Electric-Field Noise above a Thin Dielectric Layer on Metal Electrodes

The electric-field noise above a layered structure composed of a planar metal electrode covered by a thin dielectric is evaluated and it is found that the dielectric film considerably increases the noise level, in proportion to its thickness. Importantly, even a thin (mono) layer of a low-loss dielectric can enhance the noise level by several orders of magnitude compared to the noise above a bare metal. Close to this layered surface, the power spectral density of the electric field varies with the inverse fourth power of the distance to the surface, rather than with the inverse square, as it would above a bare metal surface. Furthermore, compared to a clean metal, where the noise spectrum does not vary with frequency (in the radio-wave and microwave bands), the dielectric layer can generate electric-field noise which scales in inverse proportion to the frequency. For various realistic scenarios, the noise levels predicted from this model are comparable to those observed in trapped-ion experiments. Thus, these findings are of particular importance for the understanding and mitigation of unwanted heating and decoherence in miniaturized ion traps.Comment: 27 page

Towards a loophole-free test of Bell's inequality with entangled pairs of neutral atoms

Experimental tests of Bell's inequality allow to distinguish quantum mechanics from local hidden variable theories. Such tests are performed by measuring correlations of two entangled particles (e.g. polarization of photons or spins of atoms). In order to constitute conclusive evidence, two conditions have to be satisfied. First, strict separation of the measurement events in the sense of special relativity is required ("locality loophole"). Second, almost all entangled pairs have to be detected (for particles in a maximally entangled state the required detector efficiency is 82.8%), which is hard to achieve experimentally ("detection loophole"). By using the recently demonstrated entanglement between single trapped atoms and single photons it becomes possible to entangle two atoms at a large distance via entanglement swapping. Combining the high detection efficiency achieved with atoms with the space-like separation of the atomic state detection events, both loopholes can be closed within the same experiment. In this paper we present estimations based on current experimental achievements which show that such an experiment is feasible in future.Comment: 6 pages, 3 figures, to be published in Advanced Science Letter

Highly-efficient state-selective sub-microsecond photoionization detection of single atoms

We experimentally demonstrate a detection scheme suitable for state analysis of single optically trapped atoms in less than 1 {\mu}s with an overall detection efficiency {\eta} exceeding 98%. The method is based on hyperfine-state-selective photoionization and subsequent registration of the correlated photoion-electron pairs by coincidence counting via two opposing channel electron multipliers. The scheme enables the calibration of absolute detection efficiencies and might be a key ingredient for future quantum information applications or precision spectroscopy of ultracold atoms.Comment: 4 pages, 4 figure

Komponenten für kooperative Intrusion-Detection in dynamischen Koalitionsumgebungen

Koalitionsumgebungen sollen für alle miteinander kooperierenden Mitglieder einen Vorteil bei der Verfolgung eines gemeinsamen Ziels erbringen. Dies gilt für die verschiedensten Anwendungsbereiche, etwa bei kooperierenden Strafverfolgungsbehörden, Wirtschaftsunternehmen oder Streitkräfte. Auch bei der Erkennung von sicherheitsrelevanten Vorgängen in vernetzten Computersystemen erhofft man sich von der Zusammenarbeit eine verbesserte Erkennungsfähigkeit sowie eine schnelle und koordinierte Reaktion auf Einbruchsversuche. Dieser Beitrag stellt verschiedene praxisorientierte Werkzeuge für die koalitionsweite Vernetzung von Ereignismeldungs-produzierenden Sicherheitswerkzeugen vor, die wesentliche Probleme des Anwendungsszenarios lösen helfen: Frühzeitige Anomaliewarnung – ein graphbasierter Anomaliedetektor wird als adaptives Frühwarnmodul für großflächige und koordinierte Angriffe, z.B. Internet-Würmer, eingesetzt. Informationsfilterung – Meldungen werden beim Verlassen der lokalen Domäne entsprechend der domänenspezifischen Richtlinien zur Informationsweitergabe modifiziert (d.h. insbesondere anonymisiert bzw. pseudonymisiert). Datenreduktion – zusätzliche Filter zur Datenreduzierung auf der Basis von vordefinierten Abhängigkeitsregeln steigern die Handhabbarkeit des Datenflusses. Die Funktionsfähigkeit der genannten Komponenten wird derzeit in Form einer prototypischen Implementierung eines Meta-IDS für dynamische Koalitionsumgebungen nachgewiesen

