328 research outputs found
Magnetically Charged Calorons with Non-Trivial Holonomy
Instantons in pure Yang-Mills theories on partially periodic space
are usually called calorons. The background
periodicity brings on characteristic features of calorons such as non-trivial
holonomy, which plays an essential role for confinement/deconfinement
transition in pure Yang-Mills gauge theory. For the case of gauge group
, calorons can be interpreted as composite objects of two constituent
"monopoles" with opposite magnetic charges. There are often the cases that the
two monopole charges are unbalanced so that the calorons possess net magnetic
charge in . In this paper, we consider several mechanism how such
net magnetic charges appear for certain types of calorons through the ADHM/Nahm
construction with explicit examples. In particular, we construct analytically
the gauge configuration of the -caloron with -symmetry, which has
intrinsically magnetic charge.Comment: 33 pages, 8 figure
Long-distance entanglement-based quantum key distribution over optical fiber
We report the first entanglement-based quantum key distribution (QKD) experiment over a 100-km optical fiber. We used superconducting single photon detectors based on NbN nanowires that provide high-speed single photon detection for the 1.5-µm telecom band, an efficient entangled photon pair source that consists of a fiber coupled periodically poled lithium niobate waveguide and ultra low loss filters, and planar lightwave circuit Mach-Zehnder interferometers (MZIs) with ultra stable operation. These characteristics enabled us to perform an entanglement-based QKD experiment over a 100-km optical fiber. In the experiment, which lasted approximately 8 hours, we successfully generated a 16 kbit sifted key with a quantum bit error rate of 6.9 % at a rate of 0.59 bits per second, from which we were able to distill a 3.9 kbit secure key
Maternal education level and maternal healthcare utilization in the Democratic Republic of the Congo: an analysis of the multiple indicator cluster survey 2017/18
Background
Understanding how socioeconomic factors influence maternal health services utilization is crucial to reducing preventable maternal deaths in the DRC. Maternal education is considered an important associate of maternal health service utilization. This study aims to investigate the association between maternal education and the utilization of maternal health services, as well as present geographical and socio-economic disparities in the utilization.
Methods
The MICS survey was employed as the data source, which is a nationally representative survey conducted from 2017 to 2018 in the DRC. The exposure for this study was the maternal education level, which was categorized into three groups: (1) below primary and none, (2) primary and (3) secondary and above. Prenatal care indicators included: if the mother ever received prenatal care, if the mother had antenatal checks no less than four times, and if a skilled attendant was present at birth. Postnatal care indicators included: if the mother received postnatal care and if the baby was checked after birth. Emergency obstetric interventions were indicted by cesarean sections. Descriptive analyses and logistic regressions were used as analytical methods.
Results
Of all 8,560 participants included, 21.88 % had below primary school or no education, 39.81 % had primary school education, and 38.31 % had secondary education or above. The majority of participants were from rural areas, except for Kinshasa. Overall, a better education was associated with higher utilization of antenatal care. A dose-response effect was also observed. Compared to women with below primary or no education, women with secondary and above education were more likely to receive cesarean sections. Wealth status, as well as rural and urban division, modified the associations.
Conclusions
Mothers’ education level is an important associate for utilizing appropriate maternal healthcare, with wealth and region as modifying factors. Educational levels should be considered when designing public health interventions and women’s empowerment programs in the DRC. For example, relevant programs need to stratify the interventions according to educational attainment
Transport Phenomena at a Critical Point -- Thermal Conduction in the Creutz Cellular Automaton --
Nature of energy transport around a critical point is studied in the Creutz
cellular automaton. Fourier heat law is confirmed to hold in this model by a
direct measurement of heat flow under a temperature gradient. The thermal
conductivity is carefully investigated near the phase transition by the use of
the Kubo formula. As the result, the thermal conductivity is found to take a
finite value at the critical point contrary to some previous works. Equal-time
correlation of the heat flow is also analyzed by a mean-field type
approximation to investigate the temperature dependence of thermal
conductivity. A variant of the Creutz cellular automaton called the Q2R is also
investigated and similar results are obtained.Comment: 27 pages including 14figure
Megabits secure key rate quantum key distribution
Quantum cryptography (QC) can provide unconditional secure communication
between two authorized parties based on the basic principles of quantum
mechanics. However, imperfect practical conditions limit its transmission
distance and communication speed. Here we implemented the differential phase
shift (DPS) quantum key distribution (QKD) with up-conversion assisted hybrid
photon detector (HPD) and achieved 1.3 M bits per second secure key rate over a
10-km fiber, which is tolerant against the photon number splitting (PNS)
attack, general collective attacks on individual photons, and any other known
sequential unambiguous state discrimination (USD) attacks.Comment: 14 pages, 4 figure
Theory of superconductivity of carbon nanotubes and graphene
We present a new mechanism of carbon nanotube superconductivity that
originates from edge states which are specific to graphene. Using on-site and
boundary deformation potentials which do not cause bulk superconductivity, we
obtain an appreciable transition temperature for the edge state. As a
consequence, a metallic zigzag carbon nanotube having open boundaries can be
regarded as a natural superconductor/normal metal/superconductor junction
system, in which superconducting states are developed locally at both ends of
the nanotube and a normal metal exists in the middle. In this case, a signal of
the edge state superconductivity appears as the Josephson current which is
sensitive to the length of a nanotube and the position of the Fermi energy.
Such a dependence distinguishs edge state superconductivity from bulk
superconductivity.Comment: 5 pages, 2 figure
Gated Mode Superconducting Nanowire Single Photon Detectors
Single Photon Detectors (SPD) are fundamental to quantum optics and quantum
information. Superconducting Nanowire SPDs (SNSPD) [1] provide high performance
in terms of quantum efficiency (QE), dark count rate (DCR) and timing jitter
[2], but have limited maximum count rate (MCR) when operated as a free-running
mode (FM) detector [3, 4]. However, high count rates are needed for many
applications like quantum computing [5] and communication [6], and laser
ranging [7]. Here we report the first operation of SNSPDs in a gated mode (GM)
that exploits a single photon triggered latching phenomenon to detect photons.
We demonstrate operation of a large active area single element GM-SNSPD at
625MHz, one order of magnitude faster than its FM counterpart. Contrary to
FM-SNSPDs, the MCR in GM can be pushed to GHz range without a compromise on the
active area or QE, while reducing the DCR
Conservation Laws in Cellular Automata
If X is a discrete abelian group and B a finite set, then a cellular
automaton (CA) is a continuous map F:B^X-->B^X that commutes with all X-shifts.
If g is a real-valued function on B, then, for any b in B^X, we define G(b) to
be the sum over all x in X of g(b_x) (if finite). We say g is `conserved' by F
if G is constant under the action of F. We characterize such `conservation
laws' in several ways, deriving both theoretical consequences and practical
tests, and provide a method for constructing all one-dimensional CA exhibiting
a given conservation law.Comment: 19 pages, LaTeX 2E with one (1) Encapsulated PostScript figure. To
appear in Nonlinearity. (v2) minor changes/corrections; new references added
to bibliograph
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