Quantum enhanced positioning and clock synchronization

A wide variety of positioning and ranging procedures are based on repeatedly sending electromagnetic pulses through space and measuring their time of arrival. This paper shows that quantum entanglement and squeezing can be employed to overcome the classical power/bandwidth limits on these procedures, enhancing their accuracy. Frequency entangled pulses could be used to construct quantum positioning systems (QPS), to perform clock synchronization, or to do ranging (quantum radar): all of these techniques exhibit a similar enhancement compared with analogous protocols that use classical light. Quantum entanglement and squeezing have been exploited in the context of interferometry, frequency measurements, lithography, and algorithms. Here, the problem of positioning a party (say Alice) with respect to a fixed array of reference points will be analyzed.Comment: 4 pages, 2 figures. Accepted for publication by Natur

Assessment of the genotoxic impact of pesticides on farming communities in the countryside of Santa Catarina State, Brazil

The aim of this study was to assess the use of pesticides on farms located in the Lambedor River watershed in Guatambu, State of Santa Catarina, as well as to determine, by micronucleus testing, the risk of genotoxic impact. Samples from locally collected Cyprinus carpio, Hypostomus punctatus, Rhamdia quelen and Oreochromis niloticus gave evidence of a mean increase in micronuclei frequency from 6.21 to 13.78 in 1,000 erythrocytes, a clear indication of the genotoxic potenciality of pesticide residues in regional dams, and their significant contribution to local environmental contamination

Experimental delayed-choice entanglement swapping

Motivated by the question, which kind of physical interactions and processes are needed for the production of quantum entanglement, Peres has put forward the radical idea of delayed-choice entanglement swapping. There, entanglement can be "produced a posteriori, after the entangled particles have been measured and may no longer exist". In this work we report the first realization of Peres' gedanken experiment. Using four photons, we can actively delay the choice of measurement-implemented via a high-speed tunable bipartite state analyzer and a quantum random number generator-on two of the photons into the time-like future of the registration of the other two photons. This effectively projects the two already registered photons onto one definite of two mutually exclusive quantum states in which either the photons are entangled (quantum correlations) or separable (classical correlations). This can also be viewed as "quantum steering into the past"

Entangling Independent Photons by Time Measurement

A quantum system composed of two or more subsystems can be in an entangled state, i.e. a state in which the properties of the global system are well defined but the properties of each subsystem are not. Entanglement is at the heart of quantum physics, both for its conceptual foundations and for applications in information processing and quantum communication. Remarkably, entanglement can be "swapped": if one prepares two independent entangled pairs A1-A2 and B1-B2, a joint measurement on A1 and B1 (called a "Bell-State Measurement", BSM) has the effect of projecting A2 and B2 onto an entangled state, although these two particles have never interacted or shared any common past[1,2]. Experiments using twin photons produced by spontaneous parametric down-conversion (SPDC) have already demonstrated entanglement swapping[3-6], but here we present its first realization using continuous wave (CW) sources, as originally proposed[2]. The challenge was to achieve sufficiently sharp synchronization of the photons in the BSM. Using narrow-band filters, the coherence time of the photons that undergo the BSM is significantly increased, exceeding the temporal resolution of the detectors. Hence pulsed sources can be replaced by CW sources, which do not require any synchronization[6,7], allowing for the first time the use of completely autonomous sources. Our experiment exploits recent progress in the time precision of photon detectors, in the efficiency of photon pair production by SPDC with waveguides in nonlinear crystals[8], and in the stability of narrow-band filters. This approach is independent of the form of entanglement; we employed time-bin entangled photons[9] at telecom wavelengths. Our setup is robust against thermal or mechanical fluctuations in optical fibres thanks to cm-long coherence lengths.Comment: 13 pages, 3 figure

Effect of propolis gel on the in vitro reduction of dentin permeability

OBJECTIVE: The aim of this study was to evaluate the capacity of potassium oxalate, fluoride gel and two kinds of propolis gel to reduce the hydraulic conductance of dentin, in vitro. MATERIAL AND METHODS: The methodology used for the measurement of hydraulic conductance of dentin in the present study was based on a model proposed in literature. Thirty-six 1-mm-thick dentin discs, obtained from extracted human third molars were divided into 4 groups (n=9). The groups corresponded to the following experimental materials: GI-10% propolis gel, pH 4.1; GII-30% propolis gel; GIII-3% potassium oxalate gel, pH 4,1; and GIV-1.23% fluoride gel, pH 4.1, applied to the dentin under the following surface conditions: after 37% phosphoric acid and before 6% citric acid application. The occluding capacity of the dentin tubules was evaluated using scanning electron microscopy (SEM) at ×500, ×1,000 and ×2,000 magnifications. Data were analyzed statistically by two-way ANOVA and Tukey's test at 5% significance level. RESULTS: Groups I, II, III, IV did not differ significantly from the others in any conditions by reducing in hydraulic conductance. The active agents reduced dentin permeability; however they produced the smallest reduction in hydraulic conductance when compared to the presence of smear layer (P<0.05). The effectiveness in reducing dentin permeability did not differ significantly from 10% or 30% propolis gels. SEM micrographs revealed that dentin tubules were partially occluded after treatment with propolis. CONCLUSIONS: Under the conditions of this study, the application of 10% and 30% propolis gels did not seem to reduce the hydraulic conductance of dentin in vitro, but it showed capacity of partially obliterating the dentin tubules. Propolis is used in the treatment of different oral problems without causing significant great collateral effects, and can be a good option in the treatment of patients with dentin sensitivity

Prophylactic treatment of migraine; the patient's view, a qualitative study

Contains fulltext : 109202.pdf (publisher's version ) (Open Access)BACKGROUND: Prophylactic treatment is an important but under-utilised option for the management of migraine. Patients and physicians appear to have reservations about initiating this treatment option. This paper explores the opinions, motives and expectations of patients regarding prophylactic migraine therapy. METHODS: A qualitative focus group study in general practice in the Netherlands with twenty patients recruited from urban and rural general practices. Three focus group meetings were held with 6-7 migraine patients per group (2 female and 1 male group). All participants were migraine patients according to the IHS (International Headache Society); 9 had experience with prophylactic medication. The focus group meetings were analysed using a general thematic analysis. RESULTS: For patients several distinguished factors count when making a decision on prophylactic treatment. The decision of a patient on prophylactic medication is depending on experience and perspectives, grouped into five categories, namely the context of being active or passive in taking the initiative to start prophylaxis; assessing the advantages and disadvantages of prophylaxis; satisfaction with current migraine treatment; the relationship with the physician and the feeling to be heard; and previous steps taken to prevent migraine. CONCLUSION: In addition to the functional impact of migraine, the decision to start prophylaxis is based on a complex of considerations from the patient's perspective (e.g. perceived burden of migraine, expected benefits or disadvantages, interaction with relatives, colleagues and physician). Therefore, when advising migraine patients about prophylaxis, their opinions should be taken into account. Patients need to be open to advice and information and intervention have to be offered at an appropriate moment in the course of migraine