Geometric quantum computation with NMR

The experimental realisation of the basic constituents of quantum information processing devices, namely fault-tolerant quantum logic gates, requires conditional quantum dynamics, in which one subsystem undergoes a coherent evolution that depends on the quantum state of another subsystem. In particular, the subsystem may acquire a conditional phase shift. Here we consider a novel scenario in which this phase is of geometric rather than dynamical origin. As the conditional geometric (Berry) phase depends only on the geometry of the path executed it is resilient to certain types of errors, and offers the potential of an intrinsically fault-tolerant way of performing quantum gates. Nuclear Magnetic Resonance (NMR) has already been used to demonstrate both simple quantum information processing and Berry's phase. Here we report an NMR experiment which implements a conditional Berry phase, and thus a controlled phase shift gate. This constitutes the first elementary geometric quantum computation.Comment: Minor additions at request of referees. 4 pages revtex including 2 figures (1 eps). Nature in pres

Essential and checkpoint functions of budding yeast ATM and ATR during meiotic prophase are facilitated by differential phosphorylation of a meiotic adaptor protein, Hop1

A hallmark of the conserved ATM/ATR signalling is its ability to mediate a wide range of functions utilizing only a limited number of adaptors and effector kinases. During meiosis, Tel1 and Mec1, the budding yeast ATM and ATR, respectively, rely on a meiotic adaptor protein Hop1, a 53BP1/Rad9 functional analog, and its associated kinase Mek1, a CHK2/Rad53-paralog, to mediate multiple functions: control of the formation and repair of programmed meiotic DNA double strand breaks, enforcement of inter-homolog bias, regulation of meiotic progression, and implementation of checkpoint responses. Here, we present evidence that the multi-functionality of the Tel1/Mec1-to-Hop1/Mek1 signalling depends on stepwise activation of Mek1 that is mediated by Tel1/Mec1 phosphorylation of two specific residues within Hop1: phosphorylation at the threonine 318 (T318) ensures the transient basal level Mek1 activation required for viable spore formation during unperturbed meiosis. Phosphorylation at the serine 298 (S298) promotes stable Hop1-Mek1 interaction on chromosomes following the initial phospho-T318 mediated Mek1 recruitment. In the absence of Dmc1, the phospho-S298 also promotes Mek1 hyper-activation necessary for implementing meiotic checkpoint arrest. Taking these observations together, we propose that the Hop1 phospho-T318 and phospho-S298 constitute key components of the Tel1/Mec1- based meiotic recombination surveillance (MRS) network and facilitate effective coupling of meiotic recombination and progression during both unperturbed and challenged meiosis

Sosa on Knowledge, Judgment and Guessing

In Chapter 3 of Judgment and Agency, Sosa (Judgment and Agency, 2015) explicates the concept of a fully apt performance. In the course of doing so, he draws from illustrative examples of practical performances and applies lessons drawn to the case of cognitive performances, and in particular, to the cognitive performance of judging. Sosa’s examples in the practical sphere are rich and instructive. But there is, I will argue, an interesting disanalogy between the practical and cognitive examples he relies on. Ultimately, I think the source of the disanalogy is a problematic picture of the cognitive performance of guessing and its connection to knowledge and defeat. Once this critical line of argument is advanced, an alternative picture of guessing, qua cognitive performance, is articulated, one which avoids the problems discussed, and yet remains compatible with Sosa’s broader framework

Imaging Coulomb Islands in a Quantum Hall Interferometer

In the Quantum Hall regime, near integer filling factors, electrons should only be transmitted through spatially-separated edge states. However, in mesoscopic systems, electronic transmission turns out to be more complex, giving rise to a large spectrum of magnetoresistance oscillations. To explain these observations, recent models put forward that, as edge states come close to each other, electrons can hop between counterpropagating edge channels, or tunnel through Coulomb islands. Here, we use scanning gate microscopy to demonstrate the presence of quantum Hall Coulomb islands, and reveal the spatial structure of transport inside a quantum Hall interferometer. Electron islands locations are found by modulating the tunneling between edge states and confined electron orbits. Tuning the magnetic field, we unveil a continuous evolution of active electron islands. This allows to decrypt the complexity of high magnetic field magnetoresistance oscillations, and opens the way to further local scale manipulations of quantum Hall localized states

