Time-Resolved Detection of Individual Electrons in a Quantum Dot

We present measurements on a quantum dot and a nearby, capacitively coupled, quantum point contact used as a charge detector. With the dot being weakly coupled to only a single reservoir, the transfer of individual electrons onto and off the dot can be observed in real time in the current signal from the quantum point contact. From these time-dependent traces, the quantum mechanical coupling between dot and reservoir can be extracted quantitatively. A similar analysis allows the determination of the occupation probability of the dot states.Comment: 3 pages, 3 figure

Finite bias charge detection in a quantum dot

We present finite bias measurements on a quantum dot coupled capacitively to a quantum point contact used as a charge detector. The transconductance signal measured in the quantum point contact at finite dot bias shows structure which allows us to determine the time-averaged charge on the dot in the non-blockaded regime and to estimate the coupling of the dot to the leads.Comment: 6 pages, 4 figure

Glomus intraradices dominates arbuscular mycorrhizal communities in a heavy textured agricultural soil

Arbuscular mycorrhizal fungal (AMF) spore communities were surveyed in a long-term field fertilization experiment in Switzerland, where different amounts of phosphorus (P) were applied to soil. Plots receiving no P as well as plots systematically fertilized in excess to plant needs for 31 years were used to test the hypothesis that application of P fertilizer changes the composition and diversity of AMF communities. AMF spores were isolated from the field soil, identified, and counted so as to quantify the effect of P fertilization on AMF spore density, composition, and diversity. Trap cultures were established from field soil with four host plants (sunflower, leek, maize, and Crotalaria grahamiana), and the spore communities were then analyzed in substrate samples from the pots. Altogether, nine AMF species were detected in the soil. No evidence has been acquired for effect of P fertilization on spore density, composition, and diversity of AMF in both the field soil and in trap cultures. On the other hand, we observed strong effect of crop plant species on spore densities in the soil, the values being lowest under rapeseed and highest under Phacelia tanacetifolia covercrop. The identity of plant species in trap pots also significantly affected composition and diversity of associated AMF communities, probably due to preferential establishment of symbiosis between certain plant and AMF species. AMF spore communities under mycorrhizal host plants (wheat and Phacelia in the fields and four host plant species in trap pots) were dominated by a single AMF species, Glomus intraradices. This resulted in exceptionally low AMF spore diversity that seems to be linked to high clay content of the soi

Kaehler submanifolds with parallel pluri-mean curvature

We investigate the local geometry of a class of K\"ahler submanifolds $M \subset \R^n$ which generalize surfaces of constant mean curvature. The role of the mean curvature vector is played by the $(1,1)$-part (i.e. the $dz_id\bar z_j$-components) of the second fundamental form $\alpha$, which we call the pluri-mean curvature. We show that these K\"ahler submanifolds are characterized by the existence of an associated family of isometric submanifolds with rotated second fundamental form. Of particular interest is the isotropic case where this associated family is trivial. We also investigate the properties of the corresponding Gauss map which is pluriharmonic.Comment: Plain TeX, 21 page

Effect of Heavy Metal Contaminated Shooting Range Soils on Mycorrhizal Colonization of Roots and Metal Uptake by Leek

