3,367 research outputs found
Recent Developments: Tierco Maryland, Inc. v. Williams: Injection of Racial Considerations Is Improper When Statements Are Irrelevant to the Causes of Action Pled or Relief Sought
Recent Developments: Tierco Maryland, Inc. v. Williams: Injection of Racial Considerations Is Improper When Statements Are Irrelevant to the Causes of Action Pled or Relief Sought
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Livelihoods and basic service support in the drylands of the Horn of Africa
This technical brief was commissioned by the Technical Consortium for Building Resilience in the Horn of Africa as one of a series of briefs. The Technical Consortium was established to support the Intergovernmental Authority on Development (IGAD) and national governments in the Greater Horn of Africa. ILRI is the host organization of the technical consortium, which seeks to develop regional, national and investment programs for the long-term development of the arid and semi-arid lands (ASALs) in the Horn of Africa. The objective is to support IGAD and common program frameworks to end drought related emergencies and build resilience in the Horn of Africa
Extracting Radial Velocities of A- and B-type Stars from Echelle Spectrograph Calibration Spectra
We present a technique to extract radial velocity measurements from echelle
spectrograph observations of rapidly rotating stars ( km
s). This type of measurement is difficult because the line widths of
such stars are often comparable to the width of a single echelle order. To
compensate for the scarcity of lines and Doppler information content, we have
developed a process that forward-models the observations, fitting the radial
velocity shift of the star for all echelle orders simultaneously with the
echelle blaze function. We use our technique to extract radial velocity
measurements from a sample of rapidly rotating A- and B-type stars used as
calibrator stars observed by the California Planet Survey observations. We
measure absolute radial velocities with a precision ranging from 0.5-2.0 km
s per epoch for more than 100 A- and B-type stars. In our sample of 10
well-sampled stars with radial velocity scatter in excess of their measurement
uncertainties, three of these are single-lined binaries with long observational
baselines. From this subsample, we present detections of two previously unknown
spectroscopic binaries and one known astrometric system. Our technique will be
useful in measuring or placing upper limits on the masses of sub-stellar
companions discovered by wide-field transit surveys, and conducting future
spectroscopic binarity surveys and Galactic space-motion studies of massive
and/or young, rapidly-rotating stars.Comment: Accepted to ApJ
Spin Amplification for Magnetic Sensors Employing Crystal Defects
Recently there have been several theoretical and experimental studies of the
prospects for magnetic field sensors based on crystal defects, especially
nitrogen vacancy (NV) centres in diamond. Such systems could potentially be
incorporated into an AFM-like apparatus in order to map the magnetic properties
of a surface at the single spin level. In this Letter we propose an augmented
sensor consisting of an NV centre for readout and an `amplifier' spin system
that directly senses the local magnetic field. Our calculations show that this
hybrid structure has the potential to detect magnetic moments with a
sensitivity and spatial resolution far beyond that of a simple NV centre, and
indeed this may be the physical limit for sensors of this class
Integrated control of vector-borne diseases of livestock--pyrethroids: panacea or poison?
Tick- and tsetse-borne diseases cost Africa approximately US$4-5 billion per year in livestock production-associated losses. The use of pyrethroid-treated cattle to control ticks and tsetse promises to be an increasingly important tool to counter this loss. However, uncontrolled use of this technology might lead to environmental damage, acaricide resistance in tick populations and a possible exacerbation of tick-borne diseases. Recent research to identify, quantify and to develop strategies to avoid these effects are highlighted
A Silicon Surface Code Architecture Resilient Against Leakage Errors
Spin qubits in silicon quantum dots are one of the most promising building
blocks for large scale quantum computers thanks to their high qubit density and
compatibility with the existing semiconductor technologies. High fidelity
single-qubit gates exceeding the threshold of error correction codes like the
surface code have been demonstrated, while two-qubit gates have reached 98\%
fidelity and are improving rapidly. However, there are other types of error ---
such as charge leakage and propagation --- that may occur in quantum dot arrays
and which cannot be corrected by quantum error correction codes, making them
potentially damaging even when their probability is small. We propose a surface
code architecture for silicon quantum dot spin qubits that is robust against
leakage errors by incorporating multi-electron mediator dots. Charge leakage in
the qubit dots is transferred to the mediator dots via charge relaxation
processes and then removed using charge reservoirs attached to the mediators. A
stabiliser-check cycle, optimised for our hardware, then removes the
correlations between the residual physical errors. Through simulations we
obtain the surface code threshold for the charge leakage errors and show that
in our architecture the damage due to charge leakage errors is reduced to a
similar level to that of the usual depolarising gate noise. Spin leakage errors
in our architecture are constrained to only ancilla qubits and can be removed
during quantum error correction via reinitialisations of ancillae, which ensure
the robustness of our architecture against spin leakage as well. Our use of an
elongated mediator dots creates spaces throughout the quantum dot array for
charge reservoirs, measuring devices and control gates, providing the
scalability in the design
Ensemble based quantum metrology
The field of quantum metrology promises measurement devices that are
fundamentally superior to conventional technologies. Specifically, when quantum
entanglement is harnessed the precision achieved is supposed to scale more
favourably with the resources employed, such as system size and the time
required. Here we consider measurement of magnetic field strength using an
ensemble of spins, and we identify a third essential resource: the initial
system polarisation, i.e. the low entropy of the original state. We find that
performance depends crucially on the form of decoherence present; for a
plausible dephasing model, we describe a quantum strategy which can indeed beat
the standard quantum limit
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