Comparison of the effects of salmeterol/fluticasone propionate with fluticasone propionate on airway physiology in adults with mild persistent asthma

<p>Abstract</p> <p>Background</p> <p>This study compared the effect of inhaled fluticasone propionate (FP) with the combination of salmeterol/fluticasone propionate (SFC) on lung function parameters in patients with mild asthma.</p> <p>Methods</p> <p>Adult patients with mild persistent asthma (≥ 80% predicted FEV₁) receiving 200–500 μg of BDP or equivalent were randomised to receive either FP 100 μg or SFC 50/100 μg twice daily from a Diskus^®inhaler for four weeks. The primary outcome was the change from baseline in airway resistance (sRaw) at 12 hrs post dose measured by whole body plethysmography. Impulse oscillometry and spirometry were also performed.</p> <p>Results</p> <p>A comparison of the geometric mean sRaw at 12 hrs post dose in the SFC group to the FP group gave a ratio of 0.76 (0.66 – 0.89, p < 0.001) at week 2 and 0.81 (0.71 – 0.94, p = 0.006) at week 4. Similarly, significant results in favour of SFC for oscillometry measurements of resistance and reactance were observed. FEV₁was also significantly superior at week 2 in the SFC group (mean difference 0.16L, 95% CI; 0.03 – 0.28, p = 0.015), but not at week 4 (mean difference 0.17L, 95% CI -0.01 – 0.34, p = 0.060).</p> <p>Conclusion</p> <p>SFC is superior to FP in reducing airway resistance in mild asthmatics with near normal FEV₁values. This study provides evidence that changes in pulmonary function in patients with mild asthma are detected more sensitively by plethysmography compared to spirometry</p> <p>Trial registration number</p> <p>NCT00370591.</p

Age and growth of the smooth hammerhead, Sphyrna zygaena, in the Atlantic Ocean: comparison with other hammerhead species

The smooth hammerhead Sphyrna zygaena (Sphyrnidae) is a pelagic shark occasionally caught as bycatch in pelagic longline fisheries, but is one of the least studied of all pelagic sharks. Age and growth of S. zygaena was studied along a wide Atlantic region covering both the northern and southern hemispheres. Data from 304 specimens, caught between October 2009 and September 2014, ranging in size from 126 to 253 cm fork length (FL), were analysed. Growth models were fitted using the three-parameter von Bertalanffy growth function (VBGF) re-parameterized to calculate L0 (size at birth). Growth models were fitted to the sample data and data from several back-calculation models. The model fit to the quadratic modified Dahl-Lea back-calculated data seems to be the most appropriate to describe growth in this species, with resulting growth parameters of Linf = 285 cm FL, k = 0.09 year−1 for males and Linf = 293 cm FL, k = 0.09 year−1 for females. Compared with other species of the same genus, estimated growth coefficients for S. zygaena seem to fall in the low to middle range. Although further work is still needed, this study adds to knowledge of the vital life-history parameters of smooth hammerheads in the Atlantic Ocean, which can be used in the management and conservation of this species.Programa Operacional Potencial Humano: IF/00253/2014info:eu-repo/semantics/publishedVersio

Some size relationships in phytoflagellate motility

Data from the literature are used to assess some hypothesised adaptive advantages of the flagellate life form among phytoplankton. Possible advantages include increased nutrient uptake by movement through a homogeneous medium as opposed to exploitation of spatial hetrogeneity of the environment. Maximal migrational amplitudes and maximal swimming velocities of phytoflagellates were compared to body size. Both were found to increase with size. Relative amplitudes and relative velocities, however, were found to decrease with size. Hydrophysical considerations show that additional gain of nutrients by swimming through a homogeneous medium is only minimal for small flagellates at their attainable swimming velocities. It is suggested that exploitation of environmental heterogeneity in nutrient distribution may be one of the most important advantages for flagellates over coccoid algae