15,717 research outputs found
Twisted Fermi surface of a thin-film Weyl semimetal
The Fermi surface of a conventional two-dimensional electron gas is
equivalent to a circle, up to smooth deformations that preserve the orientation
of the equi-energy contour. Here we show that a Weyl semimetal confined to a
thin film with an in-plane magnetization and broken spatial inversion symmetry
can have a topologically distinct Fermi surface that is twisted into a
\mbox{figure-8} opposite orientations are coupled at a crossing which is
protected up to an exponentially small gap. The twisted spectral response to a
perpendicular magnetic field is distinct from that of a deformed Fermi
circle, because the two lobes of a \mbox{figure-8} cyclotron orbit give
opposite contributions to the Aharonov-Bohm phase. The magnetic edge channels
come in two counterpropagating types, a wide channel of width and a narrow channel of width (with
the magnetic length and the momentum separation
of the Weyl points). Only one of the two is transmitted into a metallic
contact, providing unique magnetotransport signatures.Comment: V4: 10 pages, 14 figures. Added figure and discussion about
"uncrossing deformations" of oriented contours, plus minor corrections.
Published in NJ
Science materials for the gifted in grades two and three
Thesis (Ed.M.)--Boston Universit
Illness in Returned Travelers and Immigrants/Refugees: The 6-Year Experience of Two Australian Infectious Diseases Units.
BACKGROUND: Data comparing returned travelers and immigrants/refugees managed in a hospital setting is lacking. METHODS: We prospectively collected data on 1,106 patients with an illness likely acquired overseas who presented to two hospital-based Australian infectious diseases units over a 6-year period. RESULTS: Eighty-three percent of patients were travelers and 17% immigrants/refugees. In travelers, malaria (19%), gastroenteritis/diarrhea (15%), and upper respiratory tract infection (URTI) (7%) were the most common diagnoses. When compared with immigrants/refugees, travelers were significantly more likely to be diagnosed with gastroenteritis/diarrhea [odds ratio (OR) 8], malaria (OR 7), pneumonia (OR 6), URTI (OR 3), skin infection, dengue fever, typhoid/paratyphoid fever, influenza, and rickettsial disease. They were significantly less likely to be diagnosed with leprosy (OR 0.03), chronic hepatitis (OR 0.04), tuberculosis (OR 0.05), schistosomiasis (OR 0.3), and helminthic infection (OR 0.3). In addition, travelers were more likely to present within 1 month of entry into Australia (OR 96), and have fever (OR 8), skin (OR 6), gastrointestinal (OR 5), or neurological symptoms (OR 5) but were less likely to be asymptomatic (OR 0.1) or have anaemia (OR 0.4) or eosinophilia (OR 0.3). Diseases in travelers were more likely to have been acquired via a vector (OR 13) or food and water (OR 4), and less likely to have been acquired via the respiratory (OR 0.2) or skin (OR 0.6) routes. We also found that travel destination and classification of traveler can significantly influence the likelihood of a specific diagnosis in travelers. Six percent of travelers developed a potentially vaccine-preventable disease, with failure to vaccinate occurring in 31% of these cases in the pretravel medical consultation. CONCLUSIONS: There are important differences in the spectrum of illness, clinical features, and mode of disease transmission between returned travelers and immigrants/refugees presenting to hospital-based Australian infectious diseases units with an illness acquired overseas
Adaptive weight estimator for quantum error correction
Quantum error correction of a surface code or repetition code requires the
pairwise matching of error events in a space-time graph of qubit measurements,
such that the total weight of the matching is minimized. The input weights
follow from a physical model of the error processes that affect the qubits.