Iron cycling and stable Fe isotope fractionation in Antarctic shelf sediments, King George Island

Iron (Fe) fluxes from reducing sediments and subglacial environments are potential sources of bioavailable Fe into the Southern Ocean. Stable Fe isotopes (δ56Fe ) are considered a proxy for Fe sources and reaction pathways, but respective data are scarce and Fe cycling in complex natural environments is not understood sufficiently to constrain respective δ56Fe “endmembers” for different types of sediments, environmental conditions, and biogeochemical processes. We present δ56Fe data from pore waters and sequentially extracted sedimentary Fe phases of two contrasting sites in Potter Cove (King George Island, Antarctic Peninsula), a bay that is affected by fast glacier retreat. Sediments close to the glacier front contain more easily reducible Fe oxides and pyrite and show a broader ferruginous zone, compared to sediments close to the icefree coast, where surficial oxic meltwater streams discharge into the bay. Pyrite in sediments close to the glacier front predominantly derives from eroded bedrock. For the high amount of easily reducible Fe oxides proximal to the glacier we suggest mainly subglacial sources, where Fe liberation from comminuted material beneath the glacier is coupled to biogeochemical weathering processes (likely pyrite oxidation or dissimilatory iron reduction, DIR). Our strongest argument for a subglacial source of the highly reactive Fe pool in sediments close to the glacier front is its predominantly negative δ56Fe signature that remains constant over the whole ferruginous zone. This implies in situ DIR does not significantly alter the stable Fe isotope composition of the accumulated Fe oxides. The nonetheless overall light δ56Fe signature of easily reducible Fe oxides suggests pre-depositional microbial cycling as it occurs in potentially anoxic subglacial environments. The strongest 56Fe-depletion in pore water and most reactive Fe oxides was observed in sediments influenced by oxic meltwater discharge. The respective site showed a condensed redox zonation and a pore water δ56Fe profile typical for in-situ Fe cycling. We demonstrate that the potential of pore water δ56Fe as a proxy for benthic Fe fluxes is not straight-forward due to its large variability in marine shelf sediments at small spatial scales (- 2.4‰ at the site proximal to oxic meltwater discharge vs. -0.9‰ at the site proximal to the marine glacier terminus, both at 2 cm sediment depth). The controlling factors are multifold and include the amount and reactivity of reducible Fe oxides and organic matter, the isotopic composition of the primary and secondary ferric substrates, sedimentation rates, and physical reworking (bioturbation, ice scraping). The application of δ56Fe geochemistry may prove valuable in investigating biogeochemical weathering and Fe cycling in subglacial environments. This requires, however (similarly to the use of δ56Fe for the quantification of benthic fluxes), that the spatial and temporal variability of the isotopic endmember is known and accounted for. Since geochemical data from subglacial environments are very limited, further studies are needed in order to sufficiently assess Fe cycling and fractionation at glacier beds and the composition of discharges from those areas

