703 research outputs found
C1 inhibitor deficiency: 2014 United Kingdom consensus document
C1 inhibitor deficiency is a rare disorder manifesting with recurrent attacks of disabling and potentially life-threatening angioedema. Here we present an updated 2014 United Kingdom consensus document for the management of C1 inhibitor-deficient patients, representing a joint venture between the United Kingdom Primary Immunodeficiency Network and Hereditary Angioedema UK. To develop the consensus, we assembled a multi-disciplinary steering group of clinicians, nurses and a patient representative. This steering group first met in 2012, developing a total of 48 recommendations across 11 themes. The statements were distributed to relevant clinicians and a representative group of patients to be scored for agreement on a Likert scale. All 48 statements achieved a high degree of consensus, indicating strong alignment of opinion. The recommendations have evolved significantly since the 2005 document, with particularly notable developments including an improved evidence base to guide dosing and indications for acute treatment, greater emphasis on home therapy for acute attacks and a strong focus on service organisation. This article is protected by copyright. All rights reserved
Autocompensating Quantum Cryptography
Quantum cryptographic key distribution (QKD) uses extremely faint light
pulses to carry quantum information between two parties (Alice and Bob),
allowing them to generate a shared, secret cryptographic key. Autocompensating
QKD systems automatically and passively compensate for uncontrolled time
dependent variations of the optical fiber properties by coding the information
as a differential phase between orthogonally-polarized components of a light
pulse sent on a round trip through the fiber, reflected at mid-course using a
Faraday mirror. We have built a prototype system based on standard telecom
technology that achieves a privacy-amplified bit generation rate of ~1000
bits/s over a 10-km optical fiber link. Quantum cryptography is an example of
an application that, by using quantum states of individual particles to
represent information, accomplishes a practical task that is impossible using
classical means.Comment: 18 pages, 6 figures, 1 table. Submitted to the New Journal of Physic
Performance of various quantum key distribution systems using 1.55 um up-conversion single-photon detectors
We compare the performance of various quantum key distribution (QKD) systems
using a novel single-photon detector, which combines frequency up-conversion in
a periodically poled lithium niobate (PPLN) waveguide and a silicon avalanche
photodiode (APD). The comparison is based on the secure communication rate as a
function of distance for three QKD protocols: the Bennett-Brassard 1984 (BB84),
the Bennett, Brassard, and Mermin 1992 (BBM92), and the coherent differential
phase shift keying (DPSK). We show that the up-conversion detector allows for
higher communication rates and longer communication distances than the commonly
used InGaAs/InP APD for all the three QKD protocols.Comment: 9 pages, 9 figure
A high-performance integrated single-photon detector for telecom wavelengths
We have integrated a commercial avalanche photodiode (APD) and the circuitry
needed to operate it as a single-photon detector (SPD) onto a single PC-board.
