3,565 research outputs found
Relieving the frustration through Mn3+ substitution in Holmium Gallium Garnet
We present a study on the impact of Mn3+ substitution in the geometrically frustrated Ising garnet Ho3Ga5O12 using bulk magnetic measurements and low temperature powder neutron diffraction. We find that the transition temperature, TN = 5.8 K, for Ho3MnGa4O12 is raised by almost 20 when compared to Ho3Ga5O12. Powder neutron diffraction on Ho3MnxGa5-xO12 (x = 0.5, 1) below TN shows the formation of a long range ordered ordered state with k = (0,0,0). Ho3+ spins are aligned antiferromagnetically along the six crystallographic axes with no resultant moment while the Mn3+ spins are oriented along the body diagonals, such that there is a net moment along [111]. The magnetic structure can be visualised as ten-membered rings of corner-sharing triangles of Ho3+ spins with the Mn3+ spins ferromagnetically coupled to each individual Ho3+ spin in the triangle. Substitution of Mn3+ completely relieves the magnetic frustration with f = CW/TN ~ 1.1 for Ho3MnGa4O12.We acknowledge funding support from the Winton Programme for the Physics of Sustainability. Magnetic measurements were carried out using the Advanced Materials Characterisation Suite, funded by EPSRC Strategic Equipment Grant EP1M00052411
Measurement of teicoplanin by liquid chromatography-tandem mass spectrometry:development of a novel method
Teicoplanin is an antibiotic used for the treatment of endocarditis, osteomyelitis, septic arthritis and methicillin-resistant Staphylococcus aureus. Teicoplanin is emerging as a suitable alternative antibiotic to vancomycin, where their trough serum levels are monitored by immunoassay routinely. This is the first report detailing the development of a liquid chromatography-tandem mass spectrometry (LC-MS/MS) method for measuring teicoplanin in patients' serum
Achieving minimum-error discrimination of an arbitrary set of laser-light pulses
Laser light is widely used for communication and sensing applications, so the
optimal discrimination of coherent states--the quantum states of light emitted
by a laser--has immense practical importance. However, quantum mechanics
imposes a fundamental limit on how well different coher- ent states can be
distinguished, even with perfect detectors, and limits such discrimination to
have a finite minimum probability of error. While conventional optical
receivers lead to error rates well above this fundamental limit, Dolinar found
an explicit receiver design involving optical feedback and photon counting that
can achieve the minimum probability of error for discriminating any two given
coherent states. The generalization of this construction to larger sets of
coherent states has proven to be challenging, evidencing that there may be a
limitation inherent to a linear-optics-based adaptive measurement strategy. In
this Letter, we show how to achieve optimal discrimination of any set of
coherent states using a resource-efficient quantum computer. Our construction
leverages a recent result on discriminating multi-copy quantum hypotheses
(arXiv:1201.6625) and properties of coherent states. Furthermore, our
construction is reusable, composable, and applicable to designing
quantum-limited processing of coherent-state signals to optimize any metric of
choice. As illustrative examples, we analyze the performance of discriminating
a ternary alphabet, and show how the quantum circuit of a receiver designed to
discriminate a binary alphabet can be reused in discriminating multimode
hypotheses. Finally, we show our result can be used to achieve the quantum
limit on the rate of classical information transmission on a lossy optical
channel, which is known to exceed the Shannon rate of all conventional optical
receivers.Comment: 9 pages, 2 figures; v2 Minor correction
Evaluating the Chinese Revised Controlling Behaviors Scale (C-CBS-R)
The present study evaluated the utility of the Chinese version of the Revised Controlling Behaviors Scale (C-CBS-R) as a measure of controlling behaviors in violent Chinese intimate relationships. Using a mixed-methods approach, in-depth, individual interviews were conducted with 200 Chinese women survivors to elicit qualitative data about their personal experiences of control in intimate relationships. The use of controlling behaviors was also assessed using the C-CBS-R. Interview accounts suggested that the experiences of 91 of the women were consistent with the description of coercive control according to Dutton and Goodman’s (2005) conceptualization of coercion. Using the split-half validation procedure, a receiver operating characteristics (ROC) curve analysis was conducted with the first half of the sample. The area under the curve (AUC) for using the C-CBS-R to identify high control was .99, and the cutoff score of 1.145 maximized both sensitivity and specificity. Applying the cutoff score to the second half gave a sensitivity of 96% and a specificity of 95%. Overall, the C-CBS-R has demonstrated utility as a measure of controlling behaviors with a cutoff score for distinguishing high from low levels of control in violent Chinese intimate relationships
Theoretical X-Ray Absorption Debye-Waller Factors
An approach is presented for theoretical calculations of the Debye-Waller
factors in x-ray absorption spectra. These factors are represented in terms of
the cumulant expansion up to third order. They account respectively for the net
thermal expansion , the mean-square relative displacements
, and the asymmetry of the pair distribution function
. Similarly, we obtain Debye-Waller factors for x-ray and
neutron scattering in terms of the mean-square vibrational amplitudes .
