793 research outputs found
Progress in community policing
This article examines the development of community-based policing in the\ud
United States and the Netherlands. These two countries were selected because\ud
the United States has been the forerunner of research into the police and one\ud
of the first countries to attempt to introduce on a wide-scale, and conduct\ud
research into community policing. In the Netherlands, the Major Cities Policy,\ud
a governmental approach to addressing the cities' problems provided an\ud
interesting basis for comparison. Policy or operational changes in the police\ud
organization are generally influenced by the political climate and or scientific\ud
research. Both of these factors played a major role in the US. This section\ud
begins with a brief historical view of the factors which brought about changes\ud
within American policing, ultimately resulting in a new concept of community\ud
policing. This is followed by developments which led to community policing or\ud
the concept of the 'neighbourhood teams' (wijkbureaus) in the Netherlands
Investigation of Lunar Surface Chemical Contamination by LEM Descent Engine and Associated Equipment
Lunar surface and atmospheric contamination study caused by LEM rocket exhaust and inorganic, organic, and microbiological contaminant
Mode coupling control in a resonant device: application to solid-state ring lasers
A theoretical and experimental investigation of the effects of mode coupling
in a resonant macro- scopic quantum device is achieved in the case of a ring
laser. In particular, we show both analytically and experimentally that such a
device can be used as a rotation sensor provided the effects of mode coupling
are controlled, for example through the use of an additional coupling. A
possible general- ization of this example to the case of another resonant
macroscopic quantum device is discussed
Oscillation regimes of a solid-state ring laser with active beat note stabilization : from a chaotic device to a ring laser gyroscope
We report experimental and theoretical study of a rotating diode-pumped
Nd-YAG ring laser with active beat note stabilization. Our experimental setup
is described in the usual Maxwell-Bloch formalism. We analytically derive a
stability condition and some frequency response characteristics for the
solid-state ring laser gyroscope, illustrating the important role of mode
coupling effects on the dynamics of such a device. Experimental data are
presented and compared with the theory on the basis of realistic laser
parameters, showing a very good agreement. Our results illustrate the duality
between the very rich non linear dynamics of the diode-pumped solid-state ring
laser (including chaotic behavior) and the possibility to obtain a very stable
beat note, resulting in a potentially new kind of rotation sensor
Investigation of lunar surface chemical contamination by LEM descent engine and associated equipment Final report
Lunar surface contamination from LEM rocket exhaust - methods of minimizing sample contaminatio
A 1.82 m^2 ring laser gyroscope for nano-rotational motion sensing
We present a fully active-controlled He-Ne ring laser gyroscope, operating in
square cavity 1.35 m in side. The apparatus is designed to provide a very low
mechanical and thermal drift of the ring cavity geometry and is conceived to be
operative in two different orientations of the laser plane, in order to detect
rotations around the vertical or the horizontal direction. Since June 2010 the
system is active inside the Virgo interferometer central area with the aim of
performing high sensitivity measurements of environmental rotational noise. So
far, continuous not attempted operation of the gyroscope has been longer than
30 days. The main characteristics of the laser, the active remote-controlled
stabilization systems and the data acquisition techniques are presented. An
off-line data processing, supported by a simple model of the sensor, is shown
to improve the effective long term stability. A rotational sensitivity at the
level of ten nanoradiants per squareroot of Hz below 1 Hz, very close to the
required specification for the improvement of the Virgo suspension control
system, is demonstrated for the configuration where the laser plane is
horizontal
Experimental study of the delayed threshold phenomenon in a semiconductor laser
An experimental study of the delayed threshold phenomenon in a Vertical
Extended Cavity Semiconductor Emitting Laser is carried out. Under modulation
of the pump power, the laser intensity exhibits a hysteresis behavior in the
vicinity of the threshold. The temporal width of this hysteresis is measured as
a function of the modulation frequency, and is proved to follow the predicted
scaling law. A model based on the rate equations is derived and used to analyze
the experimental observations. A frequency variation of the laser around the
delayed threshold and induced by the phase-amplitude coupling is predicted and
estimated
Renormalization and Hyperscaling for Self-Avoiding Manifold Models
The renormalizability of the self-avoiding manifold (SAM) Edwards model is
established. We use a new short distance multilocal operator product expansion
(MOPE), which extends methods of local field theories to a large class of
models with non-local singular interactions. This validates the direct
renormalization method introduced before, as well as scaling laws. A new
general hyperscaling relation for the configuration exponent gamma is derived.
Manifolds at the Theta-point, and long range Coulomb interactions are briefly
discussed.Comment: 10 pages + 1 figure, TeX + harvmac & epsf (uuencoded file),
SPhT/93-07
Scaling of Selfavoiding Tethered Membranes: 2-Loop Renormalization Group Results
The scaling properties of selfavoiding polymerized membranes are studied
using renormalization group methods. The scaling exponent \nu is calculated for
the first time at two loop order. \nu is found to agree with the Gaussian
variational estimate for large space dimension d and to be close to the Flory
estimate for d=3.Comment: 4 pages, RevTeX + 20 .eps file
Conceivable security risks and authentication techniques for smart devices
With the rapidly escalating use of smart devices and fraudulent transaction of users’ data from their devices, efficient and reliable techniques for authentication of the smart devices have become an obligatory issue. This paper reviews the security risks for mobile devices and studies several authentication techniques available for smart devices. The results from field studies enable a comparative evaluation of user-preferred authentication mechanisms and their opinions about reliability, biometric authentication and visual authentication techniques
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