203 research outputs found
Dead-time optimization to increase secure distance range in prepare and measure quantum key distribution protocols
Afterpulsing is a factor limiting the distance over which discrete-variable
quantum key distribution systems are secure, and a common feature in
single-photon detectors. The relevance of this phenomenon stems from its
stochastic, self-interacting nature and the fact that its rate rises with the
number of avalanche events, which increases the quantum bit error rate. Here we
introduce an effective analytic model, including dead-time and afterpulsing
corrections, where afterpulsing correction depends on dead-time value. This
model is useful to evaluate the performance of prepare and measure quantum key
distribution protocols (standard and decoy versions) that use gated single
photon detectors. The model provides an expression to numerically optimize the
secret key rate over the full distance range for secure communication, enabling
in this way the calculation of quantum bit error rate and secure key rate. In
the conventional procedure, the dead-time value is fixed regardless of
distance, limiting the distance range of the channel due to remaining
afterpulsing effects, which are more relevant at higher operating frequencies.
Here we demonstrate that optimizing the dead-time values increases the distance
range of the channel to share secret keys.Comment: 13 pages, 9 figure
Quantum Eavesdropping without Interception: An Attack Exploiting the Dead Time of Single Photon Detectors
The security of quantum key distribution (QKD) can easily be obscured if the
eavesdropper can utilize technical imperfections of the actual implementation.
Here we describe and experimentally demonstrate a very simple but highly
effective attack which even does not need to intercept the quantum channel at
all. Only by exploiting the dead time effect of single photon detectors the
eavesdropper is able to gain (asymptotically) full information about the
generated keys without being detected by state-of-the-art QKD protocols. In our
experiment, the eavesdropper inferred up to 98.8% of the key correctly, without
increasing the bit error rate between Alice and Bob significantly. Yet, we find
an evenly simple and effective countermeasure to inhibit this and similar
attacks
Optical coherence tomography characteristics of group 2A idiopathic parafoveal telangiectasis
PURPOSE: To describe the optical coherence tomography (OCT) characteristics of patients with group 2A idiopathic parafoveal telangiectasis (IPFT) and to correlate them with biomicroscopic and fluorescein angiographic (FA) findings based on Gass and Blodi staging classification for group 2A IPFT. METHODS: Fifty-two eyes of 26 consecutive patients with IPFT underwent biomicroscopic fundus examination, color fundus photography, FA, and OCT. Main outcome measures were OCT characteristics and their correlation with biomicroscopy and FA. RESULTS: The most common OCT findings that help differentiate between stages in group 2A IPFT are 1) highly reflective dots in the inner retina that correspond with microvessels seen by FA in Stage 1 (5 eyes [62.5%]); 2) the presence of hyporeflective intraretinal spaces in the absence of retinal thickening and highly reflective dots in the retina in Stage 2 (9 [81.8%] and 10 eyes [90.9%], respectively); 3) in Stage 3, both outer and inner retina exhibit areas of similar high reflectivity. In addition, the retinal pigment epithelium (RPE)/choriocapillaris complex is thickened or disrupted as evidenced by an area of high reflectivity (13 eyes [81.2%]); 4) a highly reflective area nasal or temporal to the fovea in the inner or outer retinal layers in Stage 4 suggesting RPE proliferation and migration (13 eyes [100%]); and 5) a fusiform thickening and duplication of the highly reflective RPE/choriocapillaris complex corresponding to choroidal neovascularization in Stage 5 (4 eyes [100%]). Our OCT characteristics correlated well with biomicroscopic and FA findings for Stages 4 and 5. However, the hyporeflective spaces that are evident on OCT could not be seen clinically at the slit lamp or on FA. In addition, our OCT findings on eyes with group 2A IPFT Stage 3 have not, to our knowledge, been previously described. CONCLUSIONS: Optical coherence tomography findings in group 2A IPFT were characteristic for each stage and may be helpful in making the diagnosis as well as defining the anatomical staging proposed by Gass and Blodi. Optical coherence tomography complements biomicroscopic and FA findings in the evaluation of group 2A IPFT. © The Ophthalmic Communications Society, Inc
Feasibility of free space quantum key distribution with coherent polarization states
We demonstrate for the first time the feasibility of free space quantum key
distribution with continuous variables under real atmospheric conditions. More
specifically, we transmit coherent polarization states over a 100m free space
channel on the roof of our institute's building. In our scheme, signal and
local oscillator are combined in a single spatial mode which auto-compensates
atmospheric fluctuations and results in an excellent interference. Furthermore,
the local oscillator acts as spatial and spectral filter thus allowing
unrestrained daylight operation.Comment: 12 pages, 8 figures, extensions in sections 2, 3.1, 3.2 and 4. This
is an author-created, un-copyedited version of an article accepted for
publication in New Journal of Physics (Special Issue on Quantum Cryptography:
Theory and Practice). IOP Publishing Ltd is not responsible for any errors or
