17,856 research outputs found
Instrument accurately measures weld angle and offset
Weld angle is measured to the nearest arc minute and offset to one thousandth of an inch by an instrument designed to use a reference plane at two locations on a test coupon. A special table for computation has been prepared for use with the instrument
Electromagnetically Induced Transparency with Quantized Fields in Optocavity Mechanics
We report electromagnetically induced transparency using quantized fields in
optomechanical systems. The weak probe field is a narrow band squeezed field.
We present a homodyne detection of EIT in the output quantum field. We find
that the EIT dip exists even though the photon number in the squeezed vacuum is
at the single photon level. The EIT with quantized fields can be seen even at
temperatures of the order of 100 mK paving the way for using optomechanical
systems as memory elements.Comment: 6 pages, 5 figure
Interaction of a Modulated Electron Beam with a Plasma
The results of a theoretical and experimental investigation of the high-frequency interaction of an electron beam with a plasma are reported. An electron beam, modulated at a microwave frequency, passes through a uniform region of a mercury arc discharge after which it is demodulated. Exponentially growing wave amplification along the electron beam was experimentally observed for the first time at a microwave frequency equal to the plasma frequency. Approximate theories of the effects of 1) plasma-electron collision frequencies, 2) plasma-electron thermal velocities and 3) finite beam diameter, are given. In a second experiment the interaction between a modulated electron beam and a slow electrostatic wave on a plasma column has been studied. A strong interaction occurs when the velocity of the electron beam is approximately equal to the velocity of the wave and the interaction is essentially the same as that which occurs in traveling-wave amplifiers, except that here the plasma colum replaces the usual helical slow-wave circuit. The theory predicting rates of growth is presented and compared with the experimental results
Zitterbewegung of optical pulses in nonlinear frequency conversion
Pulse walk-off in the process of sum frequency generation in a nonlinear
crystal is shown to be responsible for pulse jittering which is
reminiscent to the Zitterbewegung (trembling motion) of a relativistic freely
moving Dirac particle. An analytical expression for the pulse center of mass
trajectory is derived in the no-pump-depletion limit, and numerical examples of
Zitterbewegung are presented for sum frequency generation in periodically-poled
lithium niobate. The proposed quantum-optical analogy indicates that frequency
conversion in nonlinear optics could provide an experimentally accessible
simulator of the Dirac equation.Comment: to be published in Journal of Physics B: Atomic, Molecular & Optical
Physic
Wide-bandwidth, tunable, multiple-pulse-width optical delays using slow light in cesium vapor
We demonstrate an all-optical delay line in hot cesium vapor that tunably
delays 275 ps input pulses up to 6.8 ns and 740 input ps pulses up to 59 ns
(group index of approximately 200) with little pulse distortion. The delay is
made tunable with a fast reconfiguration time (hundreds of ns) by optically
pumping out of the atomic ground states.Comment: 4 pages, 6 figure
Bounds on Heavy-to-Heavy Mesonic Form Factors
We provide upper and lower bounds on the form factors for B -> D, D^* by
utilizing inclusive heavy quark effective theory sum rules. These bounds are
calculated to leading order in Lambda_QCD/m_Q and alpha_s. The O(alpha_s^2
beta_0) corrections to the bounds at zero recoil are also presented. We compare
our bounds with some of the form factor models used in the literature. All the
models we investigated failed to fall within the bounds for the combination of
form factors (omega^2 - 1)/(4 omega)|omega h_{A2}+h_{A3}|^2.Comment: 27 pages, 10 figure
Include medical ethics in the Research Excellence Framework
The Research Excellence Framework of the Higher Education
Funding Council for England is taking place in 2013, its three
key elements being outputs (65% of the profile), impact (20%),
and “quality of the research environment” (15%). Impact will
be assessed using case studies that “may include any social,
economic or cultural impact or benefit beyond academia that
has taken place during the assessment period.”1
Medical ethics in the UK still does not have its own cognate
assessment panel—for example, bioethics or applied
ethics—unlike in, for example, Australia. Several researchers
in medical ethics have reported to the Institute of Medical Ethics
that during the internal preliminary stage of the Research
Excellence Framework several medical schools have decided
to include only research that entails empirical data gathering.
Thus, conceptual papers and ethical analysis will be excluded.
The arbitrary exclusion of reasoned discussion of medical ethics
issues as a proper subject for medical research unless it is based
on empirical data gathering is conceptually mistaken. “Empirical
ethics” is, of course, a legitimate component of medical ethics
research, but to act as though it is the only legitimate component
suggests, at best, a partial understanding of the nature of ethics
in general and medical ethics in particular. It also mistakenly
places medicine firmly on only one side of the
science/humanities “two cultures” divide instead of in its rightful
place bridging the divide.
Given the emphasis by the General Medical Council on medical
ethics in properly preparing “tomorrow’s doctors,” we urge
medical schools to find a way of using the upcoming Research
Excellence Framework to highlight the expertise residing in
their ethicist colleagues. We are confident that appropriate
assessment will reveal work of high quality that can be shown
to have social and cultural impact and benefit beyond academia,
as required by the framework
On causality, apparent 'superluminality' and reshaping in barrier penetration
We consider tunnelling of a non-relativistic particle across a potential
barrier. It is shown that the barrier acts as an effective beam splitter which
builds up the transmitted pulse from the copies of the initial envelope shifted
in the coordinate space backwards relative to the free propagation. Although
along each pathway causality is explicitly obeyed, in special cases reshaping
can result an overall reduction of the initial envelope, accompanied by an
arbitrary coordinate shift. In the case of a high barrier the delay amplitude
distribution (DAD) mimics a Dirac -function, the transmission amplitude
is superoscillatory for finite momenta and tunnelling leads to an accurate
advancement of the (reduced) initial envelope by the barrier width. In the case
of a wide barrier, initial envelope is accurately translated into the complex
coordinate plane. The complex shift, given by the first moment of the DAD,
accounts for both the displacement of the maximum of the transmitted
probability density and the increase in its velocity. It is argued that
analysing apparent 'superluminality' in terms of spacial displacements helps
avoid contradiction associated with time parameters such as the phase time
Dynamic method to distinguish between left- and right-handed chiral molecules
We study quantum systems with broken symmetry that can be modelled as cyclic
three-level atoms with coexisting one- and two-photon transitions. They can be
selectively optically excited to any state. As an example, we show that left-
and right-handed chiral molecules starting in the same initial states can
evolve into different final states by a purely dynamic transfer process. That
means, left- and right-handed molecules can be distinguished purely
dynamically.Comment: 4 pages, submitted to Phys. Rev.
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