At temperatures accessible with Peltier coolers (~200-240K), the PCB-SPD
achieves high detection efficiency (DE) at 1308 and 1545 nm with low dark count
probability (e.g. ~10-6/bias pulse at DE=20%, 220 K), making it useful for
quantum key distribution (QKD). The board generates fast bias pulses, cancels
noise transients, amplifies the signals, and sends them to an on-board
discriminator. A digital blanking circuit suppresses afterpulsing.Comment: (10 pages, 6 figures
Practical quantum key distribution: On the security evaluation with inefficient single-photon detectors
Quantum Key Distribution with the BB84 protocol has been shown to be
unconditionally secure even using weak coherent pulses instead of single-photon
signals. The distances that can be covered by these methods are limited due to
the loss in the quantum channel (e.g. loss in the optical fiber) and in the
single-photon counters of the receivers. One can argue that the loss in the
detectors cannot be changed by an eavesdropper in order to increase the covered
distance. Here we show that the security analysis of this scenario is not as
easy as is commonly assumed, since already two-photon processes allow
eavesdropping strategies that outperform the known photon-number splitting
attack. For this reason there is, so far, no satisfactory security analysis
available in the framework of individual attacks.Comment: 11 pages, 6 figures; Abstract and introduction extended, Appendix
added, references update
Theory of Spontaneous Polarization of Endohedral Fullerenes
A pseudo-Jahn-Teller model describing central atom distortions is proposed
for endohedral fullerenes of the form A@C where A is either a rare gas
or a metal atom. A critical (dimensionless) coupling is found, below
which the symmetric configuration is stable and above which inversion symmetry
is broken. Vibronic parameters are given for selected endohedral fullerenes.Comment: 4 pages, REVTEX, 1 Postscript figure. [Phys. Rev. Lett. (in press)
Comparison of Bond Character in Hydrocarbons and Fullerenes
We present a comparison of the bond polarizabilities for carbon-carbon bonds
in hydrocarbons and fullerenes, using two different models for the fullerene
Raman spectrum and the results of Raman measurements on ethane and ethylene. We
find that the polarizabilities for single bonds in fullerenes and hydrocarbons
compare well, while the double bonds in fullerenes have greater polarizability
than in ethylene.Comment: 7 pages, no figures, uses RevTeX. (To appear in Phys. Rev. B.
Experimental implementation of time-coding quantum key distribution
We have implemented an experimental set-up in order to demonstrate the
feasibility of time-coding protocols for quantum key distribution. Alice
produces coherent 20 ns faint pulses of light at 853 nm. They are sent to Bob
with delay 0 ns (encoding bit 0) or 10 ns (encoding bit 1). Bob directs at
random the received pulses to two different arms. In the first one, a 300 ps
resolution Si photon-counter allows Bob to precisely measure the detection
times of each photon in order to establish the key. Comparing them with the
emission times of the pulses sent by Alice allows to evaluate the quantum bit
error rate (QBER). The minimum obtained QBER is 1.62 %. The possible loss of
coherence in the set-up can be exploited by Eve to eavesdrop the line.
Therefore, the second arm of Bob set-up is a Mach-Zender interferometer with a
10 ns propagation delay between the two path. Contrast measurement of the
output beams allows to measure the autocorrelation function of the received
pulses that characterizes their average coherence. In the case of an ideal
set-up, the value expected with the pulses sent by Alice is 0.576. The
experimental value of the pulses autocorrelation function is found to be 0.541.
Knowing the resulting loss of coherence and the measured QBER, one can evaluate
the mutual information between Alice and Eve and the mutual information between
Alice and Bob, in the case of intercept-resend attacks and in the case of
attacks with intrication. With our values, Bob has an advantage on Eve of 0.43
bit per pulse. The maximum possible QBER corresponding to equal informations
for Bob and Eve is 5.8 %. With the usual attenuation of fibres at 850 nm, it
shows that secure key distribution is possible up to a distance of 2.75 km,
which is sufficient for local links.Comment: 27 pages, 6 figure
Field-effect transistors assembled from functionalized carbon nanotubes
We have fabricated field effect transistors from carbon nanotubes using a
novel selective placement scheme. We use carbon nanotubes that are covalently
bound to molecules containing hydroxamic acid functionality. The functionalized
nanotubes bind strongly to basic metal oxide surfaces, but not to silicon
dioxide. Upon annealing, the functionalization is removed, restoring the
electronic properties of the nanotubes. The devices we have fabricated show
excellent electrical characteristics.Comment: 5 pages, 6 figure
Molecular Dynamics Study of Bamboo-like Carbon Nanotube Nucleation
MD simulations based on an empirical potential energy surface were used to
study the nucleation of bamboo-like carbon nanotubes (BCNTs). The simulations
reveal that inner walls of the bamboo structure start to nucleate at the
junction between the outer nanotube wall and the catalyst particle. In
agreement with experimental results, the simulations show that BCNTs nucleate
at higher dissolved carbon concentrations (i.e., feedstock pressures) than
those where non-bamboolike carbon nanotubes are nucleated
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