1,944 research outputs found
Optimization of -Layer Systems for Josephson Junctions from a Microstructure Point of View
-layer systems are frequently used for Josephson junction-based
superconducting devices. Although much work has been devoted to the
optimization of the superconducting properties of these devices, systematic
studies on influence of deposition conditions combined with structural analyses
on the nanoscale are rare up to now. We have focused on the optimization of the
structural properties of -layer systems deposited on Si(111)
substrates with a particular focus on the thickness homogeneity of the
-tunnel barrier. A standard high-vacuum electron-beam deposition system
was used and the effect of substrate pretreatment, different Al-deposition
temperatures and Al-deposition rates was studied. Transmission electron
microscopy was applied to analyze the structural properties of the
-layer systems to determine the thickness homogeneity of the
layer, grain size distribution in the Al layers, Al-grain boundary
types and the morphology of the interface. We show that the
structural properties of the lower Al layer are decisive for the structural
quality of the whole -layer system. Optimum conditions yield an
epitaxial Al(111) layer on a Si(111) substrate with an Al-layer thickness
variation of only 1.6 nm over more than 10 and large lateral grain
sizes up to 1 . Thickness fluctuations of the -tunnel barrier are
minimized on such an Al layer which is essential for the homogeneity of the
tunnel current. Systematic variation of the Al-deposition rate and deposition
temperature allows to develop an understanding of the growth mechanisms
Correlating the nanostructure of Al-oxide with deposition conditions and dielectric contributions of two-level systems in perspective of superconducting quantum circuits
This work is concerned with Al/Al-oxide(AlO)/Al-layer systems which are
important for Josephson-junction-based superconducting devices such as quantum
bits. The device performance is limited by noise, which has been to a large
degree assigned to the presence and properties of two-level tunneling systems
in the amorphous AlO tunnel barrier. The study is focused on the
correlation of the fabrication conditions, nanostructural and nanochemical
properties and the occurrence of two-level tunneling systems with particular
emphasis on the AlO-layer. Electron-beam evaporation with two different
processes and sputter deposition were used for structure fabrication, and the
effect of illumination by ultraviolet light during Al-oxide formation is
elucidated. Characterization was performed by analytical transmission electron
microscopy and low-temperature dielectric measurements. We show that the
fabrication conditions have a strong impact on the nanostructural and
nanochemical properties of the layer systems and the properties of two-level
tunneling systems. Based on the understanding of the observed structural
characteristics, routes are derived towards the fabrication of
Al/AlO/Al-layers systems with improved properties.Comment: 28 pages, 4 figure
Generation of four-partite GHZ and W states by using a high-finesse bimodal cavity
We propose two novel schemes to engineer four-partite entangled
Greenberger-Horne-Zeilinger (GHZ) and W states in a deterministic way by using
chains of (two-level) Rydberg atoms within the framework of cavity QED. These
schemes are based on the resonant interaction of the atoms with a bimodal
cavity that simultaneously supports, in contrast to a single-mode cavity, two
independent modes of the photon field. In addition, we suggest the schemes to
reveal the non-classical correlations for the engineered GHZ and W states. It
is shown how these schemes can be extended in order to produce general
N-partite entangled GHZ and W states.Comment: RevTex file, 13 pages, 7 figures, corrected typo
Antiferromagnetic phase of the gapless semiconductor V3Al
Discovering new antiferromagnetic compounds is at the forefront of developing
future spintronic devices without fringing magnetic fields. The
antiferromagnetic gapless semiconducting D03 phase of V3Al was successfully
synthesized via arc-melting and annealing. The antiferromagnetic properties
were established through synchrotron measurements of the atom-specific magnetic
moments, where the magnetic dichroism reveals large and oppositely-oriented
moments on individual V atoms. Density functional theory calculations confirmed
the stability of a type G antiferromagnetism involving only two-third of the V
atoms, while the remaining V atoms are nonmagnetic. Magnetization, x-ray
diffraction and transport measurements also support the antiferromagnetism.
This archetypal gapless semiconductor may be considered as a cornerstone for
future spintronic devices containing antiferromagnetic elements.Comment: Accepted to Physics Review B on 02/23/1
Homeostatic maintenance of pathogen-containing vacuoles requires TBK1-dependent regulation of aquaporin-1
Membranes are an integral component of many cellular functions and serve as a barrier to keep pathogenic bacteria from entering the nutrient-rich host cytosol. TANK-binding-kinase-1 (TBK1), a kinase of the IκB kinase family, is required for maintaining integrity of pathogen-containing vacuoles (PCV) upon bacterial invasion of host cells. Here we investigate how vacuolar integrity is maintained during bacterial infection, even in the presence of bacterial membrane damaging agents. We found that Aquaporin-1 (AQP1), a water channel that regulates swelling of secretory vesicles, associated with PCV. AQP1 levels were elevated in TBK1-deficient cells, and overexpression of AQP1 in wild-type cells led to PCV destabilization, similar to that observed in tbk1 −/ − cells. Inhibition of physiological levels of AQP1 in multiple cell types also led to increased instability of PCV, demonstrating a need for tightly regulated AQP1 function to maintain vacuole homeostasis during bacterial infection. AQP1-dependent modulation of PCV was triggered by bacterially induced membrane damage and ion flux. These results highlight the contribution of water channels to promoting PCV membrane integrity, and reveal an unexpected role for TBK1 and AQP1 in restricting bacterial pathogens to the vacuolar compartment.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/72109/1/j.1462-5822.2008.01199.x.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/72109/2/CMI_1199_sm_Figs_S1-S3_and_Table_S1.pd
Clinical exercise testing in children and adolescents with cystic fibrosis.
ArticleThis is the author version of an article published in Pediatric Physical Therapy, 2009, Vol. 21, Iss. 3, pp. 275-281. The final published version is available via: http://dx.doi.org/10.1097/PEP.0b013e3181b15445PURPOSE:
To review the most common field and laboratory exercise tests available for children and adolescents with cystic fibrosis (CF).
METHODS:
Relevant studies for this review were identified by electronic search of Medline and PubMed databases between the years 1958 and 2008. The bibliographies of all accessed publications were also searched. Key descriptors were cystic fibrosis, exercise testing, aerobic fitness, children, and adolescents.
RESULTS:
Five field tests were selected for presentation, including discussion of their strengths and weaknesses. Laboratory tests measuring aerobic and anaerobic responses to exercise in children with CF were also selected for presentation and discussed along with a summary of safety considerations for exercise testing of children with CF.
CONCLUSION:
Exercise testing is regarded an important prognostic tool in CF care. However, despite its beneficial effects, clinical exercise testing seems underused. Clinicians and their staff should encourage patients with CF to be physically active and recommend exercise testing annually
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