Our method is based on density functional theory calculations of the dynamical
matrix, together with an efficient Lanczos algorithm for projected phonon
spectra within the quasi-harmonic approximation. Due to anharmonicity in the
interatomic forces, the results are highly sensitive to variations in the
equilibrium lattice constants, and hence to the choice of exchange-correlation
potential. In order to treat this sensitivity, we introduce two prescriptions:
one based on the local density approximation, and a second based on a modified
generalized gradient approximation. Illustrative results for the leading
cumulants are presented for several materials and compared with experiment and
with correlated Einstein and Debye models. We also obtain Born-von Karman
parameters and corrections due to perpendicular vibrations.Comment: 11 pages, 8 figure
Electromagnetically induced transparency in superconducting quantum circuits : Effects of decoherence, tunneling and multi-level cross-talk
We explore theoretically electromagnetically-induced transparency (EIT) in a
superconducting quantum circuit (SQC). The system is a persistent-current flux
qubit biased in a configuration. Previously [Phys. Rev. Lett. 93,
087003 (2004)], we showed that an ideally-prepared EIT system provides a
sensitive means to probe decoherence. Here, we extend this work by exploring
the effects of imperfect dark-state preparation and specific decoherence
mechanisms (population loss via tunneling, pure dephasing, and incoherent
population exchange). We find an initial, rapid population loss from the
system for an imperfectly prepared dark state. This is followed by a
slower population loss due to both the detuning of the microwave fields from
the EIT resonance and the existing decoherence mechanisms. We find analytic
expressions for the slow loss rate, with coefficients that depend on the
particular decoherence mechanisms, thereby providing a means to probe,
identify, and quantify various sources of decoherence with EIT. We go beyond
the rotating wave approximation to consider how strong microwave fields can
induce additional off-resonant transitions in the SQC, and we show how these
effects can be mitigated by compensation of the resulting AC Stark shifts
Formation of shock waves in a Bose-Einstein condensate
We consider propagation of density wave packets in a Bose-Einstein
condensate. We show that the shape of initially broad, laser-induced, density
perturbation changes in the course of free time evolution so that a shock wave
front finally forms. Our results are well beyond predictions of commonly used
zero-amplitude approach, so they can be useful in extraction of a speed of
sound from experimental data. We discuss a simple experimental setup for shock
propagation and point out possible limitations of the mean-field approach for
description of shock phenomena in a BEC.Comment: 8 pages & 6 figures, minor changes, more references, to appear in
Phys. Rev.
Towards a first principles description of phonons in NiPt disordered alloys: the role of relaxation
Using a combination of density-functional perturbation theory and the
itinerant coherent potential approximation, we study the effects of atomic
relaxation on the inelastic incoherent neutron scattering cross sections of
disordered NiPt alloys. We build on previous work, where
empirical force constants were adjusted {\it ad hoc} to agree with experiment.
After first relaxing all structural parameters within the local-density
approximation for ordered NiPt compounds, density-functional perturbation
theory is then used to compute phonon spectra, densities of states, and the
force constants. The resulting nearest-neighbor force constants are first
compared to those of other ordered structures of different stoichiometry, and
then used to generate the inelastic scattering cross sections within the
itinerant coherent potential approximation. We find that structural relaxation
substantially affects the computed force constants and resulting inelastic
cross sections, and that the effect is much more pronounced in random alloys
than in ordered alloys.Comment: 8 pages, 3 eps figures, uses revtex
Superconductivity at 2.3 K in the misfit compound (PbSe)1.16(TiSe2)2
The structural misfit compound (PbSe)1.16(TiSe2)2 is reported. It is a
superconductor with a Tc of 2.3 K. (PbSe)1.16(TiSe2)2 derives from a parent
compound, TiSe2, which shows a charge density wave transition and no
superconductivity. The crystal structure, characterized by high resolution
electron microscopy and powder x-ray diffraction, consists of two layers of
1T-TiSe2 alternating with a double layer of (100) PbSe. Transport measurements
suggest that the superconductivity is induced by charge transfer from the PbSe
layers to the TiSe2 layers.Comment: 17 pages, 4 figures. To be published in Physical Review
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