results with
those obtained for a Reissner-Nordstr\"{o}m and a Schwarzschild black hole. The
most remarkable feature which emerges from this study is that the presence of
the dilaton breaks the \emph{isospectrality} of axial and polar perturbations,
which characterizes both Schwarzschild and Reissner-Nordstr\"{o}m black holes.Comment: 15 pages, 5 figure
Estimating process capability index Cpm using a bootstrap sequential sampling procedure
Construction of a confidence interval for process capability index CPM is often based on a normal approximation with fixed sample size. In this article, we describe a different approach in constructing a fixed-width confidence interval for process capability index CPM with a preassigned accuracy by using a combination of bootstrap and sequential sampling schemes. The optimal sample size required to achieve a preassigned confidence level is obtained using both two-stage and modified two-stage sequential procedures. The procedure developed is also validated using an extensive simulation study.<br /
Dynamic Group Diffie-Hellman Key Exchange under Standard Assumptions
Authenticated Diffie-Hellman key exchange allows two principals communicating over a public network, and each holding public /private keys, to agree on a shared secret value. In this paper we study the natural extension of this cryptographic problem to a group of principals. We begin from existing formal security models and refine them to incorporate major missing details (e.g., strong-corruption and concurrent sessions). Within this model we define the execution of a protocol for authenticated dynamic group Diffie-Hellman and show that it is provably secure under the decisional Diffie-Hellman assumption. Our security result holds in the standard model and thus provides better security guarantees than previously published results in the random oracle model
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