1,648 research outputs found
Bostonia. Volume 2
Founded in 1900, Bostonia magazine is Boston University's main alumni publication, which covers alumni and student life, as well as university activities, events, and programs
Side-channel-free quantum key distribution
Quantum key distribution (QKD) offers the promise of absolutely secure
communications. However, proofs of absolute security often assume perfect
implementation from theory to experiment. Thus, existing systems may be prone
to insidious side-channel attacks that rely on flaws in experimental
implementation. Here we replace all real channels with virtual channels in a
QKD protocol, making the relevant detectors and settings inside private spaces
inaccessible while simultaneously acting as a Hilbert space filter to eliminate
side-channel attacks. By using a quantum memory we find that we are able to
bound the secret-key rate below by the entanglement-distillation rate computed
over the distributed states.Comment: Considering general quantum systems, we extended QKD to the presence
of an untrusted relay, whose measurement creates secret correlations in
remote stations (achievable rate lower-bounded by the coherent information).
This key ingredient, i.e., the use of a measurement-based untrusted relay,
has been called 'measurement-device independence' in another arXiv submission
(arXiv:1109.1473
Universal teleportation with a twist
We give a transfer theorem for teleportation based on twisting the
entanglement measurement. This allows one to say what local unitary operation
must be performed to complete the teleportation in any situation, generalizing
the scheme to include overcomplete measurements, non-abelian groups of local
unitary operations (e.g., angular momentum teleportation), and the effect of
non-maximally entangled resources.Comment: 4 pages, 1 figur
Multipartite entanglement for continuous variables: A quantum teleportation network
We show that {\it one} single-mode squeezed state distributed among
parties using linear optics suffices to produce a truly -partite entangled
state for any nonzero squeezing and arbitrarily many parties. From this
-partite entangled state, via quadrature measurements of modes,
bipartite entanglement between any two of the parties can be `distilled',
which enables quantum teleportation with an experimentally determinable
fidelity better than could be achieved in any classical scheme.Comment: 4 pages, 2 figures, published version, paper shorter, title longe
The effect of particle size on the in vivo degradation of poly(d,l-lactide-co-glycolide)/α-tricalcium phosphate micro- and nanocomposites.
UNLABELLED: This paper reports the effect of particle size within a resorbable composite on the in vivo degradation rate and host response. Resorbable composites based on poly(d,l-lactide-co-glycolide) (PLGA) reinforced with tricalcium phosphate (TCP) have shown suitable degradation, biological and mechanical properties for bone repair. Composites with nano-sized TCP particles degrade more homogenously in vitro than equivalent composites with micro-sized particles. In this study, PLGA and PLGA/TCP composites containing micro- or nano-sized α-TCP particles were implanted into an ovine distal femoral condyle defect and harvested at 6, 12, 18 and 24weeks. An intimate interface was observed between the new bone tissue and degrading implants. Visual scoring of histological images and semi-automated segmentation of X-ray images were used to quantify implant degradation and the growth of new bone tissue in the implant site. Bone growth into the implant site occurred at a similar rate for both composites and the PLGA control. However, the in vivo degradation rate of the nanocomposite was slower than that of the microcomposite and consequently more closely matched the rate of bone growth. For the first 6weeks, the rate of in vivo degradation matched that of in vitro degradation, but lagged significantly at longer time points. These results point to the potential use of ceramic particle size in controlling composite degradation whilst maintaining good bone formation. STATEMENT OF SIGNIFICANCE: This paper concerns degradable composites for orthopaedic application. The effect of particle size on implant degradation in vivo is not yet well characterised and these results give the first opportunity to directly compare in vitro and in vivo degradation rates for composites with micro- and nano-sized particles. This type of data is vital for the validation of models of composite degradation behaviour, which will lead to the design and manufacture of composites with a tailored, predictable degradation profile. The trainable segmentation tool can be used for future studies where X-rays of partially degraded implants (which have complicated greyscales and morphologies) need to be quantified without bias.The authors gratefully acknowledge funding from EPSRC grant: DT/E005233/1 (TP/5/REG/6/I/HO106A/DT/E006469/1). S M Bennett is grateful for sponsorship from Lucideon Ltd. and an EPSRC Doctoral Training Account grant. SW is grateful to Ms. Charlotte Fay von Karsa, for funding his Ph.D. studies. XCZ gratefully acknowledges funding from a Royal Society Industrial Fellowship. Dr RA Brooks gratefully acknowledges funding from the National Institute of Health Research.This is the final version of the article. It first appeared from Elsevier at http://dx.doi.org/10.1016/j.actbio.2016.08.046
Gene network analysis of Arabidopsis thaliana flower development through dynamic gene perturbations
Understanding how flowers develop from undifferentiated stem cells has occupied developmental biologists for decades. Key to unraveling this process is a detailed knowledge of the global regulatory hierarchies that control developmental transitions, cell differentiation and organ growth. These hierarchies may be deduced from gene perturbation experiments, which determine the effects on gene expression after specific disruption of a regulatory gene. Here, we tested experimental strategies for gene perturbation experiments during Arabidopsis thaliana flower development. We used artificial miRNAs (amiRNAs) to disrupt the functions of key floral regulators, and expressed them under the control of various inducible promoter systems that are widely used in the plant research community. To be able to perform genomeâwide experiments with stageâspecific resolution using the various inducible promoter systems for gene perturbation experiments, we also generated a series of floral induction systems that allow collection of hundreds of synchronized floral buds from a single plant. Based on our results, we propose strategies for performing dynamic gene perturbation experiments in flowers, and outline how they may be combined with versions of the floral induction system to dissect the gene regulatory network underlying flower development
Perfect quantum error correction coding in 24 laser pulses
An efficient coding circuit is given for the perfect quantum error correction
of a single qubit against arbitrary 1-qubit errors within a 5 qubit code. The
circuit presented employs a double `classical' code, i.e., one for bit flips
and one for phase shifts. An implementation of this coding circuit on an
ion-trap quantum computer is described that requires 26 laser pulses. A further
circuit is presented requiring only 24 laser pulses, making it an efficient
protection scheme against arbitrary 1-qubit errors. In addition, the
performance of two error correction schemes, one based on the quantum Zeno
effect and the other using standard methods, is compared. The quantum Zeno
error correction scheme is found to fail completely for a model of noise based
on phase-diffusion.Comment: Replacement paper: Lost two laser pulses gained one author; added
appendix with circuits easily implementable on an ion-trap compute
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