1,658 research outputs found
A gradient index metamaterial
Metamaterials--artificially structured materials with tailored
electromagnetic response--can be designed to have properties difficult to
achieve with existing materials. Here we present a structured metamaterial,
based on conducting split ring resonators (SRRs), which has an effective
index-of-refraction with a constant spatial gradient. We experimentally confirm
the gradient by measuring the deflection of a microwave beam by a planar slab
of the composite metamaterial over a broad range of frequencies. The gradient
index metamaterial represents an alternative approach to the development of
gradient index lenses and similar optics that may be advantageous, especially
at higher frequencies. In particular, the gradient index material we propose
may be suited for terahertz applications, where the magnetic resonant response
of SRRs has recently been demonstrated
Coherent energy migration in solids: Determination of the average coherence length in one‐dimensional systems using tunable dye lasers
The coherent nature of energy propagation in solids at low temperatures was established from the time resolved response of the crystal to short optical pulses obtained from a dye laser (pumped by a nitrogen gas laser). The trapping and detrapping of the energy by shallow defects (x traps) was evident in the spectra and enabled us to extract the coherence length: l≳700 Å=186 molecules for the one‐dimensional triplet excitons of 1,2,4,5‐tetrachlorobenzene crystals at T<4.2° K. This length which clearly exceeds the stochastic random walk limit is related to the thermalization mechanisms in this coupled exciton–trap system, and its magnitude supports the notion that exciton–phonon coupling is responsible for the loss of coherence on very long molecular chains (trap concentration is 1/256 000)
Demonstration of Robust Quantum Gate Tomography via Randomized Benchmarking
Typical quantum gate tomography protocols struggle with a self-consistency
problem: the gate operation cannot be reconstructed without knowledge of the
initial state and final measurement, but such knowledge cannot be obtained
without well-characterized gates. A recently proposed technique, known as
randomized benchmarking tomography (RBT), sidesteps this self-consistency
problem by designing experiments to be insensitive to preparation and
measurement imperfections. We implement this proposal in a superconducting
qubit system, using a number of experimental improvements including
implementing each of the elements of the Clifford group in single `atomic'
pulses and custom control hardware to enable large overhead protocols. We show
a robust reconstruction of several single-qubit quantum gates, including a
unitary outside the Clifford group. We demonstrate that RBT yields physical
gate reconstructions that are consistent with fidelities obtained by randomized
benchmarking
Anisotropy and oblique total transmission at a planar negative-index interface
We show that a class of negative index (n) materials has interesting
anisotropic optical properties, manifest in the effective refraction index that
can be positive, negative, or purely imaginary under different incidence
conditions. With dispersion taken into account, reflection at a planar
negative-index interface exhibits frequency selective total oblique
transmission that is distinct from the Brewster effect.
Finite-difference-time-domain simulation of realistic negative-n structures
confirms the analytic results based on effective indices.Comment: to appear in Phys. Rev.
A Template Analysis of Intimate Partner Violence Survivors’ Experiences of Animal Maltreatment: Implications for Safety Planning and Intervention
This study explores the intersection of intimate partner violence (IPV) and animal cruelty in an ethnically diverse sample of 103 pet-owning IPV survivors recruited from community-based domestic violence programs. Template analysis revealed five themes: (a) Animal Maltreatment by Partner as a Tactic of Coercive Power and Control, (b) Animal Maltreatment by Partner as Discipline or Punishment of Pet, (c) Animal Maltreatment by Children, (d) Emotional and Psychological Impact of Animal Maltreatment Exposure, and (e) Pets as an Obstacle to Effective Safety Planning. Results demonstrate the potential impact of animal maltreatment exposure on women and child IPV survivors’ health and safety
Nonlocal Homogenization Model for a Periodic Array of Epsilon-Negative Rods
We propose an effective permittivity model to homogenize an array of long
thin epsilon-negative rods arranged in a periodic lattice. It is proved that
the effect of spatial dispersion in this electromagnetic crystal cannot be
neglected, and that the medium supports dispersionless modes that guide the
energy along the rod axes. It is suggested that this effect may be used to
achieve sub-wavelength imaging at the infrared and optical domains. The
reflection problem is studied in detail for the case in which the rods are
parallel to the interfaces. Full wave numerical simulations demonstrate the
validity and accuracy of the new model.Comment: (10 pages
Children exposed to intimate partner violence: Identifying differential effects of family environment on children\u27s trauma and psychopathology symptoms through regression mixture models
The majority of analytic approaches aimed at understanding the influence of environmental context on children\u27s socioemotional adjustment assume comparable effects of contextual risk and protective factors for all children. Using self-reported data from 289 maternal caregiver-child dyads, we examined the degree to which there are differential effects of severity of intimate partner violence (IPV) exposure, yearly household income, and number of children in the family on posttraumatic stress symptoms (PTS) and psychopathology symptoms (i.e., internalizing and externalizing problems) among school-age children between the ages of 7–12 years. A regression mixture model identified three latent classes that were primarily distinguished by differential effects of IPV exposure severity on PTS and psychopathology symptoms: (1) asymptomatic with low sensitivity to environmental factors (66% of children), (2) maladjusted with moderate sensitivity (24%), and (3) highly maladjusted with high sensitivity (10%). Children with mothers who had higher levels of education were more likely to be in the maladjusted with moderate sensitivity group than the asymptomatic with low sensitivity group. Latino children were less likely to be in both maladjusted groups compared to the asymptomatic group. Overall, the findings suggest differential effects of family environmental factors on PTS and psychopathology symptoms among children exposed to IPV. Implications for research and practice are discussed
Refraction at Media with Negative Refractive Index
We show that an electromagnetic (EM) wave undergoes negative refraction at
the interface between a positive and negative refractive index material. Finite
difference time domain (FDTD) simulations are used to study the time evolution
of an EM wave as it hits the interface. The wave is trapped temporarily at the
interface and after a long time, the wave front moves eventually in the
negative direction. This explains why causality and speed of light are not
violated in spite of the negative refraction always present in a negative index
material.Comment: 5 pages, 4 figures, submitted to Phys. Rev. Let
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