Effects of Intermittent Reinforcement Upon Fixed-Ratio Discrimination

Four pigeons had discrimination training that required the choice of a left side-key following completion of a fixed-ratio 10 an the center key, and a right side-key response after fixed-ratio 20. Correct choices were reinforced on various fixed-interval, fixed-ratio, random-interval, and random-ratio schedules. When accuracy was examined across quarters of intervals (fixed-interval schedules) or quarters of median interreinforcerrent intervals (fixed-ratio schedules), accuracy was usually laver in the second quarter than in the first, third, or fourth quarters. When accuracy was examined across quarters of ratios (fixed-ratio schedules) or quarters of median number of correct interreinforcement trials (fixed-interval schedules), accuracy increased across quarters. These accuracy patterns did not occur m random-interval or random-ratio schedules. The results indicate that, when choice patterns differed on fixed-interval and fixed-ratio schedules, these differences were due to the methods of data analyses

Secure gated detection scheme for quantum cryptography

Several attacks have been proposed on quantum key distribution systems with gated single-photon detectors. The attacks involve triggering the detectors outside the center of the detector gate, and/or using bright illumination to exploit classical photodiode mode of the detectors. Hence a secure detection scheme requires two features: The detection events must take place in the middle of the gate, and the detector must be single-photon sensitive. Here we present a technique called bit-mapped gating, which is an elegant way to force the detections in the middle of the detector gate by coupling detection time and quantum bit error rate. We also discuss how to guarantee single-photon sensitivity by directly measuring detector parameters. Bit-mapped gating also provides a simple way to measure the detector blinding parameter in security proofs for quantum key distribution systems with detector efficiency mismatch, which up until now has remained a theoretical, unmeasurable quantity. Thus if single-photon sensitivity can be guaranteed within the gates, a detection scheme with bit-mapped gating satisfies the assumptions of the current security proofs.Comment: 7 pages, 3 figure

Controlling an actively-quenched single photon detector with bright light

We control using bright light an actively-quenched avalanche single-photon detector. Actively-quenched detectors are commonly used for quantum key distribution (QKD) in the visible and near-infrared range. This study shows that these detectors are controllable by the same attack used to hack passively-quenched and gated detectors. This demonstrates the generality of our attack and its possible applicability to eavsdropping the full secret key of all QKD systems using avalanche photodiodes (APDs). Moreover, the commercial detector model we tested (PerkinElmer SPCM-AQR) exhibits two new blinding mechanisms in addition to the previously observed thermal blinding of the APD, namely: malfunctioning of the bias voltage control circuit, and overload of the DC/DC converter biasing the APD. These two new technical loopholes found just in one detector model suggest that this problem must be solved in general, by incorporating generally imperfect detectors into the security proof for QKD.Comment: Expanded discussions, updated references, added a picture of decapsulated APD, reformatted to single-column style. Accepted to Opt. Express. 11 pages, 6 figure

Comment on "Resilience of gated avalanche photodiodes against bright illumination attacks in quantum cryptography"

This is a comment on the publication by Yuan et al. [Appl. Phys. Lett. 98, 231104 (2011); arXiv:1106.2675v1 [quant-ph]].Comment: 2 page

Thermal blinding of gated detectors in quantum cryptography

It has previously been shown that the gated detectors of two commercially available quantum key distribution (QKD) systems are blindable and controllable by an eavesdropper using continuous-wave illumination and short bright trigger pulses, manipulating voltages in the circuit [L. Lydersen et al., Nat. Photonics DOI:10.1038/nphoton.2010.214]. This allows for an attack eavesdropping the full raw and secret key without increasing the quantum bit error rate (QBER). Here we show how thermal effects in detectors under bright illumination can lead to the same outcome. We demonstrate that the detectors in a commercial QKD system Clavis2 can be blinded by heating the avalanche photo diodes (APDs) using bright illumination, so-called thermal blinding. Further, the detectors can be triggered using short bright pulses once they are blind. For systems with pauses between packet transmission such as the plug-and-play systems, thermal inertia enables Eve to apply the bright blinding illumination before eavesdropping, making her more difficult to catch.Comment: 10 pages, 12 figure

Franchise i dagligvarebransjen : hvilke forskjeller finnes i franchisesystemene i Rema 1000 og Ica Norge, og kan disse forskjellene forklare hvorfor det har oppstått misnøye og internt bråk i én av kjedene?

Denne oppgaven tar for seg forskjeller i franchisesystemene til Rema 1000 og Ica Norge, for å forklare hvorfor det er intern misnøye og bråk i den ene kjeden og hvorfor vi ikke ser det i den andre. Vi fant med utgangspunkt i intervjuer med kjøpmenn fra begge kjedene at det er store forskjeller mellom de ulike franchisesystemene, der noen forskjeller var viktigere enn andre til å forklare hvorfor misnøye og bråk oppstår. De forskjellene vi har sett på er faglig og sosialt miljø, franchisekontrakten, samarbeid og kommunikasjon med ledelsen, i hvilken grad kjøpmennene er fornøyd med kjeden sin, og hvordan franchisesystemene fungerer i praksis. Ut ifra våre analyser har vi funnet ut at de faktorene som er mest utslagsgivende for hvordan trivselen er blant franchisetakerne er samarbeidet mellom partene i kjeden, herunder kommunikasjon, grad av tillitt til ledelsen og konsekvensene av økonomien i kjeden. Disse faktorene bestemmer derfor i hvilken grad det vil kunne oppstå internt bråk og klager fra franchisetakerne