We grew leek (Allium porrum) in soils of two shooting ranges heavily contaminated with heavy metals in the towns of Zuchwil and Oberuzwil in Switzerland as a bioassay to test theactivity of arbuscular mycorrhizal (AM) fungi in these soils.Soil samples were taken from (1) front of the shooting house(HOUSE), (2) the area between house and target (FIELD) and (3) the berm (BACKSTOP). Samples of Ribwort plantain (Plantagolanceolata) growing naturally within the shooting ranges werealso collected and the colonization of its roots by mycorrhizalfungi was measured. The number of AM spores in the soils wassignificantly reduced concomitant with the increase in thedegree of soil contamination with metals. In Zuchwil,mycorrhizal fungi equally colonized roots of Ribwort plantainsampled from BACKSTOP and HOUSE. In Oberuzwil, however, plantsfrom BACKSTOP had lower colonization when compared with thosesampled from HOUSE. Colonization of leek was strongly reducedin the BACKSTOP soil of Zuchwil and slightly reduced in theBACKSTOP soil of Oberuzwil when compared with plants grown inrespective HOUSE soil. Concentrations of Cd, Cr, Cu, Ni, Pb andZn in the leaves of leek grown in the BACKSTOP soil was withinthe range considered toxic for human consumption. This pointsto the high degree of bio-availability of these metal in thesesoils. Significant decrease in the number of mycorrhizal sporesin the BACKSTOP soils in Zuchwil and the low colonization ofleek roots grown in these soils point to possible changes inthe species diversity of mycorrhizal fungi in these soil

Cotunneling-mediated transport through excited states in the Coulomb blockade regime

We present finite bias transport measurements on a few-electron quantum dot. In the Coulomb blockade regime, strong signatures of inelastic cotunneling occur which can directly be assigned to excited states observed in the non-blockaded regime. In addition, we observe structures related to sequential tunneling through the dot, occuring after it has been excited by an inelastic cotunneling process. We explain our findings using transport calculations within the real-time Green's function approach, including diagrams up to fourth order in the tunneling matrix elements.Comment: 4 pages, 3 figure

Effect of Ta 2 O 5 , Nb 2 O 5 , and HfO 2 Alloying on the Transformability of Y 2 O 3 -Stabilized Tetragonal ZrO 2

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/65528/1/j.1151-2916.1990.tb05100.x.pd

MacDowell-Mansouri gravity and Cartan geometry

The geometric content of the MacDowell-Mansouri formulation of general relativity is best understood in terms of Cartan geometry. In particular, Cartan geometry gives clear geometric meaning to the MacDowell-Mansouri trick of combining the Levi-Civita connection and coframe field, or soldering form, into a single physical field. The Cartan perspective allows us to view physical spacetime as tangentially approximated by an arbitrary homogeneous "model spacetime", including not only the flat Minkowski model, as is implicitly used in standard general relativity, but also de Sitter, anti de Sitter, or other models. A "Cartan connection" gives a prescription for parallel transport from one "tangent model spacetime" to another, along any path, giving a natural interpretation of the MacDowell-Mansouri connection as "rolling" the model spacetime along physical spacetime. I explain Cartan geometry, and "Cartan gauge theory", in which the gauge field is replaced by a Cartan connection. In particular, I discuss MacDowell-Mansouri gravity, as well as its more recent reformulation in terms of BF theory, in the context of Cartan geometry.Comment: 34 pages, 5 figures. v2: many clarifications, typos correcte

100 Hz ROCS microscopy correlated with fluorescence reveals cellular dynamics on different spatiotemporal scales

Fluorescence techniques dominate the field of live-cell microscopy, but bleaching and motion blur from too long integration times limit dynamic investigations of small objects. High contrast, label-free life-cell imaging of thousands of acquisitions at 160 nm resolution and 100 Hz is possible by Rotating Coherent Scattering (ROCS) microscopy, where intensity speckle patterns from all azimuthal illumination directions are added up within 10 ms. In combination with fluorescence, we demonstrate the performance of improved Total Internal Reflection (TIR)-ROCS with variable illumination including timescale decomposition and activity mapping at five different examples: millisecond reorganization of macrophage actin cortex structures, fast degranulation and pore opening in mast cells, nanotube dynamics between cardiomyocytes and fibroblasts, thermal noise driven binding behavior of virus-sized particles at cells, and, bacterial lectin dynamics at the cortex of lung cells. Using analysis methods we present here, we decipher how motion blur hides cellular structures and how slow structure motions cover decisive fast motions

Fibrous Monolithic Ceramics: III, Mechanical Properties and Oxidation Behavior of the Silicon Carbide/Boron Nitride System

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/66176/1/j.1151-2916.1994.tb05399.x.pd