Fe isotopes revealing mineral-specific redox cycling in sediments

Reactive Fe (oxyhydr)oxides preferentially undergo early diagenetic cycling and cause a diffusive flux of dissolved Fe2+ towards the sediment-water interface. The partitioning of sedimentary Fe has traditionally been studied by applying sequential extractions. We modified an existing leaching method [1] in order to enable δ56Fe measurements on specific Fe mineral fractions. Those are siderite/sorbed Fe, ferrihydrite/lepidocrocite, goethite/hematite, and magnetite. The selectivity of extractions was tested by leaching pairs of 58Fe-spiked and unspiked synthetic minerals. Insignificant amounts of goethite and hematite are dissolved in hydroxylamine-HCl targetting ferrihydrite/lepidocrocite. The determination of reducible oxides leached by dithionite was found to be slightly compromised in presence of magnetite. Removal of extraction matrix was achieved by repetitive oxidation, heating, Fe precipitation, and column separation. The new method was applied to a short sediment core from the North Sea. Downcore mineral-specific variations in δ56Fe revealed differing contributions of Fe oxides to redox cycling. Acetic acid soluble Fe and ferrihydrite/lepidocrocite-Fe showed increasing δ56Fe values with depth in accordance with progressive dissimilatory iron reduction (DIR). Low δ56Fe in acetic acid soluble Fe relative to ferric hydrous oxide-Fe is consistent with the fractionation pattern between sorbed Fe(II) and ferric substrate during DIR experiments [2]. Goethite/hematite-and magnetite-Fe do not show δ56Fe trends with depth. The results demonstrate the importance of δ56Fe analysis on individual Fe fractions that differ in origin and reactivity. The developed procedure provides a basis for specific Fe isotope studies in past and present environments that undergo or underwent redox changes. [1] Poulton and Canfield (2005), Chemical Geology 214, 209-221. [2] Crosby et al., Geobiology 5 (2007), 169-189

Thermally Activated Magnetization and Resistance Decay during Near Ambient Temperature Aging of Co Nanoflakes in a Confining Semi-metallic Environment

We report the observation of magnetic and resistive aging in a self assembled nanoparticle system produced in a multilayer Co/Sb sandwich. The aging decays are characterized by an initial slow decay followed by a more rapid decay in both the magnetization and resistance. The decays are large accounting for almost 70% of the magnetization and almost 40% of the resistance for samples deposited at 35 $^oC$. For samples deposited at 50 $^oC$ the magnetization decay accounts for $\sim 50$ of the magnetization and 50% of the resistance. During the more rapid part of the decay, the concavity of the slope of the decay changes sign and this inflection point can be used to provide a characteristic time. The characteristic time is strongly and systematically temperature dependent, ranging from $\sim1$x$10^2 s$ at 400K to $\sim3$x$10^5 s$ at 320K in samples deposited at $35 ^oC$. Samples deposited at 50 $^oC$ displayed a 7-8 fold increase in the characteristic time (compared to the $35 ^oC$ samples) for a given aging temperature, indicating that this timescale may be tunable. Both the temperature scale and time scales are in potentially useful regimes. Pre-Aging, Scanning Tunneling Microscopy (STM) reveals that the Co forms in nanoscale flakes. During aging the nanoflakes melt and migrate into each other in an anisotropic fashion forming elongated Co nanowires. This aging behavior occurs within a confined environment of the enveloping Sb layers. The relationship between the characteristic time and aging temperature fits an Arrhenius law indicating activated dynamics

Digital Mechanism and Gear Library – Multimedia Collection of Text, Pictures and Physical Models

Περιέχει το πλήρες κείμενοWe are presenting a digital engineering library – the Digital Mechanism and Gear Library (DMG-Lib). The existing worldwide knowledge in form of books, drawings, physical models etc. is mostly scattered, difficult to access and does not comply with today’s requirements concerning a rapid information retrieval. Therefore the development of a digital, internet-based library for mechanisms and gears is necessary, which makes the worldwide knowledge about mechanisms and gears available: http://www.dmg-lib.org. The Digital Mechanism and Gear Library is of particular importance not only for engineers, product designers and researchers, but also for teachers, students and historians

Reduced inclination of cervical spine in a novel notebook screen system : implications for rehabilitation

Background: Professional working at computer notebooks is associated with high requirements on the body posture in the seated position. By the high continuous static muscle stress resulting from this position at notebooks, professionals frequently working at notebooks for long hours are exposed to an increased risk of musculoskeletal complaints. Especially in subjects with back pain, new notebooks should be evaluated with a focus on rehabilitative issues. Methods: In a field study a new notebook design with adjustable screen was analyzed and compared to standard notebook position. Results: There are highly significant differences in the visual axis of individuals who are seated in the novel notebook position in comparison to the standard position. Also, differences are present between further alternative notebook positions. Testing of gender and glasses did not reveal influences. Conclusion: This study demonstrates that notebooks with adjustable screen may be used to improve the posture. Future studies may focus on patients with musculoskeletal diseases