omissions in this version of the manuscript or any version derived from i
Retrospective outcome analysis of urethroplasties performed for various etiologies in a single South African centre
This is the author’s version of a work that was accepted for publication of the article: African Journal of Urology. Changes resulting from the publishing process, such as peer review, editing, corrections, structural formatting, and other quality control mechanisms may not be reflected in this document. Changes may have been made to this work since it was submitted for publication. A definitive version was subsequently published in African Journal of Urology, VOL 18, Issue 3, 2012, DOI: 10.1016/j.afju.2012.03.001.Objectives: To compare the results of anastomotic versus augmentation urethroplasty (buccal mucosa graft (BMG) onlay), as well as dorsal versus ventral BMG techniques. Methods: A retrospective audit of 69 patients who underwent urethroplasty at Eersteriver Hospital in Cape Town, South Africa between October 2004 and July 2011 was undertaken. Analysis included stricture etiology, location and length, type of surgery performed as well as complication rates over the follow-up period. Results: The predominant stricture etiologies were traumatic and infective causes (55%), with a mean stricture length of 3 cm (0.5–15 cm). Forty two patients had bulbar urethra strictures (61%), with 8 (11%) located in the posterior, and penile & bulbar regions, respectively. The remaining strictures were located in the penile urethra (16%). Surgery performed included bulbar (12) and membranous anastomotic (8) urethroplasty, ventral (13) and dorsal (22) buccal mucosa onlay grafts (BMG), and 2-stage urethroplasty (14). Overall stricture recurrence was seen in 9 patients (13%), including 1 patient (8%) of the anterior end-to-end anastomotic group compared to 2 patients (6%) of the onlay BMG group (p = 0.77). The re-stricture rates were 5% and 8% in the dorsal (1/22) and ventral BMG onlay groups (1/13), respectively (p = 0.72)
Razvoj matriksnih sustava za transdermalnu isporuku pentazocina: In vitro/in vivo ispitivanje
The present study aimed to develop hydroxypropyl methylcellulose based transdermal delivery of pentazocine. In formulations containing lower proportions of polymer, the drug released followed the Higuchi kinetics while, with an increase in polymer content, it followed the zero-order release kinetics. Release exponent (n) values imply that the release of pentazocine from matrices was non-Fickian. FT-IR, DSC and XRD studies indicated no interaction between drug and polymer.
The in vitro dissolution rate constant, dissolution half-life and pharmacokinetic parameters (Cmax, tmax, AUC(s), t1/2, Kel, and MRT) were evaluated statistically by two-way ANOVA. A significant difference was observed between but not within the tested products. Statistically, a good correlation was found between per cent of drug absorbed from patches vs. Cmax, and AUC(s). A good correlation was also observed when per cent drug released was correlated with the blood drug concentration obtained at the same time point. The results of this study indicate that the polymeric matrix films of pentazocine hold potential for transdermal drug delivery.U radu je opisan razvoj transdermalnih sustava na bazi hidroksipropil metilceluloze za isporuku pentazocina. U pripravcima koji sadrže manje udjele polimera, otpuštanje lijeka slijedilo je Higuchijevu kinetiku. Međutim, ako je udio polimera veći oslobađanje je najbolje odgovaralo kinetici nultog reda. Vrijednost eksponenta n implicira da oslobađanje pentazocina iz matriksa nije po Fickovom zakonu. FT-IR, DSC i X RD studije ukazuju da nema interakcije između ljekovite tvari i polimera.
In vitro konstanta oslobađanja, poluvrijeme oslobađanja i farmakokinetički parametri (Cmax, tmax, AUC(s), t1/2, Kel, i MRT) procijenjeni su statistički koristeći ANOVA program. Značajna razlika primijećena je između, ali ne i unutar testiranih pripravaka. Pronađena je dobra korelacija između lijeka apsorbiranog iz flastera i Cmax i AUC(s) te oslobođenog lijeka i koncentracije lijeka u krvi. Rezultati ukazuju da su polimerni matriksni filmovi pentazocina potencijalno dobri sustavi za transdermalnu primjenu lijeka
Topical application of ALA and ALA hexyl ester on a subcutaneous murine mammary adenocarcinoma: tissue distribution
Although 5-aminolevulinic acid (ALA)-based photodynamic therapy (PDT) has proven to be clinically beneficial for the treatment of certain cancers, including a variety of skin cancers, optimal tissue localisation still remains a problem. An approach to improve the bioavailability of protoporphyrin IX (PpIX) is the use of ALA derivatives instead of ALA. In this work, we employed a subcutaneous murine mammary adenocarcinoma to study the tissue distribution pattern of the ALA hexyl ester (He-ALA) in comparison with ALA after their topical application in different vehicles. He-ALA induced porphyrin synthesis in the skin overlying the tumour (SOT), but it did not reach the tumour tissue as efficiently. Only 5 h after He-ALA lotion application, tumour porphyrin levels surpassed control values. He-ALA delivered in cream induced a substantially lower porphyrin synthesis in SOT, reinforcing the importance of the vehicle in the use of topical PDT. Porphyrin levels in internal organs remained almost within control values when He-ALA was employed. The addition of DMSO to ALA formulation slightly increased tumour and SOT porphyrin biosynthesis, but it did not when added to He-ALA lotion
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