This approach becomes problematic if the system has sources of error that
change over time. Here we show how the weights can be determined from the
measured data in the absence of an error model. The resulting adaptive decoder
performs well in a time-dependent environment, provided that the characteristic
time scale of the variations is greater than , with the duration of one error-correction cycle and
the typical error probability per qubit in one cycle.Comment: 5 pages, 4 figure
Using Intelligent Agents to Manage Business Processes
This paper describes work undertaken in the ADEPT (Advanced Decision Environment for Process Tasks) project towards developing an agent-based infrastructure for managing business processes. We describe how the key technology of negotiating, service providing, autonomous agents was realised and demonstrate how this was applied to the BT business process of providing a customer quote for network services
Engaging Students Engaging Industry Engaging Enterprise
A reflective piece on how a small team of students and academics gained more awareness of their own sense of enterprise and creativity. The case study examines the phases and crisis points of the whole event process and identifies some of the key learning outcomes for all involved
Violation of the Leggett-Garg inequality with weak measurements of photons
By weakly measuring the polarization of a photon between two strong
polarization measurements, we experimentally investigate the correlation
between the appearance of anomalous values in quantum weak measurements, and
the violation of realism and non-intrusiveness of measurements. A quantitative
formulation of the latter concept is expressed in terms of a Leggett-Garg
inequality for the outcomes of subsequent measurements of an individual quantum
system. We experimentally violate the Leggett-Garg inequality for several
measurement strengths. Furthermore, we experimentally demonstrate that there is
a one-to-one correlation between achieving strange weak values and violating
the Leggett-Garg inequality.Comment: 5 pages, 4 figure
Swift observations of the 2006 outburst of the recurrent nova RS Ophiuchi: II. 1D hydrodynamical models of wind driven shocks
Following the early Swift X-ray observations of the latest outburst of the
recurrent nova RS Ophiuchi in February 2006 (Paper I), we present new 1D
hydrodynamical models of the system which take into account all three phases of
the remnant evolution. The models suggest a novel way of modelling the system
by treating the outburst as a sudden increase then decrease in wind mass-loss
rate and velocity. The differences between this wind model and previous
Primakoff-type simulations are described. A more complex structure, even in 1D,
is revealed through the presence of both forward and reverse shocks, with a
separating contact discontinuity. The effects of radiative cooling are
investigated and key outburst parameters such as mass-loss rate, ejecta
velocity and mass are varied. The shock velocities as a function of time are
compared to the ones derived in Paper I. We show how the manner in which the
matter is ejected controls the evolution of the shock and that for a
well-cooled remnant, the shock deceleration rate depends on the amount of
energy that is radiated away.Comment: 9 pages, 5 figure
Guidelines for the management of chronic obstructive pulmonary disease : Working group of the South African pulmonology society
Objective: This guideline has been developed in order to optimise the management of patients with chronic obstructive pulmonary disease (COPD) at all levels health care systems in South Africa. It contains an action plan for early recognition and appropriate treatment of this common condition.Options: Treatment regimens are recommended for patients with mild (stage I), and severe (stage III) disease.Outcomes: Optimal management of patients with COPD may achieve a reduction in breathlessness, improved quality of life, prevention of complications and limitation of disease progression.Evidence: The working Group comprised mainly pulmonologists, but included an anaesthetist, a pharmacologist and physiotherapist. Detailed literature review with particular attention to similar guideline documents from Europe and the USA was performed before the meeting.Recommendations: Steps in the management of patients with COPD include early recognition of the disease, smoking cessation, treatment of airflow obstruction with appropriate drugs (singly or in combination), education and pulmonary rehabilitation, and limitation of disease progression and complications. Detailed recommendations are made with regard to the use and interpretation of a trial of oral corticosteroid therapy. Indications for hospitalisation, intensive care unit admission and ventilatory support are provided.Validation: This guideline is similar to those recommended by other groups outside South Africa. It was developed by a working group of the South Africa Pulmonology Society and is endorsed by the Medical Association of South Africa.Sponsors: The meeting of the Working Group was sponsored by Boehringer Ingelheim. This sponsorship did not influence the activities of the Group
Chirality blockade of Andreev reflection in a magnetic Weyl semimetal
A Weyl semimetal with broken time-reversal symmetry has a minimum of two
species of Weyl fermions, distinguished by their opposite chirality, in a pair
of Weyl cones at opposite momenta that are displaced in the direction
of the magnetization. Andreev reflection at the interface between a Weyl
semimetal in the normal state (N) and a superconductor (S) that pairs
must involve a switch of chirality, otherwise it is blocked. We show that this
"chirality blockade" suppresses the superconducting proximity effect when the
magnetization lies in the plane of the NS interface. A Zeeman field at the
interface can provide the necessary chirality switch and activate Andreev
reflection.Comment: 15 pages, 9 figures. V2: added investigation of the dependence of the
chirality blockade on the direction of the magnetization and (Appendix C)
calculations of the Fermi-arc mediated Josephson effec
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