3,914 research outputs found
Reduction of Effective Terahertz Focal Spot Size By Means Of Nested Concentric Parabolic Reflectors
An ongoing limitation of terahertz spectroscopy is that the technique is
generally limited to the study of relatively large samples of order 4 mm across
due to the generally large size of the focal beam spot. We present a nested
concentric parabolic reflector design which can reduce the terahertz focal spot
size. This parabolic reflector design takes advantage of the feature that
reflected rays experience a relative time delay which is the same for all
paths. The increase in effective optical path for reflected light is equivalent
to the aperture diameter itself. We have shown that the light throughput of an
aperture of 2 mm can be increased by a factor 15 as compared to a regular
aperture of the same size at low frequencies. This technique can potentially be
used to reduce the focal spot size in terahertz spectroscopy and enable the
study of smaller samples
Diverse Diversions:Youth Justice Reform, Localized Practices, and a ‘New Interventionist Diversion’?
The recent resurgence of practices aimed at ‘diverting’ young people from prosecution appears to suggest a sea change from the interventionism which characterized New Labour’s approach to young law-breakers. Drawing on interviews with youth justice practitioners at two sites in England, we argue this is overly simplistic, since the ‘interventionist diversion’ they describe reflects the continued influence of New Labour reforms, as well as older approaches. We conclude that more empirical research is needed to establish where such interventions sit within the broader – and increasingly localized – landscape of support provision, as well as the consequences of providing ‘welfare’ in this way. </jats:p
Diverse Diversions: Youth Justice Reform, Localized Practices, and a ‘New Interventionist Diversion’?
The recent resurgence of practices aimed at ‘diverting’ young people from prosecution appears to suggest a sea change from the interventionism which characterized New Labour’s approach to young law-breakers. Drawing on interviews with youth justice practitioners at two sites in England, we argue this is overly simplistic, since the ‘interventionist diversion’ they describe reflects the continued influence of New Labour reforms, as well as older approaches. We conclude that more empirical research is needed to establish where such interventions sit within the broader – and increasingly localized – landscape of support provision, as well as the consequences of providing ‘welfare’ in this way
Gauss Sums and Quantum Mechanics
By adapting Feynman's sum over paths method to a quantum mechanical system
whose phase space is a torus, a new proof of the Landsberg-Schaar identity for
quadratic Gauss sums is given. In contrast to existing non-elementary proofs,
which use infinite sums and a limiting process or contour integration, only
finite sums are involved. The toroidal nature of the classical phase space
leads to discrete position and momentum, and hence discrete time. The
corresponding `path integrals' are finite sums whose normalisations are derived
and which are shown to intertwine cyclicity and discreteness to give a finite
version of Kelvin's method of images.Comment: 14 pages, LaTe
Ultrafast (but Many-Body) Relaxation in a Low-Density Electron Glass
We present a study of the relaxation dynamics of the photoexcited
conductivity of the impurity states in the low-density electronic glass,
phosphorous-doped silicon Si:P. Using optical pump-terahertz probe spectroscopy
we find strongly temperature and fluence dependent glassy power-law relaxation
occurring over sub-ns time scales. Such behavior is in contrast to the much
longer time scales found in higher electron density glassy systems. We also
find evidence for both multi-particle relaxation mechanisms and/or coupling to
electronic collective modes and a low temperature quantum relaxational regime.Comment: 4 pages, 4 figures, Appeared in Phys. Rev. Let
Optical spectra of the heavy fermion uniaxial ferromagnet UGe
We report a detailed study of UGe single crystals using infrared
reflectivity and spectroscopic ellipsometry. The optical conductivity suggests
the presence of a low frequency interband transition and a narrow free-carrier
response with strong frequency dependence of the scattering rate and effective
mass. We observe sharp changes in the low frequency mass and scattering rate
below the upper ferromagnetic transition . The characteristic
changes are exhibited most strongly at an energy scale of around 12 meV (100
cm). They recover their unrenormalized value above and for 40 meV. In contrast no sign of an anomaly is seen at the lower transition
temperature of unknown nature 30 K, observed in transport and
thermodynamic experiments. In the ferromagnetic state we find signatures of a
strong coupling to the longitudinal magnetic excitations that have been
proposed to mediate unconventional superconductivity in this compound
Time-reversal symmetry breaking versus superstructure
One of the mysteries of modern condenced-matter physics is the nature of the
pseudogap state of the superconducting cuprates. Kaminski et al.1 claimed to
have observed signatures of time-reversal symmetry breaking in the pseudogap
regime in underdoped Bi2Sr2CaCu2O8+d (Bi2212). Here we argue that the observed
dichroism is due to the 5x1 superstructure replica of the electronic bands and
therefore cannot be considered as evidence for the spontaneous time-reversal
symmetry breaking in cuprates.Comment: 5 pages, pd
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