6,582 research outputs found

    Splitting electronic spins with a Kondo double dot device

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    We present a simple device made of two small capacitively coupled quantum dots in parallel. This set-up can be used as an efficient "Stern-Gerlach" spin filter, able to simultaneously produce, from a normal metallic lead, two oppositely spin-polarized currents when submitted to a local magnetic field. Our proposal is based on the realization of a Kondo effect where spin and orbital degrees of freedom are entangled, allowing a spatial separation between the two spin polarized currents. In the low temperature Kondo regime, the efficiency is very high and the device conductance reaches the unitary limit, e2h\frac{e^2}{h} per spin branch.Comment: 3 pages, 2 figure

    Effects of low incubation temperatures on the bactericidal activity of anti-tuberculosis drugs

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    OBJECTIVES: to explore the effect of low incubation temperatures and the consequent slowing of bacterial metabolism on the bactericidal action of anti-tuberculosis drugs against Mycobacterium tuberculosis. METHODS: counting of surviving bacteria during exposure of static cultures to 1 mg/L isoniazid, 2 mg/L rifampicin, 0.5 or 2 mg/L TMC207 and 40 or 160 mg/L pyrazinamide, usually for periods of 21 days at temperatures of 37, 25, 22, 19, 16 or 8°C. RESULTS: the bactericidal activities of isoniazid and rifampicin were progressively reduced at 25 and 22°C, and were minimal at lower temperatures. TMC207 was immediately bactericidal at 37°C, in contrast to the early static phase reported with log phase cultures, and showed less change in activity as incubation temperatures were reduced than did rifampicin or isoniazid. Pyrazinamide was more bactericidal when incubation temperatures were reduced below 37°C and when the static seed cultures were most dormant. CONCLUSIONS: these results can be explained by the surmise that at low temperatures bacterial energy is at a low level with only just sufficient ATP to maintain homeostasis, making the bacteria more susceptible to the blocking of ATP synthesis by TMC207. Insufficient ATP at low temperature would also hinder the export of pyrazinoic acid, the toxic product of the pro-drug pyrazinamide, from the mycobacterial cell by an inefficient efflux pump that requires energ

    Investigating eye movement acquisition and analysis technologies as a causal factor in differential prevalence of crossed and uncrossed fixation disparity during reading and dot scanning

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    Previous studies examining binocular coordination during reading have reported conflicting results in terms of the nature of disparity (e.g. Kliegl, Nuthmann, &amp; Engbert (Journal of Experimental Psychology General 135:12-35, 2006); Liversedge, White, Findlay, &amp; Rayner (Vision Research 46:2363-2374, 2006). One potential cause of this inconsistency is differences in acquisition devices and associated analysis technologies. We tested this by directly comparing binocular eye movement recordings made using SR Research EyeLink 1000 and the Fourward Technologies Inc. DPI binocular eye-tracking systems. Participants read sentences or scanned horizontal rows of dot strings; for each participant, half the data were recorded with the EyeLink, and the other half with the DPIs. The viewing conditions in both testing laboratories were set to be very similar. Monocular calibrations were used. The majority of fixations recorded using either system were aligned, although data from the EyeLink system showed greater disparity magnitudes. Critically, for unaligned fixations, the data from both systems showed a majority of uncrossed fixations. These results suggest that variability in previous reports of binocular fixation alignment is attributable to the specific viewing conditions associated with a particular experiment (variables such as luminance and viewing distance), rather than acquisition and analysis software and hardware.<br/

    Spin-orbital Kondo decoherence by environmental effects in capacitively coupled quantum dot devices

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    Strong correlation effects in a capacitively coupled double quantum-dot setup were previously shown to provide the possibility of both entangling spin-charge degrees of freedom and realizing efficient spin-filtering operations by static gate-voltage manipulations. Motivated by the use of such a device for quantum computing, we study the influence of electromagnetic noise on a general spin-orbital Kondo model, and investigate the conditions for observing coherent, unitary transport, crucial to warrant efficient spin manipulations. We find a rich phase diagram, where low-energy properties sensitively depend on the impedance of the external environment and geometric parameters of the system. Relevant energy scales related to the Kondo temperature are also computed in a renormalization-group treatment, allowing to assess the robustness of the device against environmental effects.Comment: 13 pages, 13 figures. Minor modifications in V

    Real estate prices and corporate investment: theory and evidence of heterogeneous effects across firms

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    In this paper, we investigate the effect of real estate prices on productive investment. We build a simple theoretical framework of firms’ investment with credit rationing and real estate collateral. We show that real estate prices affect firms’ borrowing capacities through two channels. An increase in real estate prices raises the value of the firms’ pledgeable assets and mitigates the agency problem characterizing the creditor-entrepreneur relationship. It simultaneously cuts the expected profit due to the increase in the cost of inputs. While the literature only focuses on the first channel, the identification of the second channel allows for heterogeneous effects of real estate prices on investment across firms. We test our theoretical predictions using a large French database. We do find heterogeneous effects of real estate prices on productive investment depending on the position of the firms in the sectoral distributions of real estate holdings. Our preferred estimates indicate that a 10% increase in real estate prices causes a 1% decrease in the investment rate of firms in the first decile of the distribution but a 6% increase in the investment rate of firms belonging to the last decile

    Validation of some species- and genus-group names in Melitta (Hymenoptera: Melittidae)

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    Four recently proposed names in the genus Melitta Kirby (Melittidae: Melittinae) were left as nomenclaturally unavailable owing to minor conflicts with the recently established criteria for electronic publication.  These oversights are here corrected, thereby validating the following new names: Melitta (Afromelitta) Michez &amp; Kuhlmann, new subgenus; Melitta (Afromelitta) richtersveldensis Michez &amp; Kuhlmann, new species; Melitta (Plesiomelitta) Michez &amp; Kuhlmann, new subgenus; and M. (Plesiomelitta) avontuurensis Michez &amp; Kuhlmann, new species

    Metallic foam processing from the liquid state

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    A model is developed to describe the formation of metallic foams in which liquid drainage acts to collapse the foam before it can freeze. Numerical solution of the foam drainage equation, combined with the equations of heat conduction, provides new insight into the competition between these two processes. It also stimulates and confirms a theoretical analysis which leads to criteria for creating uniform samples of frozen metal foam. The analysis suggests new experiments to clarify the role of the various processes leading to foam formation
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